Conservative Treatment of Keratoconus by Riboflavin-UVA-Induced Cross-Linking of Corneal Collagen: Qualitative Investigation of Corneal Epithelium and Subepithelial Nerve Plexus Regeneration by in vivo HRT II System Confocal Microscopy in Humans

Safety of accelerated corneal collagen cross-linking in keratoconus patients on the basis of macular segmentation

PURPOSE

To investigate the safety of accelerated corneal collagen cross-linking (A-CXL) in patients with keratoconus on the basis of thickness analysis measurements of retinal layers and retinal morphology.

STUDY DESIGN

This was a retrospective and comparative study.

METHODS

The study included 64 eyes of 32 patients with keratoconus disease. One eye of the patients underwent A-CXL for progressive keratoconus (CXL group) and the fellow eye was followed due to the absence of progression. Patients with at least 1-year follow-up after A-CXL were included. Keratometry, pachymetry and corrected-distance visual acuity (CDVA) levels of the patients were compared. The segmentation analysis of the individual retinal layers of the eyes with (CXL group) and without CXL (no CXL group) was compared with spectral domain-optical coherence tomography automatic segmentation program at baseline and at the last follow-up. The thickness of the retinal nerve fiber layer, ganglion cell layer, inner plexiform layer, inner nuclear layer, outer plexiform layer, outer nuclear layer and retina pigment epithelium layer in the central 1-mm subfield defined by the ETDRS was analyzed.

RESULTS

The mean age of keratoconus patients was 23.9 ± 5.4 years, patients were more likely to be male (21/11, 65.6%), and the mean follow-up duration was 13.9 ± 1.5 months. When keratometry, pachymetry and CDVA levels were compared, only a significant difference was found between CDVA at the last follow-up (0.21 vs. 0.11 LogMAR). No significant difference was observed in neither retinal morphology nor segmentation of individual retinal layers at baseline and at the final evaluation (P > 0.05).

CONCLUSIONS

It has been observed that the A-CXL protocol did not cause a significant change in both retinal layer thickness and macular morphology.

Morphology of the Corneal Limbus Following Standard and Accelerated Corneal Collagen Cross-Linking (9 mW/cm2) for Keratoconus

PURPOSE

To evaluate the morphological features of the corneal limbus as measured by in vivo confocal microscopy (IVCM) following standard and accelerated corneal collagen cross-linking (CXL) for keratoconus.

METHODS

Patients with progressive keratoconus scheduled to undergo standard CXL (group 1; 31 patients, 3 mW/cm, 370 nm, 30 minutes), or accelerated CXL (group 2; 20 patients, 9 mW/cm, 370 nm, 10 minutes) in the worse eye were included in this prospective study. Thirty eyes of 30 age-matched patients served as controls (group 3). All patient eyes underwent IVCM scanning of the central cornea and the inferior limbal area at baseline and 1, 3, and 6 months after CXL.

RESULTS

After CXL, epithelial regrowth was complete by day 4 in both groups 1 and 2. There were no statistically significant differences between the baseline mean central corneal wing or basal cell density, limbus-palisade middle or basal cell densities of groups 1, 2, or 3. At postoperative months 1, 3, and 6, there were no statistically significant differences in either central or limbus-palisade epithelial cell densities or diameters in keratoconic eyes that underwent standard or accelerated CXL (P > 0.05). The morphology of the limbal cells was preserved as well.

CONCLUSIONS

The morphology of limbus structures seems to be preserved following standard and accelerated CXL in short-term follow-up, as measured using IVCM.

In Vivo Confocal Microscopy of Corneal Nerves in Health and Disease

In vivo confocal microscopy (IVCM) is becoming an indispensable tool for studying corneal physiology and disease. Enabling the dissection of corneal architecture at a cellular level, this technique offers fast and noninvasive in vivo imaging of the cornea with images comparable to those of ex vivo histochemical techniques. Corneal nerves bear substantial relevance to clinicians and scientists alike, given their pivotal roles in regulation of corneal sensation, maintenance of epithelial integrity, as well as proliferation and promotion of wound healing. Thus, IVCM offers a unique method to study corneal nerve alterations in a myriad of conditions, such as ocular and systemic diseases and following corneal surgery, without altering the tissue microenvironment. Of particular interest has been the correlation of corneal subbasal nerves to their function, which has been studied in normal eyes, contact lens wearers, and patients with keratoconus, infectious keratitis, corneal dystrophies, and neurotrophic keratopathy. Longitudinal studies have applied IVCM to investigate the effects of corneal surgery on nerves, demonstrating their regenerative capacity. IVCM is increasingly important in the diagnosis and management of systemic conditions such as peripheral diabetic neuropathy and, more recently, in ocular diseases. In this review, we outline the principles and applications of IVCM in the study of corneal nerves in various ocular and systemic diseases.

Effects of Corneal Collagen Crosslinking on Confocal Microscopic Findings and Tear Indices in Patients with Progressive Keratoconus

Background:

To evaluate any change in tear indices and confocal microscopic findings after corneal collagen crosslinking (CXL) in patients with progressive keratoconus.

Methods:

Thirty-two consecutive eyes from 23 patients having progressive keratoconus were enrolled in this prospective, interventional cohort study. The standard crosslinking surgery was performed for all patients. Visual, refractive, and topographic evaluations were done before and at 6 months after surgery. Tear function tests and confocal microscopic examination were performed before and at 1 month and 6 months after the procedure.

Results:

There was no significant change in Schirmer-1 test results and tear osmolarity at 1 month and 6 months after CXL. Using confocal microscopy, all eyes showed reduced or absent subepithelial nerve plexus. Differences in basal epithelial cell density, epithelial mean cell area, and keratocyte density in anterior and middle stroma and endothelial cell pleomorphism were all significant at 1 month and 6 months after CXL (P < 0.05). No significant change was noted in endothelial cell count and their polymegathism at 6 months follow-up. Significant improvement was noted in uncorrected visual acuity, best corrected visual acuity, flattest corneal meridian (K₂), and maximum keratometry in Pentacam (K_max) after 6 months of the procedure.

