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Do Young Park, Changwon Kee; Applicability of ISNT rule using BMO-MRW to differentiation between healthy and glaucomatous eyes. Invest. Ophthalmol. Vis. Sci. 2018;59(9):2083. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Although ISNT rule is widely used to distinguish glaucomatous optic discs from healthy discs, it has limitations because it is based on a two-dimensional assessment of neuroretinal rim (NRR) of the optic disc and it is difficult to apply it to deformed discs such as myopic tilted disc. In the present study, we evaluated the applicability of ISNT rule using Bruch’s membrane opening minimum rim width (BMO-MRW), which is known to reflect more reliable NRR margins, in the diagnosis of normal tension glaucoma (NTG).
This study was designed as a cross-sectional observational study. Using color disc photographs, NRR thickness was measured at superior, inferior, nasal, and temporal side of the optic discs. Using the radial scan images of spectral domain optical coherence tomography (SD-OCT), BMO-MRW was measured at the same regions. We compared the diagnostic ability of ‘violation of ISNT rule’ for the diagnosis of NTG between two methods. If the NRR was not clearly distinguished on the disc photographs, we classified these eye into an ‘indistinguishable NRR’ group and tested only the applicability of ISNT rule using BMO-MRW.
This study involved 103 healthy eyes and 118 NTG eyes. When BMO-MRW was used, the specificity of ‘violation of ISNT rule’ in the diagnosis of glaucoma was higher than using disc photographs (66.3% vs 42.2%), while the sensitivity did not show statistically significant difference between two methods (91.7% vs 86.5%). ‘Indistinguishable NRR’ group included 42 eyes (20 in normal group and 22 in NTG group). Compared to the eyes with distinguishable NRR, the eyes with indistinguishable NRR had higher axial length, more negative refractive error, and higher tilt ratio. In the eyes with indistinguishable NRR, diagnostic ability of ‘violation of ISNT rule’ using BMO-MRW was not statistically significantly different from the eyes with distinguishable NRR (p>0.05).
Application of ISNT rule using BMO-MRW shows superiority in distinguishing between healthy and glaucomatous optic discs compared to using disc photographs. ISNT rule using BMO-MRW can be applied even when NRR is indistinguishable on the disc photograph, such as myopic tilted discs.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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