Retinal Nerve Fiber Layer Bundle Angle at the Optic Disc in Human Eyes

Abstract

Purpose: : For diagnosis of glaucoma, correspondence between the functional changes of visual field defects and the structural changes of the optic disc is essential. Octopus EyeSuite Polar Graph (HAAG-STREIT, Swiss) is a visual field (VF) representation similar to a radar graph that rearranges the test locations round the optic disc based on a model of the retinal nerve fiber layer (RNFL) bundle. Here we evaluated the RNFL bundles in our subjects using scanning laser ophthalmoscope (SLO: F-10, NIDEK) and the RNFL bundle angles at the optic disc.

Methods: : Subjects were 15 eyes of 15 normal subjects and 5 eyes of 5 patients with glaucoma. All the subjects had corrected visual acuity > 0.8 and equivalent sphere of -11.0 D to +3.0 D. Patients’ fundus images were obtained by SLO with a blue laser (490-nm) and the SLO images were averaged using the software tracking method with Registax V4.0 to construct clear RNFL bundle images. Furthermore, a 60-degree panorama of the fundus image was constructed. To overlap the VF test locations on the SLO image, we detected the blind spot in each subject using the custom test with one-degree intervals and matched it to the optic disc. We traced the RNFL bundle and measured the RNFL bundle angle at the optic disc for each test location and compared the obtained angles to those used in polar graph.

Results: : For all the VF test points, the average difference in the RNFL bundle angle at the optic disc between the polar graph model and our subjects was 10.4°±8.0°. Among the subjects, we further assessed the RNFL bundle angles in the myopic eyes with equivalent sphere ≤ -6.0 D and the non-myopic eyes with equivalent sphere of -3.0 D to +3.0 D. We found that the myopic eyes had bigger angles in the superior VF and smaller angles in the inferior VF than the non-myopic eyes.

Conclusions: : When comparing patient’s RNFL bundle pattern to the polar graph model in a clinical examination, we should take account of a possible maximum difference of 26° in the RNFL bundle angle at the optic disc.

Keywords: imaging/image analysis: clinical • visual fields • optic disc