Pacific University Pacific University

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College of Optometry Theses, Dissertations and Capstone Projects

5-1973

Binocular refraction- a comparative technique Binocular refraction- a comparative technique

David Bickell Pacific University

Terry Cole Pacific University

Graham Dawdy Pacific University

Recommended Citation Recommended Citation Bickell, David; Cole, Terry; and Dawdy, Graham, "Binocular refraction- a comparative technique" (1973). College of Optometry. 342. https://commons.pacificu.edu/opt/342

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Binocular refraction- a comparative technique Binocular refraction- a comparative technique

Abstract Abstract Binocular refraction- a comparative technique

Degree Type Degree Type Thesis

Degree Name Degree Name Master of Science in Vision Science

Committee Chair Committee Chair H Haynes

Subject Categories Subject Categories Optometry

This thesis is available at CommonKnowledge: https://commons.pacificu.edu/opt/342

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Binocular Refraction -

A Comparative Technique

A Fourth Year Optometry Project

Presented To

The Faculty of the College of Optometry

Pacif~c University

In Partial Fulfillment of the

Requirement for the Degree

Doctor of Optometry

by

David Bickell Terry Cole

Graham Dawdy

Advisor Dr. H. Haynes

r-'ci?..y 197J

APPROVED

FOURTH Y'"lliA..'t OPI'OMETRY PROJECT

Chairman

Advisor

We would like to thank Dr. Harold Haynes for his help

and guida.nce in preparation of this paper. He would also

like to give special thanks to Doctors Roth and Richards

for their suggestions and help.

D,B.

T.C. G, D.

TABLE OF CONTENTS

Introduction

P.roblem •

Procedure

Results

" ...

Discussion of Results •

Suggestions for Future Studies

Summary •

Bibliography

Tablesr

Fig-u.res:

•

I •

II

III

lV

1

2

3

4

5

6

7

•

•

..

•

•

•

•

..

~

• •

• •

•

• •

·•

•

•

•

1 -

•

•

•

• •

•

2

2

3

8

15

15

16

20

3

4

6

7

1?

17

18

18

18

19

19

Introduction

Examination of the literature on distance refractive techniques

over the past thirty years shows recurrent interest in binocular

refractive techniques as compared to conventional monocular refractive

procedures. No single binocular refractive technique has developed

world wide acceptance or been shown to be superior to conventional

procedures. Quantitative comparative studies are much leas common

than are the published descriptions of techniques. Binocular

1 2 refractive techniques have been described by Sugar, • Turville, ·

Humphriss{· Van Wien~· Frantzt' Baldwin?· and many others.

Quantitative comparisons between conventional and binocular

refractive procedures have been reported by Miles?~ Morgan~' and

Rosenberg and Sherman?· Niles found an average cylind9r axis change

of 8 degrees under binocular condi tiona, Morgan found a change in

axis of 10 degrees or more in 2% of the subjects of his study. He

found no significant change in cylL~der power. Rosenberg and Sherman

u6ing the American Optical Vectographic slide studied 47 :patients

under identical conditions. They found no change in cylinder power

but found an axis change greater than 3 degrees in 10% of their

subjects under binocular conditions. Their study included measure-

menta of visual acuity, bL"locula.r instability, fixation disparity,

and stereopsis. Difference in visual acuity between the standard

and Vectographic slide of less than one line in 32 subjects and a

differe.~ce of one line in 9 subjects was reported. They main-

ta.ined that the difference was not due to the test slide because

the visual acuity difference was in only one eye, Their explanation

2

of the difference in visual acuity doesn't seem reasonable for several

reasons. Our prelLilinary clinical observations indicated that if there .

was a difference it was frequently observed in both eyes. We found

no report in the published 11 terature that indicates a significant

difference in monocular acuities under binocular viewing conditions.

Problem.

Our study .,.las conducted for several reasons. First, we wanted

direct clinical experience with a recognized binocular refl:action

method. Secondly, we wanted to compare bL~ocular refractive pro­

cedures at distance with the conventional distance refractive pro­

cedures as taught at Pacific University College of Optometry Clinic.

Thirdly, we wished to compare our results with the published 11 tera ture.

This study was designed to investigate quantitative a..'"ld qualitative

differences between these two refractive procedures as contrasted

with examiner preferences or opinions. The AO Vectographic slide was

selected for a comparative study because of its availability and

because of the study published by Rosenberg and Sherman.