Conclusions:

While CXL would have no effect on tear indices and endothelial cell count, it can cause a significant reduction in subepithelial nerve plexus and significant alterations in epithelial cell density in the anterior and middle stroma.

In Vivo Confocal Microscopy after Corneal Collagen Crosslinking

In vivo confocal microscopy (IVCM) findings of 84 patients who had undergone conventional epithelium-off corneal collagen crosslinking (CXL) and accelerated CXL (ACXL) were retrospectively reviewed. Analysis confirmed that despite a significant decrease in the mean density of anterior keratocytes in the first 6 postoperative months, cell density after CXL and ACXL returned to baseline values at 12 months. The demarcation lines observed after treatments represent an expression of light-scattering (reflectivity changes) through different tissue densities. Temporary haze of the anterior-mid stroma after conventional CXL represents an indirect sign of CXL-induced stromal collagen compaction and remodeling. IVCM showed that treatment penetration varies to some extent, but that the endothelium is not damaged and is correlated with CXL biomechanical effects. IVCM of limbal structures shows no evidence of pathological changes. Regeneration of subepithelial and stromal nerves was complete 12 months after the operation with fully restored corneal sensitivity and no neurodystrophic occurrences. IVCM allowed detailed high magnification in vivo micromorphological analysis of corneal layers, enabling the assessment of early and late corneal modifications induced by conventional and accelerated CXL. IVCM confirms that CXL is a safe procedure, which is still undergoing development and protocol adjustments.

First proposed efficacy study of high versus standard irradiance and fractionated riboflavin/ultraviolet a cross-linking with equivalent energy exposure

PURPOSE

To document the first presented report in December 2008 of high irradiance riboflavin/ultraviolet A (UVA) corneal cross-linking in comparison with that of standard irradiance and of fractionated exposure to increase the time for oxygen diffusion into the cornea.

METHODS

After in vitro studies of oxygen depletion and cross-linking density using type 1 human collagen gels, 36 ex vivo porcine globes were deepithelialized and exposed to 0.1% riboflavin drops in carboxymethylcellulose solution every 5 min for 3 initial doses and then throughout irradiation afterward. Six eyes each were irradiated with 370-nm UVA light at 2, 3, 9, and 15 mW/cm continuously and 15 mW/cm fractionated (with alternate cycles of 30 s "ON" and 30 s "OFF" exposure) using an equivalent radiant exposure of 5.4 mJ/cm. The final six eyes received no UVA exposure as a control. The exposed corneas were then dissected and subjected to extensiometry. Analysis of variance with Bonferroni post hoc test was performed between groups.

RESULTS

The stress required to induce a 10% strain for the control eyes (no UVA) was 100.6±20.9×10 N/m in comparison with the stress of 3 mW/cm (standard irradiation) at 146.7±17.6×10 N/m (P=0.009). The stress at the other equidose irradiances of 2, 9, 15 continuously, and 15 mW/cm fractionated were 140±21.9, 162.8±70, 154.1±70, and 163.0±64×10 N/m, respectively. When comparing the irradiances of 15 mW/cm continuously and fractionated to the standard irradiation, the stress was not statistically different (P=0.799 and 0.643), respectively.

CONCLUSION

High irradiance riboflavin/UVA cross-linking with equivalent energy exposure demonstrates comparable efficacy in stiffening corneal collagen with standard irradiance, but with considerably less exposure time. Over the past 6 years, since this report was first presented, the use of high irradiance cross-linking has been gaining popularity.

Standard versus trans-epithelial collagen cross-linking in keratoconus patients suitable for standard collagen cross-linking

PURPOSE

Evaluating the clinical results of trans-epithelial collagen cross-linking (CXL) and standard CXL in patients with progressive keratoconus.

METHODS

This prospective study comprised 20 eyes of 20 patients with progressive keratoconus. Ten eyes were treated by standard CXL and ten by trans-epithelial cross-linking (TE-CXL, epithelium on) with 1 year of follow-up. All patients underwent complete ophthalmologic testing that included pre- and postoperative uncorrected visual acuity, corrected visual acuity, spherical error, spherical equivalent, corneal astigmatism, simulated maximum, minimum, and average keratometry, coma and spherical aberration, optical pachymetry, and endothelial cell density. Intra-and postoperative complications were recorded. The solution used for standard CXL comprised riboflavin 0.1% and dextran 20.0% (Ricrolin), while the solution for TE-CXL (Ricrolin, TE) comprised riboflavin 0.1%, dextran 15.0%, trometamol (Tris), and ethylenediaminetetraacetic acid. Ultraviolet-A treatment was performed with UV-X System at 3 mW/cm(2).

RESULTS

In both the standard CXL group (ten patients, ten eyes; mean age, 30.4±7.3 years) and the TE-CXL group (ten patients, ten eyes; mean age, 28±3.8 years), uncorrected visual acuity and corrected visual acuity improved significantly after treatment. Furthermore, a significant improvement in topographic outcomes, spherical error, and spherical equivalent was observed in both groups at month 12 posttreatment. No significant variations were recorded in other parameters. No complications were noted.

CONCLUSION

A 1-year follow-up showed stability of clinical and refractive outcomes after standard CXL and TE-CXL.

Comparison of clinical results of two pharmaceutical products of riboflavin in corneal collagen cross-linking for keratoconus

Background

To compare the 6-month results of two formulations of Riboflavin provided by Sina Darou, Iran, and Uznach, Switzerland, in corneal collagen cross-linking (CXL) for keratoconus patients.

Findings

Considering the results of the previous study about the similarity of the formulations and the active ingredients of the two types of Riboflavin, they were used in the CXL procedure of 60 keratoconic eyes (30 eyes in each group). After 6 months, the mean improvement of UCVA (0.239), BCVA (0.707), and MRSE (0.513) did not differ significantly between the two groups. The mean decrease in max- K (0.731), mean- K (0.264), central corneal thickness (0.759), and Q-value (0.669) did not show any significant difference between the two groups. The two groups had no significant difference in endothelial cell count decrease (0.229). The Sina Darou formulation decreased corneal hysteresis more than the Swiss formulation (P = 0.057) but there were no significant differences in the mean decrease of corneal resistance factor between the two groups (P = 0.117).

