Technological Prosthetics for the Partially Sighted: A Feasibility Study

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?.'ECHNOLOGICAL P R O S T H E T I C S FOR THE PARTIALLY SIGHTED:

A F E A S I B I L I T Y STUDY

J o h n P a g e

S e p t e m b e r 1974

R e s e a r c h R e p o r t s a r e p u b l i c a t i o n s r e p o r t i n g on t h e w o r k of t h e a u t h o r . A n y v i e w s o r c o n c l u s i o n s are t h o s e of t h e a u t h o r , and do n o t n e c e s s a r i l y r e f l e c t t h o s e of I I A S A .

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PREFACE

T h i s preface is intended a s a c o v e r note to the report of a feasibility study on the application of technological prosthetics f o r the partially sighted. T h i s study was c a r r i e d out in the form.ative s t a g e s of the ILASA Bio-Medical P r o g r a m m e . It s u r v e y s the need f o r a quantitative analytical approach to the social problem of rehabilitation policy posed by the existence of partially sighted populations. These groups a r e l a r g e in n u m b e r but have not achieved salience and hence r e m a i n submerged and invisible within the whole population.

The community, in developed countries, is both a w a r e of i t s blind population and m a k e s s o c i a l provision for i t s c a r e , but is not in general actively a w a r e of i t s s e v e r e l y visually i m p a i r e d . The l a t t e r group r e p r e s e n t s a population at l e a s t five t i m e s l a r g e r than that of the totally blind, and i s handicapped both economically and socially

A p r i m a r y question a d d r e s s e d by the feasibility study was the extent to which f u r t h e r r e s e a r c h in t h i s general field of s o c i a l s y s t e m s analysis would be appropriate within the IIASA p r o g r a m m e . In conjunction with t h i s

consideration was the f u r t h e r question whether the analysis proposed would be immediately useful, with prospect of n e a r - t e r m i m p a c t , t o national M i n i s t r i e s of Health and t o other agencies responsible for rehabilitation.

O u r p r e l i m i n a r y a n s w e r , a s spelled out in detail in the r e p o r t attached, is affirmative to both of t h e s e questions Rehabilitation i s an a r e a of

concern in a l l developed countries, and to achieve adequate policy r e s p o n s e , an analysis of the type described would be n e c e s s a r y . Moreover, the full study proposed demands a broad c r o s s - s e c t i o n of s y s t e m s analytic techniques.

In s e v e r a l a r e a s of the full study it will be noted that the s y s t e m s methodology itself must be strengthened t o d e a l with the problems.

Specific a r e a s of s y s t e m s inquiry should include the following:

( i ) Definition and m e a s u r e m e n t of the problem. The r e p o r t shows that we need a m o r e broadly applicable index of p a r t i a l sight, based on the functional capability of the individuals in question. The attempt should be made t o reduce the multiple a t t r i b u t e s of sight to a v e c t o r m e a s u r e of minimal dimension This i s a problem frequently faced in contemporary s y s t e m s analysis a s societal s t a n d a r d s a r e designed to capture with minimal complication a s many a s p e c t s a s possible of a problem situation. With better deficition of the

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p a r a m e t e r s of p a r t i a l sight, the existing s t a t i s t i c a l d a t a becomes m o r e meaningful a s an i n d i c a t o r of the s i z e of population who would benefit f r o m w i d e - s p r e a d availability of technological p r o s t h e t i c s . B e c a u s e the existing c e n s u s s t a t i s t i c s a r e based upon a v a r i e t y of s t a n d a r d s and definitions, i t m a y , however, be n e c e s s a r y t o invoke synthetic s t a t i s t i c a l techniques t o i n f e r f r o m t h e s e d a t a t h e

functionally defined populations a t need.

(ii) Technology A s s e s s m e n t . T h i s would involve t h e s y s t e m a t i c prognosis of ongoing r e s e a r c h and development having possible applications t o visually i m p a i r e d individuals. T h e a s s e s s m e n t should d r a w upon existing s y s t e m s methods f o r evaluating t h e potential of new

technologies a c r o s s a s p e c t r u m of possible u s e r r e q u i r e m e n t s . A s methodology i n t h i s a r e a is r u d i m e n t a r y , attention should be paid t o t h e possibility of developing a prototype technique f o r evaluating multiple objective technology. Such a technique might be based upon aggregating technological value o v e r a b r o a d r a n g e of u s e s with s p e c i a l attention paid to t h e need f o r additional m a r g i n a l r e s e a r c h t o t a i l o r t h e g e n e r a l technology f o r specific p u r p o s e s and t o enhance t h e p r o s p e c t f o r spin-off applications.

(iii) h t e r d i s c i p l i n a r y Linkage. The s u c c e s s of t h i s study depends c r i t i c a l l y upon t h e coordination and combination of different scientific p e r s p e c t i v e s . An opthalmological input is r e q u i r e d t o understand and t o d e s c r i b e t h e effects of e y e malfunction i n t e r m s of r e m a i n i n g operational vision. T h i s m u s t however be extended by c l i n i c a l input f r o m o p t o m e t r i s t s and o t h e r s p e c i a l i s t s who a r e m o r e closely concerned with t h e c a r e and t r a i n i n g of low-vision p a t i e n t s , i n o r d e r t o provide a functional d e s c r i p t i o n of t h e capabilities of t h e i r patients. T h e input f r o m clinicians would be Linked with that of technological e x p e r t s i n o r d e r t o obtain b e t t e r definition of design o b j e c t i v e s , r e l a t e d logically t o t h e functional r e q u i r e m e n t s of t h e p a r t i a l l y sighted. Different technological solutions m a y be n e c e s s a r y f o r d i f f e r e n t clinical conditions and different functional r e q u i r e m e n t s . An input f r o m such behavioural s c i e n c e s a s sociology would be v i t a l i n d e s c r i b i n g and m e a s u r i n g t h e s o c i a l i m p a c t of p a r t i a l s i g h t e d n e s s . F i n a l l y , t h e r e a r e p r o b l e m s of organi s a t i o n r e q u i r i n g t h e

a s s i s t a n c e of management s c i e n t i s t s . They would both outline t h e i n f r a s t r u c t u r e n e c e s s a r y t o support t h e w i d e - s p r e a d application of technological p r o s t h e t i c s and suggest an o p t i m a l s e t of u s e s i o r t h e r e c o m m e n d e d prosthetic. Social analytic p r o c e d u r e s would a l s o be n e c e s s a r y i n t h e c o s t l b e n e f i t study.

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The combination of t h e s e different disciplines will not be e a s y but should be m o r e readily achieved a t I U S A than elsewhere. T h e Institute i t s e l f is s t r u c t u r e d about a recognised need f o r harmonious inter.-

disciplinary work and i t s experience in coaxing c l o s e collaboration between s c i e n t i s t s of different backgrounds is growing. The ophthalmological, clinical, and technical e x p e r t i s e r e q u i r e d can be obtained through the l i t e r a t u r e and with limited consultancies. Sociological and managemental counsel would be obtained f r o m the L a r g e Organisations P r o j e c t of IIA-SA while help i n p r e c i s e s o c i a l a n a l y s i s could be provided by the Methodology P r o j e c t .

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I . INTRODUCTION- -AIMS O F THE STUDY Technological P r o s t h e t i c s a s an A r e a f o r S y s t e m s A n a l y s i s

With t h e growth of technology, t h e i n c r e a s i n g possibility of spin-off, o r utilisation of a technology f o r p u r p o s e s o t h e r than t h o s e f o r which it w a s developed, h a s become a p p a r e n t . M o r e o v e r , once one new application h a s been m a d e , i t m a y suggest o t h e r developments which could be made in t h e new field of application.

