Assessment of visual acuity in adult patients with strabismic amblyopia: A comparison between the preferential looking method and different acuity charts

PURPOSE: Grating acuity values obtained with preferential looking techniques do not correspond to test results obtained with letter charts. The aim of the study was to investigate the agreement between grating acuity and other acuity tests. METHODS: Twenty-eight adult patients with strabismic amblyopia were assessed with the preferential looking-method and other linear and single letter and symbol tests. RESULTS: Assessment with preferential looking regularly led to an overestimation of the acuity values, but between preferential looking and single optotypes there was a much better agreement. This is most likely due to 'crowding' in strabismic amblyopia. A crowding ratio was calculated in the amblyopic eye, and crowding was found to be more prominent for comparisons of preferential looking with optotypes in rows, than for preferential looking and single optotypes. CONCLUSIONS: Strabismic amblyopia cannot be reliably identified with grating acuity. Preferential looking-testing is therefore of limited use as a screening method for the detection of amblyopia, but preferential looking could still be useful in the assessment and treatment.