Ординатура / Офтальмология / Английские материалы / Mastering Corneal Collagen Cross-linking Techniques (C3-R CCL CxL)_Garg, Kanellopoulos, O'Brart, Lovisolo, Pinelli_2008

Figure 16.2: UVA radiation with riboflavin 0.1%

One month after cross-linking treatment, contact lens use could be started. The durability of the stiffening effect is unknown. Because the collagen turnover in the cornea is estimated to be between 2 to 3 years, a repeat treatment may become necessary in the long run.3,11

CLINICAL RESULTS

The first clinical results of collagen cross-linking in keratoconus were reported by a research group from Dresden University in 2003. In this study, 23 eyes of 22 patients with keratoconus were included and only one eye of each patient was treated except one case that was treated bilaterally. The follow-up period was from 3 to 47 (23.2 ± 12.9) months. The BCVA improved in 65% of the patients by an average of 1.26 lines. The refractive correction improved by an average of 1.14D. In 70% of the patients, maximum K was flattened by an average of 2.01 D. K value remained stable in 5 patients and in 1 patient, an increase of 0.28 D was present. In 22% of the fellow control eyes, however, maximum K value increased by an average of 1.48D.3 The same research group later published their longterm results in 2008 on 153 eyes of 111 patients. The minimal follow-up time was 12 months and the maximum follow-up time was 7.5 years. Keratectasia significantly decreased in the 1st year by 2.29 D, in the 2nd year by 3.27 D, and in the 3rd year by 4.34 D. Visual acuity improved significantly in at least one

line or remained stable (i.e., no line loss) in the 1st year in 48.9% and 23.8%, respectively; in the 2nd year in 50.7% and 29.6%, respectively; and in the 3rd year in 60.6% and 36.4%, respectively. No severe side effects were observed. Three patients showed continuous progression of keratoconus and received cross-linking treatment again.12

Wiitig-Silva C et al reported the preliminary results of a randomized, controlled trial enrolling 66 eyes of 49 patients with documented progression of keratoconus. Interim analysis of treated eyes showed a flattening of the steepest simulated keratometry value (K-max) by an average of 0.74 diopters (D) at 3 months, 0.92 D at 6 months, and 1.45 D at 12 months. A trend toward improvement in best spectacle-corrected visual acuity was also observed. In the control eyes, mean K- max steepened by 0.60 D after 3 months, by 0.60 D after 6 months, and by 1.28 D after 12 months. Best spectacle-corrected visual acuity decreased by logMAR 0.003 (P = .883) over 3 months, 0.056 (P = .092) over 6 months, and 0.12 (P = .036) over 12 months. No statistically significant changes were found for spherical equivalent or endothelial cell density. These results suggest stabilization of cross-linked eyes.13

Cross-linking has also been effective following inferior-segment INTACS implantation. The addition of collagen cross-linking to the INTACS procedure resulted in greater reduction in cylinder, steep and average keratometry and lower-upper ratio in corneal topography than INTACS insertion alone.14

Since cross-linking stabilized keratoconus, the idea of treating the refractive error with PRK after crosslinking evolved. One year after cross-linking treatment, PRK was performed in one eye of a keratoconus case and an UCVA of 20/20 was achieved. This refractive result remained stable during a follow-up period of 18 months.15

RISKS AND SIDE EFFECTS

The harmful effects of UV light to the eye such as photokeratitis is well-known. This photochemical damage is caused, however, by UV-B-light. Corneal epithelium mainly absorbs UV-B (290-320 nm) in photokeratitis.2

In cross-linking treatment, a small peak-like sector of the UV-A spectrum (370 nm) is used. By the help of

photosensitizer riboflavin, UV-A absorption in the 9 5

cornea is increased, resulting in a UV-A transmission of only 7% across the cornea.2 In rabbit eyes, the cytotoxicity threshold for corneal endothelial cells is 0.36 mW/cm’. By using standard surface UVA dose of 3 mW/cm2, this cytotoxic level could only be reached if the cornea is thinner than 400 μm. Therefore, in thinner corneas, irradiation should not be performed because of the cytotoxic risk to the endothelium.16,17

The cataractogenic dose of UV-A is 70 J/cm2. With the current treatment parameters, the lens only receives 0.65 J/cm2 which is far below the cataractogeneous level. In addition, lens damage is usually induced by UV-B light which has a higher energy because of a shorter wavelength than UV-A.3

The retinal damage with complete loss of photoreceptor layer in rhesus monkeys was reported at a UVA dose of 81 mW/cm2 which is not reached with the standard treatment protocol.2

In the early clinical studies of cross-linking, no side effects other than transient corneal edema and foreign body sensation which lasts 24-48 hours were reported.

