الفهرس 
BASIC PRINCIPLES OF CROSS LINKINGOnly 14 pages are availabe for public view
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Abstract
s surgeons’ knowledge of CXL has increased and the indications for its use have widened, various modifications have emerged. Current modifications include the use of CXL without epithelial removal, variations on (UVA) fluence and duration, and the combination of CXL with procedures aimed at optical improvement and visual rehabilitation. A
There is an international controversy about if we remove or not remove the epithelium. Some researchers are in favor of leaving the epithelium intact in order to achieve faster visual rehabilitation and diminish of symptoms.Studies have demonstrated that is possible to improve epithelial permeability to riboflavin- 5-phosphate by modifying the standard riboflavin formulation.
The current understanding of the photochemical kinetics of cross-linking suggests that the increased availability of oxygen obtained during the dark period may result in generation of more of the radicals that create cross-linking than are generated with an equivalent dose of continuous wave UVA. Varying the relative lengths of the light and dark phase influences efficiency of the process. Laboratory work demonstrates that shorter light phases result in enhanced availability of oxygen for dark phase chemistry and therefore greater cross-linking.
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Summary
To achieve the energy at level of the stroma that is obtained in epithelium-off cross-linking, a higher surface dose is required. This may be achieved by increasing either the total treatment time or increasing the irradiance of the UVA light applied. Accelerated cross-linking protocols have been employed to shorten total procedure time.
Although CXL stops the keratectatic process in most cases, the procedure itself often is not sufficient to provide visual rehabilitation. Ophthalmologists, therefore, have attempted to combine CXL with various refractive surgical techniques.
One of the major disadvantages of LASIK is the reduction of the biomechanical stability of the cornea. If one could then establish that biomechanical stability has recurred after use of CXL in routine LASIK cases (lasik Xtra), then that would further enforce LASIK as the primary refractive procedure because it has a favorable safety record, is tolerated by patients very well, and enables a rapid return into daily activities.
The use of topography-guided transepithelial PRK followed by CXL has also been shown to improve visual acuity and stabilize KC. Same-day PRK followed by CXL appears to be superior to sequential PRK after CXL, and the former has been widely used as the Athens protocol.
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Summary
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Combined kerarings insertion and CXL can be performed safely in one session or two sessions. However, the same-session procedure is more effective regarding improvement in corneal shape.
Combining CXL with the implantation of a phakic toric IOL safely and effectively corrects myopic astigmatism in eyes with mild to moderate KC.
The triple procedure of CXL combined with topographyguided PRK to regularize the corneal shape and the implantation of a pIOL to optimize the refraction may rehabilitate the patient’s vision with a higher predictability of the refractive outcome compared with CXL combined with topography-guided PRK alone.
Three stages approach of Keraring ICRS implantation followed by corneal CXL and then posterior chamber toric implantable collagen copolymer pIOL implantation is an effective treatment in keratoconic eyes with high myopic astigmatism and resulted in significant improvements in UDVA and CDVA.