The bio-medical a r e a i s a growing field f o r t h e application of technol- o g i e s such a s m i n i a t u r i s e d e l e c t r o n i c s . T h e r e a r e in fact a wide v a r i e t y of technological p r o s t h e t i c s which a r e available f o r p r e s c r i p t i o n by clini- c i a n s , ranging f r o m h e a r t p a c e m a k e r s f o r c e r t a i n c o r o n a r y conditions and d i a l y s i s machines f o r a c u t e kidney malfunctions, to improved a r t i f i - c i a l l i m b s . It w a s thought that a study of t h e p r o c e s s by which technolog- i c a l p r o s t h e t i c s a r e applied in the health c a r e s y s t e m would be a n appro- p r i a t e a r e a f o r s y s t e m s a n a l y s i s . Specifically, a b e t t e r understanding of t h e p r o c e s s f r o m t h e initial concept, development of a n a c t u a l device and i t s application t o p a r t i c u l a r d i s a b i l i t i e s , through i t s evaluation and acceptance (both by clinicians and p a t i e n t s ) , t o g e n e r a l application a s a s t a n d a r d t r e a t m e n t , would give a b a s i s f o r policy guidance. F o r t h i s purpose i t would be n e c e s s a r y t o develop m e a n s of r e l a t i n g c o s t to s o c i a l and individual benefits of p a r t i c u l a r p r o s t h e t i c s . F o r p r a c t i c a l r e a s o n s , a g e n e r a l i s e d a n a l y s i s would be difficult. However, a study of one field of application- -not n e c e s s a r i l y a single p r o s t h e t i c device- -might not only provide policy guidance i n t h e health c a r e a r e a concerned, but could a l s o indicate whether t h e methods used w e r e of m o r e g e n e r a l value.

R e a s o n s f o r Study of Visual I m p a i r m e n t

Out of t h e many possible d i s a b i l i t y / p r o s t h e t i c s y s t e m s , t h e p r o b l e m of s & e r e v i s u a l i m p a i r m e n t w a s s e l e c t e d a s t h e prototype study a r e a : blindness i s a u n i v e r s a l p r o b l e m . A WHO study group points out that t h e

" c a s e f o r t h e elimination of u n n e c e s s a r y blindness i s justified not only on h u m a n i t a r i a n grounds but a l s o by i t s s o c i a l and economic consequences.

In t e r m s of economic l o s s , blindness i s t h e m o s t expensive of a l l c a u s e s of s e r i o u s disablement. ^{I t}

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The WHO study group e s t i m a t e s that t h e r e a r e t e n s of millions of s e - v e r e l y visually i m p a i r e d p e r s o n s i n the world today. M o r e o v e r , the incidence of blindness and s e v e r e visual i m p a i r m e n t is likely t o r i s e in the future, both because of world population growth and because of extended life expectancy. Some types of blindness a r e preventable in the s e n s e that they can be controlled by attacking the infections o r d i s e a s e s which cause t h e m . T r a c h o m a and onchocerciasis a r e d i s e a s e s which r e s u l t in s e v e r a l nlillion c a s e s of blindness o r n e a r blindness in the developing countries in t r o p i c a l o r subtropical regions. Xerophthalmia, while apparently not an infectious d i s e a s e but r a t h e r a condition a s s o c i a t e d with s e v e r e m a l - nutrition, could also be c l a s s e d a s a cause of blindness which could be e r a d i c a t e d by preventive medical and s o c i a l m e a s u r e s .

T h e r e r e m a i n o t h e r m a j o r c a u s e s of blindness, however, f o r which no specific preventive m e a s u r e s can presently be applied; t h e s e affect the developed and developing regions alike. In s o m e c a s e s ( e . g. c a t a r a c t and r e t i n a l detachment), s u r g e r y may r e s t o r e useful sight, but in o t h e r s (glaucoma, r e t i n a l degeneration, diabetic retinopathy, and optic n e r v e atrophy), the conditions a r e l a r g e l y i r r e v e r s i b l e . P r o s t h e t i c s a r e t h e r e f o r e vitally important in t h e s e c a s e s .

What is the magnitude of t h e problem? In discussion of the s t r a t e g y f o r prevention and t r e a t m e n t of blindness, the WHO group considered that a s much a s two-thirds of the w o r l d ' s blindness is preventable, and twenty percent of it (that due to c a t a r a c t ) is c u r a b l e . In Section III of t h i s r e p o r t , t h e available s t a t i s t i c s on blindness and p a r t i a l sight will be examined in d e t a i l , but it is sufficient h e r e to note that t h e r e is a substantial hidden population not r e p r e s e n t e d in national o r international s t a t i s t i c s of "blindness" and not p a r t of the so-called "blindness s y s t e m . ^" To t h i s population m u s t a l s o be added those who a r e blind by the c u r r e n t l e g a l definitions hut who have sufficient r e s i d u a l sight t o benefit f r o m p r o s t h e t i c s .

While the s i z e of t h e problem and its economic and social consequences a r e adequate s t r a t e g i c r e a s o n s f o r selecting v i s u a l a i d s a s the a r e a f o r a prototype study, t h e r e a r e a l s o t a c t i c a l considerations. They c e n t r e on t h e selection of the s u b s y s t e m of technological prosthetics f o r partially sighted p e r s o n s r a t h e r than aids f o r totally blind p e r s o n s .

1) A break-through i n applying technology t o rehabilitation of v i c t i m s of s e v e r e visual i m p a i r m e n t h a s o c c u r r e d i n r e c e n t y e a r s :

closed- c i r c u i t television devices (CCTV). While fully developed f r o m a technical point of view, they a r e not at p r e s e n t a routine p r e s c r i p t i o n . T h e r e ^ist h u s a p r a c t i c a l situation needing a n a l y s i s , which h a s a policy content.

2) Sufficient n u m b e r s of CCTV a i d s a r e a l r e a d y in s e r v i c e t o make i t a t l e a s t theoretically possible t o evaluate p e r f o r m a n c e i n t e r m s

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of a c t u a l operational u s e , a s distinct f r o m l a b o r a t o r y o r clinical r e s u l t s . The study could proceed on the b a s i s of a c c e s s i b l e d a t a . 3) In addition t o the development of CCTV a i d s , t h e r e a r e r e s e a r c h

and development in applying t h i s type of technology t o the wider population--the totally blind. A b a s i s t h e r e f o r e e x i s t s f o r broaden- ing the scope of the study if initial r e s u l t s a r e p r o m i s i n g , and t h u s f o r studying t h e s e types of technological a i d s a s a t o t a l s y s t e m . 4) Initial inquiries showed that sufficient agencies and institutions

w e r e i n t e r e s t e d in the problem a s a whole, and thought t h e study proposals relevant t o i t , t o provide a possibility of s u c c e s s . In p a r t i c u l a r , they p r o m i s e d a c c e s s t o data and cooperation in o t h e r ways.

