Discordance of Disc-Fovea Raphe Angles Determined by Optical Coherence Tomography and MP-3 Microperimetry in Eyes With a Glaucomatous Hemifield Defect

Ability of Macular Inner Retinal Layer Thickness Asymmetry Evaluated by Optical Coherence Tomography to Detect Preperimetric Glaucoma

Purpose

We assessed the ability to detect preperimetric glaucoma (PPG) based on asymmetry in the thickness of the macular inner retinal layers measured by spectral-domain optical coherence tomography.

Methods

We studied 45 normal eyes and 50 PPG eyes retrospectively. Three-dimensional optical coherence tomography macular area scans were used to obtain the thickness of the retinal nerve fiber layer (RNFL), ganglion cell layer/inner plexiform layer (GCL/IPL), and ganglion cell complex (GCC). We calculated the thickness differences between the upper and lower macular hemispheres for the corresponding superpixels, then evaluated the mean absolute value of the thickness differences and the number of superpixels in which the thickness difference was greater than X µm, where X is an integer number from 1 to 10. Areas under the receiver operating characteristic curves (AUCs) for their PPG diagnostic performances were compared to the average thickness measurements of the total and hemiretinal sectors. X was determined at the maximum AUC value.

Results

The AUC for the mean absolute value of the difference in GCL/IPL thickness (0.923) was higher than the difference in RNFL and GCC thickness (0.710 and 0.905, respectively). The AUC for the number of superpixels in which the GCL/IPL thickness difference was greater than 8 µm (X = 8) was 0.914. The ability to diagnose PPG using these GCL/IPL parameters was statistically higher than for total or superior and inferior hemiretinal GCL/IPL thicknesses.

Conclusions

Asymmetry in the thickness of the GCL/IPL shows good PPG diagnostic performance.

Translational Relevance

This approach would be useful in the early detection of glaucoma.

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

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 (+0 to -13 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.