To report retinal nerve fiber layer thickness (RNFLT) in eyes with amblyopia compared with contralateral healthy eyes.In this cross-sectional study, we included patients with anisometropic amblyopia, strabismic amblyopia, and mixed amblyopia. All subjects underwent complete ophthalmic examination, including RNFLT measurement with time-domain OCT (Stratus OCT) and scanning laser polarimeter (GDX VCC). A paired "t" test was used to compare average and quadrant-wise RNFL thickness between the amblyopic and contralateral normal eyes. In addition, an analysis of variance test was used to compare various RNFL thickness parameters between the three groups.A total of 33 eyes of 33 subjects with anisometropic amblyopia, 20 eyes of 20 subjects with strabismic amblyopia, and 38 eyes of 38 subjects with mixed amblyopia were included. In the anisometropic amblyopia group, the average RNFLT in the amblyopic eye was 98.2 μm and 99.8 μm in the fellow normal eye (P = 0.5), the total foveal thickness was 152.82 μm (26.78) in the anisometropic eye and 150.42 μm (23.84) in the fellow eye (P = 0.38). The difference between amblyopic and contralateral normal eye for RNFL and macular parameters was statistically insignificant in all three groups. The RNFL thickness in four quadrants was similar in the amblyopic and non-amblyopic eye between all three groups and statistically non-significant.Our study showed that RNFL thickness was similar in amblyopic and non-amblyopic eyes between all three amblyopia groups.
In the current issue of this Journal, authors report an interesting paper titled "analysis of macular, foveal, and retinal nerve fiber layer thickness in children with unilateral anisometropic amblyopia and their changes following occlusion therapy."[1] Although the pioneering work of Hubel and Weiss[2] showed that amblyopia related changes occur in the visual cortex, the role of retinal structural changes in amblyopia has always been contemplated. With the advent of optical coherence tomography, many researchers have tried to understand changes in the retinal nerve fibre layer (RNFL) and macular thickness following amblyopia therapy.[34] These reports suggest conflicting results about the changes in RNFL thickness but more consistently increased macular thickness in the amblyopic eyes thickness.[567] In a further leap, authors in the current study report changes in these parameters following occlusion therapy. The current study is well-designed. The study population is uniform with unilateral anisometropic amblyopes. Inclusion and exclusion criteria are well-defined. Controls are appropriately selected. Authors report that amblyopic eyes had similar RNFL thickness, but higher macular and foveal thickness at baseline as compared to the normal eyes. The study showed a reduction in the average macular and foveal thickness of amblyopic eyes following compliant amblyopia therapy, whereas there was no significant change in the age-matched controls. However, there was no statistically significant change in the overall RNFL thickness. Prior studies by Yan et al.[5] and Pang et al.[6] showed similar results, and they attributed increase in baseline central macular thickness to the 'arrest of the postnatal foveal maturation in amblyopic eyes.' They proposed that during the process of normal maturation, there is a reduction in the central macular thickness and reorganization in the Henle's layer during maturation, also called as foveal delamination. They proposed following amblyopia therapy with glasses and occlusion, improvement in the quality of the image on the fovea might accelerate this process, leading to a reduction in average macular thickness. This explains overall change in the central macular and foveal thickness at the inception of amblyopia therapy. From this hypothesis, one would expect an increase in the overall RNFL thickness as well, however, it was not observed in the current study or prior studies. One possible explanation might be that the maturation of the foveal area is a more of a process of re-organization in the Henle's layer and it might be more sensitive to the improvement in visual acuity than changes in the RNFL. In a similar study, Yoon et al.[7] had shown a small reduction in the foveal volume following compliant amblyopia therapy. However, their study did not have any control groups. Although the study is well-designed, the major limitation of the study is small sample size especially for sub-group analysis by age and refractive error. The authors did perform the subgroup analysis according to age and reported more reduction in the macular thickness (MT) and foveal thickness (FT) following occlusion therapy in younger children (5–10 years) vs. older children (10–15 years). This is again expected given the more sensitive visual system in younger children. The authors have also reported the changes in the best corrected visual acuity (BCVA), macular, foveal thickness, and RNFL thickness following occlusion therapy according to refractive errors of the patient. The authors report that the change in the macular thickness was maximum for the myopic patients, however, the maximum improvement in the BCVA occurred in hypermetropes. This is little surprising and might raise concern about the hypothesis proposed by the authors. In general, amblyopia is denser among hypermetropes. It is possible that hypermetropes had worse BCVA at presentation itself, and therefore, these patients had more scope for improvement in BCVA than myopes. Moreover, greater change in the average macular and foveal thickness than improvement in the BCVA in myopes suggests possibly that other factors might also influence the change in these parameters than amblyopia therapy alone. Prior studies have also shown myopes tend to have overall thinner macular and RNFL as compared to hypermetropes.[8] Hence, overall change in macular and foveal thickness might be influenced by the age-related development processes in different refractive error subgroups. These questions might be answered by future studies with adequate sample size in each subgroup. In spite these considerations, this work represents significant insight into the changes in the retinal thickness that take place following amblyopia therapy and should open doors for more research in this field. More studies with stringent design and adequate sample size are needed to validate the results shown by the authors. Further studies should also include children with stimulus deprivation and strabismic amblyopia as well to be able to extrapolate the results to these populations as well.
A preschool girl presented with sudden-onset bilateral painless loss of vision from 2 days prior. Child’s examination showed light perception vision, sluggishly reacting pupils, otherwise normal anterior segment, healthy optic disc and retina in both eyes. MRI of brain and orbit with contrast revealed thickened left part of the optic chiasm with contrast enhancement extending proximally to bilateral optic tract and hyperintensities in the left thalamus and periventricular white mater. Considering the topographical distribution of lesions in the brain, neuromyelitis optica spectrum disorder was suspected. The child was started on intravenous methylprednisolone followed by tapering oral steroids. Serological testing was positive for myelin oligodendrocyte glycoprotein (MOG) and negative for aquaporin-4 antibodies. This case represents an unusual case of MOG associated demyelination disorder where the distribution of lesions showed chiasmal involvement along with optic tract, thalamus and deep white mater lesions.
Various surgical approaches have been described for the management of Duane retraction syndrome (DRS), a type of congenital cranial dysinnervation disorder (CCDD), the goals of which include correcting the primary position deviation and abnormal head posture (AHP), minimizing globe retraction and overshoots and improving the ocular rotations. Vertical rectus transposition (VRT) is one such technique, found more effective in improving abduction and thereby expanding the field of binocular vision, as compared to horizontal muscle surgery. VRT, however, is associated with the risk of inducing vertical deviations and also poses a risk for development of anterior segment ischemia. To overcome these concerns, transposition of only the superior rectus to the lateral rectus was proposed and evaluated to reveal improvement in alignment, AHP and motility comparable to VRT but with lesser surgical time and fewer post-operative complications. With promising results in the management of DRS, superior rectus transposition (SRT) has been extensively studied and has evolved over the last decade with several modifications to further increase the efficiency and reduce the risk of post-operative complications. This article focusses on the pre-operative considerations while planning SRT in DRS, various approaches and surgical techniques described, and the outcomes and complications of SRT in DRS. The role of SRT in the management of other CCDDs may be explored with further studies.
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