The Technological P e r s p e c t i v e

Until1 r e c e n t l y , t h e only aid available t o enable p e r s o n s with s e v e r e v i s u a l handicaps t o r e a d wa.s B r a i l l e . But it r e q u i r e d s p e c i a l and p r o - longed t r a i n i n g t o obtain reasonably f a s t reading s p e e d s and w a s applicable only t o m a t e r i a l s published in B r a i l l e . N e v e r t h e l e s s , reading s p e e d s of 70 t o 1 2 5 w o r d s p e r minute can be achieved by t h e t r a i n e d B r a i l l e r e a d e r . Another traditional mode of communication w a s t h e replacement of sight by h e a r i n g i n , f o r e x a m p l e , t h e s o - called "talking books. ^"While t h e r e was s e v e r a l e a r l y a t t e m p t s t o u s e television techniques f o r image magnification, p r a c t i c a l CCTV devices have only been available f o r the past few y e a r s ; they a r e now in limited production in a n u m b e r of c o u n t r i e s . T h e r e have been a t t e m p t s t o r e p l a c e sight electronically by u s e of t h e t a c t i l e o r audio s e n s e s ; a device of the f i r s t t y p e , f o r conversion of printed m a t t e r into t a c t i l e i m p r e s s i o n of t h e l e t t e r s t h e m s e l v e s , h a s been successfully developed by Linvill et a l . a t Stanford University. The o t h e r handicap which blind o r s e v e r e l y visually i m p a i r e d individuals experience i s r e - s t r i c t e d mobility, and f o r t h i s p u r p o s e an u l t r a s o n i c t o r c h i s now com- m e r c i a l l y available. It t r a n s m i t s a pulsed u l t r a s o n i c b e a m with v a r i a b l e frequency, t h e echo signal being mixed with the t r a n s m i t t e d signal and fed into earphones. With t h i s device it i s possible t o e s t i m a t e distance and s t r u c t u r e of objects at a range of a few m e t e r s . S i m i l a r head-mounted u l t r a s o n i c pathfinders a r e under development. In t h e r e s e a r c h s t a g e a r e m o r e e l a b o r a t e devices which convey t o the w e a r e r a t a c t i l e i m p r e s s i o n of n e a r b y objects. F i n a l l y , b a s i c r e s e a r c h on the d i r e c t e l e c t r i c a l s t i m - ulation of t h e visual c o r t e x i s now in p r o g r e s s .

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T h e F e a s i b i l i t y Study

While t h e initial indications w e r e p r o m i s i n g , i t was felt n e c e s s a r y t o look at s o m e of t h e p r o b l e m s in g r e a t e r d e t a i l t o a s s e s s t h e p r a c t i c a b i l - i t y of meeting t h e g e n e r a l objectives s t a t e d above. In p a r t i c u l a r , it was n e c e s s a r y

a) t o examine t h e d e g r e e t o which existing s t a t i s t i c s of blindness and p a r t i a l sight could be r e l a t e d . T h i s would not only t o give a r e a s o n a b l y r e l i a b l e f i g u r e of t h e t o t a l population likely t o benefit f r o m t h e s e a i d s , but would a l s o provide a b a s i s f o r quantita- t i v e estimation of t h e d e g r e e t o which the need could be s a t i s f a c - t o r i l y m e t by different types of p r o s t h e t i c s ;

b) t o s u r v e y briefly available clinical d a t a t o d e t e r m i n e whether t h r e s h o l d s could be defined f o r t h e v a r i o u s t y p e s of a i d s , i . e . m e a s u r e m e n t s r e l a t e d t o remaining vision which might define t h e l i m i t s of u s e f u l n e s s of p a r t i c u l a r aids; and

c) t o t e s t the practicability of collecting d a t a on a c t u a l operating effectiveness of s y s t e m s c u r r e n t l y i n u s e .

F i n a l l y , on t h e organisational l e v e l i t w a s advisable f i r s t t o l e a r n how health c a r e and s o c i a l s e c u r i t y s y s t e m s o p e r a t e i n support of t h e p a r t i a l l y sighted and blind population. T h i s p a p e r p r e s e n t s t h e r e s u l t s of t h i s f e a - sibility a n a l y s i s and d i s c u s s e s t h e d a t a i m m e d i a t e l y available.

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11. DEFINITION O F BLINDNESS AND PARTIAL SIGHT

To p e r m i t useful discussion of the available s t a t i s t i c a l information it i s n e c e s s a r y f i r s t t o look a t the definitions of blindness and p a r t i a l sight commonly in u s e . The f i r s t point t o note is tha.t objective definitions in t e r m s of m e a s u r e m e n t s a r e not u n i v e r s a l and indeed m a y have only limited usefulness in p r a c t i c e . However, s i n c e t h e available s t a t i s t i c s a r e often quoted in t e r m s of m e a s u r e m e n t s of v i s u a l acuity it i s n e c e s s a r y t o understand the v a r i o u s s t a n d a r d s proposed.

Visual Acuity M e a s u r e m e n t s

T h e s e m e a s u r e m e n t s a r e e s s e n t i a l l y a r a t i o based on the s m a l l e s t symbol ( e . g. a l e t t e r ) an individual can identify on a standard c h a r t . We c o m p a r e , f o r example, a person with defective vision with one having p e r - fect vision; if the l a t t e r can identify a symbol at a distance of x units and the p e r s o n with imperfect vision can only identify it at y units of d i s t a n c e , tnen t h e v i s u a l acuity of t h e person with defective vision i s g . Y In the pub- l i s h e d l i t e r a t u r e , v a r i o u s d i f f e r e n t n u m b e r s f o r t h e b a s e value x a.re often quoted and t h i s can cause s o m e confusion, but generally t h e f i g u r e s m o s t often quoted f o r x a r e 10, 20, and 60. If v e r y low acuities a r e being m e a s u r e d higher base f i g u r e s a r e n e c e s s a r y one one t h e r e f o r e often en- counters b a s e f i g u r e s in the hundreds. In t h i s r e p o r t , we will t r y i o avoid confusion by reducing a l l such f i g u r e s quoted t o a d e c i m a l fraction, i . e . 0. 1 , 0 . 05, e t c .

However, it i s n e c e s s a r y t o recognise t h e limitations of t h e m e a s u r e - m e n t s , and t o emphasize in p a r t i c u l a r t h e i n a c c u r a c i e s which m a y o c c u r in reducing m e a s u r e m e n t s t o a standard decimal notation. A l l visual acuity m e a s u r e m e n t s a r e based on ability t o r e a d symbols ( m o s t usually l e t t e r s i n t h e c a s e of a d u l t s , f a m i l i a r outlines i n the c a s e of young chil- d r e n of p r e - r e a d i n g a g e ) , but different c h a r t s y s t e m s e x i s t , and m o r e important, t h e d e g r e e of c o n t r a s t between ambient illumination and t h e c h a r t s t h e m s e l v e s m a y not be optimum f o r a low-vision patient. In p r a c - t i c e , t h e r e m a y be d i f f e r e n c e s not only in actual visual p e r f o r m a n c e ( i n t e r m s of remaining useful functional vision) between subjects having the s a m e reduced visual a c u i t y - - m e a s u r e m e n t s made according t o one c h a r t and t e s t distance s y s t e m and another--but a l s o in the m e a s u r e m e n t s t h e m - s e l v e s . They m a y d i f f e r f o r a low vision patient depending on the m e a s u r e ment techniques used. M e h r , F r o s t , and Apple

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s t r e s s t h i s point in a s u r v e y of f o r t y low-vision patients a t the W e s t e r n Blind Rehabilitation C e n t e r in P a l o Alto, California (USA). They point out that two patients whose v i s u a l a c u i t i e s according t o t h e i r previous ophthalmic r e c o r d s w e r e f o r example 1/200 and 2/200 respectively, w e r e found on examination by the s p e c i a l low-vision techniques p r a c t i s e d a t the C e n t e r , t o

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have much b e t t e r v i s u a l acuities--10140 and 10160 respectively. While the differences m a y be e x t r e m e , t h i s is not an isolated example: most o t h e r tria.1 r e p o r t s discussed in l a t e r sections of t h i s r e p o r t comment on the need f o r s p e c i a l p r o c e d u r e s if the v i s u a l acuity of low-vision patients is t o be a c c u r a t e l y a s s e s s e d .

