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Editors Selection IGR 21-4

Glaucoma and myopia: Glaucoma diagnosis in myopic eyes

Comment by Toru Nakazawa on:

67243 Diagnostic Accuracy of Optical Coherence Tomography and Scanning Laser Tomography for Identifying Glaucoma in Myopic Eyes, Malik R; Belliveau AC; Sharpe GP et al., Ophthalmology, 2016; 123: 1181-1189

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Malik et al. evaluated the accuracy of optical coherence tomography (OCT) and confocal scanning laser tomography (CSLT) in the diagnosis of glaucoma in myopic eyes. In Asia, where myopia is more common than in Western countries, myopia is especially important as a risk factor for normal tension glaucoma (NTG). Commonly, glaucoma is diagnosed based on a characteristic appearance of the optic nerve head (ONH), including undermining of the cup and rim thinning, and on corresponding visual field loss. In myopic eyes, however, disc appearance can vary significantly, making the diagnosis of glaucoma based on structural factors such as ONH morphology very difficult. In particular, myopic eyes have temporally tilted discs with peripapillary atrophy (PPA), confusing the interpretation of OCT topographical measurements of the ONH. In this study, the authors attempt to improve the accuracy of glaucoma diagnosis in myopic eyes with the use of new OCT-measured rim parameters. These parameters are based on Bruch's membrane opening (BMO) rather than the conventionally used optic disc margin (DM). Previously, the authors described a new parameter that measured the minimum distance between the BMO and the internal limiting membrane, which they termed 'BMO-minimum rim width' (BMO-MRW). They found that BMO-MRW represented the amount of neuroretinal rim tissue more accurately than conventional DM-based parameters.

BMO-MRW was more sensitive than DM-RA and similar to RNFL thickness in the identification of glaucoma in myopic eyes

The primary aim of this study was to evaluate the diagnostic accuracy of BMO-MRW, DM-based rim assessments (DM-RA), based on CSLT, and RNFL thickness by comparing their ability to distinguish myopic patients with and without glaucoma. The authors found that at a sensitivity of 90%, DM-RA had a specificity of 30%, and BMO-MRW and RNFL thickness both had a specificity of 71%. Thus, BMO-MRW was more sensitive than DM-RA and similar to RNFL thickness in the identification of glaucoma in myopic eyes. These objective parameters offer a valuable diagnostic tool for patients with glaucoma and a myopic optic disc, and may help not only clinical research into the structure and function of the glaucomatous eye, but also follow-up care for glaucoma patients with myopia.

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