Inflammation and wound healing following photorefractive keratectomy

Abstract

This study comprises different aspects on the inflammatory and wound healing responses of the eye after Photorefractive Keratectomy (PRK). The purpose was to provide basic information about the inflammatory reaction and the wound healing after surgery. PRK is considered a good technique for surgical correction of and moderate myopia. Nevertheless, pain and variability in results are still significant problems. inflammation can influence wound healing mechanisms after PRK. However, very little information about the inflammatory reaction after PRK was available up to now.

The function of the blood-aqueous barrier (BAB) is a sensitive measure of post-surgical inflammation. The BAB function was studied on humans after PRK with laser flare measurements. This technique can detect subclinical inflammatory reactions. In rabbits this method is less reliable. Samples from the aqueous humour of rabbits after PRK were collected to detect prostaglandins and white blood cells. We also studied the blockage el prostaglandin liberation in the aqueous of the rabbits after surgery by topical diclofenac. The influence of topical anti-inflammatory drugs on flare, duration of pain, visual rehabilitation, corneal topography and early epithelial healing after PRK was analysed.

A study of the presence and amount of several biochemical factors wound scrapings from human corneas with regression following surgery was performed in an attempt to understand the regression process. "Haze" is defined as the loss of the optical clarity of the cornea following PRK. "Haze" is a function of the healing process. "Haze" is generally graded subjectively in the slit-lamp. A possibility to objectively measure "haze" with a modification of the Laser Flare Meter and the Scheimpflug system was studied, in an attempt to simplify ways to analyse healing results after PRK. The local distribution of the "haze" in the ablated area and their corresponding corneal topographic images were analysed in eyes with unsatisfactory results and were compared to eyes with excellent visual outcomes after PRK.

Anterior chamber flare was significantly elevated the first days following PRK in our study. The more myo to be corrected, the more flare was found. In rabbits, prostaglandin E2 (PGE2) was liberated in the aqueous early after PRK. Diclofenac (a non-steroid anti-inflammatory drug) effectively blocked PGE2 liberation in the aqueous in rabbits after PRK. In our study, pain in human subjects started around 3 hours after PRK, reached maximum at about 7 hours and was generally over 24 hours after surgery. Topical anti-inflammatory drugs such as diclofenac and dexamethasone did not significantly reduce the duration of pain after PRK, and did not significantly diminish the anterior chamber flare reaction following surgery in our study design. However, diclofenac very significantly affected the epithelial healing negatively after surgery. Messenger RNA for TGF[beta]-1 was elevated in scrapings from regressed corneas after PRK, in coincidence with mRNA for collagen III, an immature kind of collagen only found in developing and healing corneas. "Haze" was objectively measured after surgery with a "corneal Laser Flare Meter" and a Scheimpflug system, with good correlation to clinical haze. Eyes with "central haze" after PRK suffered regression in all cases, needing a re-operation, in spite of the topical administration of steroids. Eyes with bad visual outcomes after PRK had more topographic changes, such as decentration and irregular surface, than those with excellent visual results.

In conclusion, we have shown that PRK results in a kerato-uveitic reaction, comprising an inflammatory reaction including the intra-ocular structures. This acute inflammatory reaction is, at least in part, mediated PGE2. Topical diclofenac blocks PGE2 liberation, but affects the epithelial healing negatively after PRK. TGF[beta]-1 may be involved in the local over production of extracellular matrix components, such as responsible for the myopic regression after PRK "Haze" distribution in the ablated area is important after OR and it can be used as prognostic factor in some cases. "Haze" can easy and objectively be measured by the Flare Meter.