T h e r e f o r e , while for the s a k e of simplicity v i s u a l acuity m e a s u r e - m e n t s in t h i s r e p o r t have been reduced t o d e c i m a l f r a c t i o n s , t h e r e s e r - vation should be made that t h e s e f r a c t i o n s m a y not be comparable be- c a u s e of

a ) the difficulty of r e l a t i n g one m e a s u r e m e n t s y s t e m (type of c h a r t and working distance) t o a n o t h e r , and

b) the inherent weaknesses of t h e method of c h a r t reading at s t a n - d a r d distances and in ambient illumination f o r low-vision patients.

International and National Definitions of Blindness and Partial. Sight F r o m a brief inspection of available data, it is c l e a r that t h e r e is no u n i v e r s a l s y s t e m of r e c o r d i n g "blindness" o r " p a r t i a l sight" in t e r m s of m e a s u r e m e n t s of v i s u a l acuity, however inexact such m e a s u r e m e n t s m a y be a s an index of useful vision. F o r s e v e r a l y e a r s , however, WHO h a s been i n c r e a s i n g l y concerned with the p r o b l e m s a r i s i n g on an international s c a l e in the c o l l e c t i o ~ i of adequate s t a t i s t i c s ; the question of uniform definitions is of o b v i - J S i.mportance in t h i s r e g a r d . A 1966 WHO r e p o r t [3]

identified a s many a s sixty-five definitions of blindness, and in 1969, the Twenty-Second World Health A s s e m b l y adopted a resolution requesting the D i r e c t o r - G e n e r a l "lo undertake a study on the information which is a t p r e s e n t available on the extent and a l l t h e c a u s e s of preventable and c u r a b l e blindness. "*

The study was undertaken by m e a n s of a questionnaire submitted t o governments. WHO published a r e p o r t on i t s findings in M a r c h 1972 [4].

T h i s r e p o r t was submitted t o the Twenty-Fifth World Health A s s e m b l y in May 1972, following which a new resolution**was adopted. In t h i s , the D i r e c t o r - G e n e r a l was requested t o obtain additional data on v i s u a l i m - pairment and blindness, t o promote f u r t h e r s t u d i e s on the most efficient and economical m e a n s of preventing blindness, t o a s s i s t M e m b e r States in educational p r o g r a m m e s r e l a t e d t o blindness

. . . .

Following t h i s r e - solution, a study group was s e t up in l a t e 1972. In i t s r e p o r t , t h e Study Group recommended a new s e r i e s of definitions of blindness and v i s u a l i m p a i r m e n t . These a r e presented i n Table I.

*WHO 1971 Handbook of resolutions and decisions of the WHA and the Executive B o a r d , 1 l t h ed. 87 (WHA 22. 29) .

* *

Off. R e c . WHO 1972, No. 201, Resolution WHA 25. 55.

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Table 1

C a t e g o r i e s of Visual I m p a i r m e n t and Blindnessa

C a t e g o r y Visual acuity

(with both e y e s , using the best possible c o r r e c t i o n ) of v i s u a l

i m p a i r m e n t b m a x i m u m l e s s than m i n i m u m equal t o o r b e t t e r than

3/60 1 / 6 0 ( F i n g e r counting a t 1 m e t r e )

3 1 / 2 0 (0. 05) 1 / 5 0 (0. 02)

--

²⁰¹⁴⁰⁰ 51300 (20/1200)

1 / 6 0 ( F i n g e r counting a t 1 m e t r e )

4 1 / 5 0 (0. 02) Light perception

5/ 300

5 No light perception

9 Undetermined o r unspecified

"1f t h e extent of t h e v i s u a l field i s t o be considered a l s o , patients with a field of l e s s than 10' but m o r e than 5' around c e n t r a l fixation should be placed i n c a t e g o r y 3 and patients with a field l e s s than 5' around c e n t r a l fixation should be placed i n c a t e g o r y 4 , even i f t h e c e n t r a l acuity is not i m p a i r e d .

b ~ h e s e c a t e g o r i e s a r e intended t o c o r r e s p o n d with t h e fourth digit of t h e numbering s y s t e m u s e d i n the International Classification of D i s e a s e s . In t h i s s y s t e m , the digit 9 c u s t o m a r i l y signifies "unspecified!'

T h e group f u r t h e r recommended that "while e a c h country m u s t define blindness i n relation to i t s own s o c i a l and economic conditions ( p r e f e r - ably using t h e s t a n d a r d c a t e g o r i e s given i n t h i s r e p o r t ) , t h e r e i s need f o r an internationally accepted definition of blindness f o r the p u r p o s e s of com- piling international s t a t i s t i c a l d a t a . The group recommended tliat t h i s definition of blindness should include c a t e g o r i e s 3, 4 , and 5 . " T h e above t a b l e w a s accepted a s a n amendment t o t h e WHO i n t e r n a t i o n a l calssification of d i s e a s e s and f r o m t h e point of view of i n t e r n a t i o n a l classification (not yet a p p a r e n t l y r e f l e c t e d i n c u r r e n t national s t a t i s t i c s ) t h e t h r e s h o l d of blind- n e s s and p a r t i a l sight would a p p e a r 0. 05 but with a d j u s t m e n t s f o r v i s u a l field i m p a i r m e n t .

On t h e national l e v e l , t h e following b r i e f n o t e s s u m m a r i s e t h e posi- tion in two c o u n t r i e s only, t h e U. S . A . and the U. K . While much m o r e information will be n e c e s s a r y f o r t h e study p r o p e r , t h e s e notes m a y s e r v e t o i n d i c a t e s o m e of t h e p r o b l e m s which will be encountered in t h e a n a l y s i s of t h e way in which t h e "blindness s y s t e m " o p e r a t e s , o r f a i l s t o o p e r a t e ,

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f o r the s e v e r e l y visually handicapped p e r s o n .

A definition of blindness (and of p a r t i a l s i g h t , when such a definition e x i s t s ) , i s on t h e national level not s i m p l y a r e s e a r c h tool o r a guide to c o m p i l e r s of health s t a t i s t i c s ; r a t h e r is i t a s o c i a l o r l e g a l i n s t r u m e n t which d e t e r m i n e s how the community will d e a l with p a r t i c u l a r individuals with v i s u a l handicaps. Many c o u n t r i e s have a l e g a l definition of blindness based on v i s u a l acuity m e a s u r e m e n t s in t h e i r s o c i a l s e c u r i t y legislation.

F o r e x a m p l e , i n the United S t a t e s a p e r s o n is considered "blind" if h i s best c o r r e c t e d v i s u a l acuity is no g r e a t e r than 0. 1 o r i f h i s v i s u a l acuity exceeds 0. 1 but t h e d i a m e t e r of t h e v i s u a l field d o e s not exceed 20' i n any d i r e c t i o n . T h e r e a p p e a r s to be no s i m i l a r a d m i n i s t r a t i v e definition f o r p a r t i a l s i g h t . O t h e r c o u n t r i e s u s e l e g a l definitions r e l a t e d to functional c o n s i d e r a t i o n s , tied in s o m e way t o v i s u a l acuity m e a s u r e m e n t s . F o r e x a m p l e , t h e United Kingdom defines a blind p e r s o n a s one* " s o blind a s to be unable t o p e r f o r m

any

work f o r which eye sight is e s s e n t i a l . I' T h i s , however, is a s s o c i a t e d with v i s u a l acuity m e a s u r e m e n t s i n t h r e e c a t e - g o r i e s . A p e r s o n is legally blind i n t h e UK i f h i s best c o r r e c t e d v i s u a l acuity is 1 / 2 0 (0. 05) o r below, but m a y be c o n s i d e r e d blind i f t h e v i s u a l acuity l i e s between 0 . 1 and 0 . 05 with considerable r e s t r i c t i o n of t h e v i - s u a l field. With a v i s u a l acuity b e t t e r than 0. 1 he m a y be r e g a r d e d a s legally blind i f s e v e r e r e s t r i c t i o n of t h e v i s u a l field is a l s o p r e s e n t . In t h e UK p a r t i a l sight is defined a s follows:

"1. T h e r e is no s t a t u t o r y definition i n t h e National A s s i s t a n c e A c t , 1948, of p a r t i a l - s i g h t , but t h e M i n i s t r y of Health h a s advised that a p e r s o n who is not blind within the meaning of t h e Act of 1348, ( s e e Appendix 111) but who i s , n e v e r t h e l e s s , substantially and permanently handicapped by congenitally defective vision o r i n whose c a s e i l l n e s s o r i n j u r y h a s c a u s e d defective vision of a s u b - s t a n t i a l and permanently handicapping c h a r a c t e r is within t h e s c o p e of t h e w e l f a r e s e r v i c e s which t h e l o c a l authority a r e e m - powered t o provide f o r blind p e r s o n s - - b u t t h i s does not apply t o o t h e r benefits s p e c i a l l y enjoyed by t h e blind, e . g. pension a t age 40, additional a s s i s t a n c e g r a n t .

