Assessment of a Clinical Test for Detection of Alteration in Visual Perception Due to Astigmatism

Abstract

Purpose

Astigmatism blurs the retinal image of a circular spot along a particular orientation rendering it an elliptical shape. Astigmatic patients demonstrate adaptation to residual astigmatic blur that may affect their discrimination between oval and circular targets. The Wilkins Egg and Ball Test (WEBT) was created to detect altered visual perception due to residual astigmatic blur by discriminating a circle within a row of oval elements. This prospective, cross-sectional study examined the utility of WEBT in detecting uncorrected residual astigmatism on the perception of form symmetry in astigmatic and keratoconic participants as well as normal participants with induced astigmatism at four primary meridians.

Methods

The mean search time (sT) and number of errors (noE) of 33 non-astigmatic controls (mean age: 24±5, range: 18–43, 6 males), 23 astigmatic participants (mean age: 36±12, range: 18–43, 6 males) and 13 keratoconic participants (N=22 eyes, mean age: 36±12, range: 18–58, 6 males) were measured under baseline, and 2.00 DC induced cylinder at four primary meridians, and for uncorrected, spherical-correction only, and fully corrected conditions, respectively. Mean sT and noE were converted to Z-scores, combined for each condition, and compared using repeated measures ANOVA with post-hoc analysis.

Results

Combined Z-scores for the controls were significantly worse (p<0.001) for all induced cylinder conditions. The induced 180° condition was significantly better than 45° and 90° conditions (p=0.04), but not the 135° condition. For both astigmatic and keratoconic cohorts, Z-scores of the uncorrected condition were significantly worse than the fully corrected condition (both p<0.01), but the fully corrected and spherical-only conditions did not differ significantly (p=0.06 and p=0.05, respectively).

Conclusion

In accommodating young adults, WEBT detected altered visual perception due to overall blur, and moderate-high amounts of uncorrected induced astigmatism and keratoconus, but is not useful as a tool for detection of altered visual perception due to small residual astigmatic blur.

Keywords:

• astigmatism
• Wilkins egg and ball test
• visual search
• keratoconus
• search time
• number of errors

Acknowledgment

Preliminary findings of this study were previously presented at the Academy for Research in Vision and Ophthalmology conference in 2021.

Disclosure

The authors report no conflicts of interest in this work.

Additional information

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors. Parts of this study were funded by the Hadassah Academic College Conference and Research Board grant awarded to Eyal Gal.