Negative effects on stereoaccuracy induced by commonly used red-green filters have been a subject of recent investigation1. This study was designed to determine if correcting, with lenses, the chromatic anisometropia induced by these red-green filters could increase the accuracy of stereopsis. The lens power difference needed to correct the chromatic anisometropia was found to be 0.37°, divided between the two eyes. In the control condition the subjects viewed the Randot Circle Stereotest with only the required polarizing glasses. One of the remaining two test conditions used the polarizers in combination with red-green filters, while for the other condition the chromatic anisometropia from the red-green filters was corrected with appropriate lenses. The amount of light transmitted by the filters was kept constant. The chromatic anisometropia correction over the red-green filters significantly reduced stereopsis errors induced by the red-green filters alone (21%, p \u3c 0.05). However, the correction only partially restored stereopsis to control values. A mild anisometropic correction added to the red-green glasses could help improve stereopsis in most individuals

Kovach, Peter E

Powell, Timothy C

English

CommonKnowledge

Pacific University 
CommonKnowledge 
College of Optometry Theses, Dissertations and Capstone Projects 
3-1987 
Correcting the chromatic anisometropia of red-green glasses and 
its effect on stereoaccuracy 
Peter E. Kovach 
Pacific University 
Timothy C. Powell 
Pacific University 
Recommended Citation 
Kovach, Peter E. and Powell, Timothy C., "Correcting the chromatic anisometropia of red-green glasses 
and its effect on stereoaccuracy" (1987). College of Optometry. 810. 
https://commons.pacificu.edu/opt/810 
This Thesis is brought to you for free and open access by the Theses, Dissertations and Capstone Projects at 
CommonKnowledge. It has been accepted for inclusion in College of Optometry by an authorized administrator of 
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Correcting the chromatic anisometropia of red-green glasses and its effect on 
stereoaccuracy 
Abstract 
Negative effects on stereoaccuracy induced by commonly used red-green filters have been a subject of 
recent investigation1. This study was designed to determine if correcting, with lenses, the chromatic 
anisometropia induced by these red-green filters could increase the accuracy of stereopsis. The lens 
power difference needed to correct the chromatic anisometropia was found to be 0.37°, divided between 
the two eyes. In the control condition the subjects viewed the Randot Circle Stereotest with only the 
required polarizing glasses. One of the remaining two test conditions used the polarizers in combination 
with red-green filters, while for the other condition the chromatic anisometropia from the red-green filters 
was corrected with appropriate lenses. The amount of light transmitted by the filters was kept constant. 
The chromatic anisometropia correction over the red-green filters significantly reduced stereopsis errors 
induced by the red-green filters alone (21%, p < 0.05). However, the correction only partially restored 
stereopsis to control values. A mild anisometropic correction added to the red-green glasses could help 
improve stereopsis in most individuals. 
Degree Type 
Thesis 
Degree Name 
Master of Science in Vision Science 
Committee Chair 
Paul Kohl 
Keywords 
Stereopsis, Chromatic Anisometropia, Polarizing Filters, Red-Green Filters, Chromatic Aberration 
Subject Categories 
Optometry 
This thesis is available at CommonKnowledge: https://commons.pacificu.edu/opt/810 
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Correcting the Chromatic Anisometropia of 
Red-Green Glasses and its Effect on Stereoaccuracy 
A Thesis Presented 
to the Faculty of 
Pacific University 
In Partial Fulfillment of 
the Requirements for the 
Degree Doctor of Optometry 
Submitted by · ?ter. a~ B. S. & Timothy C. Powell B. S. 
11£ l ~ Ad. VISOrS: 
Paul Kohl 0. D. & Nile~ Roth M. Opt. Ph.D. q/~ '~L~Kith 
March 1987 

