Collagen Cross-Linking Using Rose Bengal and Green Light to Increase Corneal Stiffness

Abstract

PURPOSE. Photochemical cross-linking of corneal collagen is an evolving treatment for keratoconus and other ectatic disorders. We evaluated collagen cross-linking by rose bengal plus green light (RGX) in rabbit eyes and investigated factors important for clinical application.METHODS. Rose bengal (RB, 0.1%) was applied to deepithelialized corneas of enucleated rabbit eyes for 2 minutes. The diffusion distance of RB into the stroma was measured by fluorescence microscopy on frozen sections. RB-stained corneas were exposed to green (532-nm) light for 3.3 to 9.9 minutes (50-150 J/cm 2 ). Changes in the absorption spectrum during the irradiation were recorded. Corneal stiffness was measured by uniaxial tensiometry. The spatial distribution of the stromal elastic modulus was assessed by Brillouin microscopy. Viable keratocytes were counted on H&E-stained sections 24 hours posttreatment. RESULTS.RB penetrated approximately 100 lm into the corneal stroma and absorbed >90% of the incident green light. RGX (150 J/cm 2 ) increased stromal stiffness by 3.8-fold. The elastic modulus increased in the anterior approximately 120 lm of stroma. RB was partially photobleached during the 2-minute irradiation, but reapplication of RB blocked light transmission by >70%. Spectral measurements suggested that RGX initiated cross-linking by an oxygen-dependent mechanism. RGX did not decrease keratocyte viability.CONCLUSIONS. RGX significantly increases cornea stiffness in a rapid treatment (@12 minutes total time), does not cause toxicity to keratocytes and may be used to stiffen corneas thinner than 400 lm. Thus, RGX may provide an attractive approach to inhibit progression of keratoconus and other ectatic disorders.

Toward New Engagement Paradigms For Intraocular Lenses: Light-Initiated Bonding of Capsular Bag to Lens Materials

“…16,24 The photoinitiator used is a standard of eye care used topically, 17 and experimental studies in rabbit eyes have revealed that it is nontoxic intracapsularly and does not compromise corneal endothelial cell integrity. 18 Exposure times and fluences of the green light used are comparable to those used in two other applications of green light and RB, namely, photobonding amniotic membrane to cornea and photo-crosslinking of the cornea.…”

“…14 Corneal collagen photo-crosslinking has also been demonstrated with other photosensitizers, such as Rose Bengal (RB) and green light irradiation. 15,16 One advantage of the use of RB is that it is a US Food and Drug-approved compound widely used in ophthalmology, for example, in dry eye staining tests. 17 In addition, intracapsular use of RB was shown to be nontoxic in rabbit eye models, actually reducing the rate of posterior capsular opacification.…”

Corticosteroids and Anti-Complement Therapy in Retinal Diseases

“…Of note, this treatment did not induce the keratocyte apoptosis that is seen with riboflavin and UVA treatment. Due to the more shallow penetration of Rose Bengal, the cross-linking effect is more anterior in the stroma; however, this may be beneficial in patients with thin corneas who would otherwise be excluded from riboflavin and UVA cross-linking (Cherfan et al 2013). Another possibility that has been studied in animal models is that of palladium bacteriochlorin 13 0 -(2-sulfoethyl)amide dipotassium salt (WST11) and near-infrared (NIR) illumination.…”

Corneal Collagen Crosslinking with Riboflavin and Ultraviolet - A Irradiation in the Management of Progressive Ectatic Corneal Disorders. Review Article

“…The technique halts keratoconus progression without significant complications, however, longer follow-up and studies with larger patient populations are needed to assess the real effectiveness of this technique 64,65 . Other methodologies currently under pre-clinical investigation to facilitate trans-epithelial riboflavin stromal absorption include the use of ultrasound 83 , nano-emulsion systems 84 , and other epithelial permeation enhancers such as d-alpha-tocopheryl poly (ethyleneglycol) 1000 succinate (Vitamin E-TPGS) 85 .…”

“…In order to overcome the contra-indication of treating corneas with a thickness bordering on 400μm, Hafezi and co-workers, and other authors 73,75 replaced the standard iso-osmolar riboflavin solution (containing dextran) with a hypo-osmolar riboflavin solution (without dextran) to swell the cornea to an acceptable thickness prior to cross-linking. Using the modified technique, Hafezi and co-workers 73 treated 20 patients with thin corneas (minimum preoperative stromal thickness of 323μm) and reported a cessation of keratoconus progression in all cases.…”