There isn’t a commonplace epi-on surgical method, however generally the approach leaves the corneal epithelium intact and achieves penetration of riboflavin in a wide range of manners such because the addition of chemical brokers meant to loosen the epithelial barrier, iontophoresis, or partial disruption of the epithelium[2]. That is adopted by an identical time interval of UVA irradiation with continued intermittent administration of the riboflavin answer throughout irradiation.
Contents
Purported benefits of Epi-off
Purported benefits of Epi-on
Inclusion/exclusion standards
Historically a corneal thickness of lower than 400 microns after epithelial elimination was thought-about a contraindication to CXL, however stories utilizing hypo-osmolar riboflavin options to induce corneal swelling throughout therapy counsel that a very skinny cornea could now not be a barrier to therapy, so long as the cornea will be delivered to an thickness previous to UV publicity[3].
Exclusion standards contains situations that might predispose the eyes to additional issues reminiscent of present an infection, historical past of ocular herpes zoster or herpes simplex, autoimmune issues, historical past of poor epithelial therapeutic, and extreme or central corneal scarring. There are various completely different measurements used to doc corneal ectasia, however typically modifications in corneal topography reminiscent of will increase in Kmax or will increase in astigmatism and refractive error are used.
Epithelial elimination methods
For PTK/laser scrape, an excismer laser is used at a relentless depth of fifty microns in a central corneal space of 6.5 mm, after which the debridement space is prolonged to 9 mm mechanically with a scalpel or rotating brush[4]. Phototherapeutic Keratectomy (PTK) laser scrape has additionally been reported as a way for eradicating epithelium for the needs of CXL. Different investigators have pre-treated the epithelium with ethyl alcohol adopted by mechanically rubbing the epithelium with a cellulose sponge.
Riboflavin options used
This answer remains to be generally used however many medical research now use an isotonic answer suspended in Hydroxypropyl methylcellulose (HPMC) as an alternative of dextran. For corneas that have been beforehand regarded as too skinny for CXL therapy hypo-osmolar 0.1% riboflavin answer will be utilized to induce corneal swelling to not less than 400 microns earlier than UVA irradiation[3].
The preliminary Riboflavin answer used was 0.1% Riboflavin in 20% dextran answer.
30-minute vs accelerated protocols
Some research display equal efficacy and security[5][6] [7] in medical parameters, whereas others display that the accelerated protocol produces much less topographical flattening and stiffening than the Dresden protocol. Probably the most extensively studied method is the Dresden protocol which entails utility of Riboflavin each 3 minutes for half-hour, adopted by half-hour of UVA irradiation. Some researchers have tried an accelerated protocol whereby UVA illumination depth is elevated whereas UVA irradiation time is decreased.