BLOG: Novel parameter may aid value in glaucoma diagnostics
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The cornerstone of glaucoma diagnosis and monitoring relies on an assessment of optic nerve structure and function. Advancements in OCT have allowed glaucoma care providers to evaluate optic nerve structure to an unparalleled degree.
Principally, three OCT-derived parameter categories may be used for this purpose: retinal nerve fiber layer (RNFL), macular and optic nerve head. For good reason, more weight is typically placed on RNFL and macular parameters than on optic nerve head parameters. However, a novel optic nerve head parameter, Bruch’s membrane opening minimum rim width (BMO-MRW; Heidelberg Spectralis, Heidelberg Engineering), may also add value to one’s diagnostic assessment.
An opening within Bruch’s membrane allows the optic nerve to exit the eye. The margins of this opening can be used to objectively demarcate the border of the optic rim. Without this objective marker, assessment of the optic nerve rim is fraught with high variability. The BMO-MRW parameter is derived from a protocol that automatically identifies the borders of Bruch’s membrane opening and then acquires 24 radial B-scan images centered on the optic nerve. The shortest distance from each of these points to the internal limiting membrane is measured and averaged overall as well as with respect to six optic rim sectors (Figure). Each sector measurement is then compared with age-matched controls and color-coded based on this comparison. The inferotemporal sector has been shown to have the highest diagnostic performance.
The future of glaucoma diagnostics will likely involve the use of a combined index that takes into account values from the various parameter categories and potentially also functional data. As imaging quality continues to improve, a wealth of data will become available to aid clinicians in making a treatment decision.
References:
- Hong SW, et al. Am J Ophthalmol. 2019;doi:10.1016/j.ajo.2018.10.027.
- Stagg BC, et al. Ophthalmol Glaucoma. 2020;doi:10.1016/j.ogla.2019.11.008.
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