The frequency of non-pathologically thin corneas in young healthy adults.

Measurement of normal corneal thickness and corneal epithelial thickness is important in keratorefractive surgery, glaucoma, following extended contact lens wear, and in patients with corneal disease. Clinically, a central corneal thickness less than 500 µm is considered to be moderately-to-extremely thin. The purpose of this study was to compare biological differences in patients with clinically thin compared to normal corneal thickness values in healthy young adults using Fourier domain optical coherence tomography. In total, 168 eyes from 84 patients aged 19-38 years were scanned using an Avanti optical coherence tomographer. To eliminate circadian effects on corneal thickness, all patients were scanned within a 4-hour window. Corneal thickness was measured across the central 6 mm of the cornea. Total central corneal thickness, corneal epithelial thickness, and corneal stromal thickness were compared between males and females and tested for correlations with age, use of systemic hormones, degree of myopia, and corneal curvature. The average central corneal thickness for males and females was 540.5±32.0 μm and 525.2±33.0 μm, respectively (=0.020). Thirty-eight eyes had corneal thickness measurements below 500 µm; 12% (6 eyes) from males and 28% (16 eyes) from females (=0.008). All women with corneas below 500 μm were bilaterally thin. This finding differed for men. Corneal thinning was not associated with age, use of systemic hormones, or degree of myopia. Females had steeper keratometry (K) readings (=0.01 for flat K, =0.002 for steep K) than males. No differences in layer offset values between normal thickness corneas and thin corneas were evident, suggesting that the reduced thickness was not pathological. The results of this study indicate that a subpopulation of healthy young adults have non-pathologically thin corneas, well below 500 μm; and that these thinner corneas are more frequent in females. This underscores the importance of accurate corneal thickness measurements prior to keratorefractive surgery and when evaluating intraocular pressure in glaucoma.