Retinal Structure in Amplyopia

Abstract

The recent article by Philip Lempert1Lempert P. Retinal area and optic disc rim area in amblyopic, fellow, and normal hyperopic eyes: a hypothesis for decreased acuity in amblyopia.Ophthalmology. 2008; 115: 2259-2261Abstract Full Text Full Text PDF PubMed Scopus (36) Google Scholar is a welcome contribution to the growing literature on amblyopia, and possible structural differences between amblyopic and normal eyes. The author created a novel numeric description of the neural connectivity of retinal cells, the retinal area to optic disc rim area ratio, and showed that amblyopic eyes had decreased neural connectivity relative to their fellow eyes, which was in turn lower than in normal eyes. We performed a detailed assessment of a large population-based sample of Australian children, predominantly aged 6 (n = 1740) and 12 (n = 2353) years.2Huynh S.C. Samarawickrama C. Wang X.Y. et al.Macular and nerve fiber layer thickness in amblyopia: the Sydney Childhood Eye Study.Ophthalmology. 2009; 116: 1604-1609Abstract Full Text Full Text PDF PubMed Scopus (117) Google Scholar Optical coherence tomography scans were performed on both eyes using standard protocols. We found that amblyopic eyes had consistently greater foveal minimum thicknesses (interocular difference around 5.0 μm, P < 0.05) than fellow eyes. When comparing the affected eyes of amblyopic children to the right eyes of nonamblyopic children, the foveal minimum was also significantly thicker (170.2 μm vs 158.6 μm, respectively, P = 0.01). Finally, the interocular difference between affected and unaffected eyes of children with untreated amblyopia (significantly greater central macular thickness in affected than fellow unaffected eyes) was greater than this difference in children with treated amblyopia (difference of 9.2 μm vs 0.3 μm, respectively, P < 0.05). Taken together, our data show that amblyopic eyes have thicker macular regions than fellow eyes or normal eyes, and that treatment of amblyopia appears to decrease macular thickness to that of the fellow eye. Evidence for direct retinal involvement in eyes with amblyopia has been controversial.3Yen M.Y. Cheng C.Y. Wang A.G. Retinal nerve fiber layer thickness in unilateral amblyopia.Invest Ophthalmol Vis Sci. 2004; 45: 2224-2230Crossref PubMed Scopus (133) Google Scholar, 4Yoon S.W. Park W.H. Baek S.H. Kong S.M. Thicknesses of macular retinal layer and peripapillary retinal nerve fiber layer in patients with hyperopic anisometropic amblyopia.Korean J Ophthalmol. 2005; 19: 62-67Crossref PubMed Scopus (93) Google Scholar, 5Wanger P. Persson H.E. Oscillatory potentials, flash and pattern-reversal electroretinograms in amblyopia.Acta Ophthalmol (Copenh). 1984; 62: 643-650Crossref PubMed Scopus (15) Google Scholar A leading theory hypothesized by Yen et al3Yen M.Y. Cheng C.Y. Wang A.G. Retinal nerve fiber layer thickness in unilateral amblyopia.Invest Ophthalmol Vis Sci. 2004; 45: 2224-2230Crossref PubMed Scopus (133) Google Scholar suggests that the normal postnatal reduction (apoptosis) of retinal ganglion cells is arrested in amblyopia. It was further suggested that if this did occur, it is likely that the arrest of normal postnatal changes would also affect the normal maturation of the macula, including the movement of Henle's fibers away from the foveola and a consequent decrease in foveal cone diameter.6Bron A.J. Tripathi R.C. Tripathi B.J. Wolff's anatomy of the eye and orbit.8th ed. Chapman & Hall, London1997Google Scholar Our results appear to support this theory. There are thus potentially conflicting theories. Amblyopic eyes have decreased neural connectivity (lower number of ganglion cells), whereas amblyopia appears to be associated with a failure of normal postnatal apoptosis of ganglion cells (higher numbers of ganglion cells). It is likely that amblyopia has multiple pathogenetic mechanisms. One explanation to reconcile these differences is that amblyopic eyes have greater numbers of nonfunctioning ganglion cells (manifesting as thicker macular regions), but decreased functional neuronal connectivity (shown by the smaller neuroretinal rim area and larger retinal area to optic disc rim area ratio), culminating as uncorrectable low vision. Author replyOphthalmologyVol. 116Issue 10PreviewThe article by Samarawickrama, Huynh, and Mitchell confirms prior reports describing neuroretinal abnormalities in eyes presumed to be amblyopic. Their findings demonstrate that the availability of new objective quantitative devices, such as magnification corrected retinal imaging and the optical coherence tomography (OCT) instruments that they used, change the context for diagnosing vision impairments in children. Full-Text PDF