7/23/2019 Verhoeff-A New Test for Visual Acuity http://slidepdf.com/reader/full/verhoeff-a-new-test-for-visual-acuity 1/6 NEW TEST FOR VISUAL ACUITY F. H. VERHOEFF M.D. Boston Vision is so complicated a phenomenon and is dependent upon so many variables that no single test can be devised by which it can accurately be measured for all purposes. In practical life, however the most important factor in visual acuity no doubt is the resolving power of the eye. This is commonly measured by determining the smallest visual angle perceptible the minimum separable. Such determi- nations, however do not reveal the full resolving power of the eye, for the best possible vision shown by them corresponds to a visual angle of only about 30 minutes, whereas by certain methods which measure the aligning power it can be shown that the eye is capable of much finer discrimination than this. It should not be assumed from this fact, however that tests based upon the minimum separable are necessarily less precise than are those based upon the aligning power. While, so far as I know the aligning power has not been accurately correlated with the perception of the minimum separable, my own observations indicate that relative differ- ences in the former cannot be so accurately determined as relative differences in the latter. Moreover if a person has the best possible perception of the minimum separable, he will, no doubt, be found to have the best possible aligning power. The Snellen test measures the minimum separable with a considerable degree of accuracy, and the practical value of this test has been demonstrated over a period of many years. From the Howe Laboratory of Ophthalmology Harvard University, and, the Massachusetts Eye and Ear Infirmary. 6 161
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7/23/2019 Verhoeff-A New Test for Visual Acuity
http://slidepdf.com/reader/full/verhoeff-a-new-test-for-visual-acuity 1/6
NEW TEST FOR
VISUAL ACUITY
F . H.
VERHOEFF
M.D.
B o s t o n
V i s i o n
i s s o
c o m p l i c a t e d
a
p h e n o m e n o n
a n d i s
d e p e n d e n t
u p o n
s o
many
v a r i a b l e s
t h a t
n o
s i n g l e
t e s t c a n
b e
d e v i s e d
b y
w h i c h
i t
c a n
a c c u r a t e l y
b e m e a s u r e d
f o r
a l l
p u r p o s e s .
I n
p r a c t i c a l
l i f e , h o w e v e r
t h e
m o s t
i m p o r t a n t
f a c t o r
i n
v i s u a l
a c u i t y
n o d o u b t
i s t h e
r e s o l v i n g
p o w e r
o f
t h e
e y e .
T h i s
i s
c o m m o n l y
m e a s u r e d
b y d e t e r m i n i n g
t h e
s m a l l e s t
v i s u a l
a n g l e
p e r c e p t i b l e t h e
m i n i m u m
s e p a r a b l e .
S u c h
d e t e r m i -
n a t i o n s ,
h o w e v e r
d o
n o t
r e v e a l
t h e f u l l
r e s o l v i n g
p o w e r
o f
t h e
e y e ,
f o r t h e
b e s t
p o s s i b l e
v i s i o n
s h o w n
b y
t h e m
c o r r e s p o n d s
t o
a
v i s u a l a n g l e
o f
o n l y
a b o u t
3 0
m i n u t e s ,
w h e r e a s
b y c e r t a i n
m e t h o d s
w h i c h
m e a s u r e
t h e
a l i g n i n g p o w e r
i t
c a n
b e
s h o w n
t h a t
t h e
e y e
i s
c a p a b l e
o f
much
f i n e r
d i s c r i m i n a t i o n
t h a n
t h i s .
I t s h o u l d
n o t
b e
a s s u m e d
f r o m
t h i s
f a c t ,
h o w e v e r
t h a t t e s t s
b a s e d u p o n
t h e
minimum
s e p a r a b l e
a r e
n e c e s s a r i l y l e s s
p r e c i s e
t h a n
a r e
t h o s e
b a s e d
u p o n
t h e
a l i g n i n g
p o w e r .
W h i l e ,
s o
f a r
a s
I
k n o w
t h e
a l i g n i n g
p o w e r
h a s
n o t b e e n
a c c u r a t e l y
c o r r e l a t e d
w i t h t h e
p e r c e p t i o n
o f
t h e
minimum
s e p a r a b l e , m y
own
o b s e r v a t i o n s i n d i c a t e
t h a t
r e l a t i v e
d i f f e r -
e n c e s
i n t h e
f o r m e r
c a n n o t b e
s o
a c c u r a t e l y
d e t e r m i n e d
a s
r e l a t i v e d i f f e r e n c e s
i n
t h e
l a t t e r .
