Anterior chamber flare was measured with a regularly calibrated laser flare photometer (FM-600, Kowa, Tokyo, Japan). For each eye, seven consecutive readings were obtained from the lower third of the anterior chamber with <10% background scatter. The two extreme readings were crossed out, and the average of the remaining five was recorded as the flare value in photons per millisecond (ph/ms). 

Statistical analysis was performed using the repeated measures analysis of variance to compared results of the pre- and postoperative examinations. For the analysis of associations between quantitative variables, the Pearson correlation test was applied. A P value <0.05 was considered statistically significant.

Sixty eyes of 60 patients with mild to moderate keratoconus were entered into this study. Mean age of the patients was 23.8 years (range, 15−35 years). Before CXL, their mean UCVA was 0.71±0.51 logMAR and improved to 0.52±0.42 logMAR 6 months after surgery (P=0.039). Mean BCVA was also improved from 0.17±0.28 logMAR preoperatively to 0.11±0.14 logMAR 6 months after surgery (P=0.011). Table 1 summarizes clinical profiles before CXL and 6 months after the procedure.

The mean anterior chamber flare increased from 4.5 ph/ms before CXL to 7.1±7.5 ph/ms 1 week post-operatively (P=0.008). Although the mean flare value decreased slightly to 6.5±4.8 ph/ms at 1 month, it was still significantly higher than baseline (P=0.040). The changes were rather steady from month 1 up to the last visit (Figure 1). There were no statistically significant differences between mean flare values at week 1 and other follow-up visits.

Table 1 Patients’ clinical profiles at baseline and 6 months after accelerated corneal collagen cross linking

                                   UCVA, uncorrected visual acuity; BCVA, best-corrected visual acuity; CXL, collagen cross-linking. 

Figure 1 Mean anterior chamber flare with corresponding error bar depicting 95% confidence interval before, 1 week, 1, 3 and 6 months after CXL. ph/ms, photons per millisecond; CXL, collagen cross-linking.

The postoperative inflammatory response remains an important determinant of corneal wound healing. Laser flare meters allow for the quantification of the inflammatory response through objective measurement of the aqueous flare. With a high degree of accuracy and sensitivity, laser flare meters can detect minute alterations in the bloodaqueous-barrier function which may not be clinically detectable ⁽⁹⁾. 

Previous studies have shown the induction of an inflammatory response following photo ablative refractive surgeries. Tomas-Barberan and Fagerholm described a significant increase in anterior chamber flare after photorefractive keratectomy (PRK) ⁽⁵⁾. Others reported a short-lasting subclinical inflammation following uneventful laser in situ keratomileusis in virgin eyes ⁽⁶⁾ as well as corneal grafting ⁽⁷⁾. Pisella et al. showed that photo ablative refractive surgery with or without lamellar keratectomy could induce alteration in flare which is correlated with the depth of ablation ⁽⁸⁾. 

In our study, following the accelerated CXL with UVA light at an irradiance of 18 mW/cm² , an early and rather steady increase of aqueous flare occurred. Contrary to previous reports, the rise of aqueous flare was not shortterm and flare intensity did not return to baseline even up to 6 months after CXL. We speculate that the production of inflammatory mediators may have a causative role for this observation. During CXL, riboflavin molecules absorb the UVA light. In the presence of oxygen, a photo-oxidative reaction occurs and results in the excitation of riboflavin into a triplet state and generation of singlet oxygen. Excited riboflavin and oxygen free radicals catalyze biochemical reactions which result in the formation of additional covalent bonds between collagen fibers. The biochemical reaction and release of free radicals, as well as apoptosis of keratocytes lead to the local production of inflammatory cytokines which will subsequently affect the bloodaqueous-barrier function. Prior studies have shown that both mechanical and photochemical keratectomy produce inflammatory mediators such as PGE2, an observation that supports a role for cyclo-oxygenase inhibitors in postoperative therapy ^(10,11).

Conclusions