Abstract
Purpose: :
About 15% of amblyopic children have persistent residual amblyopia despite repeated attempts at treatment and excellent compliance. It has been suggested that many cases of amblyopia may be caused by subtle optic nerve hypoplasia, "optic disc dysversion" (Lempert 1998 & 2000), or gaze-holding instability of the amblyopic eye (Regan et al 1992). We sought to determine whether these abnormalities underlie persistent amblyopia.
Methods: :
Children with persistent strabismic, anisometropic, or combined mechanism amblyopia (N=21; age 5-14 yr) were enrolled. All had been treated with glasses, patching, and/or atropine for 0.8-5 years and had residual amblyopia (20/40-20/160) with no improvement for at least 6 months prior to testing despite excellent compliance. Horizontal eye movements were recorded using an infrared limbus reflection goggle system and analyzed by an author who was masked to patient characterstics. Eye movements of a normal control group were also tested. Vertical and horizontal optic disc diameters and retinal nerve fibre layer (RNFL) thickness in 6 sectors and overall average were measured using an fd-OCT radial scan for both the amblyopic eye and fellow eyes.
Results: :
Many children with persistent amblyopia had eye movement abnormalities in both the amblyopic and fellow eyes, including infantile nystagmus (9.5%), manifest latent nystagmus (42.9%), and square wave oscillations (47.6%). While some normal controls (36.4%) also had square wave oscillations, amblyopic children tended to have more intense (amplitude x frequency) and longer duration oscillations. There were no significant differences between the amblyopic and fellow eyes in optic disc diameters, optic disc shape (ratio of vertical to horizontal diameter), or RNFL thickness in any sector.
Conclusions: :
There is no fd-OCT evidence from this study supporting the hypothesis that there are optic disc or RNFL abnormalities in children with persistent amblyopia. The significant eye movement abnormalities are unlikely to be the cause of persistent amblyopia since they are present in both eyes. Instead, both persistent amblyopia and eye movement abnormalities may be consequences of fusion maldevelopment.
Keywords: amblyopia • eye movements • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)