M o r e o v e r
i f
a
p e r s o n h a s
t h e
b e s t
p o s s i b l e
p e r c e p t i o n
o f
t h e
m i n i m u m
s e p a r a b l e ,
h e
w i l l ,
n o
d o u b t ,
b e
f o u n d
t o h a v e
t h e
b e s t
p o s s i b l e
a l i g n i n g
p o w e r .
T h e
S n e l l e n
t e s t m e a s u r e s
t h e minimum
s e p a r a b l e
w i t h
a c o n s i d e r a b l e
d e g r e e
o f
a c c u r a c y ,
a n d
t h e
p r a c t i c a l
v a l u e
o f
t h i s
t e s t
h a s
b e e n
d e m o n s t r a t e d
o v e r
a
p e r i o d
o f
many
y e a r s .
From t h e
H owe
L a b o r a t o r y
o f
O p h t h a l m o l o g y
H a r v a r d
U n i v e r s i t y ,
a n d ,
t h e
M a s s a c h u s e t t s
E y e
a n d
E a r
I n f i r m a r y .
6
1 6 1
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1 6 2
V E R H O E F F : A New
T e s t
f o r V i s u a l A c u i t y
O n e
o f
i t s
p r i n c i p a l
a d v a n t a g e s
i s t h a t i t
d e t e r m i n e s
d i r e c t l y
t h e
a b i l i t y t o
r e c o g n i z e
l e t t e r s ,
w h i c h
i s
o n e
o f
t h e
m o s t
i m p o r t a n t f u n c t i o n s
o f v i s i o n
i n
d a i l y
l i f e . I t s
c h i e f
d i s -
a d v a n t a g e s a r e t h a t
d i f f e r e n t l e t t e r s u s e d i n
t h e t e s t a r e
n o t a l l a f f e c t e d a l i k e b y a s t i g m a t i s m
a n d
o t h e r
a b e r r a t i o n s
o f
t h e o p t i c a l s y s t e m
a n d
h a v e
d i f f e r e n t d e g r e e s
o f
l e g i b i l i t y .
T h e m o s t n o t a b l e
o f
t h e
a t t e m p t s t o i m p r o v e
o n
S n e l l e n s
t e s t w e r e t h o s e
o f
L a n d o l t a n d o f
I v e s . T h e
L a n d o l t
r i n g
a n d
t h e
I v e s g r a t i n g
e a c h
p o s s e s s t h e
s e r i o u s
d i s a d v a n t a g e
h o w e v e r
t h a t
n u m e r o u s
d e t e r m i n a t i o n s
m u s t
b e
m a d e
t o
a l l o w f o r t h e e f f e c t
o f
a s t i g m a t i s m ,
t h u s e m p h a s i z i n g
t h e
f a c t o r s
o f
f a t i g u e
a n d
f a u l t y o b s e r v a t i o n .
R e c e n t l y
I
h a v e
d e v i s e d
a
t e s t
f o r v i s u a l
a c u i t y
t h a t
s e e m s
t o
b e n o t
o n l y m o r e d e l i c a t e
a n d
a c c u r a t e t h a n
t h e S n e l l e n
t e s t a t
l e a s t f o r
v i s u a l
a c u i t y
b e t t e r
t h a n
2 0 / 4 0 b u t
i s
a l s o
s i m p l e r . M o r e o v e r
i t s r e s u l t s s h o w a s c l o s e a
c o r r e s p o n d
e n c e
w i t h
t h e S n e l l e n
t e s t
a s
t h e
a c c u r a c y - o f
t h e l a t t e r
w i l l
d e t e r m i n e .
A s
a
t e s t
f o r
i l l i t e r a t e s
i t s
v a l u e
w i l l
a t
o n c e
b e
a p p a r e n t .
F o r
o r d i n a r y
u s e
t h e t e s t
i s
m a d e
b y
u t i l i z i n g
a
c h a r t
t o b e v i e w e d
a t
2 0 f e e t
f i g .
