Risk Factors for Progression of Keratoconus and Failure Rate After Corneal Cross-linking

Keratometry Changes Between Year One to Seven After Corneal Cross-Linking in Patients With Keratoconus

PURPOSE

We evaluated the timing at and extent to which midterm to long-term keratometric changes can occur in year 1 to 7 after corneal collagen cross-linking (CXL) in patients with keratoconus.

METHODS

We conducted a subgroup analysis of a retrospective cohort study of all consecutive patients who underwent CXL at our cornea center between 2007 and 2011. The inclusion criteria comprised CXL according to the Dresden protocol and a full set of keratometry parameters collected by Scheimpflug tomography preoperatively and at year 1, 3, 5, and 7 after CXL. In addition, best-corrected visual acuity was evaluated.

RESULTS

Sixty-three eyes of 47 patients were enrolled. Mean age was 25.46 years ±7.39 years (80.9% male patients). All relevant keratometric parameters showed significant improvement at year 1 after CXL (except for posterior astigmatism). According to mixed-effects model analysis, they all showed further significant change at different points in time between year 1, 3, 5, and 7 (except for K1). In addition, best-corrected visual acuity improved statistically significant between year 1, 3, 5, and 7. Suspected disease progression was noted in 22.2% of patients, mostly between year 1 and 3 after CXL.

CONCLUSIONS

After initial improvement 1 year after CXL, keratometric and functional parameters were stable until year 5 after CXL in most cases; further improvement can take place even after up to 7 years post-CXL. By contrast, in case of disease progression, changes seem to occur already between year 1 and 3 after CXL.

Prediction model for treatment outcomes 3 years after corneal cross-linking for keratoconus

PURPOSE

This study aimed to identify preoperative factors that predict visual acuity and Kmax 3 years after corneal cross-linking (CXL) in patients with keratoconus (KC), and to develop a prediction model.

METHODS

We enrolled 68 patients with KC and followed up on 100 eyes that received CXL for at least 3 years. Preoperative data, including age, UDVA, CDVA, cylinder, SE, and the parameters of tomography including Kmax were collected as predictors. The primary outcomes were changes in CDVA (Delta CDVA) and Kmax (Delta Kmax) postoperatively. Univariate and multivariate linear regression were used to identify the correlation between the primary outcomes and predictors and establish prediction models.

RESULTS

Both CDVA and Kmax remained stable from baseline to 3 years after CXL: from 0.25 ± 0.18 to 0.22 ± 0.20 (P = 0.308) and from 58.70 ± 9.52 D to 57.02 ± 8.83 D (P = 0.187), respectively. Multivariate analysis showed that worse preoperative CDVA (ß coefficient - 0.668, P < 0.001) and lower preoperative Kmean (ß coefficient 0.018,P < 0.001) were associated with greater improvement in CDVA after CXL. A smaller preoperative eccentricity (ß coefficient 8.896, P = 0.01) and a higher preoperative Kmean (ß coefficient - 1.264, P < 0.001) predicted a more flattening of postoperative Kmax. The prediction model for CDVA (R2 = 0.43) and Kmax (R2 = 0.37) could accurately estimate treatment outcomes.

CONCLUSIONS

CXL is highly effective in halting or preventing further progression of KC. The preoperative factors CDVA and Kmean were able to predict visual acuity changes 3 years after CXL. And preoperative eccentricity and Kmean could predict Kmax changes 3 years after CXL.

Crosslinking with UV-A and riboflavin in progressive keratoconus: From laboratory to clinical practice - Developments over 25 years

