CornealCrosslinking Dr. David Edmison 14th, 2012
Corneal Crosslinking• CXL proposed by Dr. Theo Seiler (Dresden) in 2000.• Combination of riboflavin & UVA (3mw/cm2 at 370nm) to strengthen the cornea.• Involves photopolymerization of stromal fibers which increases the rigidity of corneal collagen and its resistance to deformation.• After UVA exposition the riboflavin is excited into a triplet state and generates singlet oxygen. These induce the formation of new covalent bonds between the amino acids of neighbouring collagen fibres and results in a stiffening of the cornea.
Keratectasia Keratoconus Post LASIK ectasia Pellucid Marginal Degenaration Therapeutic treatment – variable Rx and K’s during post-op period (1-6 mths)
KeratectasiaKeratoconus 1/2000: usually in adolescence, peaks at age 20-35 Thinning of corneal stroma Clinically: irregular scissor reflex on retinoscopy Vertical striae (Vogt) Fleischer’s ring (hemosiderin) Stromal edema with breaks in Descemet’s → hydrops Munson’s sign Path: defects in Bowman’s Etiology: genetic, atopic disease, asthma, exzema, eye rubbing 10-25% require transplant or lamellar Sx.
Corneal Crosslinking Intrastormal ring segments + CXL Intrastromal ring segments + CXL
KeratectasiaPost LASIK ectasia Variable degrees of corneal thinning in stromal bed and flap Macrostriae in stromal bed Steepening of central cornea +/- iron ring around steepening. Thinning of stromal collagen lamellae Occasional scarring at flap-stromal bed interface
KeratectasiaPellucid Marginal Degenaration Thinning in periphery of cornea Usually high against the rule astigmatism.
Corneal CrosslinkingOther indications for CXL Recalcitrant corneal ulcers Reduces pathogen load Increases resistance to collagenases Reducing corneal edema in Bullous keratopathy & Fuch’s Reducing hyperopic shift following RK Prophylactic for all patients treated with PRK with high myopia or Forme Fruste K
Corneal Crosslinking Bacteria can be eliminated using the combination of UV-A and riboflavin
Corneal Crosslinking85-year-old woman with anadvanced infectious ulcer,including presence of hypopyon.
Corneal CrosslinkingAdvantages Stabilizes (slows or stops) progression of keratectasia. Some flattening of the cornea Studies show results last at least 3 years Synergistic effect with PRK as seen in Athens protocol. Helps treat resistant bacterial ulcers.
Corneal CrosslinkingDisadvantages No long term data Stabilizing effect shown but minimal improvement in VA for patients. Of 200 reported studies only 10 are prospective, randomized and controlled. No titration of dose to degree of keratectasia. Sterile infiltrates and stromal scars reported. Rare corneal melt and damage to endothelium. Estimated that CXL has same stiffening impact on cornea as 30 years of aging.