1 ,
w i t h
g r a d a t i o n s
c o r r e s p o n d i n g
t o
t h e
u s u a l S n e l l e n c h a r t
a n d
a n
a d d i t i o n a l
g r a d a t i o n
c o r r e s p o n d i n g
t o V .
= 2 0 / 1 2 . 5 .
T h e
c h a r t , h o w e v e r c a n ,
o f
c o u r s e ,
b e
a d a p t e d
t o t h e f i v e - m e t e r
o r
d e c i m a l
s y s t e m .
T h e r e
a r e e i g h t
r o w s o f
f i g u r e s ,
e a c h r o w
c o n s i s t i n g
o f
t w o
u n i t s . I f
t w o
c o m p l e t e
c i r c l e s a r e s e e n
i n
t h e
f i g u r e
o n
t h e
l e f t
i n
t h e
f i r s t
r o w
V .
=
2 0 / 2 0 0 ;
i f
t h r e e c i r c l e s
a r e s e e n i n
t h e
f i g u r e
o n
t h e
r i g h t ,
V .
= 2 0 / 1 0 0 .
I n
t h e
s e c o n d
r o w
t h e
f i g u r e s
c o r r e s p o n d
t o V .
=
2 0 / 7 0
a n d
V .
=
2 0 / 5 0 ,
r e s p e c t i v e l y .
I f
t h e
v i s u a l
a c u i t y
i s
f o u n d
t o
b e
b e t t e r
t h a n
t h i s ,
t h e
p a t i e n t
i s
i n s t r u c t e d
t o
l o o k a t t h e o t h e r
r o w s
f r o m
a b o v e
d o w n w a r d
a n d
t o s e l e c t
t h e
l o w e s t
r o w
i n
w h i c h
h e
c a n
s t i l l m a k e o u t
t w o
c i r c l e s
i n
t h e
f i g u r e
o n
t h e
l e f t .
L e t u s
s u p p o s e ,
f o r
e x a m p l e
t h a t
h e s e l e c t s
r o w
N o .
4
f i g . 2 ) :
He
i s
t h e n
a s k e d
i f
t h e t w o
f i g u r e s
i n
r o w
N o . 5
l o o k
a l i k e .
I f
t h e y
d o l o o k
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7 0
oo
4
5
0 0
6
I s
1 2 S
8
1 0
F i g .
1 . C h a r t a s
seen w i t h
a
n o r m a l
e y e .
F i g .
3 . C h a r t
as
seen b y
an
eye
w i t h s i m p l e a s t i g m a t i s m ,
a n d
v i s u a l
a c u i t y
o f
2 0 / 4 0 .
F i g . 2 . C h a r t a s seen
b y a m y o p i c
o r
h y p e r m e t r o p i c
eye
w i t h
v i s u a l a c u i t y
s l i g h t l y
b e t t e r
t h a n
2 0 / 3 0 .
F i g . 4 . C h a r t as
seen
b y
an e y e
w i t h
c o m p o u n d
s t i g m t i s m
a n d v i s u a l
a c u i t y
o f
2 0 / 1 0 0 .
s o
4 0
3 0
2 0
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V E R H O E F F :
A
New T e s t f o r
V i s u a l A c u i t y
a l i k e , h i s v i s u a l a c u i t y
c o r r e s p o n d s
t o
r o w N o .
4 ,
a n d
i s
2 0 / 3 0 .
I f
h e
s t a t e s
t h a t
t h e
t w o
f i g u r e s
i n
r o w N o .
5
d o
n o t
l o o k
a l i k e ,
b u t
t h a t t h o s e
i n
r o w N o . 6
d o l o o k a l i k e ,
h i s
s e l e c t i o n
o f
r o w
N o .
4
w a s i n a c c u r a t e
a n d
h i s v i s u a l
a c u i t y
i s
n e a r l y
2 0 / 2 0 . A s t i l l h i g h e r d e g r e e o f a c c u r a c y
may
b e
o b t a i n e d b y c h a n g i n g t h e d i s t a n c e
f r o m
t h e
c h a r t .
F o r
e x a m p l e
s u p p o s e
t h e p a t i e n t
s e l e c t s
r o w
N o .
5
V .
=
2 0 / 2 0 ) .
By
b r i n g i n g
h i m c l o s e r t o t h e
c h a r t
i t
may
b e f o u n d t h a t a t
1 8
f e e t
h e s e l e c t s r o w N o . 6 , i n d i c a t i n g V .
