| Purpose:To observe the long-term safety and efficacy of corneal collagen cross-linking(CXL)induced by hypoosmolar riboflavin in the treatment of advanced keratoconus patients with ultra-thin cornea(thinnest corneal thickness less than or equal to 330μm).Methods:This study retrospectively collected keratoconus patients who underwent CXL.Inclusion criteria:1.The mean keratometry(Kmean)of the central cornea ≥53D,and the maximum keratometry(Kmax)of the anterior cornea ≥58D;2.The thinnest corneal thickness(TCT)≤330μm;Patients were examined at baseline,1,3,5 years after CXL and the examinations included the slit-lamp evaluation,corneal topography,visual acuity,optical coherence tomography,corneal endothelial microscopy,intraocuIar pressure(IOP)etc.Results:1.General situationA total of 12 patients(13 eyes)were enrolled in this study,including 8 males(8 eyes)and 4 females(5 eyes).The ratio of males to females is about 2:1.The average age was 22.69±7.96 years(14-38 years).All patients were successfully operated without complications.2.Kmax(1)The mean Kmax was 76.55±9.83D before CXL.It decreased to 71.54±9.12D at 1 year and 69.40±8.30D at 3 years and 67.02±7.03D at 5 years after CXL with the statistically significant difference(P<0.05).A small increase in Kmax was observed at 3 and 5 years of follow-up in one case.(2)Correlation analysis of preoperative Kmax and preoperative TCT:no correlation was found between them(p=0.0689).(3)△ Kmax is defined as the difference between the preoperative and postoperative Kmax values of the same sample.The mean value of △ Kmax was 5.01 ± 3.94D,7.15 ±3.98D and 9.52 ± 4.97D at 1,3 and 5 years after operation,respectively.△Kmax increased with time,and only one case did not follow this trend.(4)Correlation analysis between △Kmax and preoperative Kmax:no correlation was found between △Kmax at 1 year after CXL and preoperative Kmax(p=0.2090).There was a positive correlation between △Kmax at 3 years after CXL and preoperative Kmax(r=0.5574,P=0.0478).There was a positive correlation between △Kmax at 5 years after CXL and preoperative Kmax(r=0.7362,P=0.0041).(5)Correlation analysis between △Kmax and preoperative TCT:There was a negative correlation between △Kmax at 1 year after CXL and preoperative TCT(r=-0.6081,P=0.0275).There was a negative correlation between △Kmax at 3 years after CXL and preoperative TCT(r=-0.6737,P=0.0116).There was a negative correlation between △Kmax at 5 years after CXL and preoperative TCT(r=-0.5697,P=0.0421).3.Other K values of corneal topography(1)Flat keratometry(Kf):The median Kf was 51.3(55.10,63.05)D before CXL.It decreased to 49.85(51.50,58.85)D at 1 year and 49.45(51.10,58.25)D at 3 years and 49.05(50.40,56.80)D at 5 years after CXL with the statistically significant difference(P<0.05).(2)Steep keratometry(Ks):The mean Ks was 64.25±8.32D before CXL.It decreased to 60.33±7.27D at 1 year and 58.84±6.00D at 3 years and 57.03±5.44D at 5 years after CXL with the statistically significant difference(P<0.05).(3)Kmean:The median Kmean was 54.85(57.75,67.73)D before CXL.It decreased to 52.6(55.25,62.30)D at 1 year and 51.9(55.00,61.75)D at 3 years and 51.08(53.90,61.08)D at 5 years after CXL with the statistically significant difference(P<0.05).4.Uncorrected visual acuity(UCVA)The mean UCVA(LogMAR)was 0.99±0.29 before CXL.It decreased to 0.83±0.28 at 1 year and 0.73±0.26 at 3 years and 0.66±0.28 at 5 years after CXL with the statistically significant difference(P<0.05).In one case,it increased at 1 year after CXL and returned to the preoperative level at 3 years after CXL.5.Best-corrected visual acuity(BCVA)The mean BCVA(LogMAR)was 0.83±0.37 before CXL.It decreased to 0.60±0.29 at 1 year and 0.44±0.26 at 3 years and 0.34±0.21 at 5 years after CXL with the statistically significant difference(P<0.05).6.TCTThe mean TCT was 314.23±13.75μm before CXL.It decreased to 302.00±13.44μm at 1 year and 300.77± 13.32μm at 3 years and 299.77± 13.6μm at 5 years after CXL with the statistically significant difference(P<0.05).Five cases showed thickening ranging from 1 to 6μm compared with the previous follow-up.7.Endothelial cell density(ECD)The mean ECD was 3012.54± 137.10 cells/mm2 before CXL.It decreased to 2939.71±140.88 cells/mm2 at 1 year and 2895.50±118.59 cells/mm2 at 3 years and 2873.17±152.73 cells/mm2 at 5 years after CXL with the statistically significant difference(P<0.05).8.IOPThere was no obvious change in preoperative IOP compared with 1,3 and 5 years after CXL,and the differences were not statistically significant(P>0.05).Conclusions:CXL induced by hypoosmolar riboflavin can safely and effectively control the progression of advanced keratoconus with ultra-thin cornea(thinnest corneal thickness less than or equal to 330μm)for a long time,and the thinner the cornea and the larger the Kmax,the more effective it is.It can be considered as the first choice for ultra-thin advanced keratoconus. |
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