Conclusions

Based on the early results, the results of visual acuity, refraction, and corneal topography using Sina Darou and Uznach formulations of Riboflavin showed that both were effective in CXL. However, considering the relatively significant difference in corneal hysteresis changes between the two groups, this study will continue to report the long-term results.

A case of medication-resistant acanthamoeba keratitis treated by corneal crosslinking in Turkey

Purpose. To report a case of medication-resistant acanthamoeba keratitis (AK) treated successfully by corneal crosslinking (CXL). Methods. A 26-year-old male with medication-resistant AK underwent a standard CXL procedure with local anesthesia, followed by central corneal epithelial debridement, application of riboflavin 0.1%, and UV-A irradiation. Results. The patient experienced a dramatic symptomatic improvement within 24 hours. At two months, keratitis was healed with a semitransparent paracentral scar that did not affect visual acuity. Conclusions. Our experience, considered in the context of recent studies, suggests that CXL may be an option for selected patients with medication-resistant AK and corneal melting. CXL allows patients to avoid emergency keratoplasty and experience rapid symptomatic relief.

Corneal sensitivity in keratoconus: a review of the literature

Corneal sensitivity has recently received much attention given the crucial role the corneal nerves play in maintaining normal corneal structure and function. An increased understanding of the corneal sensitivity and dry eye disease in keratoconus, including alterations of the conjunctival cells, may help explain the pathogenesis of this disorder. There is histological evidence of the involvement of corneal nerves in the pathology of keratoconus and it has been suggested that this plays a role in the pathophysiological features and progression of the disease. In this review, the impaired corneal sensitivity found on keratoconus and corneal sensitivity changes after cross-linking performed in patients with keratoconus are reported.

Intraoperative and postoperative corneal thickness change after collagen crosslinking therapy

PURPOSE

To assess intraoperative and postoperative changes in corneal thickness subsequent to riboflavin-UVA (collagen crosslinking [CXL]) treatment.

METHODS

Forty-one eyes of 41 patients (mean age 27.97 ± 6.97 years) were treated with CXL technique. During treatment, isotonic riboflavin was instilled and corneal thickness measurements were obtained at the cornea apex, the thinnest point, and the pupil center at 15 and 30 minutes, then 3 days, 1 week, and 1, 3, 6, and 12 months after surgery using Pentacam HR and an ultrasound pachymeter.

RESULTS

A decrease in corneal thickness was detected 15 minutes intraoperatively with a value of 108.95 ± 48.6 µm, and 112.35 ± 47.3 µm at 30 minutes (p<0.001). Three days after the operation, no deviation was found from the initial values (p = 0.17). No further changes were detected during the follow-up period.

CONCLUSIONS

Isotonic riboflavin solution used during CXL treatment resulted in a significant decrease in corneal thickness, but its effect had disappeared by postoperative day 3.

Corneal Debridement Update: Adjuvant Therapies and Wound Healing

Corneal debridement techniques have seen evolution in instrumentation and indication. Although the techniques themselves are simple and usually effective, there is often the need for adjuvant topical therapies to augment healing and/or prevent recurrence of disease. To better understand the requirement for adjuvant therapies, the current theories of corneal wound healing are reviewed.

Transepithelial corneal collagen crosslinking for progressive keratoconus in a pediatric age group

PURPOSE

To evaluate the effectiveness and safety of transepithelial corneal collagen crosslinking (CXL) in children with keratoconus and the refractive changes induced by this treatment.

SETTING

Ophthalmology Department, Ain-Shams University Hospitals, Cairo, Egypt.

DESIGN

Prospective comparative case series.

METHODS

Patients younger than 18 years with bilateral keratoconus had transepithelial CXL with the use of transepithelial riboflavin. The other eye was used as a control and was treated conservatively. The uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), and corneal tomography at 12 months were the main outcome measures.

RESULTS

The mean age of the 22 patients (22 eyes) was 15.7 years ± 2.1 (SD). After transepithelial CXL, the improvement in the mean UDVA was statistically significant (from 0.95 ± 0.34 logMAR to 0.68 ± 0.45 logMAR) (P<.05). No eye lost lines of preoperative UDVA; 1 eye lost 1 line of preoperative CDVA. There was no improvement in the control group in UDVA or CDVA (P>.05). The mean simulated keratometry (K) decreased by a mean of 2.03 diopters (D), with mean flattening of the apical K by 2.20 D; both results were statistically significant (P<.05). In the control group, the simulated K increased by a mean of 0.59 D (P>.05), with mean steepening of the apical K by 2.9 D (P<.05). No significant changes occurred in the endothelial cell count in either group.

CONCLUSION

Preliminary results of transepithelial CXL in children with keratoconus were encouraging, with no evidence of progression of keratoconus over 12 months.

Transepithelial corneal collagen crosslinking for progressive keratoconus: 24-month clinical results

PURPOSE

To assess the clinical results of transepithelial collagen crosslinking (CXL) in patients 26 years and younger with progressive keratoconus suitable for epithelium-off (epi-off) CXL.

SETTING

Department of Ophthalmology, Siena University Hospital, Siena, Italy.

DESIGN

Prospective case series.

METHODS

The study included 26 eyes (26 patients) treated by transepithelial (epithelium-on) CXL. The mean age was 22 years (range 11 to 26 years) (10 younger than 18 years; 16 between 19 years and 26 years). Preoperative and postoperative examinations included uncorrected (UDVA) and corrected (CDVA) distance visual acuities, simulated maximum keratometry (K), coma and spherical aberration, and corneal optical coherence tomography optical pachymetry. The solution for transepithelial CXL (Ricrolin TE) comprised riboflavin 0.1%, dextran 15.0%, trometamol (Tris), and ethylenediaminetetraacetic acid. Ultraviolet-A treatment was performed with the Caporossi Baiocchi Mazzotta X Linker Vega at 3 mW/cm(2).

RESULTS

After relative improvement in the first 3 to 6 months, the UDVA and CDVA gradually returned to baseline preoperative values. After 12 months of stability, the simulated maximum K value worsened at 24 months. Coma aberration showed no statistically significant change. Spherical aberration increased at 24 months. Pachymetry showed a progressive, statistically significant decrease at 24 months. Fifty percent of pediatric patients were retreated with epi-off CXL due to significant deterioration of all parameters after 12 months of follow-up.

