Radial keratotomy (RK) was an incisional refractive surgery that gained popularity in the late 80s and early 90s for the treatment of short and long sight. Although results from RK seemed initially to be good, with patients enjoying significant improvement in vision, what became apparent from long terms studies and in particular the PERK (prospective evaluation of radial keratotomy) study was that eyes after RK were far from refractively stable, with a tendency toward increasing long sight and astigmatism as a result of progressive corneal flattening. Moreover many patients were demonstrated to experience changes in their overall glasses prescription throughout the day, from morning to evening. These changes possibly occur due to biomechanical instability due the RK incisions and changing intraocular pressure and tissue hydration through the day. For the patient this presents a frustrating situation that is difficult to correct with glasses as the glasses that may have worked in the morning are unlikely to work in the evening!.
Options for stabilisation of this diurnal fluctuation have until now been limited. However corneal collagen cross-linking, a treatment now widely used in the treatment of patients with keratoconus has been shown to effectively strengthen the cornea and stabilise patient's eyes and their prescriptions. Collagen cross-linking works by creating additional bonds between corneal collagen fibers, thereby stiffening and strengthening the cornea. This added rigidity appears to prevent the diurnal changes that happen in RK eyes. Moreover, once the refraction has stabilised it may be possible to treat the patient and correct their long sight and astigmatism with either laser eye surgery or with lens based surgeries such as refractive lens exchange or the implantable contact lens, depending on the patients age. Collagen cross-linking is a relatively safe technique with a low complication rate.