This prospective study found that axial length and, accordingly, refractive status, affected peripapillary RNFL thickness profiles measured by RTVue spectral-domain OCT (SD-OCT).
This is significant because it suggests that results from SD-OCT should be adjusted for axial length. In myopic eyes, the scan circle diameter is larger and farther from the center of the optic nerve head, and therefore shows a thinner RNFL, potentially leading to a mis- or over-diagnosis of glaucoma. The inverse is true for hyperopic patients, with the potential for under-diagnosis of glaucoma.
The authors performed RTVue SD-OCT to examine the RNFL of 35 myopic eyes with a mean axial length of 25.8 mm, 30 emmetropic eyes with a mean axial length of 23.9 mm, and 33 hyperopic eyes with a mean axial length of 21.8 mm.
Average peripapillary RNFL thickness had a negative correlation with axial length (r=-0.741, P < 0.001). However, after correction of the magnification effect, the significant differences disappeared.
Average RNFL thickness and the RNFL thicknesses of the superotemporal, superonasal, inferotemporal and lower temporal sectors were significantly different between myopic and emmetropic eyes. Average RNFL thickness and RNFL thicknesses of the upper temporal and inferonasal sectors were significantly different between hyperopic and emmetropic eyes. RNFL thickness values were lower in myopic eyes than in hyperopic eyes in all sectors except for upper and lower nasal.
The authors conclude that to make a correct diagnosis of glaucoma in varying degrees of myopia or hyperopia, either the axial length-induced magnification effect should be corrected by ophthalmologists or the current RTVue OCT database should be improved by taking axial length into account.