Changes in the biomechanical and biochemical properties of the human cornea play an important role in the pathogenesis of ectatic diseases. A number of conditions in primarily acquired (keratoconus or pellucid marginal degeneration) or secondarily induced (iatrogenic keratectasia after refractive laser surgeries) ectatic disorders lead to decreased biomechanical stability. Corneal collagen cross-linking (CXL) represents a technique to slow or even halt the progression of ectatic pathologies. In this procedure, riboflavin is applied in combination with ultraviolet A radiation. This interaction induces the production of reactive oxygen species, which leads to the formation of additional covalent bonds between collagen molecules and subsequent biomechanical corneal strengthening. This procedure is so far the only method that partially interferes etiopathogenetically in the treatment of ectatic diseases that slows or stops the process of corneal destabilization, otherwise leading to the need for corneal transplantation. Besides, CXL process increases markedly resistance of collagenous matrix against digesting enzymes supporting its use in the treatment of corneal ulcers. Since the discovery of this therapeutic procedure and the first laboratory experiments, which confirmed the validity of this method, and the first clinical studies that proved the effectiveness and safety of the technique, it has been spread and adopted worldwide, even with further modifications. Making use of the Bunsen-Roscoe photochemical law it was possible to shorten the duration of this procedure in accelerated CXL and thus improve the clinical workflow and patient compliance while maintaining the efficacy and safety of the procedure. The indication spectrum of CXL can be further expanded by combining it with other vision-enhancing procedures such as individualized topographically-guided excimer ablation. Complementing both techniques will allow a patient with a biomechanically stable cornea to regularize it and improve visual acuity without the need for tissue transplantation, leading to a long-term improvement in quality of life.

[Ophthalmic disqualification from the military services: Multicentric cross-sectional study]

PURPOSE

This article aims to describe the causes of ophthalmological disqualification from the military services detected during specialist consultations conducted at Army Training Hospitals.

METHODS

This observational, cross-sectional, multicenter study retrospectively included individuals deemed as "unfit for military service" due to eye diseases identified during the specialist consultation conducted at 3 ATHs between January 2020 and December 2021. The data collected included age, medical and surgical history, reasons for ophthalmological disqualification, uncorrected distance visual acuity, best corrected distance visual acuity and cycloplegic refraction.

RESULTS

Over this period, 133 subjects (98 men and 35 women) were included. Thirty-eight candidates (28.6%) were declared unfit due to a refractive error beyond the required limits, including 30 myopic subjects in excess of -10 diopters (D) and 8 hypermetropic subjects over +8 D. Twenty-five candidates (18.8%) were unfit under the age of 21 years due to corneal refractive surgery performed before the required age. Four subjects (3.0%) were unfit due to phakic intraocular lenses. Degenerative conditions were observed in 23 subjects (17.3%), including 21 patients with severe keratoconus. Other causes of incapacity were linked to oculo-orbital trauma in 11 subjects (8.3%), moderate or severe amblyopia in 7 patients (5.3%), congenital causes in 7 subjects (5.3%), inflammatory or infectious diseases in 7 candidates (5.3%), hereditary causes in 6 subjects (4.5%) and undetermined visual dysfunctions in 4 subjects (3.0%).

CONCLUSION

The three main causes of ophthalmological disqualification were high ametropia, refractive surgery performed before the required age and keratoconus.

A comparison of keratoconus progression following collagen cross-linkage using standard or personalised keratometry thresholds

OBJECTIVE

To define how estimates of keratoconus progression following collagen cross-linking (CXL) vary according to the parameter selected to measure corneal shape.

MATERIALS AND METHODS

We estimated progression following CXL in 1677 eyes. We compared standard definitions of keratoconus progression based on published thresholds for Kmax, front K2, or back K2, or progression of any two of these three parameters, with the option of an increased threshold for Kmax values ≥ 55D. As corneal thickness reduces unpredictably after CXL, it was excluded from the principal analysis. We then repeated the analysis using novel adaptive estimates of progression for Kmax, front K2, or back K2, developed separately using 6463 paired readings from keratoconus eyes, with a variation of the Bland-Altman method to determine the 95% regression-based limits of agreement (LoA). We created Kaplan-Meier survival plots for both standard and adaptive thresholds. The primary outcome was progression five years after a baseline visit 9-15 months following CXL.

RESULTS

Progression rates were 8% with a standard (≥ 1.5D) threshold for K2 or 6% with the static multi-parameter definition. With a ≥ 1D threshold for Kmax, the progression was significantly higher at 29%. With adaptive Kmax or K2, the progression rates were similar (20%) but less than with the adaptive multi-parameter method (22%).

CONCLUSIONS

Estimates of keratoconus progression following CXL vary widely according to the reference criteria. Using adaptive thresholds (LoA) to define the repeatability of keratometry gives estimates for progression that are markedly higher than with the standard multi-parameter method.

Repeat corneal collagen cross-linking after failure of primary cross-linking in keratoconus

BACKGROUND

Primary corneal collagen cross-linking (CXL) stabilises 96% of progressive keratoconus. There is limited evidence for the treatment of choice when this fails. We present 10 years of repeat CXL and compare with our published experience of primary CXL to (1) identify perioperative risk factors of primary CXL failure and (2) demonstrate the safety and efficacy of repeat CXL.

