Binocular and Monocular Vision

The measurement of visual functions (such as refraction, acuity, and so on) is the first essential part of any ocular examination and the process being assessed is complex and requires the interaction of many factors, both physiological and psychological. Pupil size is an important factor in relation to visual functions such as refraction, acuity, contrast sensitivity and so on. Its effects, however, are complex. We investigated the effects of pupil size and optical aberrations on visual functions under binocular and monocular conditions. Pupil diameters were continuously recorded during examination of contrast sensitivity (CS) and visual acuity (log MAR scale). Aberrometry was measured with OPD-Scan. Zernike coefficients were calculated for the pupil diameters under binocular and monocular conditions using Schwiegerling's method of recalculating the expansion coefficient. Significant differences were found between binocular log CS and monocular log CS. Binocular visual acuity was significantly better than monocular visual acuity. Mean pupil diameters examined under binocular conditions decreased significantly as compared to monocular conditions. With the increases in pupil diameter, optical aberrations increased significantly. These results suggest that decrease in pupil diameter from monocular to binocular conditions causes a decrease in optical aberration, resulting in the improved subjective visual performance. We should consider the major effects of pupil size change on vision testing from monocular to binocular viewing condition, and vice versa.