2. T h e following c r i t e r i a should be u s e d a s a g e n e r a l guide when d e t e r m i n i n g whether a p e r s o n f a l l s within t h e s c o p e of t h e wel- f a r e provisions f o r t h e partially-sighted, a s w e l l a s i n r e c o m - mending, w h e r e t h e p e r s o n is under 16 y e a r s of a g e , t h e a p p r o - p r i a t e type of school f o r the p a r t i c u l a r child concerned:

-

(i) f o r r e g i s t r a t i o n p u r p o s e s and t h e provision of w e l f a r e s e r v i c e s the following p e r s o n s m a y be r e g a r d e d a s p a r t i a l l y - sighted - t h o s e with v i s u a l acuity:

( a ) 3/60 t o 6 / 6 0 with full field;

(b) up t o 6/24 with m o d e r a t e contraction of t h e field, o p a c i t i e s i n m e d i a , o r aphakia;

* ~ e f i n i t i o n s a s given i n UK M i n i s t r y of Health c i r c u l a r 4 / 5 5 , published 2 M a r c h 1955.

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(c) 6/18 o r even better i f t h e r e i s a g r o s s field defect, e . g. hemianopia, o r t h e r e i s marked contraction of the field a s in pigmentary degeneration, glaucoma etc.

(ii) for children whose visual acuity will have a bearing on the appropriate methods of education

-

(a) s e v e r e visual disabilities- -to be educated in Special Schools by methods involving vision - 3/60 to 6/24 with glasses;

(b) visual impairment- -to be educated at ordinary schools by special consideration-better than 6/24 with g l a s s e s .

NOTES

(a) Infants and young children with congenital anomalies unless ob- viously blind should be classed a s partially-sighted and r e f e r r e d for hospital supervision and c a r e until aged 4 and then be r e - viewed.

(b) At age 4 and over- -binocular corrected vision should be the c r i t e - rion.

(c) All in (ii) (a) and (b) above should be re-examined every 12 months- o r e a r l i e r i f t h e r e i s reason to suspect any worsening.

(d) In making recommendations about persons under the age of six- teen, examining ophthalmologists should bear in mind that t h e r e a r e other factors ( s e e paragraph 13 of the Circular) which may influence local education authorities in their decision about the special educational treatment to be provided. "

Functional Definitions of Blindness

The imperfections inherent in visual acuity measurements a s a mea- s u r e of blindness and partial sight, whether o r not they a r e associated with qualifying statements relative to field defects, have resulted in sug- gestions that m o r e operational definitions should be used. F o r example, in a r r i v i n g at the recommended international definition listed in Table 1 above, the WHO Director-General's report [4] stated that t h e r e was a further need f o r clarification in definitions. In that report, the question- n a i r e responses of many participating countries demonstrated the need for extending definitions outside the range of simple visual acuity o r vi-- sual field measurements. The concepts of "economic and social blindness" were mentioned, and these concepts have been elaborated by other authors. The lack of c l e a r definitions r e f l e c t s the difficulty of dealing with that part of the population which has only partial sight and i s t h e r e - f o r e handicapped in earning a living o r in social relations. F o r example,

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in Table 1 quoted above, categories 1 and 2 were described a s partial impairment of vision and social blindness respectively. With category 3, t r u e blindness begins

-

-the t e r m "virtual blindness" being used to des- cribe those individuals in this category, and category 4 , total blindness.

Several workers in the field have commented on the incomplete o r unsa.tisfactory nature of definitions of blindness and partial sight related solely t o visual acuity and visual field measurements. Genensky [5] , for example, concludes that, from t h e viewpoint of regulatory social security agencies, definitions based on the functional capabilities of the visually impaired population would be more logical. He has in fact proposed a s e r i e s of four classifications a s follows:

1) functionally blind o r nonfunctionally sighted, 2) functionally sighted,

3) functionally sighted with aided mobility, and

41 functionally sighted with neither sighted literacy nor sighted illiteracy.

The classifications he gives a r e specifically related a) to the mobility of the individual and b) to his ability to read and write (hence the need to exclude illiteracy due to non -visual handicaps). A key concept in Genensky' s functional classification scheme i s an attempt to define a "visually impaired person1'; this concept i s important both from the general social considerations discussed above and in the limited context of this report. We a r e trying h e r e to establish 1) what i s meant by the words "the partially sighted population'1, 2) how l a r g e this population i s , and 3) within what ranges technological prosthetics a r e particularly applicable. Genensky' s revised definition s t a t e s that a person i s "visually impaired i f the visual acuity in his better eye with corrective lenses does not exceed 20/70. o r if the visual acuity in his better eye, with o r without corrective leneses, does exceed 20170, but his visual field i s so r e s t r i c t e d that he i s unable to maneuver safely in an unfamiliar environment without the aid of a sighted person, a dog, o r a cane. ^"[6] This revised definition includes a visual acuity measurement, but Genensky e x p r e s s e s misgivings about quoting a precise limit:

I t . .

.

by doing so, t h e r e i s always t h e chance that I may exclude from

the ranks of the visually impaired, people who need one o r m o r e of the s e r v i c e s that a r e provided o r should be provided to the partially sighted. ^{I '} [6] While f o r the reason stated above, visual acuity measurements, unless qualified by a statement of precise functional limitations, a r e unsatisfac- tory a s a general all-purpose definition, they could be used a s an indica- tion of the threshold below which the partially sightea population begins :for the purpose of t h i s study. It will be observed that 20170 (0.285) very closely corresponds to the WHO category 1 - - p a r t i a l impairment of vision

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(maximum visual acuity 0. 3). F u r t h e r light on the subject is provided by Goldish [7] in a study concerned with t h e establishment of t h e U. S.

m a r k e t f o r visual aids and s e r v i c e s . Goldish h a s commented extensively on t h e question of m e a s u r e m e n t s t a n d a r d s f o r visual handicaps. F r o m t h i s different point of view h e c o m e s t o v i r t u a l l y the s a m e conclusion a s Genensky: he points out that t h e t y p e s of a i d s and s e r v i c e s depend on the extent t o which visual function i s i m p a i r e d , r a t h e r than on visual acuity n u m b e r s . T h e r e a r e however indications that t h e r e i s a rough c o r r e l a - tion between visual functioning and ranges of v i s u a l acuity n u m b e r s . He s u g g e s t s t h e fcllowing definitions:

Visual malfunction- -wearing of c o r r e c t i v e l e n s e s

Visual i m p a i r m e n t - -"trouble s e e i n g , " even with c o r r e c t i v e l e n s e s S e v e r e v i s u a l impairment

