Measuring Bruch's membrane opening minimum rim width could help you distinguish whether the patient has glaucoma or compressive optic neuropathy. Photo: James Fanelli, OD. Click image to enlarge.
Diagnosing glaucoma is often straightforward, but the differential includes some potentially more serious conditions, such as compressive optic neuropathy. Researchers recently determined a method that can significantly improve accuracy by looking at the relationship between two OCT measurements: minimum rim width (MRW) and peripapillary retinal nerve fiber layer (pRNFL) thickness. The first metric describes the shortest distance between Bruch’s membrane opening and the internal limiting membrane. The team suggested the ratio of MRW to pRNFL may be the most helpful parameter in clinical practice for this particular differential diagnosis.
This prospective, cross-sectional study included 115 eyes of 77 subjects (34 with compressive optic neuropathy from chiasmal lesions, 21 with glaucoma and 22 normal controls). The investigators used OCT to determine MRW, pRNFL and the ratio of the two for each optic disc sector as well as the global average.
MRW and pRNFL measurements were significantly reduced in both compressive neuropathy and glaucoma compared with controls. In glaucoma patients, however, the MRW was thinner in most measurements than results found in compressive optic neuropathy patients, though a significant overlap was observed in many parameters. Using the ratio of the two increased the ability to discriminate between compressive optic neuropathy and glaucoma, especially in the nasal disc sector and the nasal and temporal averages, the researchers found.
“Although further studies are necessary to confirm our findings, we believe that MRW:pRNFL ratios will prove a useful addition to the differential diagnosis of glaucoma and compressive optic neuropathy,” the study authors concluded.
de Souza Andrade T, de Araújo RB, do Nascimento Rocha AA, et al. Bruch’s membrane opening minimum rim width and retinal nerve fiber layer helps differentiate compressive optic neuropathy from glaucoma. Am J Ophthalmol. August 25, 2021. [Epub ahead of print].