No persistent epithelial defect of the cornea, endotheliopathy, cataract and glaucoma were observed. However in 2007, corneal haze after collagen linking was reported by various authors. In one case report, corneal haze after cross-linking treatment for keratoconus disappeared only gradually despite intensive topical anti-inflammatory therapy.18 In a clinical study, haze that is not effecting vision was developed in 2 of 5 eyes with grade 3 keratoconus (according to Krumeich keratoconus clinical staging). No haze was observed in grade I or II eyes. In vivo confocal microscopy of the eyes that developed haze revealed reticular hyporeflective microstriae preoperatively. The authors suggested that the detection of reticular hypo-reflective microstriae by in vivo confocal analysis could represent a relative contraindication to perform cross-linking.19

The effect of cross-linking treatment on epithelium and subepithelial/stromal nerve plexus was studied by in vivo HRT II confocal microscopy in humans. The epithelium reached regular morphology and density in 5 days. Disappearance of subepithelial stromal nerve fibers was observed in the central irradiated area where, 1 month after the operation, initial reinnervation was observed. Six months after the operation, the anterior subepithelial stroma recolonized by nerve

9 6 fibers with restoration of corneal sensitivity.20

Corneal melting on a case with severe atopic disease and keratoconus following cross-linking and deep anterior lamellar keratoplasty (DALK) due to subclinical infection with Herpes simplex virus (HSV) was reported. Penetrating keratoplasty and intensive antiviral and immunosuppressive medical treatment were necessary to control that infection.21

REFERENCES

1.Feder RS, Kshettry P. Noninflammatory ectatic disorders. In: Krachmer JH, Mannis MJ, Holland EJ, (Eds): Cornea, China, Elsevier Mosby 2005;955-74.

2.Wollensak G. Cross-linking treatment of progressive keratoconus: new hope. Curr Opin Ophthalmol 2006;17(4):356-60.

3.Wollensak G, Spoerl E, Seiler T. Riboflavin/ultraviolet-a- induced collagen cross-linking for the treatment of keratoconus. Am J Ophthalmol 2003;135(5):620-27.

4.Wollensak G, Spoerl E, Seiler T. Stress-strain measurements of human and porcine corneas after riboflavin-ultraviolet—A induced cross-linking. J Cat Refract Surg 2003;29(9):1780-85.

5.Spoerl E, Wollensak G, Dittert DD, Seiler T. Thermomechanical behavior of collagen-cross-linked porcine cornea. Ophthalmologica 2004;218(2):136-40.

6.Wollensak G, Wilsch M, Spoerl E, Seiler T. Collagen fiber diameter in the rabbit cornea after collagen cross-linking by riboflavin/UVA. Cornea 2004;23(5):503-07.

7.Spoerl E, Wollensak G, Seiler T. Increased resistance of crosslinked cornea against enzymatic digestion. Curr Eye Res 2004;29(1):35-40.

8.Wollensak G, Redl B. Gel electrophoretic analysis of corneal collagen after photodynamic cross-linking treatment. Cornea 2008;27(3):353-56.

9.Wollensak G, Aurich H, Pham DT, Wirbelauer C. Hydration behavior of porcine cornea crosslinked with riboflavin and ultraviolet A. J Cataract Refract Surg 2007;33(3):516-21.

10.Wollensak G, Spoerl E, Wilsch M, Seiler T. Keratocyte apoptosis after corneal collagen cross-linking using riboflavin/UVA treatment. Cornea 2004;23(1):43-49.

