Measurement of the Inner Retinal Layers of Megalopapilla by Optical Coherence Tomography

The main purpose of this study was to assess the differences in the peripapillary retinal nerve fiber layer (pRNFL) and ganglion cell-inner plexiform layer (GCIPL) thicknesses between subjects with megalopapilla (MP) and those with large (physiological) cup discs (LCD) measured by spectral-domain optical coherence tomography. The secondary purpose was to determine whether pRNFL and GCIPL thicknesses increase with the optic nerve head (ONH) area. This cross-sectional study included 184 eyes (92 eyes with MP and 92 eyes with LCD). The subjects with LCD were used as sex-and-age-matched controls. All subjects were imaged using the Cirrus HD-OCT system. Macula and pRNFL thickness maps were obtained for all subjects. The inferior quadrant pRNFL thickness was higher in the MP group than in the LCD group (P < 0.05). There were no differences in the GCIPL thickness between the two groups. A positive correlation was found between average, superior, and inferior quadrant pRNFL thicknesses and the ONH area (P < 0.05). The slope of the correlation curve was higher for the inferior quadrant. No correlation was found between the GCIPL thickness and the ONH area. In comparison to patients with LCD, the inferior quadrant pRNFL thickness of patients with MP was higher. As the ONH area increased, the average, superior, and inferior quadrant pRNFL thicknesses also increased. In patients with MP, the assessment of a glaucomatous lesion based on pRNFL thickness measurements may not be reliable. It is recommended that in these patients, the evaluation of glaucomatous damage be based on the GCIPL thickness map analysis rather than on the pRNFL thickness.