Health & Medical Eye Health & Optical & Vision

Ocular Surface Diseases and Corneal Refractive Surgery

Ocular Surface Diseases and Corneal Refractive Surgery

Surgical Options


The options for laser refractive surgery include LASIK, advanced surface ablation and small-incision lenticule extraction (SMILE). The various forms of surface ablation procedures include phototherapeutic keratectomy (PRK); epi-LASIK, wherein a dull microkeratome is used to create an epithelial flap; and laser-assisted sub-epithelial keratomileusis (LASEK), wherein alcohol is used to loosen the epithelium flap, which is then preserved and replaced over the stromal bed at the end.

It is postulated that PRK has less risk of causing tear dysfunction when compared with LASIK because the LPCN are preserved, leading to quicker recovery of corneal sensation and there is less decrease in Schirmer scores. PRK patients have less change from their preoperative tear breakup time and tear osmolarity. However, subjectively, patients do not report a statistically significant increase of dry eye symptoms after LASIK when compared with PRK.

Thin flap LASIK may decrease corneal sensation less and patients generally return to normal tear function faster than traditional LASIK When thin flap LASIK is compared with PRK, PRK eyes had less absolute decrease in corneal sensitivity, but there was no difference in Schirmer scores between the two treatment modalities.

Another study comparing LASEK with traditional LASIK concluded that LASEK results in less decrease in corneal sensitivity than LASIK and in a faster recovery. LASIK patients complained of more severe dry eye symptoms up to 16 months postoperatively, while dry eye symptoms in LASEK patients returned to baseline at 3 months. However, when comparing thin flap LASIK versus LASEK, no statistically significant difference was found in postoperative corneal sensitivities up to 6 months postoperatively.

When comparing microkeratome versus femto-second LASIK flaps, FS-LASIK appears to lead to a quicker normalization of the ocular surface, as a faster recovery time in central corneal sensitivity and less dry eye symptoms occurred in the femtosecond-assisted LASIK group.

SMILE procedure is a fairly new procedure that is rapidly gaining popularity. This procedure involves placing femtosecond incisions in the posterior surface of the lenticule, the lenticule border, the anterior surface of the lenticular and the side cut incision to access the lenticule. After that, a thin spatula is inserted via the side-cut incision to blunt dissect the intrastromal lenticule. This lenticule is the extracted from the cornea. It has been proposed that SMILE induces less inflammatory reaction and cell death when compared with FS-LASIK, as it does not entail creating and lifting a corneal flap. The process of corneal wound healing after flap creation involves a variety of cytokines and growth factors that directly induce keratocyte apoptosis and consequently attract inflammatory cells.

Because SMILE is still a very new technique, there are conflicting views whether SMILE refractive surgery decreases central corneal sensitivity or not. When subjectively comparing dry eye symptoms using the Ocular Surface Disease Index (OSDI) between FS-LASIK versus SMILE, OSDI scores increased significantly in both groups in comparison to preoperative scores but returned to preoperative levels by 1 month postoperatively. Tear secretion levels also showed a transient decrease after undergoing FS-LASIK. There is conflicting evidence between the literature, but in general, it appears that in post-FS-LASIK, tear secretion reaches preoperative levels by at least 6 months postoperatively. Patients undergoing a SMILE procedure had significantly less corneal fluorescein staining that patients undergoing FS-LASIK. SMILE procedures seem to have less postoperative ocular surface issues because there is less transection of corneal nerves in the anterior third of the corneal stroma as compared with FS-LASIK, which is one of the main causes of postrefractive surgery ocular surface disease.

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