Patient Satisfaction and Early Changes in Tear Fluid Proteomics After Femtosecond Laser-Assisted Keratorefractive Surgery

Refractive surgery has gained popularity during the recent decades as an alternative method to glasses and contact lenses for correcting refractive errors. Femtosecond laser-assisted in situ keratomileusis (FS-LASIK) and small-incision lenticule extraction (SMILE) are currently the most popular laser-based keratorefractive procedures. These methods involve reshaping the anterior cornea with femtosecond or excimer lasers, or with both, for treating myopia, hyperopia or astigmatism. The outcome of surgery is traditionally evaluated with objective measurements such as postoperative visual acuity or refractive error. The patients, however, evaluate the success of refractive surgery in terms of their subjective assessment of their vision and the incidence of any eye-related side effects. Being a part of aesthetic surgery having a target to improve the quality of the life, patient-reported surgical outcomes must also be included and be an important part of analyses.

The operated tissue, the cornea, is very sensitive and is covered with a thin tear film, which consists of water, electrolytes, lipids, mucins and more than 1500 proteins. A normally functioning tear film maintains the good visual properties and welfare of the corneal surface and is also a vital part of the wound healing process after corneal injury. Refractive surgery initiates a complex wound healing process, which is reflected in the composition of the tear fluid, which allows an analysis of these processes. Tear fluid is relatively easy to collect from the ocular surface, allowing the analysis of tear protein levels through different methods. Modern mass spectrometry (MS) methods allow the identification and quantification of large sets of proteins from small-volume samples and are therefore suitable for tear fluid proteomic analysis after refractive surgery.

In this thesis we investigated and compared patient satisfaction with far and near vision, and dry eye symptoms as the most common adverse reaction after refractive surgery, with clinical factors in subjects who underwent FS-LASIK or SMILE surgery in a real-live study in a private eye clinic. For the analysis of subjective patient satisfaction, we used self-administered questionnaires employing the visual analog scale (VAS) preoperatively and one month after surgery. In Study I, the FS-LASIK and SMILE methods were studied and compared in myopic corrections, while Study II focused on eyes treated with hyperopic FS-LASIK.

The second aim of thesis was to investigate processes related to the corneal wound healing by analyzing protein changes in tear fluid samples collected with microcapillary tubes preoperatively and 1.5 hours as well as 1 month postoperatively. The samples were analyzed with sequential windowed acquisition of all theoretical mass spectra (SWATH-MS) method immediately after FS-LASIK and SMILE surgery, to better understand the initial healing process after normal corneal refractive surgery. In Study III we evaluated the changes in tear protein profiles after FS-LASIK surgery. We further analyzed pathways of the healing process and identified the proteins correlating with the surgical variables. The differences between the protein profiles after FS-LASIK and SMILE surgeries were compared in Study IV in a similar way.

In the study comparing FS-LASIK and SMILE surgeries (Study I), the clinical outcomes were comparable, although more postoperative astigmatism was found after SMILE than after FS-LASIK. Satisfaction with far vision improved significantly after both FS-LASIK and SMILE, but only FS-LASIK resulted in significant improvements in satisfaction with near vision. Among FS-LASIK-treated hyperopic monovision patients (Study II), satisfaction with both far and near vision improved significantly. Self-reported dry eye symptoms remained at the preoperative level one month after myopic and hyperopic FS-LASIK treatments but decreased in SMILE-treated myopic eyes. The major determinants of patient satisfaction with both far and near vision appeared to be the accuracy of the refractive correction, especially astigmatism, and dry eye symptoms.

Studies III and IV revealed that FS-LASIK surgery induced significant changes in cell migration and inflammation-associated tear fluid protein profiles 1.5 hours after the operation. Although the expression levels of the majority of proteins returned almost completely to their preoperative values during the first month, a small subset of proteins did not. These findings demonstrate that some wound healing processes continue also in the tear fluid one month after the operation. The changes in tear protein profiles, compared in Study IV, were very similar between the FS-LASIK and SMILE surgeries. However, some differences were found in proteins associated with the inflammatory process, which was likely induced by the larger epithelial defect after FS-LASIK than after SMILE. Several proteins were found to be correlated with the amount of refractive correction, flap thickness and flap diameter after myopic FS-LASIK, indicating that surgical variables can affect individual wound healing responses. These identified proteins are potential targets for follow-up and future studies concerning the healing process after keratorefractive surgery.

In conclusion, this dissertation provides information on what factors are important for patient satisfaction and how biological wound healing processes are reflected in the tear fluid after modern refractive surgery. Although this thesis presents results from a limited follow-up time, these issues are likely to also be important for the long-term satisfaction and health of the patient. With future studies, these findings may help to improve and predict surgical outcomes, as well as to develop novel therapies for the postoperative phase of corneal refractive surgery.