Purpose: To evaluate and compare corneal thickness in normal and dry eyes.
Methods: The Orbscan corneal topography system was used to measure the corneal thickness at nine locations in the central and peripheral (superior, superonasal, nasal, inferonasal, inferior, inferotemporal, temporal, superotemporal) cornea in 38 eyes of 21 patients with aqueous tear deficiency dry eye and 34 eyes of 21 normal subjects.
Results: The average thickness of nine sites in the central and midperipheral cornea was significantly decreased in dry eyes compared with that of normal eyes. The superior cornea was found to be the thickest area in both groups, measuring 0.629 +/- 0.030 mm in normal eyes and 0.589 +/- 0.031 mm in dry eyes. The center of the cornea was noted to be the thinnest in both groups, measuring 0.571 +/- 0.028 mm and 0.534 +/- 0.034 mm in normal and dry eyes, respectively. In color-coded pachymetry maps, the oval pattern was observed in 67.6% of normal corneas and 39.5% of dry eyes, while the decentered oval pattern was noted in 2.9% and 31.6% of normal and dry eyes, respectively (p < 0.025 for oval pattern and p < 0.005 for decentered oval map). The mean astigmatism was 0.99 +/- 0.43 diopter (D) in normal corneas and 1.42 +/- 0.92 D in dry eyes (p = 0.015). In the anterior elevation maps, the island pattern was the most commonly observed pattern in both groups, 88.3% in normal corneas and 60.5% in dry eyes (p < 0.01). No significant difference in the patterns of posterior corneal elevation maps and axial power maps of the anterior corneal surface was noted between groups.
Conclusion: The corneal thickness of the central and midperipheral cornea was significantly decreased in the dry eyes. It is possible that the chronic state of desiccation and immune activation in dry eye may contribute to the observed corneal thinning. Perhaps the frank corneal ulceration that occurs in some dry eyes is a more severe manifestation of this phenomenon.