The Study Of Corneal Thickness Changes And Corneal Irritation Control During Ultraviolet-A/Riboflavin Corneal Cross-linking

Objective To evaluate the safety of epithelium-off ultraviolet-A/riboflavincorneal cross-linking (CCL) and epithelium-on CCL with riboflavin byiontophoresis.Methods1. Central corneal thickness (CCT) using ultrasonic pachymetry wasperformed during the epithelium-off CCL procedure of20patients (26eyes) withprogressing keratoconus. The corneal endothelial cell density (CD) was measuredpre-operation and1-month after operation．2.27cases (38eyes) withprogressing keratoconus which had undergone epithelium-off CCL were randomlydivided into two groups: G1was given Fluorometholone eye drops, while G2combined with Pranoprofen eye drops. Corneal irritation and haze were comparedand observed between these two groups．3. The right eyes of24New Zealandwhite rabbits were divided into three groups, epithelium-off (G1), epithelium-on(G2) and iontophoresis (G3); the left eyes were the control group (G4). Theriboflavin concentrations were determined by high-performance liquidchromatography (HPLC).4. The right eyes of24New Zealand white rabbits weredivided into three groups, epithelium-off (G1), epithelium-on (G2) andiontophoresis (G3); the left eyes were the control group (G4). CCT measurementusing ultrasonic pachymetry was performed during the procedure. Cornealirritation and haze were compared and observed after operation．Results1. There were statistically decreases of CCT during the operation.26eyesundergoing CCL were divided into2groups (Ⅰwith CCT≥400μm after UVAirradiation and Ⅱwith CCT<400μm after UVA irradiation). There was statisticallydifference between preoperative and postoperative CD in Group Ⅱ (P<0.05).2.In1to3days after operation，the corneal irritation in the G2was significantlyreduced compared with G1(P<0.05). The average of haze in the G2wassignificantly lower than the G11-month after operation (P<0.05).3. In the G1, the mean riboflavin concentration was20.89±2.30μg/g tissue, as to the G2it was1.25±0.47μg/g tissue and to the G3it was8.66±1.18μg/g tissue. There weresignificant differences statistically in comparison between any two groups(P<0.01).4. There were statistically significant decreases of CCT betweenpre-operation and post-operation in G1(P<0.05) while no significant difference inG2and G3．The time of epithelium regenerated in G1was significantly longerthan G2and G3(P<0.01). The average of haze in G1was significantly higherthan G2and G3after operation (P<0.01).Conclusions1. During the procedure of epithelium-off CCL, a statisticallysignificant decrease of CCT was demonstrated, even to a level such that thecorneal endothelium may be damaged.2. The combined use of Fluorometholoneand Pranoprofen can significantly alleviate corneal irritation at early stage afterepithelium-off CCL，effectively control the average of haze.3. Iontophoresis iseffective at delivering riboflavin to the cornea, but the best effect of importconditions remains to be further research.4. Epithelium-on CCL with riboflavinby iontophoresis might become an effective method for remaining CCT during theprocedure, reducing the operation time, alleviating corneal irritation andproducing the average of haze. Further long-term studies are necessary tocomplete the evaluation of the efficacy of the modified cross-linking technique.