CONCLUSIONS

Functional results after transepithelial CXL showed keratoconus instability, in particular in pediatric patients 18 years old and younger; there was also functional regression in patients between 19 years and 26 years old after 24 months of follow-up. mentioned.

Early confocal microscopy findings after cross-linking treatment

OBJECTIVE

To determine the effects of in vivo cross-linking treatment of the cornea.

METHODS

Eighteen eyes of eighteen keratoconus patients underwent cross-linking treatment using a 0.1% riboflavin solution and ultraviolet A radiation at 370 nm at 3 mW/cm² for 30 minutes. In vivo confocal microscopy was performed before, and at 1 week and 1 month after treatment.

RESULTS

At 1 week after treatment, keratocyte activation and collagen fiber organization showed as hyper-reflective structures and were observed from the first sub-epithelial image to a corneal stromal depth of 275.1 ± 85.9 μm. At 1 month after treatment, activated keratocytes and fiber organization were also observed from the first sub-epithelial image to a corneal stromal depth of 324.9 ± 66.0 μm. The deepest hyper-reflective structures at 1 month showed as thick, linear-shaped hyper-reflective structures.

CONCLUSION

In vivo confocal microscopy in humans showed corneal stromal changes at 1 week and 1 month after cross-linking treatment, in some cases at depths in excess of 300 μm.

Transepithelial corneal collagen crosslinking for keratoconus: qualitative investigation by in vivo HRT II confocal analysis

PURPOSE

This was a qualitative investigation of corneal microstructural modifications in keratoconic patients undergoing experimental transepithelial crosslinking (TE CXL).

METHODS

Ten patients with keratoconus intolerant to gas-permeable rigid contact lenses were enrolled. Corneal thickness was in the range 350-390 µm at the thinnest point measured by Visante AC optical coherence tomography system (Zeiss, Jena, Germany). All patients underwent TE CXL with 0.1% riboflavin-15% dextran solution supplemented with TRIS plus sodium EDTA (Ricrolin TE, Sooft Italia) according to Siena protocol. In vivo Heidelberg retinal tomograph II laser scanning confocal analysis (Rostock Cornea Module, Heidelberg, Germany) was performed with the following follow-up: preoperative and postoperative assessments at 1, 3, and 6 months. The following morphologic parameters were evaluated: epithelium, subepithelial, and anterior stroma nerve plexi, keratocytes apoptosis, stromal changes, and the endothelium.

RESULTS

After TE CXL, epithelial cells showed apoptosis, with mosaic alterations gradually disappearing. Keratocytes apoptosis was variable, superficial, and uneven, with a maximum depth of penetration at about 140 µm, measured from the surface of epithelium. Treatment respected subepithelial and stromal nerves that did not disappear. No variation in cell count or endothelial mosaic was observed.

CONCLUSIONS

In vivo confocal analysis of corneal modifications induced by TE CXL showed a limited apoptotic affect of this treatment, about one-third of classic epi-off crosslinking procedure. The TE CXL respected sub-basal and anterior stroma nerve fibers, resulting safe for corneal endothelium. According to limited penetration, its mid- to long-term efficacy needs to be determined in different clinical settings related to patient age and keratoconus progression.

Morphological and functional correlations in riboflavin UV A corneal collagen cross-linking for keratoconus

PURPOSE

To investigate the correlations between corneal structural modifications assessed by in vivo corneal confocal microscopy with visual function [uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA)] and morphological data (corneal topography, pachymetry, elevation analysis) after riboflavin UV A corneal collagen cross-linking (CXL) for the stabilization of progressive keratoconus.

METHODS

Forty-four eyes with progressive keratoconus were enrolled in the Siena Eye Cross Study (prospective nonrandomized phase II open trial). All eyes underwent Riboflavin UV A CXL. Preoperative and postoperative evaluation comprised: UCVA, BSCVA, optical pachymetry (Visante OCT, Zeiss, Germany), corneal topography (CSO, Florence, Italy) and tomography (Orbscan IIz; B&L, Rochester, NY, USA) and in vivo confocal microscopy (Heidelberg Retina Tomograph II; Rostock, Heidelberg Gmbh, Germany). Examinations were performed preoperatively 6 months and one day before treatment and at 1, 3, 6 and 12 months of follow-up.

RESULTS

In vivo corneal confocal microscopy showed time-dependent postoperative epithelial and stromal modifications after cross-linking. Epithelial thinning associated with stromal oedema and keratocytes apoptosis explained initial tendency towards slightly reduced VA and more glare one month postoperatively in 70% of eyes. Furthermore, a statistically not significant early worsening of topographic mean K values was observed. Orbscan II analysis significantly underestimated pachymetric values after treatment. Pachymetric underestimation was rectified by high-resolution optical pachymetry provided by the Visante OCT system. After the third post-CXL month, epithelial thickening, disappearance of oedema and new collagen compaction recorded by in vivo corneal confocal microscopy explained the improvements in visual performance during the follow-up. Changes in stromal reflectivity and collagen compaction observed by in vivo confocal microscopy were associated with corneal flattening and reduction in anterior elevation values recorded by differential topographic analysis.

CONCLUSION

Corneal structural changes assessed by in vivo corneal confocal microscopy demonstrated significant correlations with visual function (UCVA and BSCVA) and morphological (corneal topography, pachymetry, elevation analysis) findings recorded after riboflavin-UV A-induced CXL.

The effect of standard and transepithelial ultraviolet collagen cross-linking on human corneal nerves: an ex vivo study

PURPOSE

To evaluate the early effect of standard and transepithelial collagen cross-linking on human corneal nerves in donor eyes by ex vivo confocal microscopy and acetylcholinesterase staining.

DESIGN

Experimental laboratory investigation.

METHODS

Eight human eye bank corneal buttons (mean age, 73.6 years) were included. Ultraviolet A collagen cross-linking was performed postmortem on 3 corneas with the standard protocol involving epithelial debridement and 4 corneas by the transepithelial approach. One cornea served as a control. Corneal nerves were evaluated using confocal microscopy and acetylcholinesterase histology.