METHODS

Patients undergoing repeat accelerated epithelium-off CXL at St James's University Hospital, Leeds, UK January 2012-August 2022 were identified through electronic patient record, and compared with a previously published cohort of primary CXL patients at the same site.

RESULTS

Twenty-one eyes underwent repeat CXL. The mean interval between primary and repeat CXL treatments was 47.1 months (SD 22.5). Twenty (95%) eyes stabilised after repeat CXL at a mean follow-up of 29.9 months. These cases were compared with 151 cases of primary CXL from our previous study. Patients failing primary CXL were significantly younger (21.3 years (SD 7.0) vs 26.7 years (SD 6.5), p=0.0008). Repeat CXL and primary CXL induced a similar amount of flattening of Kmax (-1.2 D (SD 3.9) vs -0.7 D (SD 4.4), p=0.22). A small, but clinically insignificant, improvement in best-corrected visual acuity was found in the repeat CXL group (-0.04 (SD 0.17) vs -0.05 (SD 0.13), p=0.04). No complications of repeat CXL were noted.

CONCLUSION

Younger age may be associated with failure of primary CXL. Repeat CXL is an effective and safe treatment for progressive keratoconus despite primary CXL.

Oxygen-supplemented and topography-guided epithelium-on corneal crosslinking with pulsed irradiation for progressive keratoconus

PURPOSE

To investigate the effects of customized topography-guided epithelium-on crosslinking (epi-on CXL) with oxygen supplementation on procedural efficacy and corrected distance visual acuity (CDVA) in patients with progressive keratoconus (KC) at 1 year.

SETTING

Private eye clinic, Brisbane, Australia.

DESIGN

Retrospective, single-center, nonrandomized case series.

METHODS

Topography-guided epi-on CXL using the Mosaic system was performed on patients with progressive KC. Oxygen goggles; transepithelial riboflavin; and pulsed, high UV-A irradiance (1 second on, 1 second off; 30 mW/cm2) were applied to enhance oxygen kinetics and bioavailabilities of riboflavin and UV-A. Guided by baseline topography, a higher UV-A dose (15 J/cm2) was applied to the area of steepest anterior curvature with decreasing fluence (as low as 7.2 J/cm2) toward the outer 9 mm. Postoperative CDVA and maximum keratometry (Kmax) were evaluated.

RESULTS

102 eyes (80 patients) were followed for 11.5 ± 4.8 months. At the latest follow-up, mean CDVA (logMAR), mean K, and Kmax (diopters [D]) improved from 0.18 ± 0.28, 46.2 ± 3.8, and 53.0 ± 5.67 at baseline to 0.07 ± 0.18, 45.8 ± 3.7, and 51.9 ± 5.56, respectively (P < .001). 3 eyes (3%) lost more than 1 CDVA line, and another 3 eyes (3%) had increased Kmax greater than 2 D. 43 eyes were followed for at least 12 months (n = 43): mean CDVA, mean K, and Kmax improved from 0.19 ± 0.33 logMAR, 46.5 ± 3.5 D, and 53.6 ± 5.67 D to 0.07 ± 0.17 logMAR, 46.0 ± 3.5 D, and 52.33 ± 5.49 D, respectively (P ≤ .002). No complications were observed.

CONCLUSIONS

Tailoring oxygen-supplemented epi-on CXL with differential UV-A energy distributions, guided by baseline topography, in patients with KC seems to be safe and effective. At 1 year, study reports sustained improved CDVA and corneal stabilization.

Case of Progressive Keratoconus With Newly Diagnosed Pellucid Marginal Degeneration After Corneal Cross-Linking

PURPOSE

The purpose of this study was to document, to our knowledge, the first reported case of keratoconus progression accompanied with newly diagnosed pellucid marginal degeneration after corneal cross-linking (CXL).

METHODS

A novel case of further keratoconus progression plus development of pellucid marginal degeneration in the same eye after CXL was documented with supporting evidence from Scheimpflug and optical coherence tomography imaging.

RESULTS

A male patient was diagnosed with progressive keratoconus in the left eye and treated with CXL when aged 25 years. Although strongly cautioned not to rub his eyes, he admitted that he continued eye rubbing in association with atopic disease. At a follow-up examination 3.5 years after CXL, progressive keratoconus was detected and pellucid marginal degeneration was newly diagnosed in the left eye. The eye was retreated with CXL.