-

-"legal blindness", "blindness"

o r "inability t o r e a d newsprint even with c o r r e c t i v e l e n s e s . "

He s u g g e s t s that the threshold between visual i m p a i r m e n t and s e v e r e visual i m p a i r m e n t c o r r e s p o n d t o v i s u a l a c u i t i e s of about 0. 3 o r 0 . 2 and it i s t h e s e f i g u r e s with which he a s s o c i a t e s the s e v e r e l y visually i m - p a i r e d U . S. population. In another paper Goldish 2nd M a r x [8] indicate what they believe t o be the boundary values f o r eye malfunctions. While t h e upper l i m i t s of visual i m p a i r m e n t can l i e anywhere between a visual acuity of 0. 5 and 0. 3, the p a r t of t h e visually i m p a i r e d population falling within t h e s e two l i m i t s can usually have t h e i r v i s u a l function r e s t o r e d t o acceptable l i m i t s by conventional ophthalmological t r e a t m e n t . T h e r e e x i s t s a s i m i l a r boundary a r e a at t h e lower and of the s c a l e , i. e . w h e r e s e v e r e visual i m p a i r m e n t m e r g e s into functional blindness. T h e s e l i m i t s l i e between 0. 025 and the point a t which the individual is able t o p e r c e i v e light but h a s l i t t l e o r no useful vision. The US definition of legal blind- n e s s (at l e a s t a s f a r a s the v i s u a l acuity m e a s u r e m e n t is concerned) r e - p r e s e n t s paractically a median point of p a r t i a l sight ( s e v e r e visual i m - p a i r m e n t ) at a v i s u a l acuity figure of 0. 1 .

In Table 2 the WHO s t a n d a r d s a r e compared'with the boundary conditions f o r p a r t i a l sightedness and blindness suggested by Goldish and M a r x with the tentative v i s u a l acuity threshold suggested by Genensky f o r visual i m p a i r m e n t . The l e g a l definition of blindness f o r t h e U. K . is a l s o added. .

It will be noted that t h e r e i s s o m e m e a s u r e of a g r e e m e n t a s t o w h e r e p a r t i a l s i g h t n e s s begins i n t e r m s of visual acuity, i. e . between 0. 3 and 0. 25. T r u e blindness (in t e r m s of useful vision remaining) must begin a t the l e v e l defined by WHO a s "virtual b l i n d n e s s , " i . e . at a visual acuity of 0. 017, although Goldish would put t h i s a l i t t l e higher a t 0. 025.

T h i s bandwidth, i . e . f r o m 0. 3 t o 0 . 02, will be used t o define t h e partially sighted population i n this r e p o r t .

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Tb.31E Ii .TiiE APPRBXlMATE BOUNDS OF PAREAL SIGHT IN TERMS OF V lSUAL ACUITY

IMPAIRMENT" NOR MA L 20 140 20 RW zoiroo

51zol

LIGHT ABSOLUTE 1201201

I

ACUITY W IT H BEST

I

PROJECTION BLW9HE55 CORRECT ION 20 1 1200 GENENSKY "VISUALLY IMPAIRED"

UK "LEGAL BLINDNESS"

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Other F a c t o r s in Definition of P a r t i a l Sight

Although from a purely statistical point of view a definition of partial sight in t e r m s of the bandwidth of visual acuity given i s adequate for this study, t h e r e a r e further social consequences which must be employed a s a qualification.

F i r s t , the omission of any reference to the remaining visual field could exclude a fraction of the partially sighted population whose central visual acuity i s above 0. 3 . It i s for this reason that Genensky, in his functional classification scheme distinguishes between "functionally sighted"

and "functionally sighted with aided mobility. " Both c l a s s e s a r e "visually i m p a i r e d , " but the f i r s t i s able to "maneuver safely in an unfamiliar environment without the aid of a sighted person, a dog, o r a cane," while the second i s not able so to manoeuvre. Severe restriction of the visual field is in itself a specific handicap in movement.

The second consequence is concerned with the relation of legal definitions to operational o r functional considerations. In the two countries for which data h a s been examined f o r this feasibility study, it s e e m s ap- parent that the legal definitions of blindness do not relate solely t o that part of the population which is truly blind--i. e . little o r no useful vision-- but neither do they include any particular fraction of the partially sighted.

Yet many of the partially sighted a r e handicapped socially and economically, particularly in t h e i r reading ability: the threshold of reading newsprint for example i s usually regarded a s about 0 . 4 in t e r m s of visual acuity.

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111. STATISTICAL DATA Size i f the Severelv Visuallv I m ~ a i r e d P o ~ u l a t i o n

On the basis of questionnaire responses f r o m the WHO member governments, the WHO Director General's 1972 report [4] to the Twenty- Fifth World Health Assembly estimated that t h e r e a r e ten to fifteen million "blind" people in the world. It is a difficult problem to establish with any degree of consistency what i s meant by "blind" in the above context. F o r example, the USA statistics included in this computation gave a blind population of 385,000 which other sources show to be the number of legally blind persons registered in the USA in 1960. The WHO estimate is based on frsgmentary and non-homogeneous data. But even assuming that a l l the reporting countries have a definition of "legal blindness" s i m i - l a r to that m the US, the total world population of partially sighted, i. e . those who a r e socially o r economically blind in t e r m s of the WHO r e - commended classification, must amount to at least t h r e e t i m e s this num - b e r , i. e . thirty million. Genensky [6] points out that an estimate of this kind, which is based on the ratio of partially sighted to legally blind in develcped countries such a s the USA, must be an underestimate since it is reasonable to a s s u m e that the incidence of partial sightedness i s sig- nificantly lower in developed countries. While it i s impossible to quantify t h i s difference, weight i s lent to this supposition by comparison of the blind r a t e s per 100,000 of population quoted by WHO [4]: whereas for developed countries the range is approximately from 50 to 200, the r a t e for developing countries can bz a s l a r g e a s several thousand. F o r the purpose of this feasibility study, however, we can limit the analysis to the USA and the UK a s examples of developed countries for which reliable statistics exist.

U. S. Statistics

In a report issued in 1971*, the US National Academy of Sciences considered that in 1970 there were approximately 420,000 legally blind persons out of a total population of 203. 2 million in the USA. Similar figures have been quoted by other s o u r c e s . At that date t h e r e were an additional 1 . 2 8 million Americans who were unable to read newspapers with best corrected vision, i . e . with visual acuities of l e s s than 0 . 4 . On the basis of these figures Genensky [6] concludes that by 1973 t h e r e would be 1 33 million individuals outside the qualification of "legal blindness!'

*Rehabilitation Engineering

-

A P l a n f o r Continued P r o g r e s s (Com- mittee on Prosthetics Research and Development :f the National Academy of Sciences)

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To these should be added approximately 4 3 6 , 0 0 0 legally blind, making an estimated total of 1 . 7 6 6 million partially sighted plus legally blind persons in 1 9 7 3 . Using figures based on the sample of partially sighted persons subjects in the RANDSIGHT CCTV r e s e a r c h , Genensky also con- cludes that about 7070 of legally blind persons a r e in fact partially sighted within h i s definitions. Thus, he concludes that the t r u e population of partially sighted persons in the USA in 1 9 7 3 amounted to 1 . 64 million.

