Comparison of visual acuity measured with Allen figures and Snellen letters using the B-VAT II monitor.

Objective: Allen figure optotypes commonly are used to measure visual acuity in young children. Children with normal acuity measured with Allen figures sometimes are found to have unsuspected amblyopia that is detected when they are tested with Snellen letters. The correlation between visual acuities measured with these two optotype charts has not been well studied. The authors compared visual acuities measured with Allen figure and Snellen letter optotypes using the Mentor B-VAT II monitor.

Design: The study design was a nonrandomized, comparative clinical trial.

Participants: The study was composed of 12 adult subjects.

Intervention: Visual acuities were measured using both Allen figure and Snellen letter optotypes using the B-VAT II monitor. The images were progressively blurred using plus lenses.

Main Outcome Measures: Visual acuity was measured.

Results: At visual acuity levels of 20/60 or better, Allen figure testing averaged 1.5 lines better than Snellen letter testing; between 20/70 and 20/200 visual acuities, the difference was 2.5 lines.

Conclusions: Allen figure testing with the B-VAT II monitor overestimates visual acuity compared with testing with Snellen letters. This appears to result primarily from the construction of the optotypes. This discrepancy should be considered when visual acuity is measured in young children.