Binocular summation with low contrast
Reviewed by Fiona Rowe

The magnitude of binocular summation was investigated in normal control subjects using four different letter charts of varying type with fixed and variable contrast levels and spatial frequency to determine which tests most readily reveal binocular summation in normal subjects. Tests included the low contrast Early Treatment Diabetic Retinopathy Study (ETDRS) and Pelli Robson contrast sensitivity charts plus high contrast ETDRS chart at 2.5 and 1.25% levels. One hundred and twenty-nine subjects were tested: 61% female, 39% male. A significant difference in binocular summation was found in different age groups for 2.5% and 1.25% Sloan low contrast acuity charts and the Pelli Robson chart, but not for high contrast ETDRS visual acuity. Generally scores increased over the first three decades of life and reduced from the fifth decade. Linear regression showed significant associations between increased intraocular differences and reduced binocular summation and increased age and reduced binocular summation. Low contrast acuity charts may be useful clinical measures of binocular summation.

Normative reference ranges for binocular summation as a function of age for low contrast letter charts.
Pineles SL, Velez FG, Yu F, et al.
STRABISMUS
2014;22:167-75.