ABSTRACT 
Negative effects on stereoaccuracy induced by commonly used red-green filters 
have been a subject of recent investigation1. This study was designed to determine if 
correcting, with lenses, the chromatic anisometropia induced by these red-green filters 
could increase the accuracy of stereopsis. The lens power difference needed to 
correct the chromatic anisometropia was found to be 0.37°, divided between the two 
eyes. In the control condition the subjects viewed the Randot Circle Stereotest with 
only the required polarizing glasses. One of the remaining two test conditions used the 
polarizers in combination with red-green filters, while for the other condition the 
chromatic anisometropia from the red-green filters was corrected with appropriate 
lenses. The amount of light transmitted by the filters was kept constant. The chromatic 
anisometropia correction over the red-green filters significantly reduced stereopsis 
errors induced by the red-green filters alone (21 °/o, p < 0.05). However, the correction 
only partially restored stereopsis to control values. A mild anisometropic correction 
added to the red-green glasses could help improve stereopsis in most individuals. 
Key Words: Stereopsis, Chromatic Anisometropia , Polarizing Filters, Red-Green 
Filters, Chromatic Aberration 
INTRODUCTION 
Red-green glasses play an important role in many offices and clinics providing 
vision training. These glasses and associated materials are generally less expensive 
than polarizing materials and are probably more widely used. Concerns that the 
red-green materials may not be as good as polarizing materials for the testing and 
training of patients have been, until recently, left unanswered. Because of this concern, 
work has been initiated to see if differences between the red-green materials and 
polarizing materials exist, and if so, what are their types and magnitudes? If there are 
deficiencies in the red-green materials what can be done to correct them? 
A study designed to test for transmittance differences between red and green filters 
showed that commonly used red-green glasses have a significant luminous 
transmittance imbalance2 combined with their inherent chromatic imbalance. A 
second study aimed at determining if the transmittance or the chromatic differences 
had any effect on stereoaccuracy showed that the transmittance difference had no 
significant effect on stereoaccuracy. However the chromatic difference did have a 
significant role in diminishing a subject's stereoaccuracy 1. It has been shown in other 
studies that chromatic differences can create a stereoacuity loss3 and can simulate an 
anisometropic condition.4,5,6 The purpose of this study was to determine if correcting 
the chromatic anisometropia would retrieve some or all of the lost stereoaccuracy 
induced by the red-green glasses. 
Using the values obtained from a literature search of the chromatic anisometropia 
of the eye?,S,9,10 combined with a subjective measurement of the subjects involved in 
the experiment, the chromatic anisometropia was determined to be 0.37° with a range 
of 0.12°. This value was divided about evenly between the two eyes and was used in 
one of the test conditions in the form of a correction. 
The study consisted of three test conditions, all of them requiring polarizers. One 
condition used red-green filters with the polarizers. A second conditon used red-green 
filters combined with the chromatic correction and the polarizers. A third condition, the 
control, used only the polarizers. The number of stereopsis judgement errors on a 
Randotm Circle Stereotest was monitored for each condition. 
2 
METHODS 
Subjects: 
Thirty subjects volunteered for this study. They consisted mostly of optometry 
students, some undergraduates, and staff. There were 22 males and 8 females with 
ages ranging from 22 to 32 with an average of 25. The subjects met or exceeded the 
standard of 40 arc seconds of stereoacuity as measured by a Randot Circle Stereotest 
at 40 em (16 inches). 
Methods and Materials: 
Standard Bernella red-green filters and polarizing glasses were used with a 
standard Randot Circle Stereotestb. The light source illuminating the target consisted 
of either three or five 150 watt bulbs depending on the amount of illumination needed 
on the target. A uniformly gray partition about 47 em (19 inches) wide and 30 em (12 
inches) high separated the subject from the target. In the center of the partition was a 
small rectangular opening large enough for one cell of the Randot target to be viewed 
