| Purpose Keratoconus is a kind of corneal non-inflammatory ectasic disease.characterized by the protrusion of the central or paracentral region leading to corneal thinning, steepening and scarring. The disease often happens bilaterally at puberty and can lead to blindness. The incidence of keratoconus is about 1:2000. It is a contrainindication for corneal refractive surgeries such as photorefractive keratectomy (PRK),laser in situ keratomileusis (LASIK), sub-Bowman keratomileusis(SBK ), and so on. But it occasionally happens after the corneal refractive surgeries and it would seriously affect the visual acuity. The traditional treatments are wearing rigid gas permeable contact lens(RGP) and corneal penetrating or lamellar transplantation. These therapies are not always satisfied. Riboflavin/ultraviolet A corneal collagen crosslinking (CXL) is a new hope for keratoconus and corneal ectasia because it makes the corneal collagen fiber crosslinking and strengthens the cornea. Many documents have declared that it is effected and safe for CXL to control keratoconus and corneal ectasia.Traditionally, keratoconus is defined as central keratoconus when the maximum keratometry (Kmax) of the cornea located in the central 3mm zone, while peripheral keratoconus when the corneal Kmax located out of the central 3mm zone. As to the diverse types of keratoconus. it might manifest different results after CXL. With the hypothesis, we designed the study to compare the therapy of CXL for diverse types of keratoconus.Patients and MethodsPatients Sixty progressive keratoconus patients (88 eyes) underwent CXL from July 2012 to June 2014 were included in the study. Inclusive criteria were progressive keratoconus or corneal ectasia confirmed by corneal topography and being followed up for 2 years and meeting one of the following terms within the past 1 year: (1) Kmax increased ?1D,(2) astigmatism increased ?1 D or the spherical equivalent (SE) ?0.5D.Exclusive criteria were history of corneal surgeries (except for LASIK),chemical injury, delayed epithelial healing, corneal thickness < 350?m and pregnant in the two years. A written consent was obtained from all the patients. The patients were divided to two subgroups according to different standards: (?) the central and peripheral keratoconus groups;(2) the keratoconus and the post-LASIK corneal ectasia groups.CXL Under topical anesthesia, the epithelium diameter about 9mm was removed by mechanical debridement. Riboflavin (Medio-Cross riboflavin/dextran solution, 0.1%) was administered topically for 30 minutes at intervals of 2 minutes. Optical coherence tomography (OCT)was performed and when the thinnest corneal thickness? 400?m, the cornea was illuminated for 30 minutes using a UV light lamp (UV-X 1000 system, IROC lnnocross AG Co, Switzerland; wavelength 365 nm,irradiance 3 mW/cm2? total dose 5.4 J/cm2 ). Riboflavin administration was continued during UV illumination at the same intervals. If the thinnest corneal thickness < 400?m? hypotonic riboflavin (0.1 % in sterile water) was administered one drop every 10 seconds for 2 minutes. OCT was performed to confirm that the thinnest stroma had swollen to ? 400?m. This was repeated until adequate corneal thickness had been obtained. Antibiotic and fluorometholone drops were administered and a bandage contact lens was placed after CXL.The bandage contact lens was removed after healing of corneal epithelium in 3 to 5 days postoperatively. Antibiotic drops were used for a week and fluorometholone drops for two weeks.Observation The uncorrected distant visual acuity (UDVA), the best corrected distant visual acuity (CDVA), refraction, slit lamp bioscopy,topography (mainly Kmax, mean keratometry (Km), astigmatism) and non-contact tonometer were examined and recorded before and after CXL 2 years.Statistical analysis IBM SPSS 19.0 was used for statistical analysis.Independent-samples t test was used to analyze the differences between the separate groups. Paired-samples t test was used to analyze the difference of the same group between pre-operation and post-operation.The Partial correlation analysis was used to study the correlations between age, duration of the disease, the distance of Kmax from corneal center, Km and the changes of UDVA, BDVA, Kmax, corneal astigmatism. Regression analysis was used to study the quantitative relationship between the changes of UDVA, BDVA, Kmax, corneal astigmatism and the preoperative characteristics. Differences were considered statistically significant when the P value was<0.05.Results1. Preoperative characteristicsThe mean age of the 60 patients was 22.1±5.1 years and the ratio of male to female was 39:21. The mean duration of the disease was 23.4±22.4 months. The distance from Kmax to the corneal center was 2.7±1.5mm and the mean corneal thickness was 439.7±61.0?m.There were 44 patients (64 eyes) in the central keratoconus group and 16 patients (24 eyes) in the peripheral keratoconus group. The preoperative age, gender, duration of the disease and corneal thickness between the two groups had no statistical differences (P>0.05) while the distance from Kmax to the corneal center had statistical difference between the two groups ( P< 0.01 ).There were 45 patients (67 eyes) in the keratoconus group and 15 patients (21 eyes) in the post-LASIK ectasia group. The preoperative age, gender, duration of the disease and corneal thickness between the two groups had no statistical differences (P> 0.05 ) while the distance from Kmax to the corneal center had statistical difference between the two groups (P<0.01).There were 5 post-LASIK ectasia patients (11.4%) in the central keratoconus group and 6 keratoconus patients (37.5%) in the peripheral keratoconus group.2. The therapy of combined groupPreoperative UDVA and CDVA were 0.9±0.5 and 0.4±0.4 logMAR respectively. After CXL 2 years, UDVA and CDVA significantly improved to 0.7±0.4 and 0.3±0.3 logMAR (P<0.01).Preoperative Kmax and astigmatism were 61.5114.7D and 4.0±2.9D respectively. After CXL 2 years, Kmax and astigmatism significantly decreased to 57.0±10.4 and 3.3±2.2D (P<0.01).3. The comparison of the central and peripheral keratoconus groups3.1 The changes of UDVA and BDVACentral keratoconus group. Preoperative UDVA and BDVA were 0.9±0.4 and 0.5±0.4 logMAR respectively. After CXL 2 years, UDVA and BDVA significantly improved to 0.8±0.4 and 0.4±0.3 logMAR (P<0.01).Peripheral keratoconus group. Preoperative UDVA and BDVA of the were 0.8±0.7 and 0.2±0.4 logMAR respectively. After CXL 2 years,UDVA significantly improved to 0.4±0.4 logMAR (P< 0.01) while BDVA improved to 0.2±0.3 logMAR and the difference had no statistical significance (P>0.05).The changes of UDVA of the central and paracentral keratoconus groups were -0.1±0.2 and -0.4±0.5 logMAR respectively and the difference between them was statistically significant(P< 0.01). The changes of BDVA of the two groups were -0.1±0.3 and -0.04±0.2 logMAR respectively and the difference between them had no statistical significance(P=0.25).3.2 The changes of Kmax and astigmatismCentral keratoconus group. Preoperative Kmax and astigmatism were 65.6±15.0D and 4.6±3.0D respectively. After CXL 2 years, Kmax and astigmatism significantly decreased to 60.1±10.3 and 3.3±2.2D respectively (P<0.01).Paracentral group. Preoperative Kmax and astigmatism were 50.3±5.3 and 2.4±1.7D respectively. After CXL 2 years, Kmax significantly decreased to 48.8±4.6 (P < 0.01) while astigmatism remained 2.2±1.8 D(P>0.05).The changes of Kmax of the central and peripheral groups were-5.6±8.3D and -1.6±2.1D respectively and the difference between them was statistically significant (P=0.01). At the same time, the changes of astigmatism were -1.3 ± 2.2D and -0.3 ± 0.8D respectively and the difference was statistically significant too (P=0.04).4. The comparison of the keratoconus and post-LASIK ectasia groups4.1 The changes of UDVA and BDVAKeratoconus group. Preoperative UDVA and CDVA were 0.8±0.5 and 0.4±0.4 logMAR,respectively. After CXL 2 years, UDVA and CDVA significantly improved to 0.7±0.4 and 0.3±0.3 logMAR (P<0.01).Post-LASIK ectasia group. Preoperative UDVA and CDVA were 0.9±0.6 and 0.3±0.4 logMAR,respectively. After CXL 2 years. UDVA significantly improved to 0.6±0.4 logMAR (P<0.01)while CDVA remained 0.2±0.3 logMAR (P>0.05).The changes in the UDVA of the keratoconus and post-LASIK ectasia groups were -0.1±0.2 and -0.2±0.3 logMAR. separately and the changes in the CDVA of the two groups were -0.1 ±0.2 and -0.03±0.2 logMAR, separately. The differences between the values were not statistically significant (P>0.05).4.2 The changes of Kmax and astigmatismKeratoconus group. Preoperative Kmax and astigmatism were 63.3±15.6D and 4.5±3.0D respectively. After CXL 2 years, Kmax and astigmatism significantly decreased to 58.3±10.4 and 3.3±2.2D (P<0.01).Post-LASIK ectasia group. Preoperative Kmax and astigmatism were 54.4± 10.0 and 2.4±2.1D,respectively. After two years, Kmax and astigmatism decreased to 51.4±9. 1D (P< 0.01) and 2.O±1.8 D (P>0.05),respectively.The changes in the Kmax of the keratoconus and post-LASIK ectasia groups were -5.0±8.2D and -2.9±3.2D, separately, and the difference had no statistical significance (P> 0.05). The changes in astigmatism of the two groups were -1.2±2.2D and -0.5±1.2D,separately, and the difference had statistical significance (P<0.01).5. Correlation AnalysisThe age and the duration of the disease had no correlations with the changes of UDVA, BDVA, Kmax and astigmatism ( P> 0.05 ).The preoperative distance of Kmax to the corneal center had minus correlation with the changes of UDVA ( r=-0.295,P< 0.01 ) and positive correlations with the changes of Kmax and corneal astigmatism(r=0.239,0.265,P<0.05).The preoperative Km had minus correlations with the changes of BDVA, Kmax and astigmatism (r=-0.375, -0.573, -0.395.P< 0.01 ).The preoperative corneal thickness had positive correlation with the changes of Kmax (r=0.266, P=0.012).6. Regression Analysis6.1 The regression formula between the changes of UDVA ( ? UDVA)and the distance of Kmax to the corneal center was:? UDVA=-0.024-0.066* Distance of Kmax to Corneal Center6.2 The regression formula between the changes of corneal astigmatism(? astigmatism) and the distance of Kmax to the corneal center was:? Astigmatism=-1.957+0.34* Distance of Kmax to Corneal Center6.3 The regression formula between the changes of Kmax ( ? Kmax)and the corneal thickness was:? Kmax=-18.606+0.032*Corneal ThicknessConclusions1. The study confirmed that after standard CXL 2 years, the progression of keratoconus could be controlled.2. Among them, the therapy of the central keratoconus was probably better than the peripheral keratoconus and the therapy of the primary keratoconus was probably better than the corneal ectasia.3. The changes of UDVA. BDVA, Kmax and astigmatism were correlated with the preoperative distance of Kmax to the corneal center, Km and the corneal thickness.4. The distance of Kmax to the corneal center was quantitati'vely related with the changes of UDVA and astigmatism. The preoperative corneal thickness was quantitatively related with the changes of Kmax.5. Longer therapy needs further observation and study. |
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