=
1 8 / 1 5 .
I n
t h i s
way
I
h a v e
a s c e r t a i n e d
t h a t a
g o o d o b s e r v e r
w i t h
a
v i s u a l
a c u i t y
o f a b o u t
2 0 / 1 2
c a n
d e t e c t a
d i f f e r e n c e
o f
a b o u t
4
m i n u t e s
i n
t h e v i s u a l
a n g l e .
A
p r e c i s e
a n d
c o n v e n i e n t m e t h o d
o f
m a k i n g
t h e t e s t
i s
t o
t h r o w t h r e e
r o w s , 2 0 / 4 0 , 2 0 / 3 0 ,
a n d
2 0 / 2 0 ,
o n
a
s c r e e n
b y
m e a n s o f
a
p r o j e c t o r
w h i c h
v a r i e s t h e
m a g n i f i c a t i o n
s
d e s i r e d . *
I f
t h e r e
i s
u n c o r r e c t e d
a s t i g m a t i s m ,
i t
i s
e s p e c i a l l y
i m
p o r t a n t
f o r
t h e p a t i e n t
t o
o b s e r v e t h a t t h e
c i r c l e s a r e
c o m p l e t e
i n
t h e
f i g u r e c o r r e s p o n d i n g
t o h i s v i s u a l
a c u i t y
f i g s . 3
a n d
4 ) .
When
t h e r e
i s
a
c o n s i d e r a b l e a m o u n t
o f
a s t i g m a t i s m ,
h e w i l l
o b s e r v e
t h a t e a c h
f i g u r e
s h o w s
t w o
s e c t o r s , d i a m e t r i c a l l y
o p p o s i t e ,
i n
w h i c h
t h e c i r c l e s
a r e
m o s t
d i s t i n c t .
I n
c a s e
t h e
e y e
i s
e m m e t r o p i c
i n
t h e
m e r i d i a n
a t
r i g h t
a n g l e s
t o
t h e a x i s o f t h e
a s t i g m a t i s m , t h e p a t i e n t may
o b s e r v e
t h a t
t h e r e a r e
t w o
b a n d s
i n
t h e s e c t o r s
i n
t h e
f i g u r e s
o n t h e l e f t
a n d
t h r e e b a n d s
i n
t h e s e c t o r s
i n
t h e
f i g u r e s
o n
t h e
r i g h t .
I f
t h i s
s l i g h t
d i f f e r e n c e
o c c u r s ,
h e s h o u l d
b e
t o l d
t o
d i s r e g a r d
i t .
I n
t h e
f i r s t
t w o
r o w s o f
f i g u r e s
o n
t h e c h a r t
e a c h
i n t e r v a l
i n t h e
f i g u r e s c o r r e s p o n d s
t o a n
a n g l e
o f
o n e
m i n u t e
a t t h e
d e s i g n a t e d
d i s t a n c e . S i n c e
l o w v i s u a l
a c u i t y
i s
o f t e n d u e t o
r e f r a c t i v e e r r o r s
w h i c h
e x a g g e r a t e t h e
e f f e c t s
o f
t h e v a r i o u s
a b e r r a t i o n s
o f
t h e
o p t i c a l s y s t e m
a n d
t h u s
p r o d u c e i r r e g u l a r
T h e
A m e r i c a n
O p t i c a l
Company i s
p r e p a r i n g
t o
s u p p l y
t h e
t e s t
c h a r t .
T h e y
w i l l
a l s o
u t i l i z e
i t i n
a new
p r o j e c t i o n
l a n t e r n .
1 6 3
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1 6 4
V E R H O E F F : A
New
T e s t
f o r V i s u a l A c u i t y
d i s t o r t i o n s
i n
t h e
r e t i n a l
i m a g e ,
t h e
e s t i m a t i o n o f
v i s u a l
a c u i t y
w i t h i n
t h i s
r a n g e
i s
l i k e l y
t o
b e
h i g h l y
i n a c c u r a t e .