CONCLUSIONS

This case illustrates that progressive keratoconus and pellucid marginal degeneration can occur in the same eye after CXL and demonstrates the deleterious effects that can develop with continued eye rubbing.

Ethnicity, Progressive Keratoconus, and Outcomes after Corneal Cross-Linking in Southern Israel

PURPOSE

To assess clinical outcomes of corneal cross-linking (CXL) intervention in a population diagnosed with progressive keratoconus.

METHODS

This single-center retrospective cohort study included consecutive patients who underwent standard CXL or accelerated CXL for progressive keratoconus at a major teaching hospital in southern Israel between January 2015 and December 2019. Patients' medical files were reviewed, and pre-operative and post-operative data regarding demographics and clinical and tomographic characteristics were extracted and analyzed.

RESULTS

This study included 166 patients (representing 198 eyes), out of which 98 patients (123 eyes) were ethnically Bedouin, and 68 patients (75 eyes) were ethnically Jewish. Overall, 126 patients (144 eyes) had a follow-up of at least 12 months (16.84 ± 5.76). The mean patient age was 20.62 ± 7.1 years old. There were significant baseline differences between the two ethnic groups in best-corrected visual acuity (BCVA; p < 0.001), uncorrected visual acuity (UCVA; p < 0.001), mean keratometry (p = 0.028), and corneal thickness (p < 0.001). Significant changes in BCVA, UCVA, and pachymetry parameters within each group were found after 12 months. Negative binomial regression analysis showed a maximal keratometry below 55D (RR = 1.247, p < 0.001), and a standard CXL procedure (RR = 1.147, p = 0.041) are significantly related to the stability of KC after 12 months. However, the effect size of the origin of patients is negligible (RR = 1.047, p = 0.47).

CONCLUSIONS

In this study, the Bedouin population suffered from more progressive keratoconus when compared to the Jewish population. CXL was significantly effective in improving BCVA and UCVA in both groups after 12 months of follow-up. The effect size of the origin of patients on the stability of KC was found to be negligible.

Evaluation of Biomechanical Changes After Accelerated Cross-Linking in Progressive Keratoconus: A Prospective Follow-Up Study

PURPOSE

The aim of this study was to analyze the biomechanical effect of accelerated corneal cross-linking (9*10) in progressive keratoconus (KC) in comparison to untreated fellow eyes using Scheimpflug-based tonometry (Corvis ST, CVS).

METHODS

Forty-three eyes of 43 patients with KC showed progressive KC and were treated using accelerated corneal cross-linking. Twenty-five untreated fellow eyes were used as the control group. All eyes were examined biomechanically (CVS) and tomographically (Pentacam) at baseline, after 1-month, 6-month, and 12-month follow-up. Statistical analysis was performed using a linear mixed model. A logistic regression was performed to attribute the effects of changes in each parameter to treatment status (treated or untreated).

RESULTS

Maximum keratometry values decreased statistically significantly at 12 months by -1.1 D (95 confidence interval: -2.0 to -0.1, P = 0.025) compared with baseline. Thinnest corneal thickness decreased significantly after 1 month ( P < 0.001) and recovered to baseline after 12 months ( P = 0.752). In the corneal cross-linking (CXL) group, biomechanical changes were observed by an increased bIOP, a shorter A2 time, and a lower integrated radius after 1 month (all P < 0.05). No biomechanical and tomographical changes were observed in the control group (all P > 0.05). Logistic regression pointed out that treated eyes can be separated from untreated eyes by differences in bIOP, corneal thickness, A1 velocity, integrated radius, and Kc mean at 1, 6, and 12 months.

CONCLUSIONS

The alterations in biomechanical parameters indicated a corneal stiffening effect after CXL treatment, which was mostly detectable 1 month after treatment, although corneal thickness was reduced. The logistic regression model showed an adequate separation between CXL-treated and untreated eyes.

Five-year results of iontophoresis-assisted transepithelial corneal cross-linking for keratoconus

PURPOSE

To assess long-term efficacy and safety of iontophoresis-assisted transepithelial corneal cross-linking (I-CXL) for keratoconus.

