Abstract
Purpose :
Binocular summation is a well-known phenomenon in letter acuity measurement. This study is to examine the relationship in binocular summation between high and low contrast letter acuities using common commercially available visual acuity charts and investigate whether people who exhibit stronger binocular summation at high contrast tend to have greater summation at low contrast.
Methods :
Corrected high and low contrast letter acuities were assessed monocularly and binocularly in 325 normal vision observers aged 18 to 40 years using Bailey-Lovie charts. All observers had high contrast acuities of 0.1 LogMAR or better and no known eye disease. Binocular summation was calculated as the difference in LogMAR between the better eye acuity and binocular acuity.
Results :
At high contrast, letter acuities for right, left and both eyes were -0.066±0.004 (SE), -0.065±0.004, and -0.130±0.003, respectively. The corresponding acuities at low contrast were 0.087±0.006, 0.087±0.006 and -0.007±0.005. Consistent with previous studies, we found binocular summation at both contrast levels with higher magnitude of summation at low contrast (0.045±0.002 for high and 0.068±0.003 for low contrast). Binocular summation at high contrast had a weak correlation with summation at low contrast (r = 0.116, p = 0.036), whereas it had a strong inverse relationship with the change in binocular summation between the two contrast levels (r = -0.614, p < 0.001).
Conclusions :
Using common commercially available letter acuity charts, we replicated the findings on binocular summation for acuity in normal vision for both high and low contrast letters. While overall binocular summation is greater for low contrast acuity, people who exhibit stronger binocular summation at high contrast tend to have less enhanced (or even reduced) summation for low contrast acuity.
This is a 2021 ARVO Annual Meeting abstract.