22 October 2021
1 min read
The cornerstone of glaucoma diagnosis and monitoring is an assessment of the structure and function of the optic nerve. Advances in OCT have enabled glaucoma care providers to assess optic nerve structure to an unprecedented degree.
Primarily, three categories of parameters derived from OCT can be used for this purpose: retinal nerve fiber layer (RNFL), macular and optic nerve head. For good reason, more emphasis is usually placed on RNFL and macular parameters than parameters of the optic nerve head. However, a new optic nerve head parameter, the minimum rim width of the Bruch membrane opening (BMO-MRW; Heidelberg Spectralis, Heidelberg Engineering), may also add value to the diagnostic evaluation.
An opening in Bruch’s membrane allows the optic nerve to exit the eye. The margins of this opening can be used to objectively delimit the edge of the optical circle. Without this objective marker, the evaluation of the optic nerve rim is fraught with variability. The BMO-MRW parameter is derived from a protocol that automatically identifies the boundaries of Bruch’s membrane opening, 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 optical rim sectors (Figure). Each sector measure is then compared to age-matched and color-coded controls based on that comparison. The inferotemporal sector has been shown to have the highest diagnostic performance.
The future of glaucoma diagnosis is likely to involve the use of a combined index that takes into account the values of different categories of parameters and potentially also functional data. As the quality of imaging continues to improve, a wealth of data will become available to help clinicians make treatment decisions.
- 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.