PATIENTS AND METHODS

Twenty-seven eyes of 21 patients (15 M, 6F) affected by progressive keratoconus were evaluated. All subjects were treated with iontophoresis-assisted transepithelial CXL. The patients were examined at baseline and each 6 months after the CXL procedure. Only subjects who completed the follow-up of 5 years were considered in this study. The main outcome measures were uncorrected visual acuity (UCVA), corrected visual acuity (CDVA), corneal transparency and corneal parameters such as K-max, central corneal thickness (CCT) and at the thinnest point, and high-order ocular aberrations (HOAs). The ABCD system was used to determine the progression and re-progression of ectasia.

SETTING

Ophthalmology Clinic, University Hospital of Messina, Messina, Italy.

RESULTS

At 5 years, significant improvements of UCVA from 0.53 ± 0.33 logMAR to 0.4 ± 0.33 logMAR (p = 0.001) and HOAs (p = 0.01) were registered. No significant changes of CDVA (p = 0.4), K-max (p = 0.75), CCT (p = 0.5) were observed at the end of follow-up period. The ABCD system showed re-progression in 25.9% of eyes after 5 years. No adverse events such as corneal opacities and infections were reported.

CONCLUSIONS

Iontophoresis-assisted transepithelial CXL resulted to be safe and effective to stabilize progressive keratoconus in adults at a long-term follow-up.

Analysis of Biomechanical Response After Corneal Crosslinking with Different Fluence Levels in Porcine Corneas

PURPOSE

To evaluate corneal stiffening of porcine corneas induced by corneal crosslinking (CXL) with constant irradiance as a function of total fluence.

METHODS

Ninety corneas from freshly enucleated porcine eyes were divided into five groups of 18 eyes. Groups 1-4 underwent epi-off CXL using a dextran-based riboflavin solution and an irradiance of 18 mW/cm2, group 5 served as the control group. Groups 1 to 4 were treated with a total fluence of 20, 15, 10.8, and 5.4 J/cm2, respectively. Thereafter, biomechanical measurements were performed on 5 mm wide and 6 mm long strips using an uniaxial material tester. Pachymetry measurements were performed on each cornea.

RESULTS

At 10% strain, the stress was 76, 56, 52, and 31% higher in groups 1-4, respectively compared to the control group. The Young's modulus was 2.85 MPa for group 1, 2.53 MPa for group 2, 2.46 MPa for group 3, 2.12 MPa for group 4, and 1.62 MPa for the control group. The difference between groups 1 to 4 and the control group 5 were statistically significant (p = <0.001; p = <0.001; p = <0.001; p = 0.021). In addition, group 1 showed significantly more stiffening than group 4 (p = <0.001), no other significant differences were found. Pachymetry measurements revealed no statistically significant differences among the five groups.

CONCLUSION

Additional mechanical stiffening can be achieved by increasing the fluence of the CXL. There was no threshold detected up to 20 J/cm2. A higher fluence could compensate the weaker effect of accelerated or epi-on CXL procedures.

Development and validation to predict visual acuity and keratometry two years after corneal crosslinking with progressive keratoconus by machine learning

Purpose

To explore and validate the utility of machine learning (ML) methods using a limited sample size to predict changes in visual acuity and keratometry 2 years following corneal crosslinking (CXL) for progressive keratoconus.

Methods

The study included all consecutive patients with progressive keratoconus who underwent CXL from July 2014 to December 2020, with a 2 year follow-up period before July 2022 to develop the model. Variables collected included patient demographics, visual acuity, spherical equivalence, and Pentacam parameters. Available case data were divided into training and testing data sets. Three ML models were evaluated based on their performance in predicting case corrected distance visual acuity (CDVA) and maximum keratometry (Kmax) changes compared to actual values, as indicated by average root mean squared error (RMSE) and R-squared (R2) values. Patients followed from July 2022 to December 2022 were included in the validation set.

Results

A total of 277 eyes from 195 patients were included in training and testing sets and 43 eyes from 35 patients were included in the validation set. The baseline CDVA (26.7%) and the ratio of steep keratometry to flat keratometry (K2/K1; 13.8%) were closely associated with case CDVA changes. The baseline ratio of Kmax to mean keratometry (Kmax/Kmean; 20.9%) was closely associated with case Kmax changes. Using these metrics, the best-performing ML model was XGBoost, which produced predicted values closest to the actual values for both CDVA and Kmax changes in testing set (R2 = 0.9993 and 0.9888) and validation set (R2 = 0.8956 and 0.8382).

