Depth Perception and Intraocular Differences in Visual Acuities Among Older Spectacle Wearers.

Background: Falls impose a heavy financial burden on society, and the incidence is age-related. The correction of refractive errors has been mooted as a valuable procedure to prevent falls. However, depth perception, estimated by stereo acuity tests, is reduced in the older population and has been cited as contributing to the higher incidence of falls in the elderly.

Objective: To explore the clinical relationship between age, interocular differences in the corrected distance and near logMAR visual acuities, refractive errors, axial (eyeball) lengths, pupil sizes, and higher-order ocular aberrations (HOAs) on clinical measures of stereoacuity and aniseikonia in asymptomatic presbyopic habitual spectacle wearers.

Methods: Total amount of 91 subjects underwent clinical assessment of i) subjective refractive error, ii) stereoacuity at 6m and 40cm (Randot Stereotests), iii) aniseikonia at 6m (Awaya test along vertical and horizontal meridian) iv) higher order aberrations (Hartman-Shack aberrometer) v) eyeball length and pupil size (IOL master 700). The Pythagorean theorem was applied to each pair of aniseikonia values to calculate the resultant aniseikonia (AR).

Results: Mean (±sd,95%CI) age of the subjects was 56.2years (±8.10,54.6-57.9). Root mean square (RMS) interocular differences (±sd,95%CI) in spherical refractive errors, axial lengths and pupil sizes were 0.66D(±0.93,0.47-0.85), 0.24mm (±0.33,0.17-0.31), 0.15mm (±0.11,0.12-0.17). The median (mode, interquartile range) values for AR were 2.8(1.0,1.3-4.0). Significant correlations (p<.01) were revealed between: a) log distance stereoacuity (y1), age (x1) and RMS difference in the corrected distance logMAR visual acuity (x2). b) log near stereoacuity (y2), RMS differences in the corrected distance (x2) and near visual acuities (x3). These key associations are best described by: y1=0.011x1+1.101x2+1.553 (r² =0.169, n=91); y2=1.715x2+1.883x3+1.725 (r² = 0.239, n=91).

Conclusion: Stereoacuity is age-related, influenced by interocular differences in the corrected visual acuities but not related to interocular differences in pupil sizes, HOAs or clinical measures of aniseikonia in older habitual spectacle wearers. Assessment of stereoacuity and aniseikonia, in older persons is useful when advising to prevent accidental mis-location and falls.