Is microtropia a reliable indicator of the presence of amblyopia in anisometropic patients?

AIM: A study was carried out to determine if the presence of microtropia with identity is a reliable indicator for the presence of amblyopia, and likely need for occlusion, following optical treatment in "straight-eyed" anisometropic children.

METHOD: A retrospective case note review was carried out of all children referred from Orthoptic school vision screening during a 10-year period. Children who had unequal visual acuity, no manifest strabismus and who were prescribed spectacles to correct anisometropia (inter-ocular difference one dioptre or more in any meridian) were included in the study. The presence or absence of microtropia with identity, determined using the 4-dioptre prism test, was recorded and children were grouped according to visual outcome as follows: Group 1: equal visual acuity after a maximum optical treatment period of 2 months; Group 2: equal visual acuity after a maximum optical treatment period of 6 months; Group 3: unequal visual acuity after a maximum optical treatment period of 6 months - no occlusion therapy undertaken; and Group 4: unequal visual acuity after a maximum optical treatment period of 6 months - occlusion therapy undertaken.

RESULTS: Case notes were available for a total of 532 children. Out of 532, 324 children achieved equal visual acuity with optical treatment alone; none had microtropia. Thirty children with microtropia achieved LogMAR acuity of 0.200 or better in the affected eye after optical treatment and did not undergo occlusion therapy; 178 children required occlusion therapy to achieve a maximum LogMAR acuity of 0.300 or better, and all had microtropia.

CONCLUSION: In this study of 532 four-five year olds, amblyopia did not exist in "straight-eyed" anisometropic children who did not have microtropia with identity. This study suggests that the presence of microtropia with identity is a reliable indicator of the presence of amblyopia, and possible need for occlusion therapy, following optical treatment in "straight-eyed" anisometropic children.