Title : A comparative study of corneal epithelial and stromal thickness between keratoconic eyes and healthy eyes exhibiting corneal astigmatism

Purpose : To compare the epithelial and stromal thickness in different zones across the cornea between keratoconic eyes and healthy eyes with corneal astigmatism. 

Methods : This hospital based, cross-sectional comparative study enrolled 63 participants (118 eyes) who attended B.P. Koirala Lions Center for Ophthalmic Studies over 12 months, comprising 59 keratoconic eyes and 59 age and gender matched healthy eyes with corneal astigmatism. Epithelial and stromal thickness was measured using anterior segment optical coherence tomography (AS-OCT) and corneal astigmatism using corenal topography. Independent t-test was used to compare epithelial and stromal thicknesses between groups, the Chi-square test/Fisher’s exact test was used to assess location of minimum thickness and a mixed repeated-measures ANOVA was used to evaluate central to peripheral stromal thickness variation.

Results: Among 63 participants (mean age 23.47±6.78 years, 71.4% males), epithelial thinning in keratoconus was predominantly localized to paracentral inferotemporal zone (45.8%), whereas healthy astigmatic eyes showed thinning in peripheral superior zone (74.1%, p<0.01). The thinnest stromal point was most commonly central in both groups, though keratoconus also showed thinning in paracentral inferotemporal (25.4%) and paracentral inferior zones (15.3%) (p<0.04). Keratoconus had significantly thinner epithelium in 12 of 17 regions. The peripheral inferotemporal, peripheral nasal, peripheral temporal and paracentral inferonasal regions didn’t  show significant thinning (p<0.05). The stroma was significantly thinner across all 17 regions (p<0.05). Center to periphery analysis revealed keratoconus showed significantly greater non uniform stromal thinning(p<0.001).

Conclusion : Keratoconus showed significant epithelial and stromal thinning as compared to healthy eyes having corneal astigmatism. In keratoconus, epithelial thinning was predominantly localized to the paracentral inferotemporal zone, while astigmatic eyes showed thinning in peripheral superior zone. Stromal thinning in keratoconus was widespread across all sectors greatest differences observed centrally and paracentral inferior region. Relatively greater center to periphery stromal thickness variation was found in keratoconic eyes.

Keywords : Corneal astigmatism, Corneal epithelial thickness, Corneal stromal thickness, Keratoconus, Optical Coherence Tomography

Sneha Karki Dhali is a final-year optometry student at the Maharajgunj Medical Campus, Institute of Medicine, Tribhuvan University. Deeply interested in optometric research, she recently served as a delegate at the Asia-Pacific Optometric Congress (APOC) 2024. Having completed her undergraduate research project, she is currently developing her manuscript for peer reviewed publication while awaiting her official final results.