I n
r a r e
i n s t a n c e s ,
o w i n g
t o
t h e
d o u b l i n g
o f
i m a g e s , i t may
e v e n
h a p p e n
t h a t t h e
p a t i e n t
f a i l s t o
s e e
t w o
c i r c l e s i n
t h e
f i g u r e o n
t h e l e f t ,
a n d
y e t s e e s t h r e e
c i r c l e s
i n
t h e f i g u r e
o n
t h e r i g h t .
s i m i l a r
i n a c c u r a c y ,
o f
c o u r s e ,
e n t e r s i n t o
t h e
S n e l l e n t e s t ,
e s p e c i a l l y w h e n
a s i s
u s u a l ,
o n l y
a
f e w
d i f f e r e n t
l e t t e r s
a r e
e m p l o y e d
b u t
a s
t h e
t w o
t e s t s
o f t e n
d o n o t c o r r e s p o n d w i t h i n
t h i s
r a n g e ,
i t i s
p r o b a b l y
b e s t , f o r
p r a c t i c a l p u r p o s e s ,
t o
r e l y h e r e u p o n
t h e
S n e l l e n t e s t ,
e x c e p t
i n t h e c a s e o f
i l l i t e r a t e s .
I n
e a c h
r o w b e l o w
t h e
s e c o n d
r o w i t
w i l l
b e
s e e n
t h a t a
new
p r i n c i p l e
i s
i n t r o d u c e d
o n
t h e
c h a r t ,
n a m e l y
t h e
u s e
o f a
f i g u r e
o n
t h e
r i g h t
f o r
c o m p a r i s o n w h i c h s e r v e s
a s a
c o n t r o l
o n t h e
p a t i e n t s -
a c c u r a c y
o f
o b s e r v a t i o n .
I n
t h e
f i g u r e s
o n
t h e
l e f t s i d e
o f
t h e c h a r t t h e
w h i t e
i n t e r v a l
b e t w e e n
t h e t w o
c i r c u l a r
b a n d s a n d t h e w i d t h
o f
t h e
i n n e r
b a n d s
e a c h
s u b t e n d s
a n
a n g l e
o f
o n e m i n u t e a t
t h e
d i s t a n c e s
d e s i g n a t e d
o n
t h e
c h a r t ,
b u t
t o
m a k e t h e
t w o
c i r c u l a r
b a n d s
h a v e
t h e s a m e
v i s i b i l i t y
i t
w a s
f o u n d
n e c e s s a r y
t o m a k e
t h e
o u t e r b a n d
s l i g h t l y
w i d e r t h a n t h e
i n n e r .
T h e
d i a m e t e r
o f
e a c h
f i g u r e
i s
g r e a t
e n o u g h
t o
g i v e
t h e maximum
v i s i b i l i t y
o f t h e i n t e r v a l s a t t h e
d e s i g n a t e d
d i s t a n c e s . T h e
f i g u r e
o n
t h e
r i g h t ,
w h i c h i s
t o b e
u s e d f o r
c o m p a r i s o n ,
c o n s i s t s
o f
t h r e e
c o n c e n t r i c
c i r c u l a r
b a n d s . T h e
w h i t e
i n t e r v a l s
a r e
e a c h
a b o u t o n e - h a l f t h a t
o f
i t s
c o m p a r i s o n f i g u r e ,
b u t
t h e
e x a c t d i m e n s i o n s
w e r e
d e t e r m i n e d
b y
t h e
m e t h o d
o f
t r i a l
a n d e r r o r , * s o t h a t when b l u r r e d
o r
j u s t
b e y o n d
t h e
l i m i t
o f
d i s t i n c t
v i s i o n ,
b o t h
f i g u r e s
w o u l d
p r e s e n t
t h e
s a m e
a p p e a r a n c e i n c l u d i n g
s i z e
a n d
i n t e n s i t y .
T h e
d i m e n s i o n s
o f
t w o
s t a n d a r d
f i g u r e s ,
c o r r e s p o n d i n g
t o
V .
2 0 / 5 0 ,
u s e d
f o r
c o n s t r u c t i n g
a l l
t h e
f i g u r e s
b e l o w r o w
N o .
2 ,
a r e a s
f o l l o w s :
F i g u r e
o n
t h e
l e f t :
d i a m e t e r ,
5 6 . 5
m m . ;
w i d t h o f
o u t e r
b a n d
F o r v a l u a b l e
a s s i s t a n c e
i n
s u c h
d e t e r m i n a t i o n s
I
a m
i n d e b t e d
t o
D r .
Hugo
L .