The upper threshold of this population corresponds to these with visual acuity measurements of between 0 . 1 and 0 . 3 illustrated in Figure 1 . Goldish [7] concludes that approximately 6 . 4 million individuals met his definition of "visual impairmenttt in 1 9 7 0 in the USA; of this total--using his threshold value of "severe visual impairment1' of 0 . 3 to 0 . 2 visual acuity--about 1 . 7 million individuals should be classified a s ''severely visually impaired. I' There thus s e e m s to be considerable agreement on what constitutes the partially sighted population of the USA who a r e not functionally blind but who a r e handicapped to the extent of not being able to read normal type. This is about 1 . 6 million, in contrast to a t r u e functionally blind population of 1 3 0 , 0 0 0 . It should be pointed out, however, that the legally blind population may itself be underestimated, resulting in a possible increase of the numbers of functionally blind p e r - sons noted above. At any event, the number of partially sighted persons compared with the total population of the USA in 1 9 7 3 , i s not insignificant:

0 . 77% of the total.

UK Statistics

The United Kingdom Ministry of Health and Social Security compiles elaborate statistics and analyzes them in almost every conceivable break- down of age, sex, and other p a r a m e t e r s including some twenty major causative eye conditions. A report on the t r e n d s in these statistics f o r the y e a r s 1948 to 1962 has been published by the NIinistry of Health follow- ing a study by Sorsby [9].

These statistics relate to the information published annually in the Register of the Blind and Partially Sighted. The compilation is based on f o r m s completed by individuals wishing to be classified a s registered blind o r partially sighted. F o r m s a r e then r e f e r r e d to the Department of Health and Social Security by the ophthalmologist o r general practl- tioner concerned with the c a s e , o r by the 'National Assistance Board so- c i a l security) o r other lay sources. Sorsby tabulates the statistics of these r e f e r r a l sources and shows that in the higher age groups the r e f e r - r a l source is mainly non-medical organisations. He comments that this makes blindness statistics dependent on social r a t h e r than ophthalmolog- i c a l f a c t o r s , and concludes that

".

. . the number registered annually will

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continue t o r e p r e s e n t only a portion of a l a r g e r - - a n d perhaps v e r y much l a r g e r - - n u m b e r . "

The partially sighted section of t h e r e g i s t e r h a s been maintained since 1951. Since the mode of accession to this r e g i s t e r i s , however, the s a m e a s that f o r t h e Blind R e g i s t e r it would be reasonable to a s s u m e that the n u m b e r s recorded cannot, f o r the s a m e r e a s o n , give a n a c c u r a t e picture of t h e incidence of p a r t i a l sightedness i n t h e UK. lMoreover, t h e r e is a f u r t h e r substantial difficulty i n i n t e r p r e t i n g t h e underestimation of t h e partially sighted i n t h e r e g i s t e r : while the r e g i s t e r e d blind p e r s o n s obtain s o c i a l s e c u r i t y benefits ( s t a t e r e t i r e m e n t pensions a t t h e age of forty and additional a s s i s t a n c e g r a n t s , etc. ), t h e s e benefits do not apply t o the p a r - tially sighted population who a r e entitled only t o welfare s e r v i c e s which can be supplied by the local authority. Thus t h e r e is much l e s s motivation t o r e g i s t e r than t h e r e is in the c a s e of those coming within the blind definition. T h e r e is considerable agreement that under these conditions a I.arge numbe-. of t h e partially sighted do not bother t o r e g i s t e r . If we :lake t h e figures for blind r e g i s t r a t i o n s i n 1962 and partially sighted r e - gistrations in the s a m e y e a r f r o m the r e p o r t r e f e r e n c e d , we obtain a fi- g u r e of 9 6 , 5 0 0 + 26,100, i . e . a t o t a l of 122,600. The populationof Eng- la.nd and Wales a s a whole f o r that y e a r was 48. 2 million: the total r e - g i s t e r e d blind and partia.12.y sighted r e p r e s e n t 0. 254% of t h e population-- t h e " r e g i s t e r e d blind" d e m e n t representing 0. 200°?0 of the population and the r e g i s t e r e d partially sighted r e p r e s e n t i n g 0. 054%.

T h e s e figures a r e c l e a r l y incompatible with the f i g u r e s f o r the USA derived above. F i r s t l y , the total proportion (0. 254% of t h e population) i s t h r e e t i m e s l e s s than that of the USA. Secondly, while one would expect that the proportion of " r e g i s t e r e d blind" i n the UK would be l e s s than that

ill the USA (by r e a s o n of t h e lower visual acuity l i m i t s - - 0 . 05 a s compared with 0. 1 - - n o field r e s t r i c t i o n s i n e i t h e r c a s e ) , one would not expect the r e l a t i v e proportion of blind t o partially sighted p e r s o n s t o be r e v e r s e d in t h e two s e t s of s t a t i s t i c s . It is always possible that t h e incidence of both blindness and p a r t i a l sight is different i n both countries. But t h e genetic and c l ~ l t u r a l differences a r e not, at f i r s t sight, s o d i s s i m i l a r a s t o give such totally incompatible r e s u l t s .

It h a s been suggested that the s t a t i s t i c s for p a r t i a l sight in England and Wales e r r by a t l e a s t 50% owing t o the lack of motivation t o r e g i s t e r . The P a r t i a l l y Sighted Society of t h e UK is studying the incidence of partial sight based on available information f r o m l o c a l s o c i a l s e r v i c e s in t h e UK.

It is r e p o r t e d that the t r e n d s e m e r g i n g i n this study indicate that t h e figure of a 50% underestimate in the Naticnal R e g i s t e r is itself an underestimate.

Whatever t h e eventual r e s u l t s of t h i s s u r v e y , t h e r e s t i l l r e m a i n s a substantial unexplained difference between the UK and USA s t s t i s t i c s .

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A full study of the statistical data will be a necessary part of an eventual project, but the immediate need i s for a cross-check of the statistics from the USA with other developed countries. This would at least allow a judgment a s to whether the UK statistics could in any way be projected to give a m o r e meaningful result in the t e r m s of this study.

The Relation of Age to Severe Visual Impairment

Blindness and partial sight a r e , to some extent, age-dependent conditions. It appears that for the USA, over 6070 of the severely visually impaired a r e aged 65 o r over. A break-down of the partially sighted population by persentage in three age groups i s given in Table 3 .

Table 3

Age Groups of the Partially Sighted USA, England, and Wales

Age Groups

-

USA England and Wales

over 65 6470 6 370

25

-

64 3270 2 370

under 25 4% 1470

The US data a r e estimates by Goldish [7] ; no particular y e a r i s quoted.

The figures a r e based on that part of the visually impaired population with visual acuities of 0. 1 o r l e s s with best correction. The England and Wales figures a r e from the Partially Sighted Register and r e f e r to the y e a r end- ing 31 March 1972. They follow the UK c r i t e r i a f o r the partially sighted, i. e . visual acuity between 0. 05 to 0. 1 (greater with visual field r e s t r i c - tions).

It i s impossible to estimate how the relative proportions of partially sighted persons in the t h r e e age groups chosen a r e affected by the general inaccuracy of the Register a s a measure of the total partially sighted population in England and Wales. But the marked difference between the percentage of young people shown by the figures for England and Wales and the estimated percentage of the s i m i l a r age group in the USA may be noted. However, the general point that well over half the partially sighted population is over ret:rement age is well illustrated by both s e t s of figures.

So f a r a s the England and Wales figures a r e concerned, the trend in new registrations during the y e a r quoted showed a r a t h e r g r e a t e r proportion of the elderly and a somewhat lower proportion of the remaining two age

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groups (only 7. 3% of the new registrations were under 25, 17.3% being between 25 and 64, and 75.4% being over 65).

If these proportions a r e borne out by examination of the statistics f r o m other countries, we could make an estimate of the number of individuals likely to benefit from

a ) special educational facilities

b) assistance to maintain t h e i r earning capacity, and c) purely social assistance.

