Corneal wound healing proteomics in femtosecond laser surgery

Abstract

Refractive errors are very common among healthy, working age people. Typically, eyeglasses are used to correct them. In 1990’s UV laser light based Laser in situ keratomileusis (LASIK) technique was developed to reshape the cornea for better vision. In early 2000 femto-LASIK, where corneal flap is opened with a pulsed femtosecond laser instead of mechanical blade. A decade later, small incision lenticule extraction, SMILE procedure appeared. In SMILE the whole surgery is done with a femtosecond laser and the cut lenticule inside the corneal stroma is pulled out with tweezers from a small opening in the side. This leaves the corneal center area intact. However, such procedures are harsh on the cornea and cause an immediate, complicated wound healing process with inflammation and sometimes infection. These processes cause changes in tear fluid and corneal surface proteomic content. Some changes are temporary, and some are permanent. Studying these changes may help to predict the operation of the eye and prevent side effects. This report is part of advanced studies in medicine / medical bachelor’s thesis, where as a part of an ophthalmic research group human eye tear film protein changes were studied in femtosecond laser refractive surgery. Research results have been accepted for publication in a peer reviewed international scientific journal, Clinical proteomics. This report concentrates on a supplementary systematic literature review on the topic and reports the search process and results. Normal eye has a thin layer of watery fluid, tear film, on top of cornea and conjunctiva. Tear film can be easily and non-invasively collected from under the eyelids with a small capillary test tube. Modern proteomic tools enable the analysis of hundreds of proteins simultaneously from small sample. In this study we collected tear film samples from over hundred LASIK and SMILE patients with 2–3 µl capillary test tubes. The final analysis was based on 70 LASIK patient data and samples. Tear film samples were collected before the operation and 1.5 h after surgery and one month later. Samples were measured with a mass spectrometer and results were analyzed with bioinformatic methods. A systematic literature review was made to supplement the understanding in femtosecond laser refractive surgery and proteomics. Search was made in OvidMedline-database and 25 search results were obtained. Some results were excluded from the final analysis based on the title and abstracts when they were clearly outside the scope of the literature review. 13 peer reviewed articles were included in the final qualitative analysis. These publications mostly reported LASIK operation related complications and protein changes in them but also newer SMILE operation related problems. In the analyzed publications tens of proteins were discussed, and most results were related to matrix metalloproteinase-9 (MMP-9), which changes appeared in, for example, keratoconus, ectasia, dry eye disease and in refractive laser surgery in general. However, the research results were mostly concentrated on histopathological and immunohistochemical studies of corneal tissue and less on tear film samples. A typical limitation of a study was the lack of before and after procedure samples for comparison and instead studies were comparing operated patients to a control group and not the patient’s protein changes due to the surgery. This problem is addressed by use of modern mass spectrometers that bring significant advantage to studying proteomic changes. This report’s most important finding may be the notice of development of research methods in refractive surgery and proteomics. Therefore, it is likely that tear film analysis will develop rapidly in the 2020’s and the predictability of operation related complications will improve significantly, despite the already very low level of occurrence.