Examples of a temporally tilted disc (A) and an inferiorly tilted disc (B).
Distribution of peripapillary nerve fiber layer (NFL) thicknesses of temporally tilted discs, inferiorly tilted discs, and normal discs presented in a linear fashion. Error bars indicate standard error of the mean.
Law SK, Tamboli DA, Giaconi J, Caprioli J. Characterization of Retinal Nerve Fiber Layer in Nonglaucomatous Eyes With Tilted Discs. Arch Ophthalmol. 2010;128(1):141-142. doi:10.1001/archophthalmol.2009.340
Clinical assessment of the optic disc and nerve fiber layer (NFL) is an important method to diagnose and monitor the progress of glaucomatous optic neuropathy but is often difficult in eyes with tilted discs.1- 3 Clinically, there are 2 orientations of tilting of the optic disc: temporal and inferior1 (Figure 1). Optical coherence tomography (OCT) demonstrates an acceptable diagnostic ability for glaucoma by comparing an individual patient's NFL thickness profile with those in a normative database.4- 6 The purpose of this study is to characterize the NFL of nonglaucomatous eyes with tilted discs using OCT.
This study was approved by the institutional review board of the University of California, Los Angeles. Our entire optic disc photograph database was screened for temporally or inferiorly tilted discs. Eyes with severely temporally tilted discs with a maximal-to-minimal disc diameter ratio higher than 1.4 and eyes with severely inferiorly tilted discs with apparent rotation of the long axis of the disc by more than 75° from the vertical meridian were selected. Patients with a diagnosis of glaucoma, glaucomatous visual field defects, intraocular pressure higher than 21 mm Hg, or history of intraocular surgery, steroid use, ocular trauma, or any ocular diseases were excluded. StratusOCT software version 3.0 or 4.0.4 (model 3000; Carl Zeiss Meditec, Inc, Dublin, California) was used to measure the thickness of the peripapillary NFL. Eyes with OCT NFL images of poor signal quality or images in which the NFL segmentation algorithm failed to identify the NFL were excluded. The OCT measurements of the NFL in eyes with temporally and inferiorly tilted discs were compared with those of aged-matched healthy individuals without tilted discs.
Stereoscopic optic disc photographs of 9435 patients were screened for severely tilted optic discs. Thirty-two eyes (21 patients [0.22%]) with temporally tilted discs and 11 eyes (7 patients [0.07%]) with inferiorly tilted disc were enrolled. The control group consisted of 57 eyes (36 patients). Both the temporally and inferiorly tilted disc groups had a statistically significantly more myopic mean refractive error (mean [SEM], −7.67 [3.81] diopters [D] and −5.25 [3.86] D, respectively), higher astigmatism (mean [SEM], 1.07 [1.12] D and 1.68 [1.90] D, respectively), and worse visual field mean deviation (mean [SEM], −2.69 [2.21] dB and −4.01 [1.69] dB, respectively) and pattern standard deviation (mean [SEM], 2.66 [1.63] dB and 3.35 [2.71] dB, respectively) than the control group (P < .01). The average NFL thicknesses of the temporally (mean [SEM], 90.7 [16.4] μm) and inferiorly (mean [SEM], 92.4 [15.7] μm) tilted disc groups were statistically significantly lower than those of the control group (mean [SEM], 102.6 [9.6] μm) (P < .001 and P = .005, respectively).
The superior peak of the temporally tilted disc group was located more temporally than that of the control group (mean [SEM], 55° [19°] vs 75° [16°], respectively; P < .001). The inferior peak of the temporally tilted disc group was also located more temporally than that of the control group, but the difference was not quite statistically significant (mean [SEM], 297° [10°] vs 291° [21°], respectively; P = .08) (Figure 2).
The mean thicknesses of the temporal, superior, and nasal quadrants of the inferior tilted disc group were very similar (mean [SEM], 84.22 [18.96] μm, 85.36 [34.53] μm, and 84.50 [21.71] μm, respectively). With the mean NFL thickness of all 256 points along the circular scan plotted, no obvious peak of NFL thickness was noted in the superior half, but a peak was noted in the inferior half of the inferiorly tilted disc group (Figure 2).
The significance of all results remained unchanged on further analysis with repeated-measures linear regression models with a compound symmetry covariance structure to account for the inclusion of fellow eyes.
Eyes with tilted discs have a different distribution of NFL thicknesses compared with normal eyes, with the peak of the superior half of the temporally tilted disc shifted temporally and the superior peak of the inferiorly tilted disc blunted. These characteristics should be considered when applying OCT to the interpretation of NFL measurements in eyes with tilted discs.
Correspondence: Dr Law, Jules Stein Eye Institute, 100 Stein Plaza 2-235, Los Angeles, CA 90095 (firstname.lastname@example.org).
Financial Disclosure: None reported.
Funding/Support: This study was supported in part by Research to Prevent Blindness.
Additional Contributions: Fei Yu, PhD, provided statistical assistance.