The impacts of contact lenses on the short- and long-term biochemical parameters of tear films and corneal thickness

Introduction: To investigate the effects of long- and short-term use of different types of contact lenses on corneal metabolism and corneal thickness. 
Materials and Method: The participants were divided into two groups in the study. In the first group, 20 of the 42 patients were administered a rigid gas-permeable lens (RGPL) with a Dk value of 92x10-11, while the remaining wore a soft contact lens with a water content of 38%. We then explored their Lactate Dehydrogenase (LHD) levels to evaluate the hypoxic effect on tear films in short- (8 hours) and long-term (2nd, 3rd, 5th months) and albumin levels to assess mechanical trauma. In the second group, the corneal thickness was measured using a Haag-Streit optical pachymeter before and at the 8th hour and 2nd month following the first set of lenses, and LDH and albumin values were simultaneously evaluated in tear film. 
Results: The results yielded no significant increase in tear film LDH and albumin levels in the short- and long-term in both the RGPL and the soft contact lens groups with similar age and sex distribution. In the second part, the corneal thickness measurements resulted in an increase of 5.5% in the RGPL group and 3.63% in the soft lens group at the 8th hour of lens use. However, the groups did not significantly differ by baseline corneal thickness at the 2nd-month follow-up. Similarly, there was no significant increase in LDH and albumin levels in the tear film samples of the same group. 
Conclusion: The absence of a long-term increase in corneal thickness and no elevated levels of albumin and LDH in tear films indicate that contact lenses fit corneal physiology.