Geometry of the Retinal Nerve Fibers From Emmetropia Through to High Myopia at Both the Temporal Raphe and Optic Nerve

Abstract

Citation: Bedggood P, Mukherjee S, Nguyen BN, Turpin A, McKendrick AM. Geometry of the retinal nerve fibers from emmetropia through to high myopia at both the temporal raphe and optic nerve. Invest Ophthalmol Vis Sci. 2019;60:4896-4903. https://doi.org/10.1167/iovs.19-27539 PURPOSE. The geometry of retinal nerve fibers may be altered with myopia, a known risk factor for glaucoma. Recent developments in high resolution imaging have enabled direct visualization of nerve fiber bundles at the temporal raphe with clinical hardware, providing evidence that this area is sensitive to glaucomatous damage. Here, we test the hypothesis that nerve fiber geometry is altered by myopia, both at the temporal raphe and surrounding the optic nerve head.METHODS. Seventy-eight healthy individuals participated, with refractive errors distributed between emmetropia and high myopia (þ0 to À13 DS). Custom high-density OCT scans were used to visualize RFNL bundle trajectory at the temporal raphe. A standard clinical OCT protocol was used to assess papillary minimum rim width (MRW) and peripapillary retinal nerve fiber layer (RNFL) thickness. RESULTS.Measures of raphe shape-including position, orientation, and width-did not depend significantly on axial length. In 7.5% of subjects, the raphe was rotated sufficiently that inversion of structure-function mapping to visual field space is predicted in the nasal step region. Low concordance to ISNT and related rules was observed in myopia (e.g., for RNFL, 8% of high axial myopes compared with 67% of emmetropes). Greater robustness to refractive error was observed for the IT rule.CONCLUSIONS. High density OCT scans enabled visualization of marked interindividual variation in temporal raphe geometry; however, these variations were not well predicted by degree of myopia as represented by axial length. That said, degree of myopia was associated with abnormal thickness profiles for the papillary and peripapillary nerve fiber layer.

Consistency Between Optical Coherence Tomography and Humphrey Visual Field for Evaluating Glaucomatous Defects in High Myopic Eyes

“…Patients with high myopia usually have a distorted optic disc, peripapillary atrophy, and posterior scleral staphyloma, which may interfere with the accuracy of RNFL thicknesses measured by OCT and glaucoma severity evaluation, as assessed by ophthalmologists. Low concordance to ISNT and related rules was observed in myopia (e.g., for RNFL, 8% of high axial myopes compared with 67% of emmetropes 20 ). Furthermore, visual eld examination of patients with high myopia often shows declining visual sensitivity and/or local visual eld loss, which would also disturb the judgment of glaucomatous visual eld defects.…”

Consistency between optical coherence tomography and humphrey visual field for evaluating glaucomatous defects in high myopic eyes

“…Hence we can't distinguish that the declined thickness of inner retinal layers (including RNFL and GCIPL) in glaucoma patients with high myopia is due to increasing axial lengths or glaucomatous defects [16,17]. Additional low concordance to the rules of inferior>superior>nasal>temporal (ISNT) was observed in myopia (e.g., for RNFL, 8% of high axial myopes compared with 67% of emmetropes [18]). Furthermore, visual field examination of patients with high myopia often shows declining visual sensitivity and/or local visual field loss, which would also disturb the judgment of glaucomatous visual field defects.…”

Anatomical Location of the Raphe and Extended Raphe in the Human Retina: Implications for Assessment of the Optic Nerve with OCT

“…Using an adaptiveoptics scanning laser ophthalmoscope, Huang et al 9 reported this angle to be 170.3°± 3.6°. Using OCT, Tanabe et al 10 found 169°± 3°and Bedggood et al [11][12][13] found 173°± 3°. With a disc-fovea angle of 7.6°(see next paragraph), our reference line (black line in Fig.…”