RESULTS

Confocal microscopy demonstrated the absence of subbasal nerves in corneas treated by the standard technique. These nerves were preserved in corneas treated by the transepithelial approach. Stromal nerves were visible in both groups. Histology of corneas treated by the standard technique revealed localized swellings of the stromal nerves with disruption of axonal membrane and loss of axonal continuity within the treatment zone. These changes were absent in corneas treated by the transepithelial approach.

CONCLUSIONS

This study highlights the immediate effects of collagen cross-linking on the corneal nerves in an ex vivo model. The absence of subbasal nerves in the early phase of treatment appears to be attributable mainly to mechanical removal of epithelium, rather than ultraviolet light-induced damage. Localized swelling of the stromal nerves was the main difference between the 2 treatment protocols. Further research on laboratory animals would be necessary to verify these changes over a specified time course without the super-addition of postmortem changes.

Collagen cross-linking: current status and future directions

Collagen cross-linking (CXL) using UVA light and riboflavin (vitamin B2) was introduced as a clinical application to stabilize the cornea by inducing cross-links within and between collagen fibers. CXL has been investigated extensively and has been shown clinically to arrest the progression of keratoconic or post-LASIK ectasia. With its minimal cost, simplicity, and proven positive clinical outcome, CXL can be regarded as a useful approach to reduce the number of penetrating keratoplasties performed. Small case series have also indicated that CXL is beneficial in corneal edema by reducing stromal swelling behavior and in keratitis by inhibiting pathogen growth. Despite these encouraging results, CXL remains a relatively new method that is potentially associated with complications. Aspects such as side effects and recurrence rates have still to be elucidated. In light of the growing interest in CXL, our paper summarizes present knowledge about this promising approach. We have intentionally endeavored to include the more relevant studies from the recent literature to provide an overview of the current status of CXL.

Corneal collagen cross-linking with riboflavin and ultraviolet-A irradiation in patients with thin corneas

PURPOSE

To report the outcomes after corneal collagen cross-linking (CXL) treatment with riboflavin and ultraviolet-A (UVA) irradiation in patients with thin corneas (minimum corneal thickness less than 400 μm after epithelial removal and before riboflavin instillation).

DESIGN

Prospective case series.

METHODS

Twelve patients (14 eyes, with minimum corneal thickness less than 400 μm after epithelial removal) were included in the study. All patients underwent riboflavin-UVA-induced CXL using the standard CXL (Dresden) protocol. Uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA) (decimal scale), manifest refraction (diopters, D), and topography were evaluated at baseline and at 1, 3, 6, and 12 months follow-up. Images of the endothelium were acquired with a modified confocal scanning laser ophthalmoscope.

RESULTS

No intraoperative or postoperative complications were observed in this patient series. Mean minimum preoperative corneal thickness at the apex of the cone after epithelial removal and before riboflavin instillation was 373.92 ± 22.92 μm (range 340-399 μm). UDVA and CDVA improved from 0.25 ± 0.15 and 0.40 ± 0.20 to 0.27 ± 0.17 and 0.49 ± 0.20 respectively at the last follow-up examination. There was a reduction of the mean keratometry readings from 51.99 ± 5.57 D to 49.33 ± 4.82 D at the last follow-up. A significant decrease of endothelial cell density was observed (preoperative: 2733 ± 180 cells/mm(2) [range 2467-3016], last follow-up visit: 2441 ± 400 cells/mm(2) [range 1448-2920], P < .01).

CONCLUSIONS

CXL in thin corneas with minimum corneal thickness less than 400 μm after epithelial removal seems to result in a significant endothelial cell density decrease postoperatively. This finding was not related to other intraoperative or postoperative complications.

Transepithelial corneal collagen crosslinking: bilateral study

PURPOSE

To evaluate the efficacy of transepithelial collagen crosslinking (CXL) in patients with bilateral progressive keratoconus.

SETTING

Outpatient ophthalmic clinic.

DESIGN

Cohort study.

METHODS

Patients with a history of bilateral progressive keratoconus were recruited. The worst eye was treated with transepithelial CXL, while the fellow eye was left untreated as a control. Transepithelial CXL was performed by applying an enhanced riboflavin solution (riboflavin 0.1%, dextrane T500 with trometamol [Tris-hydroxymethyl aminomethane] and EDTA [ethylenediaminetetraacetic] sodium salt) on the intact corneal epithelium for 30 minutes before irradiation with ultraviolet A (370 nm at 3 mW/cm(2)) for 30 minutes. Follow-up was 18 months in all eyes.

RESULTS

The study enrolled 20 patients. Transient hyperemia and mild foreign-body sensation occurred in 8 eyes (40%) after treatment; both resolved after 24 hours. In treated eyes, there were statistically significant improvements in uncorrected and corrected visual acuity and topography-derived keratometry, cone apex power, and higher-order aberrations (P<.05). In untreated control eyes, there was a general trend toward worsening of these parameters. No complications were reported.

CONCLUSIONS

Transepithelial CXL treatment appeared to halt keratoconus progression, with a statistically significant improvement in visual and topographic parameters. The treatment was safe and well tolerated. Its noninvasive nature makes it potentially useful in cases in which epithelial debridement is ideally avoided, such as pediatric cases, uncooperative patients, and thin corneas with thicknesses nearing 380 μm.

Collagen cross-linking with riboflavin and ultraviolet-A light in keratoconus: One-year results

Background:

The aim of this study is to evaluate the safety and effectiveness of riboflavin-ultraviolet type A (UV-A) light rays induced cross-linking of corneal collagen in improving visual acuity and in stabilizing the progression of keratoconic eyes. The method of corneal cross-linking using riboflavin and UV-A light is technically simple and less invasive than all other therapies proposed for keratoconus. It is the only treatment that treats not only the refractive effects of the condition but the underlying pathophysiology.

