Purpose: We report changes in the central corneal thickness during various phases of the menstrual cycle.

Methods: We recruited 16 healthy women of reproductive age and measured the central corneal thickness at 3 points in their menstrual cycle, beginning on days 1 to 3 and again at ovulation and at the end of the cycle (days 27-32). Ovulation was determined with a test that determines the peak of luteinizing hormone in the urine.

Results: We found that the central cornea was thinnest at the beginning of the cycle (mean = 536 [mu]m). Corneal thickness increased at ovulation (mean = 549 [mu]m) and at the end of the cycle (mean = 559 [mu]m). The difference in corneal thickness was statistically significant at ovulation (P = 0.003) and the end of cycle (P = 0.001) compared with values at the beginning of the cycle.

Conclusion: The central corneal thickness changes during the menstrual cycle; the cornea is thinnest at the beginning of the cycle and thickest at the end. These changes could be secondary to hormonal influences; estrogen receptors can be found in human corneas, suggesting that estrogen may have a role in corneal physiology.

Corneal thickness increased at ovulation