The Different Clinical Effects Of The UVA/Riboflavin Corneal Collagen Crosslinking On Keratoconic Patients With Different Corneal Thickness

PurposeTo evaluate the outcomes and different clinical effects of the UVA/riboflavin corneal collagen crosslinking(CXL)on keratoconic patients with different corneal thickness.MethodsA retrospective nonrandomized study was performed at the Department of Ophthalmology,Shandong Provincial Hospital.All 49 patients(70 eyes)enrolled in this research were diagnosed as keratoconus and they were all performed the CXL.According to the thinnest corneal thickness(TCT)before intervention,the 70 samples of which the TCT range before operation was 358 μm to 519 μm were divided into 4 subgroups as follows:Group 1,TCT≤400μm;Group 2,400μm<TCT≤440μm;Group 3,440μm<TCT≤480μm;Group 4,TCT>480μm.All patients were examined at baseline,6,and 12 months after CXL and the examinations included the slit lamp evaluation,maximum keratometry(Kmax),flat keratometry(Kf),steep keratometry(Ks),mean keratometry(Kmean),uncorrected visual acuity(UCVA),best-corrected visual acuity(BCVA),thinnest corneal thickness(TCT),intraocular pressure(IOP),endothelial cell count(ECD)etc.Then statistical analysis was performed using SPSS software version 20.0.According to their normal distribution or not and the purpose of the analysis,the methods of the t-test,Wilcoxon signed-rank test,one-factor ANOVA,Kruskal-Wallis H test,Mann-Whitney test and Spearman rank correlation were adopted to analyse the data.A P value less than 0.05 was considered statistically significant.Result1.Km axFor the whole samples,the mean Kmax was 61.65±10.96D before CXL.and it significantly decreased to 59.83±10.33D at 6 months and 59.37±10.40D at 12 months after CXL with the statistically significant difference(P<0.05).AKmax was defined as the difference between the postoperative Kmax and the preoperative one.At 6 months after operation,the mean Δ Kmax of the group 1 to the group 4 was 2.87±3.20D,1.99±2.14D,1.65±2.10D and 0.68±1.09D respectively,which showed a reduction and the difference between the four groups was statistically significant(P<0.05).Then the relationship found between ΔKmax at 6 months after operation and preoperative TCT was negatively correlated(P<0.01),and the correlation coefficient was-0.364.Furthermore,taking preoperative TCT as the independent variable x,taking ΔKmax at 6 months after operation as the dependent variable y,the regression equation fitted was y=-0.0154x+8.6313,which was statistically significant(P<0.05).Similarly,at 12 months after operation,the mean ΔKmax of the group 1 to the group 4 was 3.22±3.08D,2.44±2.69D,2.20±2.51D,1.12±1.08D respectively,which showed a reduction and the difference between the four groups was statistically significant(P<0.05).The relationship found between ΔKmax at 12 months after operation and preoperative TCT was negatively correlated too(P<0.01),and the correlation coefficient was-0.372.Similarly,taking preoperative TCT as the independent variable x,taking ΔKmax at 12 months after operation as the dependent variable y,the regression equation fitted was y=-0.0153x+9.0484,which was statistically significant(P<0.05).2.Kf,Ks,KmeanFor the whole samples,the mean preoperative Kf,Ks and Kmean was 48.43±5.13D,51.95±7.04D and 50.19±6.01D respectively,while the mean postoperative Kf,Ks and Kmean at 6 months was 48.02±5.30D,51.10±6.42D and 49.56±5.72D respectively,and the mean postoperative Kf,Ks and Kmean at 12 months was 47.69±5.11,50.84±6.51D and 49.26±5.72D respectively,which were all statistically significant compared with those before the operation(P<0.05).3.UCVA,BCVAIn this study of whole samples,the mean UCVA(LogMAR)was 0.85±0.41,0.75±0.37,0.67±0.31 respectively before the CXL,at 6 months after CXL and at 12 months after the CXL,while the corresponding BCVA(LogMAR)was 0.43±0.37,0.37±0.32,0.31±0.28 respectively.It can be seen that the UCVA and BCVA improved continuously after the CXL,and the difference was statistically significant compared with preoperative data respectively(P<0.05).4.TCTFor the whole samples,the mean TCT was 443.67±41.0 μm before CXL and it significantly decreased to 424.33±41.76μm at 6 months and 423.24±41.02μm at 12 months after CXL with the statistically significant difference(P<0.05).5.IOPThere was no significant difference in IOP before CXL,6 months after CXL and 12 months after CXL(P>0.05).6.ECDFor the whole samples,the mean ECD was 3095.11±277.69 cells/mm2 before CXL.And the mean ECD significantly decreased to a mean value of 3069.77±282.98 cells/mm2 at 6 months and 3074.53±280.54 cells/mm2 at 12 months after CXL with the statistically significant difference(P<0.05).ConclusionCXL is an safe and effective way to decrease the Kmax of keratoconic patients and improve their visual acuity.There was a negative linear correlation between the preoperative TCT and the level of reduction of the Kmax,and the patients with thinner TCT within limits seemed to obtain more benefits from the effects of CXL.