Materials and Methods:

In this prospective, nonrandomized clinical study, 20 eyes of 19 patients with keratoconus were treated by combined riboflavin UV-A collagen cross linking. The eyes were saturated with riboflavin solution and were subjected for 30 min under UV-A light with a dose parameter of 3 mW/cm². Safety and effectiveness of the treatment was assessed by measuring the uncorrected visual acuity, best corrected visual acuity, manifest cylinder/sphere, keratometry, pachymetry, posterior and anterior elevations from Pentacam and corneal aberrations at 6 months and 1 year post-treatment.

Results:

Comparative analysis of the pre-operative and 1 year post-operative evaluation showed a mean gain of 4.15 lines of UCVA (P= 0.001) and 1.65 lines of BCVA (P= 0.002). The reduction in the average keratometry reading was 1.36 D (P= 0.0004) and 1.4 D (P= 0.001) at the apex. Manifest refraction sphere showed a mean reduction of 1.26 D (P= 0.033) and 1.25 D (0.0003) for manifest cylinder. Topo-aberrometric analysis showed improvement in corneal symmetry.

Conclusion:

Cross-linking was safe and an effective therapeutical option for progressive keratoconus.

The effects of riboflavin/ultraviolet: a corneal cross-linking on the signs and symptoms of bullous keratopathy

Purpose:

To evaluate the effectiveness of corneal cross-linking in improving the signs and symptoms of bullous keratopathy.

Materials and Methods:

This prospective non-randomized case series evaluated 20 eyes with bullous ketratopathy that underwent corneal cross-linking (C3R) with riboflavin and ultraviolet-A (UVA, 370 nm, 3 mW/cm²). C3R was performed for 30 min in a routine procedure after removal of epithelium. Central corneal thickness (CCT), corneal haze, visual acuity (VA), and the presence of irritating symptoms were recorded before the procedure, and at 1 week, 1 months, 3 months, and 6 months after the procedure.

Results:

The mean CCT was 872 ± 162 μm (range: 665-1180 μm) before the procedure. Following the procedure, CCT was 855 ± 175 μm after 1 week, 839 ± 210 μm after 1 month, 866 ± 185 μm after 3 months, and 863 ± 177 μm after 6 months (P>0.05, all visits). There was no significant improvement in VA or corneal clarity after 6 months. Improvement of the following symptoms: burning, pain, and foreign body sensation were reported after 6 months by 83.3%, 75.0%, and 66.7% of patients, respectively. Persistent epithelial defect occurred in five patients (25%) resolved with frequent lubrication and bandage contact lenses.

Conclusion:

The outcomes of this study indicate corneal cross-linking is not an effective treatment for bullous keratopathy with respect to VA and CCT, although it can improve irritation and discomfort.

Corneal cross-linking and safety issues

Purpose:

To compile the safety aspects of the corneal collagen cross-linking (CXL) by means of the riboflavin/UVA (370 nm) approach.

Materials and Methodology:

Analysis of the current treatment protocol with respect to safety during CXL.

Results:

The currently used UVA dose density of 5.4 J/cm² and the corresponding irradiance of 3 mW/cm² are below the known damage thresholds of UVA for the corneal endothelium, lens, and retina. Regarding the photochemical damages due to the free radicals the damage threshold for endothelial cells is 0.35 mW/cm². In a 400μm thick corneal stroma saturated with riboflavin, the irradiance at the endothelial level is about 0.18 mW/cm², which is a factor of 2 smaller than the damage threshold.

Conclusion:

As long as the corneal stroma treated has a minimal thickness of 400 microns (as recommended), neither corneal endothelium nor deeper structures such as lens and retina will suffer any damages. The light source should provide a homogenous irradiance avoiding hot spots.

Comparative in vivo confocal microscopical study of the cornea anatomy of different laboratory animals

PURPOSE

The aim of the present study was to analyze and compare in vivo morphology of healthy cornea of six different laboratory animals.

MATERIALS AND METHODS

One Pomeranian Coarsewool sheep, 5 Beagle dogs, 1 Norwegian and 2 Domestic Short-haired cats, 20 New Zealand White rabbits, 6 Wistar rats, and 10 Balb/c mice were included. The examination was performed bilaterally, using Heidelberg Retina Tomograph equipped with Rostock Cornea Module. The morphology of living corneal layers was visualized and compared between species. The central corneal thickness, density of keratocytes, and endothelial cells were quantified.

RESULTS

The epithelial multilayer showed a similarity in morphology between animal types, displaying three clearly distinguishable layers: superficial, intermediate, and basal. Subbasal nerve fibers were displayed as hyperreflective structures underneath basal cells. The subbasal fibers were confirmed in all species, however, the density varied between species. A pronounced Bowman's membrane was visualized in sheep. In all other species, however, a thin acellular layer with overlying nerve fibers could be seen between basal epithelial cells and anterior stroma. The keratocytes nuclei could be demonstrated in all species except for mice, where no nuclei but only reflective structures resembling keratocytes cell bodies were detected. Overall, the density of keratocytes nuclei was significantly higher in the anterior than in the posterior stroma. Besides endothelial cells density, the endothelial cells morphology was very similar among all species, except for sheep. The endothelial cells were displayed as polygonal structures with bright cytoplasm and dark borders. In sheep, the appearance of the endothelium was very poor because of a thick hyperreflective Descemet's membrane.

CONCLUSIONS

The present study will help researchers consider appropriate models for animal experiments, depending on focus of investigation. In vivo CLSM can be used for the characterization of the living cornea over time, thus, reducing the number of animal experiments.

Clinical outcomes of posterior chamber toric phakic intraocular lens implantation for the correction of high myopic astigmatism in eyes with keratoconus: 6-month follow-up

BACKGROUND

To assess the early clinical outcomes of toric implantable collamer lenses (toric ICL™, STAAR Surgical) for the correction of high myopic astigmatism with keratoconus.

METHODS

This study evaluated 27 eyes of 14 patients with spherical equivalents of -10.11 ± 2.46 D (mean ± standard deviation) and astigmatism of -3.03 ± 1.58 D who underwent toric ICL implantation for mild keratoconus. Before, and 1, 3 and 6 months after surgery, we assessed the safety, efficacy, predictability, stability, and adverse events of the surgery.

