Early glaucoma patients may undergo visual system adaptation that preserves normal binocular summation. Photo: Andrew Rixon, OD. Click image to enlarge.

Despite structural damage, the binocular performance of patients with early glaucoma seems to remain largely intact, according to a study recently published in the Journal of Glaucoma. Based on these findings, the study authors believe that glaucoma patients in early stages of the disease may undergo an adaptation of the visual system that preserves normal binocular summation, even with reduced monocular visual input.

In the study, the researchers examined 48 early glaucoma patients (mean age: 65) who exhibited structural changes with no significant interocular acuity asymmetry or other functional deficit and 42 healthy, stereoacuity-matched controls (mean age: 60). They assessed each participant’s binocular and monocular visual acuity at high (95%) and low (20%) contrast using ETDRS charts at 6m.

The researchers reported that the control group had significantly better overall binocular and monocular visual acuity for both contrast levels. The glaucoma group demonstrated a significant difference in the binocular ratio at high and low contrast (0.01 vs. 0.04, respectively). This measure wasn’t significant in the control group (0.0 vs. 0.02, respectively).

The researchers concluded that early glaucoma patients show preserved acuity binocular summation and recommended patients undergo binocular function evaluation in the clinic. “This finding may be due to a compensatory mechanism in the presence of decreased, but not equal, monocular inputs,” they explained in their paper. “We hypothesize that this summation compensatory mechanism may break down at some point when the disease advances.”

Leibovitzh GI, Trope GE, Buys YM, et al. Binocular summation of visual acuity at high and low contrast in early glaucoma. J Glaucoma 2022. August 17, 2022. [Epub ahead of print].