Conclusion

Application of a ML approach using XGBoost, and incorporation of identifiable parameters, considerably improved variation prediction accuracy of both CDVA and Kmax 2 years after CXL for treatment of progressive keratoconus.

Innovations in Corneal Crosslinking

PURPOSE

Corneal Crosslinking (CXL) strengthens the keratoconus cornea and prevents further disease progression. Modified crosslinking protocols and different riboflavin solutions have been proposed to optimize the procedure and improve treatment success.

METHODS

PubMed research of relevant publications and report of own experiences with different CXL protocols.

RESULTS

Accelerated CXL shows comparable efficiency with shorter surgery time and similar complication rates. Customized CXL provides improved results with faster epithelial healing. CXL in a hyperoxic environment seems to be a safe and effective transepithelial alternative with presumably less complications and fewer side effects. Thin corneas (<400 µm) can be treated safely by corneal swelling using hypoosmolar riboflavin solutions and reducing the applied UV-energy. The combination of CXL with photorefractive keratectomy (PRK) can be considered in patients with contact lens intolerance improving visual acuity, however, with increased risk of visual loss compared to CXL alone. Two-Photon (2Ph) CXL is a promising new technology enabling three-dimensional CXL.

DISCUSSION

Recently developed CXL protocols offer advantages over the standard "Dresden-protocol" and should be considered in patients with progressive keratectasia.

Corneal biomechanical stiffness and histopathological changes after in vivo repeated accelerated corneal cross-linking in cat eyes

Corneal cross-linking (CXL) has been proved efficiency for treating progressive keratoconus and other corneal ectasia diseases by stabilizing corneal geometry and biomechanics. However, the necessity of repeated CXL treatment in patients is unknown. This study aimed to investigate corneal biomechanical stiffness and change in corneal histopathological characteristics after repeated accelerated CXL (A-CXL) in cat eyes. A-CXL was performed with 0.1% riboflavin applied for 10 min, followed by ultraviolet A irradiation at 30 mW/cm² for 3 min at 365 nm in 15 domestic cats. Corneas (n = 30) were divided into three groups: one-time accelerated corneal cross-linking (A-CXL*1 group), repeated accelerated corneal cross-linking (A-CXL*2 group), and an untreated control group. In A-CXL*2 group, A-CXL was repeated at 1-month intervals. In vivo ocular examinations were performed pre- and postoperatively. Biomechanical analysis was performed using a biotester biaxial testing system. We used the Mooney-Rivlin strain-energy function to describe corneal material properties. No infection in any case after A-CXL was observed. Biomechanical tests showed that the stress-strain curves of the two A-CXL groups were significantly different from those of the control group (P < 0.01), whereas stress-strain curve of the A-CXL*2 group was similar to that of the A-CXL*1 group (P > 0.05). Delayed epithelial healing and haze were observed 1 month after surgery. Stromal demarcation line depth measured with anterior spectral-domain optical coherence tomography was 187.6 ± 20.4 and 197.1 ± 11.5 μm for the A-CXL*1 and A-CXL*2 groups, respectively (P > 0.05). These results show that A-CXL can increase corneal biomechanics in cat eyes. The biomechanical enhancement of cat corneas treated with repeated A-CXL at 1-month intervals was similar to that of performing a one-time A-CXL. Repeated cross-linking procedures at short intervals may increase the risk of adverse reactions, and more caution should be taken in clinical applications.

Corneal Crosslinking With Riboflavin and UVA Light in Progressive Keratoconus: Fifteen-Year Results

PURPOSE

To analyze the 15-year results of corneal crosslinking (CXL) in progressive keratoconus.

DESIGN

Retrospective follow-up analysis of interventional study patients.

METHODS

This study included keratoconic eyes with progressive disease treated from 2001 to 2006 at the Department of Ophthalmology, Carl Gustav Carus University Hospital, TU Dresden, Germany. CXL was performed by applying riboflavin and ultraviolet A (UVA) light according to a standard protocol. The best-corrected distance visual acuity (BCVA), slitlamp examination, and corneal topography as well as corneal thickness values were recorded preoperatively and 15 years after the treatment.

