Retinal Nerve Fiber Layer Analysis of Large Optic Discs (Megalopapillae): A Spectral Domain Optical Coherence Tomography Study

Purpose:To evaluate the retinal nerve fiber layer (RNFL) thickness and the stereometric parameters of the optic nerve head (ONH) in large optic discs (megalopapillae). Methods:This study included 15 eyes of 9 subjects with an optic disc area 2.82 mm by the confocal scanning laser ophthalmoscopy (CSLO). In all eyes, the CSLO was done with the Heidelberg Retina Tomograph (HRT II; Heidelberg Engineering GmbH, Heidelberg, Germany). All subjects underwent a complete ophthalmic evaluation, including intraocular pressure (IOP) measurement, central corneal thickness (CCT) measurement and standard automated perimetry (SAP). The peripapillary RFNL thickness was measured using the spectral domain optical coherence tomography (SD-OCT) (Spectralis HRA + OCT; Heidelberg Engineering GmbH, Heidelberg, Germany). A descriptive analysis was made using Statistical Package for the Social Sciences (SPSS) for Windows, version 19.0 (SPSS Inc., Chicago, USA). Results:The mean optic disc area was 3.41 ± 0.47 mm. The IOP measurements ranged from 10 to 18 mmHg (mean 13.7 ± 2.7). The mean CCT value was 524.7 ± 33.6 μm. Mean deviation (MD) and corrected loss variance (CLV) of the SAP were, respectively, 1.3 ± 2.4 and 2.0 ± 1.7 dB. The mean peripapillary RNFL thickness was 102.40 ± 13.37 μm. Conclusions:The RNFL thickness is normal in large optic discs (megalopapillae). The RNFL assessment performed by SD-OCT is high and virtually unaffected or only minimally affected by the size of the optic disc. It may provide more consistent diagnostic evaluation across large optic discs (megalopapillae) than ONH assessment as performed by CSLO, despite the CSLO gives more information on the morphometric parameters of the ONH.