Current research findings suggest that post-LASIK dry eye is but a transient problem after the procedure and will resolve with time. The proportion of patients that go on to develop persistent, chronic dry eye problems years after surgery is poorly investigated. Even if such studies have been done, given the delay between the refractive procedure and onset of dry eyes in these patients, it is hard to prove that the refractive procedure contributed to dry eye.
Of all the pathophysiologic mechanisms implicated in post-LASIK dry eye, most resolve within one year after surgery and cannot seem to account for cases of chronic, persistent post-LASIK dry eye. As mentioned earlier, however, nerve morphology and corneal irregularities seem to be persistent defects that last beyond one year after surgery, and should be investigated for its possible effects on dry eye.
Future research in neural influences of sub-basal nerves on the corneal surface may consider investigating if nociceptive thresholds have been reduced in these cases of chronic post-LASIK dry eye, or if subtle changes in the biochemical make-up of the sub-basal nerves can account for the condition of these patients.
Advances in interferometry allow detection and localization of tear film breakup. There have been previous studies implicating corneal irregularities as the focal point for tear breakup and postulating it as a cause for post-LASIK dry eye, but more studies have to be carried out in patients who have persistent post-LASIK dry eye to establish this theory as an etiology of chronic dry eye after LASIK.
In the area of management, many novel therapeutic agents are currently in clinical trials, with many holding great promise. Of note will be E-PRP that may see greater acceptance and use in the years ahead due to its low cost and good safety profile.
ReLEx® SMILE (small-incision lenticule extraction) is a new photorefractive procedure, which is gaining popularity. This new procedure completely removes the need for flap creation or epithelial stripping, achieving the desired refractive correction by creating an intra-stromal lenticule with a femtosecond laser, and removing the lenticule thereafter by a small incision made at the limbus. Theoretically, this leaves most of the corneal nerves intact and should lead to superior post-operative preservation of corneal sensitivity than previous photorefractive procedures.
Two trials, one randomized and one non-randomized found SMILE to have better dry eye outcomes to femtosecond LASIK (femto-LASIK). In one randomized trial involving 28 patients (28 eyes underwent SMILE, contralateral eye underwent femto-LASIK), SMILE was found to result in significantly higher corneal sensitivity for up to 3 months when compared with femto-LASIK. In another non-randomized trial involving 54 eyes for femto-LASIK and 61 eyes for SMILE, corneal sensitivity was found to be superior in eyes, which have undergone SMILE compared with femto-LASIK for up to 3 months, and a complete recovery to baseline corneal sensitivity was faster and could be achieved 3 months post-operatively.
SMILE was also superior to Femtosecond Lenticule Extraction (FLEx) in preserving corneal sensitivity. Moreover, in a randomized self-controlled trial involving 35 patients, sub-basal nerve density was better preserved in SMILE than FLEx at 6 months post-operatively. This corresponded to superior corneal sensitivity of SMILE to FLEx at 6 months in the same study.
However, in both randomized trials, tear film parameters were not significantly different between the surgical methods, despite differences in post-operative corneal sensitivity. In the non-randomized trial, tear film parameters were not examined.
Expert Rev Ophthalmol. 2013;8(6):561-575. © 2013 Expert Reviews Ltd.