RESULTS

A total of 42 eyes received a complete follow-up of 15 years. The mean age of the patients at baseline was 26.9 (95% CI: 25.0-28.8) years. The maximum keratometry was 61.6 (95% CI: 58.2 - 64.9) diopters (D) preoperatively and 55.1 (95% CI: 51.6-58.4) D postoperatively; the decrease was statistically significant (P < .001). The mean keratometry value changed from 50.3 (95% CI: 48.3-52.4) D to 47.5 (95% CI: 45.3-49.4) D (P < 0.001). Furthermore, the thinnest corneal thickness decreased statistically significantly by 40 (95% CI: 24-56) µm (P < .001). The BCVA improved statistically significantly from 0.4 to 0.2 logMAR after the treatment. Retreatment was needed in 14% of cases. Mild scarring of the superficial stromal corneal layers was observed in 36% of the eyes, and in 67% of them visual acuity was stable or even improved.

CONCLUSIONS

The CXL procedure proved to be an effective method in the treatment of keratoconic eyes in the progressive stage of the disease, and achieved long-term stabilization without the occurrence of serious complications or side effects.

Analysis of riboflavin/ultraviolet a corneal cross-linking by molecular spectroscopy

Corneal cross-linking (CXL) with riboflavin and ultraviolet A light is a therapeutic procedure to restore the mechanical stability of corneal tissue. The treatment method is applied to pathological tissue, such as keratoconus and induces the formation of new cross-links. At present, the molecular mechanisms of induced cross-linking are still not known exactly. In this study, we investigated molecular alterations within porcine cornea tissue after treatment with riboflavin and ultraviolet A light by surface enhanced Raman spectroscopy (SERS). For that purpose, after CXL treatment a thin silver layer was vapor-deposited onto cornea flaps. To explore molecular alterations induced by the photochemical process hierarchical cluster analysis (HCA) was used. The detailed analysis of SERS spectra reveals that there is no general change in collagen secondary structure while modifications on amino acid side chains are the most dominant outcome. The formation of secondary and aromatic amine groups as well as methylene and carbonyl groups were observed. Even though successful cross-linking could not be registered in all treated samples, Raman signals of newly formed chemical groups are already present in riboflavin only treated corneas.

Long-Term Outcome of Corneal Collagen Crosslinking with Riboflavin and UV-A Irradiation for Keratoconus

PURPOSE

To evaluate long-term outcomes of corneal collagen crosslinking (CXL) using riboflavin and UV-A irradiation and to determine when to repeat CXL.

METHODS

In this retrospective consecutive interventional case series 131 eyes of 131 patients (95 male, 36 female, mean age 29.7 ± 11.4 years) between 2006 and 2016 received standard CXL (Dresden protocol, epithelium-off) for progressive keratoconus. Corrected distance visual acuity (CDVA) and corneal tomography (K₁, K₂, K_max) were repeatedly recorded 1 year (n = 103 eyes) to 10 years (n = 44) postoperatively. Only one eye per patient was included. Paired t-test or Wilcoxon matched-pairs signed rank test was used for parametric and nonparametric data, respectively.

RESULTS

1-3 years preoperatively, median K₂ significantly increased by 1.1 D (p < 0.001). Postoperatively, median K₂ increased by 0.1 D after 1 year, then decreased over the remaining postoperative period by 0.85 D (p = 0.021). K_max fluctuated without significant change. Median apical corneal thickness decreased by 16 µm (p = 0.012) after 5 years and then returned to preoperative values. Mean CDVA showed a significant improvement (decrease in logMAR 0.08 after 10 years, p = 0.010). CXL non-responders, defined by a postoperative increase in K_max>2 D, increased from 16% after 5 to 33% after 10 years. Risk factors for non-response were young age, high astigmatism (>4.3 D), thin cornea (<480 µm), poor initial visual acuity (CDVA ≥0.3 D), and atopic dermatitis. 4 eyes were re-treated 3-4 years after first CXL without complications and keratoconus stabilized thereafter.

CONCLUSIONS

CXL can slow or stop keratoconus progression. However, as the number of responders declines after 5 years, especially patients with risk factors may require re-treatment.

Corneal cross-linking in patients with keratoconus: up to 13 years of follow-up

INTRODUCTION

To evaluate long-term safety and efficacy of corneal collagen cross-linking (CXL) in patients with keratoconus up to 13 years.

MATERIALS AND METHODS

In this mono-centre exploratory study, we included all consecutive patients who underwent CXL in our cornea centre from 01/01/2007 to 12/30/2011 and met the inclusion criteria. CXL was performed in all patients according to the Dresden protocol. Evaluation included best-corrected visual acuity (BCVA), topographic keratometry by Scheimpflug corneal tomography and endothelial cell count (ECC). Follow-up measurements were taken up to 13 years after treatment were compared with baseline values.

