Changes In Objective Tear Film Parameters After Surface Ablation With Mitomycin C.

To evaluate the postoperative changes in the tear osmolarity and in the non-invasive tear break-up time (NI-TBUT) after photorefractive keratectomy (PRK) with the adjuvant use of mitomycin C (MMC) for the correction of myopia and/or astigmatism.

Novovisión Clinic, Madrid, Spain.

Prospective, observational study. Tear osmolarity [measured with the Tear Lab (Tear Lab Corporation, CA, USA)] and the NI-TBUT [measured with the Keratograph 5M (Oculus, Optikgërate GmbH, Wetzlar, Germany)] were evaluated preoperatively and at 1 week, 1 and 3 months after PRK with MMC.

136 consecutive eyes of 68 patients, that underwent PRK with MMC, were included in the study. The mean age was 28.9 ± 5.4 years (range, 20 to 45 years), the mean preoperative spherical defect was -3.47 ± 1.8 diopters (D) (range, 0 to -9D) and the mean preoperative cylinder was -0.66 ± 0.64 D (range, 0 to -3D). The mean preoperative values of tear osmolarity and NI-TBUT were 302.4 ± 14.0 mOsm/l and 14.6 ± 7.1 seconds, respectively. No significant differences were found in the tear osmolarity nor in the NI-TBUT at 1 week, 1 and 3 months postoperatively compared to their respective preoperative values (P > 0.05 for all comparisons).

Tear osmolarity and NI-TBUT do not significantly change after surface ablation with MMC. Based on our results, these two objective parameters traditionally used for the diagnosis of dry eye disease seem not to be useful for the evaluation of subjective dry eye symptoms that many patients have in the early postoperative period after surface ablation. PRK-induced dry eye seems not to correlate with tear film parameters such as osmolarity and NI-TBUT, and subsequently, this fact supports the hypothesis of a neuropathic origin of the post-operative ocular discomfort.