11.Mazzotta C, Balestrazzi A, Traversi C, Baiocchi S, Caporossi T, Tommasi C, Caporossi A. Treatment of progressive keratoconus by riboflavin-UVA-induced cross-linking of corneal collagen: ultrastructural analysis by Heidelberg Retinal Tomograph II in vivo confocal microscopy in humans. Cornea 2007;26(4):390-97.

12.Hoyer A, Raiskup-Wolf F, Spoerl E, Pillunat LE. Collagen cross-linking with riboflavin and UVA light in keratoconus–results from Dresden. Ophthalmologe 2008;e-pub ahead of print).

13.Wittig-Silva C, Whiting M, Lamoureux E, Lindsay RG, Sullivan LJ, Snibson GR. A randomized controlled trial of corneal collagen cross-linking in progressive keratoconus: preliminary results. J Refract Surg 2008;24(7):720-25.

14.Chan CC, Sharma M, Wachler BS. Effect of inferior-segment Intacs with and without C3-R on keratoconus. J Cataract Refract Surg 2007;33(1):75-80.

15.Kanellopoulos AJ, Bindr PS. Collagen cross-linking (CCL) with sequential topography-guided PRK: a temporizing alternative for keratoconus to penetrating keratoplasty. Cornea 2007;26(7):891-95.

16.Wollensak G, Spoerl E, Wilsch M, Seiler T. Endothelial cell damage after riboflavin-ultraviolet-A treatment in the rabbit. J Cat Refract Surg 2003;29(9):1786-90.

17.Wollensak G, Spoerl E, Reber F, Pillunat L, Funk R. Corneal endothelial cytotoxicity of riboflavin/UVA treatment in vitro. Ophthalmic Res 2003;35(6):324-28.

18.Herrmann CI, Hammer T, Duncker GI. Haze formation (corneal scarring) after cross-linking therapy in keratoconus. Ophthalmologe 2007; [Epub ahead of print]

19.Mazzotta C, Balestrazzi A, Baiocchi S, Traversi C, Caporossi A. Stromal haze after combined riboflavin-UVA corneal collagen cross-linking in keratoconus: in vivo confocal microscopic evaluation. Clin Experiment Ophthalmol 2007;35(6):580-82.

20.Mazzotta C; Traversi C, Baiocchi S, Sergio P, Caporossi T, Caporossi A. Conservative treatment of keratoconus by riboflavin-UVA-induced cross-linking of corneal collagen: qualitative investigation. Eur J Ophthalmol 2006;16(4):530-35.

21.Eberwein P, Auw-Hadrich C, Bimbaum F, Maier PC, Reinhard T. Corneal melting after cross-linking and deep lamellar keratoplasty in a keratoconus patient. Klin Monatsbl Augenheilk 2008;225(1):96-98.

INTRODUCTION

Since the 18th century’s first description of keratoconus,1,2 the ophthalmic community has long been searching for a method to stop the potentially devastating progression of the most common, naturally occurring, non-inflammatory ectatic corneal disorder. Generally bilateral, most often asymmetrical, keratoconus is characterized by ongoing stromal thinning and anterior bulging of both corneal surfaces, with the apex of the cone-shaped change located paracentrally and inferiorly.3-5 The resulting conicoid geometry of the corneal surface gives rise to unstable, irregular myopic astigmatism and asymmetrical high order aberrations,6 which can be adequately corrected by spectacles and soft contact lenses only in early stages. In mid-advanced phases, quality of vision and quality of life improvements have been usually considered as secondary aims, obtainable in the minority of cases, unless a corneal transplantation is performed, the last option to restore corneal architecture and improve eyesight.7-12 Until a genetic cure will be available, the only conservative weapon against mid-advanced keratoconus in the classic eye care armamentarium has been the rigid gas-permeable (RGP) contact lens (CL) wear, still the mainstay of the optical management of the disorder.13 The observation of some reshaping effect (a sort of “good” warpage) induced by hard CL wear on the surfaces of the cornea (corneal molding) led to the common misconception that these lenses may play a therapeutic role in arresting the evolution of the disease. Unfortunately, this statement turned out not to be true; instead, it is now clear that inadequacy of tear exchange and/or apical clearance may cause hypoxic damage and scarring of the apex of the cone, thus accelerating the way to the keratoplasty. More recently, the diffusion of reversed geometry overnight wear of CLs to temporarily correct slight myopic errors (modern orthokeratology) added a contribution to the knowledge on the plasticity of the cornea and the remodelling effect induced by a rigid contact lens was based on a more standardized approach. Eye care providers are now aware of the high sensitivity of the keratoconic cornea to be moulded, so that even a slight rubbing may alter the corneal topography,27 thus influencing its surface regularity indices and visual performance. In virgin keratoconus eyes, overnight