Quantitatively we investigated the difference in measurements

of anisometropias, astigmatic axis and :power,. and the distal endpoint

of accommodation (punctUlll. remotu:n). We also tia.Il ted to evaluate the

use of the AO Vectograhic slide in detecting binocular instabilities

and suppressions, measuring stereopsis and neutralizing fixation

dlspg.rities.

Procedure

In order to investigate the problem as previously stated, sixty­

three subjects were chosen. Their ages ranged from six to forty

years, and the age distribution varied as shown in Table I:

Table I: . . . ' ' . Age Range

6 - 11

12 - 17

18 - 23

24- 29

30 - 35

36-40

NtL'!lber of Subjects

4

3

32

18

3

3

Fifty of the sixty-three subjects were Optometry students and were

thereby classified as experienced observers. The other thirteen

subjects were a convenient sample of clinical patients. Only patients

without strabismus, and with no apparent pathology were accepted for

comparative purposes.

Standa.:rdiza.tion of instructions and the discrimination requirements

received special attention so that during the tests that were common to

both methods of refraction, the examiner could give the same instructions

to each subject. The three clL"'lical rooms used during the investigation

were carefully chosen and matched with regard to general room illumi­

nation, distance, background contrast, and det...ail and surround lumi­

~ance from ft8 screen onto which the letters were projected. The A.O.

project-o-cha.rt slide used for the conventional refraction was the

modal lllOJ, and ·the slide used for the binocular refraction was the

Jilodel 1124 ). Table II contains a description of the :room and screen

conditions.

4

Table II: • , Roo:m. Slide Detail Surround Luminous Illumination Used Luminance Luminance Contrast

0 fc Conv. 1.7 fL 72.0 fL 0.98

0 fc Binoc. 4.9 fL 15.4 fL 0.68

2.5 fc Conv. 5.4 fL 75.2 fL 0.93

2 • .5 fc Binoc. 5.1 fL 16.0 fL 0.68

14.4 fc Conv. 8.5 fL 8).2 fL 0.90

14.4 fc Binoc. 8.9 fL 20.0 fL 0.55

The zero footcandle condition occnrred under total room darkness,

the 2.5 level was the room illumination with the light nearest the

screen turned of'f, and the 14.4 level occurred under full room illwn-

ination. The lumi.l'lance contza.st was calculated from the formula

c1 = l-L1/t2 , where ~""' the detail luminance and L2= the surround

luminance. The chair in each of the rooms was moved so that the

subject sat at the angle of reflection of the projected light. The

2.5 fc level of illumination was maintained throughout each examination,

except during the Bichrome test.

The testing procedures followed the stan~ Pacific University

clinical methods9 The same tests were performed under conventional

and binooular testing conditions. A polaroid analyzer 1o1as used with

the binocular condition to effectively allow input to one eye while

the other observed an empty lighted field corresponding to the area

of letters in the eye being tested. The peripheral visual field was

common to both eyes.

A static retinoscopy with fixation at eighteen feet provided the

basis on which the successive subjective refractive procedures were

performed. The Red.-Green .Bichrome test p:rovided the lens control

for a cylinder power and axis modification. This modification was

5

accomplished with the Jackson Cross Cylinder, and this result was

further modified with a cylinder power and axis rock on the 20/40

line of letters. The "just noticeable difference'' for axis range

was recorded, An anisometropia evalua. tion was accomplished with

the Bichrome test and also with a. 20/JO Equalization. The latter

~..mployed Risley prisms during the conventional exam, and the split

ehart during the binocular e~~. A far subjective finding, the

ma..."Ci.mUll!. :plus that gave 2/J of the 20/20 line, was found and followed

by the determination of the lens that gave the subjective best

visual acuity. The acuities were noted after both the conventional

and the binocular subjective refractions. Acuities were again taken

with the binocular subjective to best visual acuity in place and

using the conventional slide. Any differences were noted. The

sequence of perfonning the conventional before the binocular exam

- was altered to the binocular before the conventional for every other

.. • + SUOJeC "•

Supplemental to the static retinoscopy and the subjective findings,

an evaluation of suppression response, fixation disparity, and stere-

opsis was obtained with the binocula.r slide. SUppressions and a mea.-

suxe of binocular instability were noted from. lines of "mixed letters",

some common to only each eye. Fixation disparity, both lata.""'a.l and

vertical was neutralized using the ta.rget w1 th the central binocular

lock. The degree of stereopsis was noted from the four line target.

