Effectiveness of occlusion therapy in ametropic amblyopia: a pilot study

Abstract

Aims/background: To examine the relative contributions of non-specific (for example, spectacle correction) and specific (that is, occlusion therapy) treatment effects on children with ametropic amblyopia. To assess the importance and practicality of objectively confirming the prescribed occlusion dose.

Methods: Subjects were entered into a two phase trial. In the first ('pretreatment') subjects were provided with spectacle correction and underwent repeat visual acuity (VA) and contrast sensitivity (CS) testing until acuity in their amblyopic eye had stabilised. Subjects then progressed to the second phase ('treatment') in which they underwent direct, unilateral occlusion for 1 hour per day for 4 weeks. Patching was objectively monitored using an occlusion dose monitor.

Results: Eight subjects completed the trial, all but one of whom achieved > 80% concordance with the occlusion regimen. Within the pretreatment phase, mean amblyopic eye VA improved by 0.19 log units (p = 0.008) while mean CS gained 0.09 log units (p = 0.01). An identical improvement in mean VA was recorded in the fellow eyes (p = 0.03) while mean CS gained 0.11 log units (p = 0.02). Within the treatment phase, mean VA further improved (0.12 log units, p = 0.009) although this gain had halved by the end of treatment and was no longer statistically significant (p = 0.09).

Conclusions: Visual performance improved significantly during pretreatment whereas further gains seen during occlusion were not sustained. Evaluation of occlusion regimens must take into consideration the potentially confounding influence of 'pretreatment effects' and the necessity to confirm objectively the occlusion dose a child receives.

Figure 1

Flow diagram indicating subjects' progression through trial. Boxes (in broken lines) (top to bottom): enrolment, pretreatment phase, treatment phase.

Figure 2

Mean (SD) visual acuity and letter contrast sensitivity of subjects' amblyopic eye (filled circles) and fellow eye (open circles). NB Error bars show variation in scores at the specified points within the trial but do not indicate changes attributable to interventions. The acuity scale has been inverted in order that improvements in visual acuity (VA) and contrast sensitivity (CS) each correspond to vertical increments on the ordinate.

Figure 3

Consecutive performance measures obtained from subject RK during trial. Occlusion was scheduled to begin on the third pretreatment visit (left arrow) but did not in fact commence until 8 weeks later (right arrow). The acuity scale has been inverted in order that improvements in visual acuity (VA) and contrast sensitivity (CS) each correspond to vertical increments on the ordinate.