RESULTS

The study enrolled 168 eyes. The mean age of our patients was 26.3 years ± 7.8 years. A complete topographic dataset was available 1 year postoperatively for 142 eyes, 5 years postoperatively for 105 eyes, 10 years postoperatively for 61 eyes and 13 years postoperatively for 9 eyes. BCVA increased statistically significant after 1 year, 5 years and 10 years and non-significantly after 13 years. All keratometric parameters with exception of posterior astigmatism showed a statistically significant decrease after 1 year, 5 years and 10 years. After 13 years, the decrease was statistically significant only in Kmax, K2 and thinnest cornea. No significant changes in ECC were detected. Three eyes received Re-CXL, none of the eyes received penetrating keratoplasty and no infections occurred in this cohort.

CONCLUSIONS

CXL can slow down or even stop the progression of keratoconus in the majority of cases. The effect is long-lasting with excellent safety.

Identification of Treatment Protocols for Effective Cross-Linking of the Peripheral Cornea: An Experimental Study

INTRODUCTION

This study aimed to test and evaluate modified corneal cross-linking (CXL) protocols regarding improved treatment effects on the peripheral cornea in terms of tissue stability and cellular response.

METHODS

Peripheral CXL (pCXL) was performed within a ring of 9-11 mm of 36 human donor corneas with variations in applied energy (5.4, 7.2, and 10 J/cm²) at 9 mW/cm² irradiance. Each energy level was additionally modulated regarding the oxygen level surrounding the cornea during treatment (21%; 100%). Stress-strain tests with endpoints at 12% strain and collagenase A-assisted digestions to complete digestion were performed to evaluate the rigidity and resistance of treated and control tissue. Further, corneas were processed histologically via TUNEL assay and H&E staining to demonstrate the effects on stromal cells during treatment under varying CXL conditions.

RESULTS

Increases in energy dosage achieved significant increases in resistance to stress in all variations except when comparing protocols A and B under normoxic conditions. Supplemental oxygen significantly increased rigidity in protocols B (p < 0.01) and C (p = 0.018). Hyperoxic conditions significantly increased resistance to digestion in all protocols. The number of DNA strand breaks in TUNEL assay staining showed significant increases in all increases in energy as well as with oxygen supplementation.

CONCLUSIONS

Increases in energy and supplemental oxygen improved the effect of CXL, though endothelial safety could not be verified with confidence in high-fluence CXL with supplemental oxygen. Results suggest that CXL protocols using 7.2 J/cm² with 100% O₂ or 10 J/cm² without supplemental oxygen prove most effective without anticipated risk of endothelial damage.

[Principles of corneal cross-linking : Presentation based on the development of the various treatment protocols]

BACKGROUND

Corneal cross-linking (CXL) is used to treat corneal ectatic diseases. The aim is to improve the reduced consolidation of the cornea in order to halt further corneal protrusion and therefore subsequent deterioration of the optical imaging proportions.

MATERIAL AND METHODS

In this article the principles of corneal cross-linking based on riboflavin and UV light are presented including recent research results. Furthermore, the most important treatment protocols including standard CXL (S-CXL), accelerated CXL (A-CXL), transepithelial CXL (TE-CXL) and the approach of the CXL procedure for thin corneas are explained.

RESULTS

The CXL method depends on four major components, the riboflavin solution, oxygen, UV light and the availability of cross-linking sites on the collagen tissue. According to the present state of knowledge, the photochemical process of the CXL method induces covalent bonds between the fibrils and proteoglycans and thus stabilizes the collagen fibers, resulting in corneal consolidation. In addition to the S‑CXL, which has proven its effectiveness and safety in a large number of studies, there are other treatment protocols that have been developed based on the Bunsen-Roscoe law of reciprocity. The A‑CXL protocol has the advantage of having a shorter irradiation time but it seems to be less effective than the S‑CXL protocol concerning the increase in corneal stiffness. The use of TE-CXL has so far not yet gained acceptance in the clinical practice.

CONCLUSION

The CXL procedures primarily aim to stabilize the cornea. In the future, in addition to stabilization of the cornea, simultaneous improvement of visual acuity will be the main focus.