Select another language:. Please enter your email address: Subscribe. Discuss these CXL definitions with the community: 0 Comments. Notify me of new comments via email. Cancel Report. Create a new account. Log In. Powered by CITE. Are we missing a good definition for CXL? Don't keep it to yourself Submit Definition. The ASL fingerspelling provided here is most commonly used for proper names of people and places; it is also used in some languages for concepts for which no sign is available at that moment.
There are obviously specific signs for many words available in sign language that are more appropriate for daily usage. Browse Definitions. Get instant definitions for any word that hits you anywhere on the web! Two clicks install ». Normal corneas have crosslinks between their collagen fibers that keep them strong and able to retain their normal shape. In keratoconus, the cornea is weak with too few cross-links or support beams.
This weakened structure allows the cornea to bulge outwards. These new cross-links help strengthen the cornea which stops the thinning process and further loss of vision.
Can CXL be performed for everyone with keratoconus? To qualify for the CXL study, patients must be at least 12 years old and their corneas cannot be too thinned or too scarred for the procedure. During your consultation, we will determine if CXL might an option for you. Our practice offers a complimentary, no-touch, painless screening test to see whether CXL might help you.
Should your relatives be tested? How effective is CXL? LASIK is a procedure that reduces or, in some cases, may even eliminate the need for glasses or contact lenses by removing corneal tissue. The CXL treatment does not remove tissue. The purpose of CXL is to prevent further deterioration of vision for most patients and to potentially improve vision. Patients will typically require a lower eyeglass prescription or can have an easier time being fit with contact lenses.
Can CXL prevent the need for corneal transplants? Many studies have shown that CXL can often prevent the need for a corneal transplant and allow patients to wear contact lenses or glasses more comfortably and safely again.
Can a corneal transplant be done after CXL? If CXL does not prevent the need for a corneal transplant, then a corneal transplant can generally be performed. In some cases, CXL can be performed after corneal transplantation. CXL is an in-office procedure that does not involve surgical incisions into the eye or stitches. It is a relatively non-invasive procedure that is done with vitamin drops and light. Corneal transplants are performed in an operating room, involving incisions into the eye and a lifelong risk of rejection of the corneal tissue.
How long does CXL treatment last? Based on CXL study results over more than a decade, the beneficial effects of CXL appear to last for many years and there is evidence that this strengthening effect may be permanent. Is CXL new? Corneal collagen cross-linking has been performed since The results and safety profile of CXL have been very positive in numerous studies throughout the world. CXL procedures are now routinely performed on patients as young as 10 years old in Europe to prevent the development of keratoconus.
Does CXL need to be repeated? In many studies, the majority of patients responded to a single vitamin and light CXL treatment and did not need to have the procedure repeated. CXL can often be repeated when treatment is not effective. How is CXL performed? The epithelium, a thin layer of clear, protective tissue like skin that covers the cornea is removed for the CXL procedure.
Next, vitamin eye drops riboflavin are used in the eye and you will be asked to look at a special blue ultraviolet light while lying comfortably on a reclining chair. What is the transepithelial or epi-on CXL technique? In this less invasive CXL treatment, the surface skin layer epithelium of the cornea is not removed so the recovery is much faster than the traditional CXL technique. This less invasive technique can only be done on corneas that are thicker than microns12, CXL can be expected to have less effect on biomechanics of artificially swollen corneas due to the lower relative concentration of collagen in the hydrated stroma [ 56 , 57 ].
Long-term follow-up studies addressing this issue are warranted. Substances such as benzalkonium chloride, ethylenediaminetetraacetic acid EDTA and trometamol, especially when combined, enhance epithelial permeability of hydrophilic macromolecules, such as riboflavin [ 58 — 61 ].
By adding the enhancers to help riboflavin penetrate to the corneal stroma through the intact epithelium, CXL can be performed without epithelial debridement transepithelial CXL [ 28 ]. Transepithelial CXL has been proposed but not proven to reduce early postoperative pain, temporary worsening of vision, as well as complications such as infectious keratitis after conventional CXL [ 62 ]. Additionally, thinner corneas may be treated safer by transepithelial compared to the conventional CXL, since the endothelium is better protected by UVA-filtering effect of the intact epithelium.
In a bilateral study, Filippello et al. The transepithelial CXL treatment appeared to halt the progression of keratoconus in all treated eyes over 18 months follow-up. It also yielded statistically significant improvements in all visual and topographic outcome measures, whereas the contralateral untreated eyes demonstrated worsening of all parameters. Spadea et al. However, the visual and topographic improvement was minimal. No endothelial cell damage was observed in either of the studies.
The safety and reproducibility of the study by Filippello et al. Seiler and Hafezi [ 24 ] first reported the demarcation line after CXL and related the depth of the line to that of keratocyte death after CXL as measured by confocal microscopy [ 65 ]. They suggested that the line represented the transition zone between cross-linked anterior and untreated posterior stroma.
It is unclear whether the shallower demarcation line using the transepithelial approach was due to limited penetration of riboflavin into the stroma or that it was a result of reduced UVA-light penetration by shielding from riboflavin-impregnated intact corneal epithelium. Iontophoresis-assisted transepithelial CXL, using a noninvasive delivery system based on a small electric current, was recently designed to enhance the penetration of riboflavin into the corneal stroma [ 66 ].