Finally if any fixation dispa_~ty existed, this was corrected for with

one Risley prism before the left eye, and the quality of the stereo

:response was re-e•talua.ted. for any subjective changes. Table III

su.m.marizes the testing sequence:

6

Table III: • . • Conventional Binocular Refraction Refraction

1. Distance sta. tic 1. Distant static retinoscopy retinoscopy

2. Red-Green Bichrome 2. Red-Green Bichrome Test - 20/50 line Test - 20/50 line

3· Jackson Cross Cylinder Test - 20/40

3. Jackson Cross Cylinder Test - 20/40

4. Cylinder Rock - 20/40 4. Cylinder Rock - 20/40

5. Equalization - use of 5· Equalization - Split Risley prisms - 20/30 Chart line

6. Subjective - maximum 6. Subjective - maxima~ :plus for 2/3 of the

plus for 2/J of the 20/20 line 20/20 line

?. Subjective best visual ?. Subjective best vis- acuity - 20/15 line

ual acuity - 20/15 line. B. Acuities - OD, OS, ou

8. Acuities - OD, OS, 9. Suppressions and binocular ou instabilities -mixed

letters 9. Acuities - OD, OS,

OU with the binocu- 10. Fixation disparity -lar subjective and central lock the conventional slide, 11. Stereopsis - with and

without fiXation disparity neutralized.

The recording form is shown in Table IV, listing each test's results

in a side by side manner for easy comparison.

0 3

0 -3 ___ __ .. ___ -----·-~--

o:; __ ::_L_f?_Q__ __ _

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------OD ---,......., 1..'·.:.>---~--

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o D _ _::,_:l.O It :;­

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OU C2o;,..:;-____...._.. .. _ ... __

, . sai'?'1.R....· cv-~.?wd~,/z.~ on 1/"1/l l ·~J_; le.:tters .. _ 1 v r"

,Q' (I) 0 S IA-f p J!'-~- 5 S l () ':'3 • _ 3 t 4 eso - -f:(Y.:..o....bu:;V) d:srard~--:; "f- .s be.r'- e .o psi~ = 1[ tj., ll vuu

7

8

Results

L"1 order to obtain a measure of the reliability of each method

of refraction - the conventional and the binocular mathod, thre-e

s:peciflc subjects were reexamined over four successive days. The

testing procedures .-re:re exactly the sa1ne as :performed during the

main clinical investigation (see Table III).

Subject T.B. (22) was a 1 • .50 D myope with less t:r..a.n .50 D

cylinder. Subject .P.K. (27) was a 1.00 D hyperope with less than

.50 D cylinder. Subject T.C. (24) was a compound myopic astigmatic

of 2.00 D to 2.50 D.

The daily variation in measurement of s::phere and cylinder power

was observed by fully repeating the e~~ination routine on four

successive days. The comparison of binocular and conventional

metheds for any given day yielded no mare tl:'>.a.n 0. 25 D difference

be.tween the two. 'rhis difference was considered to be a simple

:random m~urement error. See scatterg:ram 1 Hhich plotted each

subject's daily sphere a.11d cylinder measurement,

'I'lle varia. tion betwee.."l successive days ls plotted for each

subject on graph I. The extreme variation was a • 50 D cylinder

measurement wi-th subject P.K., which i<1'"aS no·t present after the first

day's testing. For a.t1y given day of the four testing days no greater

tl:>.an a 0. 25 D difference Has noted.

As a result of repeating our measurements on three subjects over

:four successive days, 11e concluded that further evaluation of test­

retest reliability '}ri th more subjects '1-?as not necessary.

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· Figure 1 displays a comparison of the r ed-green bichrome test

for sphere at eighteen feet, under .monocular and binocular conditions.

Each frequency distribution represents the absolute difference between

the right eye under monocular and binocular conditions and the left

eye under monocular and binocular cond.i tions. Nonocular measurements

under binocular conditions were achieved by the use of the vectographic

slide with the eye being measured being the only eye able to see the

letters. Statistically there is no significant difference between red­

green sphere values. Inspection of the distribution suggests a slight

tendency for the binocular red-green sphere values to show- more :plus.

Further analysis shows tba t out of 126 eyes examined only 16 showed

a difference greater than .2.5D and of these only two showed the

difference in the same direction and ma.gni tude. This indicates that

the differences greater tl'l.an • 25D are probably random variations.

Figure 2, a frequency distribution of differences of cylinder power

under monocular and binocular conditions, indicates no significant

difference in cylinder power. Of the 63 right eyes and 63 left eyes

examined, there were no differences in cylinder power in 43 right and

44 left eyes. Of the seve.n eyes showing a difference greater than • 25D

only one subject showed the difference in both eyes. This iridicates

that the dif'fsrences are probably due to random test variations rather

tban systematic differences between monocular and binocular procedures.