RESULTS

LogMAR uncorrected visual acuity (UCVA) and LogMAR best spectacle-corrected visual acuity (BSCVA) were -0.09 ± 0.16 and -0.15 ± 0.09 respectively, 6 months after surgery. The safety and efficacy indices were 1.12 ± 0.18 and 1.01 ± 0.25. At 6 months, 85% and 96% of the eyes were within ±0.5 and ±1.0 D respectively of the targeted correction. Manifest refraction changes of 0.00 ± 0.35 D occurred from 1 week to 6 months. No vision-threatening complications occurred during the observation period.

CONCLUSIONS

Toric ICL implantation was good in all measures of safety, efficacy, predictability, and stability for the correction of spherical and cylindrical errors in eyes with early keratoconus throughout the 6-month follow-up period, suggesting its viability as a surgical option for the treatment of such eyes.

The absorption characteristics of the human cornea in ultraviolet-a crosslinking

OBJECTIVES

With respect to the safety of ultraviolet-A (UVA) crosslinking for the corneal endothelium, an absorption coefficient is used that has been calculated in riboflavin soaked porcine corneas. We aim to validate this value for clinical use by measuring the absorption coefficient for UVA 365 nm in postmortem human corneas after instilling riboflavin on the corneal surface.

METHODS

Corneal thickness was measured in nine pairs of human donor eyes of which one eye was subjected to manual removal of the epithelium, whereas the epithelium of the fellow eye was left intact. Both eyes were instilled with riboflavin 0.1% in dextran 20% on the intact globe. After 20 min, the corneas were rinsed, and a corneoscleral button was trephined. The transmission of the cornea for UVA 365 nm was measured by transillumination, which allows calculation of the absorption coefficient.

RESULTS

Measurement of average corneal thickness was 658.5 +/- 51.5 microm when the epithelium was removed, and 758.3 +/- 98.8 microm without epithelial removal. The average transmittance for UVA 365 nm was 12.89 +/- 4.10% with epithelial debridement and 28.52 +/- 4.39% without (P<0.05). The resultant average absorption coefficient is 32 +/- 5 cm when the epithelium is removed and 17 +/- 2 cm when it is left intact (P<0.05).

CONCLUSIONS

Our results show an absorption coefficient for human corneas that is much lower than the values reported in the literature. This finding may be relevant when considering endothelial safety of the clinical crosslinking treatment.

Effects of riboflavin/UVA corneal cross-linking on keratocytes and collagen fibres in human cornea

PURPOSE

To evaluate the effects of corneal cross-linking on keratocytes and collagen fibres in human corneas.

METHODS

Fifteen corneal buttons were examined. Ten were from patients with keratoconus submitted to penetrating keratoplasty and five of them were treated with cross-linking 6 months before penetrating keratoplasty. Five normal corneal buttons from healthy donors were used as controls. All samples were prepared for TUNEL assay and Western blot analysis for the detection of keratocyte apoptosis and immunohistochemical analysis for the morphological evaluation of keratocytes and collagen fibre diameter.

RESULTS

Normal corneas exhibited no TUNEL-positive keratocytes and keratoconic and cross-linked corneas showed moderate apoptotic cells mainly in the anterior part of the stroma. This apoptotic trend was confirmed by the cleavage of poly (ADP-ribose) polymerase assessed using Western blot. The Ki-67 staining showed a significant increase in the keratocyte proliferation in cross-linked corneas compared with normal and keratoconus. In cross-linked corneas CD34-positive keratocytes were regularly distributed throughout the whole corneal stroma as in the control, and keratoconus was associated with patchy loss of immunoreactivity. The immunohistochemical analysis of collagen type I showed a significant increase in fibre diameter of cross-linked corneas compared with control and keratoconus.

CONCLUSION

Corneal cross-linking leads to keratocyte damage; after 6 months a repopulation by proliferating cells, a distribution of CD34-positive keratocytes as in control and an increase in collagen fibre diameter were observed. These modifications are the morphological correlate of the process leading to an increase in biomechanical stability.

Long-term results of riboflavin ultraviolet a corneal collagen cross-linking for keratoconus in Italy: the Siena eye cross study

PURPOSE

To report the long-term results of 44 keratoconic eyes treated by combined riboflavin ultraviolet A collagen cross-linking in the first Italian open, nonrandomized phase II clinical trial, the Siena Eye Cross Study.

DESIGN

Perspective, nonrandomized, open trial.

METHODS

After Siena University Institutional Review Board approval, from September 2004 through September 2008, 363 eyes with progressive keratoconus were treated with riboflavin ultraviolet A collagen cross-linking. Forty-four eyes with a minimum follow-up of 48 months (mean, 52.4 months; range, 48 to 60 months) were evaluated before and after surgery. Examinations comprised uncorrected visual acuity, best spectacle-corrected visual acuity, spherical spectacle-corrected visual acuity, endothelial cells count (I Konan, Non Con Robo; Konan Medical, Inc., Hyogo, Japan), optical (Visante OCT; Zeiss, Jena, Germany) and ultrasound (DGH; Pachette, Exton, Pennsylvania, USA) pachymetry, corneal topography and surface aberrometry (CSO EyeTop, Florence, Italy), tomography (Orbscan IIz; Bausch & Lomb Inc., Rochester, New York, USA), posterior segment optical coherence tomography (Stratus OCT; Zeiss, Jena, Germany), and in vivo confocal microscopy (HRT II; Heidelberg Engineering, Rostock, Germany).

RESULTS

Keratoconus stability was detected in 44 eyes after 48 months of minimum follow-up; fellow eyes showed a mean progression of 1.5 diopters in more than 65% after 24 months, then were treated. The mean K value was reduced by a mean of 2 diopters, and coma aberration reduction with corneal symmetry improvement was observed in more than 85%. The mean best spectacle-corrected visual acuity improved by 1.9 Snellen lines, and the uncorrected visual acuity improved by 2.7 Snellen lines.

CONCLUSIONS

The results of the Siena Eye Cross Study showed a long-term stability of keratoconus after cross-linking without relevant side effects. The uncorrected visual acuity and best spectacle-corrected visual acuity improvements were supported by clinical, topographic, and wavefront modifications induced by the treatment.