without the subject knowing which cell was presented. A forehead and chin rest 
system was used to support the subject's head comfortably at eye level with the test 
cell. Standard lenses from a trial lens cased were used to correct the chromatic 
anisometropia. 
The light level for each condition was established by measuring luminance through 
the filter combinations at 1 meter from the target, the location of the subject during 
testing. This was accomplished by using a Tektronix J-16 Photometer- Radiometer 
joined with a J-6523 Luminance Probec aimed just above the aperture of the partition. 
Photometric conditions for the experiment are summarized in Table 1. 
Insert Table 1 about here 
For each test condition subjects were presented each of the ten Randot cells four 
times in a computer generated random pattern. The condition sequence was also 
randomized among subjects. The subjects were required to make a response on each 
cell presented within a ten second time limit. One experimenter manipulated the target 
and monitered the subject while the other experimenter recorded responses. 
3 
In order to determine the chromatic anisometropia induced by the particular 
red-green filters used, subjects were given a monocular subjective test to determine 
their chromatic interval. A manifest refraction was done to determine baseline data. 
Two more forced choice refractions with the same instructional set were done; one 
with the red filter placed over the phoropter aperture and another with the green filter 
placed over the aperture. The result was a consistent choice of 0.37D difference 
between red and green with an occasional subject choosing 0.50D. It was decided 
that the chromatic anisometropia correction to be used was 0.37D with +0.12D over the 
red filtered eye and -0.25D over the green filtered eye. This agrees with results found 
in the literature where chromatic anisometropia induced by similar red-green filters 
was found to be close to 0.37DJ,9,10 The three conditions are listed below. 
CONDITION 1 : 
Control: Subjects viewed the cell through only the polarizing filters and were 
asked to make stereo judgements. 
CONDITON 2: 
Red-Green Chromatic Imbalance: Subjects viewed the cells through both 
red-green filters and polarizing filters with the red filter over the right eye and the green 
filter over the left eye. 
CONDITION 3: 
Red-Green Chromatic Anisometropia Corrected by Lenses: Subjects viewed the 
cells with a polarizing and red filter over the right eye and a polarizing and green filter 
over the left eye. The 0.37D anisometropia correction was divided into+0.12D over the 
right eye and -0.25D over the left eye. 
RESULTS 
The total number of stereo judgement errors for the entire group in Condition 1 was 
309; in Condition 2 there were 548 errors, in Condition 3 there were 435 errors. (Table 
2 and Figure 1) 
Insert Table 2 & Figure 1 about here. 
---~---------------------------------------------
4 
Using a t-test and ANOVA (Analysis of Variance) with repeated measures, 
Conditions 1 and 2 differed significantly, as expected and previously shown.1 
Conditions 1 and 3 also differed significantly. The comparision of Condition 2 to 
Condition 3 showed that the effect of correcting the chromatic anisometropia was 
statistically significant. All significances were at or above the 0.05 level. (Table 2) 
Also, when questioned, over 63 °/o of the patients preferred Condition 3 to 
Condition 2 with the rest saying they could see no difference. 
DISCUSSION 
These results show a statistically significant improvement in stereoaccuracy when 
the chromatic anisometropia of red-green filters is corrected by low power lenses. 
Although the original stereoaccuracy is not completely recovered, enough is recovered 
to show promise in improving the red-green materials presently in use. 
Red-green filters have a variety of uses, such as motor and sensory fusion testing 
and training, stereopsis testing and training, monocular fixation in a binocular field, and 
other activities. Since red-green materials are commonly used in visual training 
oriented offices a specific tailoring of the filters and the lens correction can be designed 
for each patient. The use of lenses to correct the induced anisometropia can provide a 
more balanced binocular task for the patient. 
Cornforth, Johnson, et.al. reported that cell 7, which is 40 arc seconds, on the 
Randot Circle Stereotest evoked the greatest number of errors of all the cells, even 
greater than the cells with smaller disparities.1 This irregularity has been noted by 
