Original article
One Eye or Two: A Comparison of Binocular and Monocular Low-Contrast Acuity Testing in Multiple Sclerosis

https://doi.org/10.1016/j.ajo.2011.01.023Get rights and content

Purpose

To determine the magnitudes of binocular summation for low- and high-contrast letter acuity in a multiple sclerosis (MS) cohort, and to characterize the roles that MS disease, age, interocular difference in acuity, and a history of optic neuritis have on binocular summation. The relation between binocular summation and monocular acuities and vision-specific quality of life (QoL) was also examined.

Design

Cross-sectional observational study.

Methods

Low-contrast acuity (2.5% and 1.25% contrast) and high-contrast visual acuity (VA) were assessed binocularly and monocularly in patients and disease-free controls at 3 academic centers. Binocular summation was calculated as the difference between the binocular and better eye scores. QoL was measured using the 25-item National Eye Institute Visual Functioning Questionnaire (NEI VFQ-25) and the 10-item neuro-ophthalmic supplement. The relation of the degree of binocular summation to monocular acuity, clinical history of acute optic neuritis, age, interocular acuity difference, and QoL was determined.

Results

Binocular summation was demonstrated at all contrast levels, and was greatest at the lowest level (1.25%). Increasing age (P < .0001), greater interocular differences in acuity (P < .0001), and prior history of optic neuritis (P = .015) were associated with lower magnitudes of binocular summation; binocular inhibition was seen in some of these patients. Higher magnitudes of summation for 2.5% low-contrast acuity were associated with better scores for the NEI VFQ-25 (P = .02) and neuro-ophthalmic supplement (P = .03).

Conclusion

Binocular summation of acuity occurs in MS but is reduced by optic neuritis, which may lead to binocular inhibition. Binocular summation and inhibition are important factors in the QoL and visual experience of MS patients, and may explain why some prefer to patch or close 1 eye in the absence of diplopia or ocular misalignment.

Section snippets

Methods

Patients and disease-free control subjects were enrolled as part of an ongoing prospective study of visual outcome measures in MS at the University of Pennsylvania, Johns Hopkins University, and the University of Texas Southwestern Medical Center at Dallas. MS was diagnosed by standard clinical and neuroimaging criteria.9

A history of 1 or more episodes of acute optic neuritis was determined for eyes of patients with MS by self-report and physician diagnosis, and confirmed by medical record

Results

Among 1007 patients with MS and 324 disease-free control participants, the mean age of the 2 groups was similar (43 ± 11 years for MS and 40 ± 11 years for controls, P = .19). Within the MS group, 46% of patients had a prior history of acute optic neuritis.

The mean VA and low-contrast acuity scores for each patient group are summarized in Table 2. All groups demonstrated evidence of binocular summation for each measure of visual function. Magnitudes of binocular summation were significantly

Discussion

Binocular high-contrast VA and low-contrast acuity measures are now frequently used for testing of visual function in MS clinical trials.1, 2, 3, 4, 13 Although binocular low-contrast acuity has been correlated with vision-related QoL,2 MRI lesion burden,3 retinal nerve fiber layer thickness measures,13, 14 and treatment effects4 in MS, it has been unclear whether binocular low-contrast acuity scores reflect those of the better eye, the worse eye, or a value in between the 2 eyes. Binocular

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