Corneal Haze after Excimer Laser Refractive Surgery: Objective Measurements and Functional Implications

Abstract

Postoperative changes in corneal transparency is a major concern after PRK. Data were obtained from 69 human eyes treated with excimer laser photorefractive keratectomy in order to evaluate a relationship between objective measurements of corneal transparency and visual performance. A CCD-camera device was employed and by using polarizing filters the system could discriminate between reflected and scattered light. We observed two groups of postoperative behaviour in corneal transparency. Each group showed an increase in both scattered and reflected light signals with a maximum at around two months postoperatively. In the majority group (70%) this was followed by a subsequent decline of the scattered light signal, whereas the combined signal generated by reflected and scattered light showed a biphasic curve with a second peak at around 4 to 5 months postoperatively. In the minority patient group (30%) the timebase variations in pattern of both signals were indistinguishable throughout the period of observation. In all patients we observed a good correlation between the signal generated by scattered light alone and the reduction in the 5% contrast visual acuity performance, whereas correlation was poor when the combined signal of reflected and scattered light was considered. These disturbances in low contrast visual performance were only significant during the first three to four months postoperatively and thereafter most patients returned to their preoperative value. Eighteen percent of our patients discontinued topical steroids postoperatively. No differences in either corneal transparency or final refraction was observed. We consider that PRK is an effective form of refractive surgery and the marginal loss of corneal transparency should only be a problem during the first three or four months postoperatively.

Pathogenesis, clinical features and management of recurrent corneal erosions

“…63,64 Human studies have shown that the basal epithelial layer forms hemidesmosomes and new basement membrane within 2 weeks of photoablation. 65 In addition, undulations are most noticeable on the edge of the ablated zone, which would greatly increase the surface area of attachment. Thus, new hemidesmosomes, anchoring fibrils, and epithelial basement membrane are synthesized rapidly and in increasing amounts after PRK, and problems with epithelial instability would therefore not be expected.…”

Measurement of correlation between transmission and scattering during wound healing in hen corneas

“…The small amount of scattered light produced by this tissue has in particular been extensively researched in the literature [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. All previous theories explaining corneal transparency [21][22][23][24][25][26][27] have focused on light propagation in the stromal extracellular matrix.…”

“…They can be caused by microstructural alterations, the irregular organization of the extracellular matrix, or by cells [22]. Many studies have attempted to relate form, density, and cell size to the structure of the scattered light [1][2][3][4][5][6][7]17,18]. Mourant et al [12,13] suggest that the cell itself is responsible for scattering at a small angle.…”

Pirenoxine prevents oxidative effects of argon fluoride excimer laser irradiation in rabbit corneas: biochemical, histological and cytofluorimetric evaluations

“…Different basic mechanisms underlying the evolution of wound healing which leads to haze formation have been proposed [15][16][17]. Various authors mention the important role of organic free radicals and reactive oxygen species (ROS) generated by UV laser irradiation of the corneal tissue, which could invasively react with the lipid components of cell membranes, nucleic acids and sulfur-containing enzymes and then trigger keratocyte death [18][19][20].…”