A short-term study of corneal collagen cross-linking with hypo-osmolar riboflavin solution in keratoconic corneas

AIM: To report the 3mo outcomes of collagen crosslinking(CXL) with a hypo-osmolar riboflavin in thin corneas with the thinnest thickness less than 400 μm without epithelium.METHODS: Eight eyes in 6 patients with age 26.2±4.8y were included in the study. All patients underwent CXL using a hypo-osmolar riboflavin solution after its de-epithelization. Best corrected visual acuity, manifest refraction, the thinnest corneal thickness, and endothelial cell density were evaluated before and 3mo after the procedure.RESULTS: The mean thinnest thickness of the cornea was 408.5 ±29.0 μm before treatment and reduced to369.8 ±24.8 μm after the removal of epithelium. With the application of the hypo-osmolar riboflavin solution, the thickness increased to 445.0 ±26.5 μm before CXL and recover to 412.5 ±22.7 μm at 3mo after treatment, P =0.659). Before surgery, the mean K-value of the apex of the keratoconus corneas was 57.6 ±4.0 diopters, and slightly decreased(54.7±4.9 diopters) after surgery(P =0.085). Mean best-corrected visual acuity was 0.55 ±0.23 logarithm of the minimal angle of resolution, and increased to 0.53±0.26 logarithm after surgery(P =0.879).The endothelial cell density was 2706.4 ±201.6 cells/mm2 before treatment, and slightly decreased( 2641. 2 ±218.2 cells/mm2) at last fellow up(P =0.002).CONCLUSION: Corneal collagen cross-linking with a hypo-osmolar riboflavin in thin corneas seems to be a promising treatment. Further study should be done to evaluate the safety and efficiency of CXL in thin corneas for the long-term.

Evaluation of corneal endothelium after UVA/riboflavin cross-linking in thin keratoconic corneas

Dear Sir,UVA/riboflavin cross-linking （CXL） has been used clinically applied for the treatment of keratoconus and corneal edema via enhancement of corneal stiffness The safety of the corneal endothelium is of prime importance during CXL treatment. In clinical practice, a corneal thickness （CT） of 400um has traditionally been regarded as the minimum treatable thickness, thereby avoiding damage to the corneal endothelium Although CXL has been applied to thinner corneas, using a hypoosmotic solution onto cornea and inducing edema . CXL safety still needs further evaluation because of lower relative concentration of collagen in the hydrated stroma . This study aims to evaluate the changes of corneal endothelial density （ECD） in cases where the CT is 〈400 um before iatrogenic corneal swelling and CXL treatment.

Riboflavin-UVA collagen cross-linking for the treatment of acanthamoeba keratitis

In this review,recent studies regarding riboflavin-ultraviolet A(UVA)collagen cross-linking for the treatment of acanthamoeba keratitis(AK)were reviewed.English written studies about acanthamoeba,keratitis,riboflavin and collagen cross-linking were retrieved from PubMed search engine(www.ncbi.nlm.nih.gov/pubmed).Although there were significant numbers of cases reporting the effectiveness of riboflavin-UVA collagen cross-linking in AK,experimental studies(in vivo and in vitro)failed to verify amoebicidal or cysticidal effect of riboflavin-UVA collagen cross-linking.In conclusion,the efficacy of riboflavin-UVA collagen cross-linking for the treatment of AK is still debatable.It is necessary to conduct a prospective case-control study for clear guidance for clinicians.

Analysis of the effective dose of ultraviolet light in corneal cross-linking

AIM: To analyze the efficacy of ultraviolet (UV) light initiating corneal cross-linking (CXL). METHODS: The time-dependent absorption of UV light due to the depletion of the initiator (riboflavin) was calculated. The effective dose of CXL with corneal surface covered by a thin layer of riboflavin was derived analytically. The cross linking time was calculated by the depletion level of the riboflavin concentration. A comprehensive method was used to derive analytic formulas. RESULTS: The effective dose of CXL was reduced by a factor (R) which was proportional to the thickness (d) and concentrations (C-0) of the riboflavin surface layer. Our calculations showed that the conventional dose of 5.4 J/cm(2) had a reduced effective dose of 4.3 and 3.45 J/cm(2), for d was 100 and 200 pm, respectively, and C-0=0.1%. The surface cross linking time was calculated to be T*=10.75s, for a depletion level of 0.135 and UV initial intensity of 30 mW/cm(2). The volume T* was exponentially increasing and proportional to exp (bdC(0)), with b being the steady state absorption coefficient. CONCLUSION: The effective dose of CXL is reduced by a factor proportional to the thickness and concentrations of the riboflavin surface layer. The wasted dose should be avoided by washing out the extra riboflavin surface layer prior to the UV light exposure.

