The corneal barrier function in myopic eyes after laser in situ keratomileusis and after photorefractive keratectomy in eyes with haze formation.

BACKGROUND

Corneal barrier function following photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) was evaluated to determine corneal damage and to compare the amount of corneal trauma associated with haze development with the two procedures.

METHODS

The PRK and LASIK procedures were performed with the Nidek EC-5000 excimer laser. The Chiron Hansatome microkeratome was used in the LASIK procedures. We followed 1528 eyes of myopic patients (range, -1.00 to -23.00 D) classified into three groups according to age. Each group was divided into four subgroups depending on the amount of myopia (-1.00 to -2.75 D; -3.00 to -5.75 D; -6.00 to -9.75 D; -10.00 to -23.00 D). In eyes with haze formation, haze intensity and postoperative period of haze development were evaluated. The corneal uptake was 5.6 carbonfluorescein 5%, and a computer program analyzed video slit-lamp corneal images.

RESULTS

PRK and LASIK increased corneal permeability to fluorescein (2 to 8 weeks after PRK and 4 to 6 weeks after LASIK). Deeper ablations showed higher corneal fluorescein permeability for longer periods. In eyes with haze formation, an increased index of corneal fluorescein permeability was observed in the eyes with early postoperative haze formation (1 to 2 months) and a decreased index of corneal permeability was observed in eyes with late postoperative period haze formation (after 3 months). This finding suggests a difference in the haze that developed in the early and later postoperative periods. Fluorescein permeability after PRK returned to normal in 2 to 8 weeks and remained constant. Following LASIK, fluorescein permeability returned to normal in 4 to 6 weeks. Decreasing corneal permeability to fluorescein was observed 2 to 6 months after LASIK, and returned to normal at 6 months.

CONCLUSION

Photorefractive surgery disrupts corneal barrier function for up to 6 months postoperatively, even though other clinical tests of the cornea may be normal. This finding may help explain some mechanisms of pathogenesis of complication development following PRK and LASIK. The fluorescein permeability findings demonstrated different mechanisms for early and late haze formation after PRK.