B a i r ,
o f
t h e
Howe
L a b o r a t o r y
o f
O p h t h a l m o l o g y
H a r v a r d
U n i
v e r s i t y .
7/23/2019 Verhoeff-A New Test for Visual Acuity
http://slidepdf.com/reader/full/verhoeff-a-new-test-for-visual-acuity 6/6
V E R H O E F F :
A
New
T e s t f o r V i s u a l A c u i t y
5 . 2
m m . ;
w h i t e
i n t e r v a l , 4 . 4 3 m m . ;
w i d t h o f i n n e r b a n d
4 . 4 3
mm.
C o n t r o l
f i g u r e :
d i a m e t e r ,
5 6 . 5
m m . ;
w i d t h
o f
o u t e r
b a n d
3 . 5 m m . ;
w i d t h
o f
o u t e r w h i t e i n t e r v a l , 2 . 5 6
m m . ; w i d t h
o f m i d d l e
b a n d 2 . 6 8 m m . ;
w i d t h
o f
i n n e r w h i t e
i n t e r v a l ,
2 . 5 8 m m . ;
w i d t h
o f
i n n e r
b a n d 2 . 9 5 mm.
T h e
c h a r t
w i l l a l s o b e
f o u n d
s u p e r i o r
t o t h e S n e l l e n
c h a r t
i n
e s t i m a t i n g ,
b y
m e a n s
o f
t r i a l
l e n s e s ,
t h e
r e f r a c t i o n
o f
t h e
e y e , i n c l u d i n g
t h e
a m o u n t a n d a x i s
o f
a s t i g m a t i s m , f o r
i n
u s i n g
t h e S n e l l e n
c h a r t f o r t h i s
p u r p o s e
i t
i s
n e c e s s a r y
f o r
t h e
p a t i e n t
t o
o b s e r v e
d i f f e r e n c e s i n
a w h o l e r o w
o f
l e t t e r s ,
w h e r e a s
i n
t h e
p r e s e n t
c h a r t h e h a s
m e r e l y
t o c o n f i n e
h i s
a t t e n t i o n
t o o n e
s i m p l e
f i g u r e .
T h e
m o s t
s u i t a b l e
f i g u r e
f o r h i m
t o
s e l e c t
i s
t h e l o w e s t
f i g u r e
o n
t h e l e f t
i n
w h i c h
h e c a n
s e e
t w o
c i r c l e s . A s
t h e v i s u a l
a c u i t y
i s
i m p r o v e d
b y
t h e l e n s e s ,
t h e
f i g u r e
s e l e c t e d
w i l l ,
o f
c o u r s e , b e l o w e r
d o w n .
I f
t h e
p a t i e n t
s e e s s e c t o r s
i n
a n y
o f
t h e
f i g u r e s ,
h i s
a s t i g m a t i s m
h a s
n o t b e e n
a c c u r a t e l y c o r r e c t e d .
A s
r e g a r d s
i l l u m i n a t i o n ,
t h e
s a m e
p r i n c i p l e s a p p l y
a s
i n
t h e c a s e o f
t h e
S n e l l e n
t e s t ,
b u t
i t
i s
e s p e c i a l l y
d e s i r a b l e
f o r
t h e
f i g u r e s
o n
t h e
r i g h t
a n d
o n
t h e l e f t t o
h a v e
t h e
s a m e
i l l u m i n a t i o n .
I f
i t
i s
d e e m e d
d e s i r a b l e ,
a
f i n a l
c h e c k o n
t h e v i s u a l
a c u i t y
may
b e m a d e
b y s h o w i n g ,
o n e a t
a
t i m e , t h r o u g h
a n
o p e n i n g ,
t h e t w o
f i g u r e s
i n
t h e
r o w
s u p p o s e d
t o
c o r r e s p o n d
t o
t h e
v i s u a l
a c u i t y .
T h e
p a t i e n t
s h o u l d
t h e n
b e
a b l e t o
s e l e c t
w i t h o u t a
s i n g l e
e r r o r t h e
f i g u r e
w i t h
t w o
c i r c l e s .
T h i s
p r o c e d u r e may
p r o v e
o f
v a l u e
i n
t h e c a s e o f
p e r s o n s
who
c l a i m
h i g h e r
v i s u a l
a c u i t y
t h a n
t h e y
r e a l l y
p o s s e s s .
1 6 5
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