Clinical characteristics of microtropia--is microtropia a fixed phenomenon?

Abstract

Background/aims: Microtropia is believed to be a static condition, in which accepted achievable levels of vision are those of 6/12-6/9 maximum, with the inability to achieve "normal" levels of stereopsis. The aim of this paper was to present the results of treatment of 30 consecutively presenting primary microtropes, and assess their outcomes using a more active treatment strategy than that conventionally used.

Methods: Visual acuity, stereoacuity, fixation, and the presence of a central suppression scotoma were assessed in all patients before, during, and after treatment, which comprised wearing maximum refractive correction, and an occlusion strategy aiming for equal visual acuity.

Results: Equal visual acuity of 6/5 Snellen was achieved in 43% of the 30 patients, while 87% achieved 6/9 Snellen or better visual acuity in the microtropic eye. Stereoacuity of better than 60" of arc was attained in 37%, and foveal fixation on visuscopy in 55%. The treatment outcome was not affected by the patient's age, initial visual acuity, or the amount of anisometropia. A change in the patient's diagnosis was noted in 50%, with nine patients recovering completely.

Conclusions: The results show that microtropia is not static. Equal 6/5 vision is attainable, as is high grade stereoacuity. The pattern of fixation may change during treatment and elimination of the microtropia is possible in some cases. There is a requirement for management protocols to be changed in order to treat this condition more effectively.

Figure 1

Appearance of the visuscopy fixation graticule superimposed on the fundus, of a patient with steady eccentric fixation 1° nasal to the fovea.

Figure 2

Visual acuity in the amblyopic eye both before and after treatment, corresponding to the patient's age.

Figure 3

Final visual acuity outcome in both eyes (detailing residual amblyopia).

Figure 4

Visual acuity in the amblyopic eye before and after treatment, related to the degree of anisometropia (SER difference).