Due to the corneal sub-edema, small changes of aided and unaided visual vision were observed during early recovery. Moderate improvements started from the third month. Two and three-year data showed a significant reduction of the spherical equivalent and of the mean K-reading detected topographically (about 2.00 D), as well as a positive change of the topographic indices of corneal morphology and symmetry, with a reduction in lower order (myopic astigmatism) and higher order aberrations (coma in particular), which may explain the improvement in uncorrected and best- spectacle-corrected visual acuity. Patients often describe a better quality of vision with less ghosting, glare and starbursting around light sources at night, despite an almost unchanged corneal topography. The optical and visual performances improvement seems to be related to an increased corneal symmetry induced by a restored corneal rigidity after collagen shrinkage.56-59

The knowledge on the combination of C3-R and ICR is very limited; after C3-R, a complete apoptotic 100 damage of keratocytes and mild inflammatory reaction

occur. Cell loss is completely repaired by keratocyte repopulation by six weeks, when cytoarchitecture of the cornea seemed back to normal;34 it is therefore considered advisable to perform ICR implantation not earlier than six months post-C3-R for safety reasons. Before these data were available, however, we implanted ten eyes six months after C3-R and twelve eyes immediately before C3-R. In all patients, we found no specific complication but a significant reduction of the expected reshaping effect of the corneal surface. Instead, C3-R application after ICR surgery (from three months to years) has shown to augment the positive effect of ICR segment surgery in all cases (Carlo Lovisolo, unpublished data).

PURPOSE, METHODS AND MATERIALS

To determine whether a triple procedure, i.e. the addition of C3-R to our standard approach (ICR surgery plus corneal molding) may be more effective to treat keratoconus, we performed a retrospective nonrandomized comparative case series study.

Figures 17.5A to D: Site of incision and segment placement positions are marked (A). As an alternative to the femtolaser, the incision cut, the pocketing and the channelization may be performed manually (B,C,D) with appropriate instrumentation

channels was made, the plastic ring segments were positioned. Incision borders were gently hydrated and left sutureless in all cases. A 65% hydration, 8.7-mm base curve soft bandage contact lens was applied. Then a regimen of antibiotic-steroid combination plus an aggressive use of lubricant drops was recommended (Figures 17.5A to D).

Phase 2: Overnight CL corneal molding was initiated 40 days post-ICR procedure. The molding lens induces a temporary change of the shape of the cornea, taking advantage from corneal plasticity, the epithelial layer’s one in particular. While conventional CLs are designed to cause little or no effect on the corneal shape, these lenses are designed to intentionally flatten the cornea in a controlled way, to bring the eye into correct focus to compensate for the refractive error.25,26

While traditional CL designs have secondary and peripheral curves flatter than the central curve of the lens, the lenses utilized for corneal molding have one or more peripheral curves steeper than the optical zone’s curvature (“reverse-geometry CLs”)42-44 (Figures 17.6A and B).

The radius of curvature of the back optical zone is always custom-designed to determine the shape the

Figures 17.6A and B: Wood light fluorescein patterns of oldgeneration conventional RGP CL (A) and modern four-zone reverse-geometry lens (B)

cornea will assume after the molding, thus the amount of refractive error to be corrected (spherical or spherotorical). The lift of peripheral curves over the cornea around the optical zone creates a tear reservoir. In the reverse zone, joining of the optical with the alignment zone, there are one or more curves steeper than the back optical zone. The alignment zone is the bearing zone of the lens; it gives stability to the lens and keeps it centered; its curvature is flatter than the reverse zone, but steeper than the optical zone. The peripheral zone, flatter than the alignment zone, allows the lens edge to lift from the cornea, to achieve an adequate tear turnover under the lens. This tear exchange is necessary to get in new tear liquid to oxygenate the cornea, and to get out the debris and metabolic residuals formed under the lens. The controlled pressure by the edge lift minimizes the risk of corneal insults and helps the CL removal by mean of lid tension.

