Corneal and corneal epithelial thickness distribution characteristics in healthy North Indian eyes using spectral domain optical coherence tomography

Abstract

Purpose: To determine the pattern of corneal thickness and epithelial thickness distribution in healthy North Indian eyes by using spectral domain optical coherence tomography (SD-OCT).

Methods: The observational study measured total corneal and epithelial thickness in the central 2 mm zone and eight sectors each in paracentral 2-5 mm (ring 1) and midperipheral 5-7 mm (ring 2) zones on SD-OCT.

Results: The study included 67 eyes of 67 subjects with a male:female ratio of 32:35 and mean age of 25.04 ± 4.54 years. The mean central corneal and epithelial thicknesses were 505.97 ± 30.12 μm and 60.48 ± 8.37 μm, respectively. The epithelium of inferior and infero-nasal sectors in ring 1 and inferior sector in ring 2 was significantly thicker than the radially opposite sectors of the respective rings (P = 0.001; P = 0.01 and P = 0.02, respectively). Sector-wise analysis did not reveal any significant correlation between the total corneal thickness and epithelial thickness (all P > 0.05) except in the outer superior sector where there was a weak positive correlation (r = 0.28, P = 0.02). Central epithelial thickness in males (60.59 ± 9.28 μm) and females (60.37 ± 7.58 μm) was comparable (P = 0.91). Pachymetry was thinnest in the inferior, inferonasal, and inferotemporal sectors in 44.79% of eyes (n = 30), while thinnest epithelium was seen in the superior, superonasal, and superotemporal quadrants in 50.75% of eyes (n = 34).

Conclusion: The epithelial thickness distribution in this sample of topographically normal healthy North Indian eyes was nonuniform and independent of the underlying corneal thickness. Epithelium was thinner in the superior cornea, whereas total corneal thickness was minimum in the inferior part.

Keywords: Corneal epithelial thickness; corneal thickness; spectral-domain OCT.

Figure 1

(a) Reference image showing distribution of the 17 sectors within the 7-mm zone of the cornea [Central-central, (S)-superior, (ST)- superotemporal, (T) - temporal, (IT)- inferotemporal, (I)- inferior, (IN)- infero nasal, (N)- nasal, (SN)- superonasal]. (b and d) Sectoral distribution of corneal thickness (mean ± SD in µm); (c and e) Sectoral distribution of epithelial thickness (mean ± SD in µm) in the study sample. Corneal thickness (d) and epithelial thickness (e) show opposite pattern of distribution in diferent sectors. [“V” shape in d and “inverted V” in e]

Figure 2

Percentage distribution of thinnest sectors in the study population: (a and c) Total corneal thickness; (b and d) Corneal epithelial thickness

Figure 3

Sectoral distribution of total corneal thickness in μm (mean ± SD): (a) males and (c) females Sectoral distribution of epithelial thickness: (b) males and (d) females in μm (mean ± SD). Mean difference (males – females): (e) total corneal thickness (f) epithelial thickness. (P < 0.05 significant; student’s independent t test)