Such statistics would be useful in a future cost-benefit analysis of technological aids for partially sighted persons because they would permit some division into economic benefit and social benefit groups. How- e v e r , it would be unsound to break down the analysis into economic benefits for the younger age groups on the one hand, and social benefits for the older age groups on the o t h e r , since a l l age groups would presumably slzare the social benefits of increased scope of t h e i r activities. Nevertheless, the quantification of the economic benefits t o those In the school age and the working age groups will be important.

Other statistical break-downs a r e possible, e . g. by sex and by eye defect, but these s e e m hardly relevant at this stage in the study. Of m o r e importance for future examination i s the degree to whlch s e v e r e visual impairment i s related to a.bility to c a r r y on normal actlvlty, and to what extent other chronic conditions occur together with the conditions causing s e v e r e visual impairment. Some data exists on thls l a t t e r point in the US s-tatistics, but a detailed examination has been deferred since these i s s u e s a r e secondary to the objectives of the feasibility study

Conclusions

The available statistics from the USA will permit reasonably accurate estimates of the partially sighted population which could benefit from technological aios of a l l types. The estimates from two sources a r e in close agreement It i s unfortunate that the extremely detailed statistics published by the UK in the Blind Register and the Partially Sighted Register a r e probably considerable underestimates (in the view of one author by over 50% in the partially sighted c a s e ) . A study of the partially sighted population of the UK being c a r r i e d out by the Partially Sighted Society may give useful pointers to the adjustment of the statistical tables based on the R e g i s t e r , but, for the moment, t h e r e s e e m s little to be gained by attempting to extrapolate from the UK statistics.

It can be s a i d , however, that the feasibility of collecting the type of data required for the study proper has been demonstrated. The imme-

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diate next step should be to confirm that the inferences drawn from the USA figures can be cross-checked by a study of the available statistics from other countries of s i m i l a r cultural and genetic characteristics.

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IV. PROSTHETICS FOR THE SEVERELY VISUALLY IMPAIRED The Relevant E v e Conditions

E y e conditions resulting in s e v e r e l y defective vision a r e c u s t o m a r i l y divided i.nto two g e n e r a l groups: a n t e r i o r segment and p o s t e r i o r segment pathology. The f i r s t group e s s e n t i a l l y c o n s i s t s of defects of t h e r e f r a c t i v e m a t e r i a l ( i . e . t h e l e n s of the e y e ) , and the second group includes s e v e r e malfunctions of the r e t i n a o r optic n e r v e . An example of t h i s f i r s t type of condition is c a t a r a c t ; m a c u l a r degeneration of t h e r e t i n a is one of the rnore common manifestations of p o s t e r i o r segment defect. In K r i e g e r ' s clinical t r i a l of patients' reaction t o optical a i d s 222 patients (2470) had r e f r a c t i v e m a t e r i a l d i s o r d e r s a s against 695 ('7670) having r e t i n a l and op- t i c n e r v e malfunction

[lq.

In a Genensky et al. t r i a l of CCTV s y s t e m s , 5 1 s u b j e c t s (7570) w e r e found t o suffer f r o m malfunctions of r e t i n a o r op- t i c n e r v e , one f r o m defects of the r e f r a c t i v e m a t e r i a l alone, and 1 9 (2370) f r o m hoth

kg.

In hoth t r i a l s , the high proportion of m a c u l a r degeneration ill p o s t e r i o r segment defects was s t r e s s e d : i n the c a s e of t h e K r i e g e r s e r i e s 306 sc,bjects (33%) suffered f r o m t h i s condition, while in the Genensky CCr!:V t r i a l a total of 2 6 (3270) had t h i s type of condition.

3; is inappropriate h e r e t o attempt t o d e s c r i b e a l l the many eye conditions v h i c h c o m p r i s e the pathology of s e v e r e v i s u a l i m p a i r m e n t . It is sufficient i o note that t!le m o s t frequent malfunctioning of the r e f r a c t i v e m a t e r i a l ( c a t a r a c t ) c<m often be ccrrrected by s u r g e r y , while the r e t i n a and 3ptic nerS-\:e malfunctions c:?nnot be c o r r e c t e d (with t h e exception of r e t i n a l detachment). In practica! t e r m s , m o s t of t h e r e t i n a l and optic n e r v e con- d i t i o n ~ r e s u l t in a d i r e c t l o s s of vision which m a y be accompanied by visual. ::.ic:'d r e s t r i c t i o n s . Many such patients a r e not only unable t o distin- qi:.sh z:: oi;ject c l e a r l y , but, because of the destruction of t h e light sen- s i t ~ . v e i s s u e of the r e t i n a (the s o - c a l l e d cones and r o d s ) , t h e i r perception of c o n t r a s t is a l s o below n o r m a l . The i m a g e on t h e r e t i n a is thus defective in outline, and u n l e s s the object is much m o r e brightly illuminated th.a.n for a normally-sighted p e r s o n , i t is not bright enough t o provide the visual c e n t r e s of t h e brain with adequate information about the object.

A d e g r e e of a n t e r i o r segment malfunction is common: a l m o s t half t h e population of developed countries such a s the USA r e q u i r e s p e c t a c l e s -to c o r r e c t such conditions a s myopia, e t c . However, t h e s e conditions .seldom r e s u l t in impairment of vision s o s e v e r e that they cannot be c o r - r e c t e d by s p e c t a c l e s o r contact l e n s e s . Densities and i r r e g u l a r i t i e s of the r e f r a c t i v e m e d i a , including c a t a r a c t s , r e s u l t i n m o r e s e r i o u s vision l o s s , and patients suffering t h e s e conditions a r e in general t o be included in the s e v e r e l y visually i m p a i r e d population.

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F o r treatment of the s e v e r e visual impairment by low vision aids, it i s generally agreed that the actual pathological conditions a r e not c r i t e r i a f o r the prescription o r non-prescription of a n aid. There seems to be no particular correlation between types of eye malfunction and the nature of the aid prescribed. The extent and location of damage i s m o r e important than the particular pathology causing i t . However, different eye conditions a r e associated with different problems in prosthetic prescription.

Individual patients may have conditions which, for example, prevent them from reading o r writing without visual aids, while the main problem of other patients may be distance vision a s it affects their mobility. In K r i e g e r ' s sample, about 65% of patients gave a s their greatest need i m - provement in close vision while around 25% required improved distant vision a s f i r s t priority.

Optical Aids

Before the advent of CCTV s y s t e m s , the majority of visual aids for the severely visually impaired were lens systems of one kind o r another.

Their characteristics have been described in detail by Sloan 1121. Krieger, in his clinical t r i a l of 917 patients [lo], listed, in addition to standard l e n s e s , four general types of distance aids which he prescribed. They include monocular and binocular telescopes, multiple pinhole spectacles, and contact lenses.

Of these, the use of high power wide-angle telescope systems in the shape of conventional binoculars has been described in detail by Genensky [6] He points out that this commercially available item can a s s i s t the severely visually impaired person to a surprising extent. He has described how the use of binoculars played an important, i f not vital p a r t , in his own ability to benefit from a normal high school education. He h a s a visual acuity of 0.0267 in one eye only, with s e v e r e field restriction. Not only do such binoculars provide the necessary magnification (5 x s e e m s to be the average requirement), but t h e i r light-gathering power helps also to solve the contrast problem many partially sighted persons encounter in distinguishing, for example, s t r e e t signs o r traffic lights.

F o r n e a r vision, Krieger l i s t s nine aids preescribed for the subjects in h i s t r i a l , from unifocal and bifocal high power spectacle lenses to stand magnifiers and multiple pinhole spectacles. The following observations may be made about optical aids for n e a r vision:

1) None of the single o r spectacle clip-on high power lens systems solve the problem of contrast required for reading in a normally lighted room: patients whose conditions require blacklwhite contrast intensification cannot read with them without an addi-