When the lens is on the eye, the patient can see clearly, like with a conventional fitting. After the sleeping hours and CL removal when the patients wake up, the cornea retains its modified shape for a certain amount of time, and the patient continues to see well, even without the lens. This treatment is reversible and, if the patient stops wearing the lenses completely, the topographic and refractive condition of the eye will regress to the pre-treatment level.38 The overnight use has the obvious advantage of reducing the interference with the environmental factors (dust, wind, conditioned air, sports) that can give trouble during the day; in addition, the pressure of closed lids improves the rapidity of corneal molding. Since the lids are closed during overnight wear and tear circulation behind the lens is reduced by the inactivation of the blink pump, high oxygen permeable materials are

necessary to provide sufficient oxygenation to the 103

cornea.39,40 The lens material (siloxy-fluoro- methacrylate Dk 100, Boston XO, hexafocon-A) has shown to induce minimal edematous swelling of the stroma. Moreover, the morning lens removal allows for a rapid recovery,41 as well as proper cleansing and elimination of debris and waste products. The fitting procedure requires a perfect centration that is critical for the efficacy of the mold but not easy to obtain. The movement observed after each blink must be higher than 0.2 mm and lower than 1.0 mm, always inferior to a conventional RGP-CL fitting. The ideal fluorescein pattern shows an image with concentric rings: the dark center (minimal apical clearance, some times minimal touches) corresponds to the bulging conicoid area to be molded; the surrounding green area, a variable thickness tear reservoir (depending on the intended corrective effect, between 30 and 80 microns). A midperipheral dark ring (the alignment zone) with a minimal clearance, sometimes a slight touch and a thin green ring (the edge lift, 80 to 100 micron) follow (Figures 17.7A to C). The transition between the different zones should be blended and smooth. After the first adaptation, there should be no air bubbles, indicating an excessive lift in the tear reservoir zone.

LINK TO THE VIDEO

Dealing with safety of corneal molding, we observed some cases of grade 1 fluorescein staining of the epithelium, which disappeared in the evening, but no significant corneal infiltrates or ulcers or other adverse 104 events. Minimal or no changes were observed in the

central thickness of the cornea, as measured with an ultrasound pachymeter (Allergan Humphrey 850, Carl Zeiss Meditec). Confocal microscopy (Confoscan 3000, NIDEK, Japan) showed no measurable changes in the endothelium, sub-basal nerve plexus or in the anterior, intermediate and deep stroma (overall density and activation of keratocytes were not modified) while the basal layer of the epithelium showed larger and less regular cells after the molding (Figure 17.8). A slight increase in reflectivity of the matrix was observed and can be explained by a mild increase of corneal glycosaminoglycans production, that is a reversible phenomenon probably due to an aspecific reaction of an already altered corneal parenchyma (mild cellular edema due to hypoxia and/or mechanical effects).45-55

To try to explain the biomechanical working mechanism (the negligible flattening observed in the central cornea was counterintuitive), we hypothesize the role of mid-peripheral forces induced by the displacement of the epithelium that results from a proper compression by the CL alignment zone. This hypothesis certainly deserves further confirmation to accurately explain the achieved regularization of both corneal surfaces.

Phase 3 (for Group B only): Corneal Collagen Cross-linking with Riboflavin (C3-R) was performed after 3 months of CL corneal molding. Immediately after CL removal, 30 minutes of Ultraviolet A exposure (5.4 J/cm2 at 370 nm) with the VEGA CBM X-LinkerTM (CSO, Firenze, Italy)63 were applied to the central cornea (after a minimum diameter of 7 mm of epithelial