PURPOSE: To investigate the difference in circumpapillary retinal nerve fiber layer thickness (cpRNFLT) assessed on the conventional, clinically identified optic disc center and Bruch's membrane opening (BMO) center in myopic eyes. DESIGN: Cross-sectional study. PARTICIPANTS: One hundred nine eyes of 109 healthy myopic subjects with axial length of 24 mm or more. METHODS: The cpRNFLT was acquired on the disc center and BMO center aligned with the fovea. The global and sectorial cpRNFLT were computed in each eye and were compared between the 2 assessments. Furthermore, factors associated with the difference in cpRNFLT between the 2 assessments were analyzed. MAIN OUTCOME MEASURES: Differences in cpRNFLT assessed on the disc center and BMO center in myopic eyes. RESULTS: Among the included participants, the mean SE was -4.94±1.69 D, and the mean axial length was 25.55±0.89 mm. The global cpRNFLT was not significantly different between the 2 assessments; however, the temporal sector was significantly thicker, and the nasal sector was significantly thinner in the assessment on the disc center than on the BMO center (P < 0.0001 for both). Forty eyes (36.7%) exhibited more than 10 μm of difference between the 2 assessments in the temporal sector. The positions of the superior and inferior peaks of the cpRNFLT profile deviated temporally significantly in the disc-center assessment (P < 0.0001 for both). Multiple regression analysis showed that the width of γ-zone parapapillary atrophy (PPA) was associated significantly with greater difference in sectorial cpRNFLT between the 2 assessments. CONCLUSIONS: There was a significant amount of difference in the sectorial cpRNFLT acquired on the disc center and that acquired on the BMO center in the myopic eyes, which was considered to be derived from unique optic disc margin anatomy in these eyes. The eyes with wider γ-zone PPA exhibited greater cpRNFLT difference. The cpRNFLT data based on the BMO center were acquired at an anatomically accurate location, which indicated that the conventional disc-center assessment induced a substantial amount of error. The present results emphasize the importance of assessing cpRNFLT on the BMO center in myopic eyes for an improved structure-function relationship.
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