Of -the seven eyes showing a difference in cyl.L"lder power greater than • 2.5D,

six showed an increase in cylinder power under binocular conditions and

one under monocular conditions.

Figure 3, a frequency distribution of differences of cylinder axis

under monocular and binocular conditions, indicates no significant

difference in cylinder. a..'tis. Of 63 right eyes and 63 left eyes examined

12

there were no differences in cylinder axis of 43 right eyes and 43

left eyes. Of the 126 eyes examined, 30 showed a crAnge in axis

grea. ter than or equal to 5 degrees and of these 30 eyes only one

showed a change of axis greater than the subjec~s just noticeable

difference for axis. This subject had a l.OOD cylinder and changed

ten degrees with a JND of 5: Figure 4, a :frequency distribution of differences in maximum

plus to subjective best visual acuity between the monocular and the

binocula.:r slide, indicates no signif'ica:nt difference in sphere

values. The frequency distribution is a comparison of 63 right eyes

sphere values with 38 eyes showing no differences and no eyes with a

difference greater than .250. The maximum plus to subjective best

visual acuity on the vectographic slide was done on the letters that

were not :polarized and were therefore common to both eyes. The only

difference between the two slides was the readability of the letters

under the two conditions since the analyzer was not removed while

using the vectographic slide.

Figure 5, a. frequency distribution of differences in anisometropias

as determined by a 20/30 equalization under spll t prism and vectographic

techniques, indicates no signifiCL~t difference in anisometropias.

Of the 6) a.niaometropias ta.kan, 38 showed no differences and only two

showed a difference greater than • 25D • . Of the two showing a difference

in anisometropias of .son the vectographic anisometropia was more

consistent with monocular and bino~Alar red-green anisometropias.

Figure 6, displays the frequency distribution of the differences

of red-green and 20/30 equalization anisometropias under standard and

binocular slide conditions. Inspection indicates that the standard

lJ

slide shows a tendency to be more int~41ly consistent. There was

no difference in anisometropias in 39 of 63 subjects under standard

slide conditions and there was no difference in 24 of 63 subjects under

bL~ocular slide conditions. The binocular slide has fewer variations

greater than • 25D. The binocular slide had only three subjects with a

variation grea. ter than • 25D, while the standard slide had six subjects

with a variation of anisometropias greater than .25D. A larger sample

would be necessary to determine if the differences are other than

chance variation.

Figure 7. a frequency distribution of differences in visual acuity

between the binocular slide and the standard slide, indicates that there is

a significant difference in visual acuity in approximately 30,% of the

eyes examined. '!'here was a difference of one-half line (3 letters)

in 12 out of 63 right eyes and 12 out of 63 left eyes examined. There

was a difference of one line (6 letters) in eight out of 63 right eyes

and nine out of 63 left eyes. In no case was the, acuity better on the

binocular slide, but there were 43 right eyes and 42 left eyes that had

no difference in visual acuity. Nany subjects reported greater diffi­

culty calling the letters on the binocular slide as opposed to the

monocular slide even 'though they called all the letters on both.

The following is an analysis of response to the vectogra:phlc

slide to detect and where applicable measure partial or complete

suppression, binocular instability, stereopsis, and f~xation disparity.

Of the 63 subjects examined there were no complete suppressions,

but there were eight partial suppressions tba t responded. Partial

suppression responses indicate that som& or all of the letters corres­

pondi.."tg to one eye's stimulus would periodically fade out. This test

was condu.cted on the smallest line of mixed letters. Of the eight

14

partial suppressions, six showed a fixation disparity and two had no

fixation disparity.

Binocular instability response on the 20/40 mixed row of letters

oecurred when the subject reported crowding, "swimming" misalignment

vertically, separation or near-far distance cPAnge of the letters.

Seventeen subjects reported a binocular insta.bili ty response. Of

the 17 instabilities, ten manifested a fL~tion disparity a~d seven

showed no fixation disp,:1rity.

Fixation disparity responses were detected and neutralized

utilizing the central fusion lock target~ Of the 63 subjects, 17

showed a fi:xa tion disparity. There were nine eso dis pari ties of which

three were one prism diopter, four were equal to two :prism diopters,

and two were equal to four prism diopters. There . were six exo dis­

pari ties of which five 1-rere equal to one prism diopter and one was

equal to three prism diopte:rs. There were two vertical dis:pa.ri ties.