other clinicians with no apparent explanation. During this testing it was also noted that 
this cell evoked the highest number of stereo judgement errors. Cell 7 had nearly 
twice as many error judgements as the cell with the second highest number of errors, 
cell 10 (20 arc sec). See Figure 1. 
Insert Figure 1 about here 
CONCLUSION 
We conclude that a significant improvement in stereoaccuracy occurs when the 
chromatic anisometropia due to red-green filters is corrected, as shown by fewer errors 
5 
on the Randot Circle Stereotest. Even with the anisometropic correction, however, 
results were not at the level of polarizing materials alone. We feel that more work 
should be done to try to equalize the red-green materials as much as possible. Even 
though the retinal illuminance difference was found not to have a significant effect, in 
this study, we feel that it too, should be corrected, for reasons stated in a previous 
publication.1 
Future studies should investigate whether changing contrast sensitivity has an 
effect on stereopsis. If they are related a determination should be made as to how red, 
green, and polarizing filters affect contrast sensitivity and stereopsis. 
More work should be done to determine why cell 7 of the Randot Cicle Stereotest 
produces an increased error frequency when compared to cells of smaller disparity. 
Testing of other Randot circle tests, and test-retest data should be gathered. 
Comparisons to other tests are warranted. Possible consultation with the manufacturer 
of the test could help. Microscopic evaluation of the cell's disparity test pattern may 
reveal an inherent defect. 
6 
REFERENCES 
1. Cornforth,L. L., Johnson, B. L., Kohl, P., Roth, N., Chromatic Imbalance Due to 
Commonly Used Red-Green Filters Reduces Accuracy of Stereoscopic Depth 
Perception, 1986, Submitted for Publication to Am J Optom. and Physiol. Opt. 
2. Bogdanovich, G. G., Roth, N., Kohl, P., Properties of Analglyphic Materials that 
Affect the Testing and Training of Binocular Vision, J Am Optom Assoc, 1986 Dec; 
57(12):899 - 903. 
3. Matsumoto, E. R., Johnson,C. A., Post, R. B., Effect of X-Chrome Lens Wear on 
Chromatic Discrimination and Stereopsis in Color Deficient Observers. Am. J. 
Opt. 1983; 60: 297 - 302. 
4. Peters, H. B., The Influence of Anisometropia on Stereosensitivity, Am. J. Optom. 
Arch. Am. Acad. Optom. 1969; 46: 120-23. 
5. Lovasik, J. V., Szymkiw, M., Effects of Aniseikonia, Anisometropia, 
Accommodation, Retinal Illuminance, and Pupil Size on Stereopsis., Invest. 
Opthalmol. Vis. Sci.1985; 26: 741-50 
6. Larson,W. L., Lachance, A., Stereoscopic Acuity with Induced Refractive Errors. 
Am. J. Opt. 1983; 60:509-13 
7. Safir, A., Refraction and Clinical Optics, Harper and Row Publishers, San 
Francisco, 1980. 
8. Cowan, A., Refraction of the Eye, Lea and Febiger, Philadelphia, 1948. 
9. Barish, 1., Clincal Refraction, 2nd Edition, Chicago, The Professional Press, 1954. 
10. Mandell, R. B., Allen M. J., The Causes of Bichrome Test Failures, J Am Optom 
Assoc, 1960 Feb., 31 (2): 531-33. 
7 
ACKNOWLEDGMENTS 
a. Bernell Corporation, South Bend, Indiana. 
b. Stereo Optical Company Randot Stereotest, Chicago, Illinois. 
c. Tektronix Inc., Beaverton, Oregon. 
d. National P. Optical, Forest Grove, Oregon. 
Table 1: Lighting Summary 
CONDITION 1 CONDTION 2 CONDITION 3 
Distance sub. to target 1 meter for aU condtions - -
Number of lights on 3 5 5 
Dist. lights to target 160 em 73cm 73cm 
Luminance of target 24.3 nits for all conditions -
Table 2: Values and Statistics 
CONDITION 1 CONDITION 2 CONDITION 3 
TOTAL ERRORS 309 548 435 
AVERAGE ERRORS 10.3 18.27 14.5 
STD. DEVIATION 5.74 5.35 5.82 
t-TEST VALUE (N=30) 5.8 
3 vs. 2 PROBABILITY 0.0001 * 
*Significant at 99°/o 
ANOVA VALUE 
PROBABILITY 1.861 * 

100 
90 
80 
70 
60 
TOTAL 
ERRORS 50 
40 
30 
20 
Figure 2: Total Errors by Cell Number per Conditon 
~ 0~--;;==~~--------~t-----------~---------------------
............. _............ 
·~~· J...----:;~------=---·~--1-.------------
/·~ '~~-----------­~ . 
~--· 
1 2 3 4 5 6 7 8 9 10 
CELL NUMBER 
·•- COND 1 
·O- COND 2 
·•- COND 3 
Appendix: Additional Figure 2: 
Total Errors by Cell Number per Conditon 
T 100 
0 90 
T 80 
A 70 
L 60 
E 50 
R 40 
R 30 
0 20 
R 10 
s 0 
1 2 3 4 5 6 7 8 9 10 
CELL NUMBER 
• COND 1 liil COND 2 fZJ COND 3 


Correcting the chromatic anisometropia of red-green glasses and its effect on stereoaccuracy

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Correcting the chromatic anisometropia of red-green glasses and its effect on stereoaccuracy

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