A biometric investigation of ocular components in amblyopia

The aim of this study was to investigate the ocular parameters and their contribution to total axial length, and any inter-ocular differences when compared to the fellow non-amblyopic eye, in a population of paediatric amblyopes. Inter-ocular differences in visual acuity, refractive error, corneal curvature, anterior chamber depth and their contribution to total axial length were analysed in four populations: adult controls (n=26), paediatric controls (n=24), paediatric strabismic amblyopes (n=18) and paediatric anisometropic amblyopes (n=27). In the two control groups, there were small inter-ocular differences between the components, none of which were statistically or clinically significant. Anisometropic amblyopic eyes were found to have statistically and clinically significant differences in refractive error, crystalline lens power, vitreous chamber depth and total axial length when compared to the fellow eye. Anterior and vitreous chamber depths, when expressed as a percentage of the anterior and vitreous chambers in the non-amblyopic fellow eye, were approximately 95% of the size. When parameters were normalised by expressing as a percentage of total axial length, the contribution of the anterior chamber, crystalline lens and vitreous chamber to total axial length in both eyes were comparable, suggesting that all components of the anisometropic amblyopic eye are proportionately reduced in size. The strabismic amblyopic eyes were in the main isometropic. There were however statistically significant differences in anterior chamber depth, crystalline lens power, vitreous chamber depth and total axial length, but not in crystalline lens thickness. When the components were expressed as a percentage of the component in the non-amblyopic fellow eye, the anterior and vitreous chambers were approximately 90% of the size of the fellow non-amblyopic eye and made a significantly smaller contribution to total axial length when normalised. Crystalline lens thickness contributed significantly more to the total axial length in a strabismic eye. This suggests that, unlike control eyes or anisometropic amblyopic eyes, the strabismic eye is physically, though not proportionately, reduced in size.