Polymicrobial keratitis after a collagen cross-linking procedure with postoperative use of a contact lens: a case report

PURPOSE

: To report a case of polymicrobial keratitis caused by Streptococcus salivarius, Streptococcus oralis, and coagulase-negative Staphylococcus sp. in a patient who underwent collagen cross-linking for keratoconus.

METHOD

: Case report.

RESULT

: A 32-year-old male presented with a 1-day history of a painful red eye, occurring 3 days after he had undergone a collagen cross-linking with riboflavin and UV-A on his left eye for keratoconus. He admitted to removing his bandage contact lens and cleaning it in his mouth before reapplying it in his eye. On presentation, a severe keratitis with an 8-mm epithelial defect and 360-degree ring infiltrate was found. Culture results from his contact lens were positive for S. salivarius and S. oralis, and coagulase-negative Staphylococcus sp. were grown from his corneal scrapings.

CONCLUSIONS

: Collagen cross-linking is a promising procedure for the treatment of progressive keratoconus with minimal reported side effects. However, the possibility of a secondary infection after the procedure exists because the patient is subjected to epithelial debridement and the application of a soft contact lens. The role of the UV light on the immune mechanisms of the cornea and its effect on corneal wound healing warrant further investigation.

Refractive, topographic, tomographic, and aberrometric analysis of keratoconic eyes undergoing corneal cross-linking

PURPOSE

To report refractive, topographic, tomographic, and aberrometric outcomes 12 months after corneal cross-linking (CXL) in eyes with progressive advanced keratoconus.

DESIGN

Prospective, nonrandomized, single-center clinical study.

PARTICIPANTS

Twenty-eight eyes undergoing CXL between April and June 2006.

INTERVENTION

Riboflavin-ultraviolet A (UVA)-induced CXL included instillation of 0.1% riboflavin-20% dextrane solution 30 minutes before UVA irradiation and every 5 minutes for an additional 30 minutes during irradiation.

MAIN OUTCOME MEASURES

Uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), sphere and cylinder refraction, topography, tomography, aberrometry, and endothelial cell count were evaluated at baseline and at 1, 3, 6, and 12 months follow-up.

RESULTS

Mean baseline UCVA and BSCVA were 0.17+/-0.09 and 0.52+/-0.17, respectively; 12-month mean UCVA and BSCVA were 0.27+/-0.08 and 0.72+/-0.16, a statistically significant difference (P<0.05). Mean spherical equivalent refraction showed a significant decrease of 0.41 diopters (D). Mean baseline simulated keratometry (SIM K) flattest and steepest meridians and SIM K average were 46.10, 50.37, and 48.08 D, respectively; at 12 months, 40.22, 44.21, and 42.01 D, respectively, were recorded, a difference that was significant for all 3 indices (P<0.05). Mean average pupillary power (APP) changed significantly from 47.50 to 41.04 D at 12 months (P<0.05) and apical keratometry (AK) from 58.94 to 55.18 D (P<0.05). The treated eyes showed no deterioration of the Klyce indices at 6 months postoperatively, whereas the untreated (contralateral) eyes did show deterioration. For a 3-mm pupil, there was a significant reduction (P<0.05) in whole eye (total), corneal, higher order, and astigmatic wavefront aberrations. A significant difference (P<0.05) in total coma and total spherical aberration after CXL was also observed. Mean baseline pupil center pachymetry and total corneal volume decreased significantly (P<0.05) to 470.09+/-29.01 microm and 57.17+/-3.21 mm(3) from baseline values of 490.68+/-30.69 microm and 59.37+/-4.36 mm(3), respectively. Endothelial cell counts did not changed significantly (P=0.13).

CONCLUSIONS

Corneal cross-linking seems to be effective in improving UCVA and BSCVA in eyes with progressive keratoconus by significantly reducing corneal APP, AK, and corneal and total wavefront aberrations at 1 year postoperatively.

Corneal healing after riboflavin ultraviolet-A collagen cross-linking determined by confocal laser scanning microscopy in vivo: early and late modifications

PURPOSE

To assess early and late micromorphological modifications of cross-linked corneas in vivo by means of Heidelberg Retinal Tomography (HRT) II confocal microscopy.

DESIGN

Prospective nonrandomized open trial.

METHODS

Micromorphological examination of 44 cross-linked keratoconic corneas was performed in vivo by HRT II confocal laser scanning microscopy. Riboflavin ultraviolet (UV)-A-induced corneal collagen cross-linking (CXL) was performed according to the Siena protocol: pilocarpin 1% drops 30 minutes before, topical anesthesia with lidocaine 4% drops 15 minutes before irradiation, mechanical scraping of epithelium (9-mm-diameter area), preirradiation soaking for 10 minutes in riboflavin solution 0.1% (Ricrolin, Sooft, Italy) applied every 2.5 minutes for 30 minutes, 30 minutes exposure to solid-state UVA illuminator (Caporossi; Baiocchi; Mazzotta, X-linker, CSO, Italy), 8-mm-diameter irradiated area, energy delivered 3 mW/cm(2). All patients were examined by confocal scans preoperatively and at the following times after treatment: one, three, and six months, and one, two, and three years.

RESULTS

No damage to the limbal region was observed. Epithelial regrowth was complete after four days of soft contact lens bandage. The anatomy of the subepithelial plexus was restored one year after the operation with full corneal sensitivity. Increased density of extracellular matrix in late postoperative period indicated cross-linked collagen to a depth of 340 microm expressed by a late demarcation line.

CONCLUSION

In vivo confocal microscopy showed early and late modification of corneal microstructure after the treatment. The three-year stability of CXL recorded could be related to increased cross-links formation, synthesis of well-structured collagen and new lamellar interconnections.

Haze-Bildung nach Vernetzungstherapie bei Keratokonus

The aim of cross-linking therapy is to prevent keratoconus progression and stabilize the present refractive situation. A 41-year-old man was treated with collagen cross-linking in one eye. Postoperatively there were a diffuse subepithelial opacification and a paracentral corneal thinning. This superficial scarring in the sense of a "haze" disappeared only gradually despite intensive therapy.