Preclinical results showed that the iontophoresis was able to increase the concentration of riboflavin in the corneal stroma when compared to enhancer-assisted transepithelial CXL, but did not reach concentrations previously reached with conventional epithelium-off CXL. Demarcation line after iontophoresis-assisted transepithelial CXL appeared to be less easily distinguishable and shallower than in conventional CXL, however, it demonstrated features more similar to that after conventional CXL in terms of depth and visualization, compared to enhancer-assisted transepithelial CXL [ 63 , 67 ].
In general, there is consensus within the scientific community that current transepithelial CXL protocols are not as effective as conventional epithelium-off CXL [ 60 , 61 , 68 ]. In this modified CXL approach, 8. The authors suggested use of hypoosmolar riboflavin during the UVA-irradiation to avoid corneal stromal dehydration as well as to maintain the stromal riboflavin concentration. Nine months postoperatively, topography remained stable, and no endothelial cell density alteration was detected in the treated eyes.
However, a later study by Kaya et al. Four weeks after the treatment, stromal haze and demarcation line were detected in the corneal areas with epithelial debridement, but not in the areas with intact epithelium; deepithelialized stroma outside the cone region displayed total keratocyte apoptosis and honeycomb-like edema, whereas it was minimal beneath the intact epithelium [ 69 ].
In contrast, Mazzotta et al. One previous study demonstrated that the stromal uptake of riboflavin after grid pattern of full-thickness epithelial debridement was heterogeneous, with full penetration to the stroma immediately beneath the areas of epithelial debridement and no penetration to the stroma beneath the intact epithelium [ 71 ]. Inadequate riboflavin saturation together with the ability of the epithelium to absorb the UVA radiation [ 72 ] may lead to reduced CXL effect in the cone area and affect the efficacy of the whole procedure.
Long-term efficacy of this modified CXL procedure with a larger number of patients needs to be assessed. The UVA-radiation of 3. The riboflavin solution was instilled every 3 minutes during the UVA-radiation to maintain corneal saturation and to keep the pre-corneal and pre-contact lens riboflavin film uniform.
At a mean follow-up time of 6. No significant endothelium loss or signs of postoperative endothelial damage were observed. No significant change in the CDVA, or mean maximum keratometric value was detected postoperatively, although 1 D decrease of maximum keratometric value was observed in 4 eyes The advantage of the CACXL is that it is not dependent on the swelling properties of the cornea and that the cornea is not subjected to edema, which may cause Descemet membrane folds and endothelial damage.
Furthermore, oxygen diffusion, which has been demonstrated to be crucial in the CXL process, might be hindered by the contact lens. As a result, the effect of CXL may be reduced. The small patient population, short follow-up and absence of a control group are the limitations of the study. With improved screening technique in keratoconus diagnosis, most of the keratoconus eyes would be able to be treated by this protocol.
However, late diagnosed progressive keratoconus eyes often have values below this threshold. To offer CXL to this critical group of patients, several modifications have been proposed.
The overall safety of the presented protocols for CXL in thin corneas is good, as most of them managed to halt the progression of keratectasia without postoperative complications. Iseli et al. Furthermore, in accelerated CXL, pulsed UV light seems to result in a higher effect compared to continuous UV light, presumably due to optimization of oxygen availability [ 76 ].
Thus, using the pulsed mode during UVA irradiation may maximize the efficacy of CXL while maintaining or improving the safety profile of the procedure, which may be especially beneficial in treating thin corneas. Ideally, a comprehensive mathematical model should be introduced to calculate an optimal set of parameters such as concentration and tonicity of Riboflavin, as well as UV-light-power, duration and dose for any given corneal thickness. That way not only the limitation of the treatment in thin corneas will be addressed, but a customized set of parameters could lead to addressing specific needs of any individual patient.
At this point, only laboratory research can be found on the subject [ 79 , 80 ]. The evidence of safety and efficacy regarding the use of modified CXL protocols is still limited to a handful of studies. Future long-term follow-up studies with a larger number of participants are warranted. Keratoconus and related noninflammatory corneal thinning disorders.
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Int Ophthalmol Clin. Transplant Proc. Risk factors for human corneal graft failure within the Australian corneal graft registry. Thermomechanical behavior of collagen-cross-linked porcine cornea. Increased resistance of crosslinked cornea against enzymatic digestion. Curr Eye Res. Increased rigidity of the cornea caused by intrastromal cross-linking. Stress—strain measurements of human and porcine corneas after riboflavin-ultraviolet-A-induced cross-linking. J Cataract Refract Surg. Am J Ophthalmol.
Biomechanical evidence of the distribution of cross-links in corneas treated with riboflavin and ultraviolet A light. Photochemical kinetics of corneal cross-linking with riboflavin. Manifest diabetes and keratoconus: a retrospective case—control study.
Graefes Arch Clin Exp Ophthalmol. Effects of ultraviolet-A and riboflavin on the interaction of collagen and proteoglycans during corneal cross-linking. J Biol Chem. Endothelial cell damage after riboflavin-ultraviolet-A treatment in the rabbit. Ophthalmic Res.
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