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Editors Selection IGR 22-3
Refractive Errors: Optic disc changes in myopic children
Comment by Franz Grehn on:
47630 Optic Disc Change with Incipient Myopia of Childhood, Kim T-W; Kim M; Weinreb RN et al., Ophthalmology, 2011;
The analysis of the sclera and lamina cribrosa of patients with and without glaucoma has been intensively investigated during the last years. Mechanical stress within the lamina cribrosa and at the edges of the scleral canal is now considered a major risk factor in the pathogenesis of optic nerve axonal degeneration. Myopia has been associated with the development and progression of glaucoma and has been considered as a risk factor. The prevalence of myopia is high in Asian populations. The study by Kim et al. (1920) addresses the question of how disc anomalies change during scleral development in myopic children. A retrospective analysis of seriel photographs of non-glaucomatous myopic children was performed. The authors selected one eye of 118 Korean children who were assessed by serial disc photographs at intervals of one year or more. The analysis of the optic disc included (1) the measurement of the ratio of the horizontal to vertical disc diameter and (2) the ratio of the maximum peripapillary atrophy width to vertical disk diameter. The children with a mean age of 7,3 years (1-17 yrs) were followed over an average of three years (12-88 months). Nearly half of the eyes (43%) developed changes in the optic nerve head diameter ratio and/or peripapillary atrophy. During the study period, the peripapillary atrophy increased from 7% to 20% of vertical disk diameter and the ratio of horizontal versus vertical disk diameter decreased from 0.92-0.86 (vertical elongation). These changes were correlated with an increase in myopic refraction. This data is interesting in the context of morphologic development of the scleral canal during childhood. Obviously the shape of the scleral canal is changing with increasing myopic shift. Therefore, the development of the peripapillary atrophy (Beta-zone) is acquired during the development of myopia and not due to a tilted disc at birth. An interesting interpretation is put forward by the authors: As the eye ball grows axially, the temporal sclera moves back and becomes flattened on the temporal side. Hence, the optic nerve is pulled towards the temporal direction and the sclera that originally was part of the inner scleral ring is then exposed horizontally. This would explain the temporal insertion of the retina and the choriocapillaris as well as the tilted appearance of the disc. The implications on axonal degeneration in glaucoma, particularly normal tension glaucoma, however, still remain to be elucidated. On the other hand, this observation is food for thought and should be included into the considerations about risk of glaucoma in progressive myopia.
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