One w-as equal to one prism diopter and the other was six priem diopters

(equal to the amount of vertical prism in present Hx).

All subjects had all four line.s of stereopsis. A:fter the stereopsis

was tested the p;rism equal to the amount of the fixation disparity

r.'as introduced and the subjects were a.ksed if there ·was any change

in stereopsis. Of the 17 disparities neutralized, five subjects indi­

ea.ted that the :prism enhanced the stereopsis, i.e. subjective depth

was increased.

The examiners did not retest the stereopsis by removing the

neutralizing prisii_ls, a :point worthy of consideration for future

investigators,

15

Discussion of Results

Our $tudy has shown no significant quantitative differences bet-

ween conventional and binocular subjective refraction at 18' with

respect to magnitude of cylinder power, cylinder axis, red-green

spher~ 20/30 equalization for anisometropias, and maximum plus to

best subjective visual acuity. A significant difference in monocular

visual acuities was demonstra. ted. According to the work of Richards10

and Ludvigh11 the decrease in contrast from .93 to .68 cannot fully

account for the decrement in visual acuity found in 30% of our subjects.

Other factors not controlled in our study that may effect visual

acuity include: surround lumir...ance (which was the major cause of the

decrease in contrast), the effect of a blank field presented. to the

eye opposite to the eye being measured, and different perceptibility of

the test letters.

0~ study has also shown that the vectographic slide is very

useful in detecting partial suppressions, neutralization of fixation

disparities, detectL~g binocular instabilities and for testing stereopsis.

The vectographic a.p_proa.ch to refraction is thus a very useful clinical

tool

Suggestions for Future Studies

Further study is needed to factor out the effects of the various

stimulus variables not controlled 1n our study to determine the exact

effect of each on visual acuity. We suggest that further study of

changes in cylinder axis under binocular conditions be done on sub-

jects with a significant amount of cylinder power who are more sensi-

tive to small changes in axis. With respect to the physical setup

of the refracting room, a non-depola:rizing screen should be used,

,

16

the :patient should be seated at the angle of reflection and the room

illumination should be at a minimum.

Summary ,

Our study has shown that binocular refraction is reliable and that

.. there is no significant difference in distance refraction when compared

to the standard monocular methods, We have also shown that there is

a difference in . visual acuity on the veetogra.:phic slide and that con­

t...~st was a major factor. The study indicates that the A.O. slide is

useful in detecting binocular instabilities, neutralizing fixation

disparities and testing stereopsis.

--

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20

BIBLIOGRAPHY

l, Sugar, saul H.: "Binocular Refraction with Cross Cylinder Technique," Arch. Ophth,, 31(1), )4-42, Jal'1. 1944.

2. . 'I'urville, A. E. : "Outline of Infin1 ty Balance, " Rapl"l..ae1' s Ltd. , Hatton Gardin, London, 1946.

3. Humphriss, Deryck~ "The Ref'ra.ction of Binocular Vision," The Ophthalmic Optician, 987-1001, Oct. 5, 1963.

zr... Van iiient Stephen: "The Leland Refractor. . Under Binocular Conditions, " Arch. Ophth.

A Hethod for Refraction 23:104, Jan. 1940 •

5.

6.

Franz, Don A.: "Natural Color Ste:reoscopic Refraction," J, Am. Optom. Assn., 471-476, Feb,, 1959.

Baldwin, ~filliam R, 1 "Binocular Testing and Distance Correction with the BerH.n Polartest," J. Aln. Optom. Assn., 34(2), 115-12.5, Sept. , 1962.

7. IVLilee, Paul W.: "Binoc. Ref." Am. J. Ophth. 31(1), 1460-1466, NoY. , 1948;

8. Morgan, N. W. : "The Turville Infinity Balance Test," Am. J. Opto:m. a.nd Arch. Am. Acad. Optom., 26(6), 231-239, June 1949.

9. Rosenberg, Stephen and Sherman, Arnold: "Vectographic project-o- · chart slides," Am. Opt. Assoc. J9l1002-l006, .Nov, 1968,

10. Richards, o. t-1. = ''Some Seeing Problems: spectacles, driving and decline of age and :poor lighting," Am. J. Optom. 47:539-.546, 1972, (Fig. 3 P. 545).

11. Ludvigh, E.' "The Effect of' Reduced Contrast on Visual Acuity as f>leasured with Snellen Charts, K Arch. Ophth. 25:469-474, 1941.