[Objective vernier acuity testing in adults, children and infants. Possibilities and limits of a new method]

Recently, a method of objective Vernier acuity testing using a modified Catford drum was presented. A tight correlation between the objective Vernier acuity and the Snellen acuity was reported (Hopkisson et al. 1991).

In 41 cooperative patients with strabismic amblyopia and 20 normal subjects were compared the subjective Landolt acuity with the objective Vernier acuity and the individual interocular differences of the objective Vernier acuity. The Vernier method was then tested in 44 healthy 6- to 36-months-old infants. In 39 of the amblyopic and 15 of the normal subjects we compared the Landolt acuity with the grating acuity as measured with the Teller-acuity-card-test, and the interocular differences of the grating acuity. The Vernier target was a black line with an offset of one fifth of its thickness. In a distance of 1 m the offset appeared under visual angles of 15.9' to 0.3' corresponding to acuities of 0.06 to 3.2. The line was moving back and forth in its longitudinal direction. The objective Vernier acuity was defined by the smallest offset causing pursuit eye movements.

Strabismic amblyopia was detected by the Vernier method with a sensitivity of 54%. In infants, however, the sensitivity would be less than 30%. In both eyes only 45% of the infants could be tested at all. The sensitivity of the Teller-acuity-card-test was 28%.

Many cases of strabismic amblyopia will escape detection by the described method of Vernier acuity testing.