Corneal collagen crosslinking in keratoconus and other eye disease

Keratoconus is a condition characterized by biomechanical instability of the cornea, presenting in a progressive, asymmetric and bilateral way. Corneal collagen crosslinking(CXL) with riboflavin and Ultraviolet-A(UVA) is a new technique of corneal tissue strengthening that combines the use of riboflavin as a photo sensitizer and UVA irradiation. Studies showed that CXL was effective in halting the progression of keratoconus over a period of up to four years. The published studies also revealed a reduction of max K readings by more than 2 D, while the postoperative spherical equivalent(SEQ) was reduced by an average of more than 1 D and refractive cylinder decreased by about1 D. The major indication for the use of CXL is to inhibit the progression of corneal ecstasies, such as keratoconus and pellucid marginal degeneration. CXL may also be effective in the treatment and prophylaxis of iatrogenic keratectasia, resulting from excessively aggressive photo ablation. This treatment has been used to treat infectious corneal ulcers with apparent favorable results. Most recent studies demonstrate the beneficial impact of CXL for iatrogenic ecstasies, pellucid marginal degeneration, infectious keratitis, bullous keratopathy and ulcerative keratitis. Several long-term and short-term complications of CXL have been studied and documented. The possibility of a secondary infection after the procedure exists because the patient is subject to epithelial debridement and the application of a soft contact lens. Formation of temporary corneal haze,permanent scars, endothelial damage, treatment failure,sterile infiltrates, bullous keratopathy and herpes reactivation are the other reported complications of this procedure.

跨上皮快速角膜胶原交联术治疗进展期圆锥角膜

目的:研究跨上皮快速角膜胶原交联术(CXL)治疗进展期圆锥角膜的临床效果和安全性。方法:前瞻性自身前后对照研究。收集自2016-08/2019-11在我院进行跨上皮快速CXL的进展期圆锥角膜患者37例47眼,分析患者术前,术后1、3、6、12mo的裸眼视力(UCVA)和最佳矫正视力(BCVA)、屈光状态、角膜透明度、角膜前表面最大K值(Kmax)、角膜最薄点厚度、角膜内皮细胞计数、眼压。结果:术后1、3、6、12mo患者UCVA较术前提高,但总体比较无差异(F=1.372,P=0.261)。患者术后1、3、6、12mo的BCVA均较术前提高,总体比较有差异(F=3.308,P=0.019),进一步比较发现术后3、6、12mo的BCVA与术前比较有差异(P=0.04、0.01、0.007)。患者术后1、3、6、12mo的球镜度数、柱镜度数、Kmax、角膜最薄点厚度与术前总体比较无差异(F=0.293、1.378、2.448、1.970,P=0.881、0.258、0.061、0.116)。术后1mo患者角膜内皮细胞计数与术前比较无差异(t=1.156,P=0.25)。患者术后各时间点眼压与术前比较无差异(F=1.221,P=0.321)。术后7眼出现角膜Haze(1级~2级),术后3~6mo有5眼Haze消退,角膜恢复透明,1眼遗留角膜云翳,1眼角膜中央基质线状混浊,但均未对视力造成影响。结论:跨上皮快速CXL可以显著提高圆锥角膜患者BCVA,稳定患者屈光状态、角膜形态和厚度,阻止或延缓圆锥角膜进展,使患者获得更好的视功能,同时手术时间短,术后并发症少,具有较好的安全性。

角膜交联术中紫外辐射安全性分析

目的:利用人眼角膜简易模型研究和评价核黄素和UVA紫外光联合进行角膜交联术时对眼组织所产生的潜在光辐射伤害。方法:建立核黄素处理后的角膜的简化计算模型,根据国际非离子辐射防护委员会(ICNIRP)《眼科仪器光辐射对眼睛的照射指南调整》中的限值要求对设立的简化模型进行理论计算和推导,通过兔眼角膜实验数据分析UVA紫外光照射后对眼组织的辐射安全性。结果:根据所设立的简化计算模型得到核黄素处理后的角膜在365nm处的透过率限值26%,角膜交联手术中利用辐照强度3 mW/cm2(5.4mJ/cm2)UV激光对兔眼角膜照射,实际试验结果为14.46%±2.93%,小于该限值。结论:建立的简化模型在进行角膜交联手术中UVA激光安全性指标评价时不失为一种简单而有效的方法。所设立的简化计算模型,对于评价角膜交联手术中所使用的UV激光对眼组织辐射安全性来讲,具有一定的指导意义。

等渗与低渗核黄素诱导的角膜交联术治疗圆锥角膜的疗效观察

目的观察等渗与低渗核黄素溶液进行角膜交联治疗圆锥角膜的疗效。方法将圆锥角膜患者根据治疗前角膜厚度分为两组,厚角膜组采用等渗核黄素溶液进行胶原交联,薄角膜组采用低渗核黄素溶液进行胶原交联。观察交联后两组患者角膜厚度、裸眼视力、矫正视力、顶点K值、角膜内皮细胞计数等指标。结果交联术后两年两组患者角膜厚度分别降低(11±14)μm(厚角膜组)、(7±9)μm(薄角膜组),差异有统计学意义;顶点K值分别降低(1.61±2.30)D(厚角膜组)、(2.58±3.22)D(薄角膜组),差异有统计学意义;两组裸眼视力、矫正视力均较治疗前有统计学意义提高;两组患者角膜内皮细胞计数治疗前后差异无统计学意义。结论交联可以有效控制圆锥角膜的进展,厚角膜患者可以采用等渗核黄素溶液进行胶原交联,薄角膜患者可以采用低渗核黄素溶液进行胶原交联。