August 1, 2020
By Thao T.X. Ha, MD, and Huy D.M. Tran, MD, MSc
Hai Yen Vision Institute
Myopia is positively associated with glaucoma. However, diagnosing glaucoma in those eyes is a challenge due to the changes in retinal structure and function that result from axial elongation. This article describes potential diagnostic dilemmas that confound diagnosis and monitoring of glaucoma in myopic eyes and possible solutions to overcome the issues. Many assessments used to detect glaucoma are discussed in detail and include neuroretinal rim thickness, retinal nerve fiber layer (RNFL) thickness, ganglion cell/inner plexiform layer thickness, RNFL texture, microvasculature of the optic nerve head, visual fields and anterior segment, and IOP. We have summarized the content for a couple of the various parameters considered in the article.
Peripapillary RNFL thickness is a useful clinical parameter for diagnosing and monitoring glaucoma. In myopic eyes, the superotemporal and inferotemporal RNFL bundles tend to get closer together temporally, leading to an abnormal thickened temporal RNFL and thinned out inferior and superior RNFL in high myopes. The thinning in inferior regions may lead to false positives, whereas the thickening in the temporal region may mask underlying possible papillomacular bundle defects. To overcome these issues, it is suggested to consider angle kappa and position of the temporal vascular arcades and, if possible, to consult a custom normative database of myopes.
Visual field testing is an essential tool in the evaluation of glaucoma. In myopic eyes, the presence of visual field defects related to myopic macular degeneration or macular lesions or suspicious optic disc can challenge and confound glaucoma-related changes. In such instances, closer monitoring of progression, pattern of the defect, location, and agreements with other structural-functional assessments may be needed. For example, in non-myopic glaucoma, visual field defects are normally Bjerrum area, and nasal steps with central visual field spared until later stages. In comparison, myopic glaucoma may often be early central or paracentral scotomas. The use of appropriate perimetric protocols in highly myopic eyes is recommended. Additionally, the use of high-powered spectacle lenses is considered to influence the results of peripheral visual field testing, and it is suggested that it may be advisable to consider the use of contact lenses for the test.
The authors advocate a multimodal approach to evaluating glaucoma in a myopic eye where consideration is given both structural and functional assessments. They also advise that it is vital to understand the limitations (such as a lack of appropriate normative databases for structural correlates) and potential sources of error for each test used in the evaluation and administering the most appropriate based on the clinical scenario.
Nicholas Y Q Tan, Chelvin C A Sng, Jost B Jonas, Tien Yin Wong, Nomdo M Jansonius, Marcus Ang.
Myopic eyes have an increased risk of glaucoma. However, glaucomatous changes in a myopic eye are often difficult to detect. Classic structural and functional investigations to diagnose glaucoma may be confounded by myopia. Here, we identify some of the common pitfalls in interpreting these structural parameters and the possible solutions that could be taken to overcome them. For instance, in myopic eyes, we discuss the limitations and potential sources of error when using neuroretinal rim parameters, and retinal nerve fiber layer and ganglion cell/inner plexiform layer thickness measurements. In addition, we also review new developments and potential adjuncts in structural imaging such as the assessment of the retinal nerve fiber layer texture, and the examination of the microcirculation of the optic nerve head using optical coherence tomography angiography. For the functional assessment of glaucoma, we discuss perimetric strategies that may aid in detecting characteristic visual field defects in myopic glaucoma. Ultimately, the evaluation of glaucoma in myopia requires a multimodal approach to allow correlation between structural and functional assessments. This review provides overview on how to navigate this diagnostic dilemma.
Tan, N. Y., Sng, C. C., Jonas, J. B., Wong, T. Y., Jansonius, N. M., & Ang, M. (2019). Glaucoma in myopia: diagnostic dilemmas. British Journal of Ophthalmology, bjophthalmol-2018.