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First Author: L.Sullivan UK
Co Author(s): Z. Varga A. Morrell J. Ball
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Recent studies have reported successful outcomes in the treatment of keratoconic astigmatism with the Keraring, and average improvements in patients visual acuity, keratometric observations and magnitude of astigmatism have been observed. However, the degree of improvement is seen to vary over a wide range. It has previously been postulated that intrastromal corneal ring placement in patients with a centrally positioned cone will fare badly. In order to assess how individual preoperative patient characteristics affect the likelihood of success and degree of improvement post keraring insertion we conducted a retrospective study of eyes treated with femtosecond laser assisted KERARING implantation.
St James university hospital in Leeds, United Kingdom is a large teaching hospital and tertiary referral centre that has been implanting Kerarings for over 14 months using the Zeiss visumax femtosecond laser to create an intrastromal corneal pocket.
We retrospectively reviewed 37 eyes treated with Keraring implant for keratoconus. The Snellen Unaided visual acuity (UAVA), Best Corrected visual acuity (BSCVA), subjective and retinoscopic refraction, Atlas (Zeiss) Topography including Kmax, Kmin and dK readings were collected pre- and postoperatively for study patients. We analysed preoperative magnitude of cyl and compared this with postoperative change in the above variables. In addition we identified cone position using ORBscan readings of pachymetry, anterior and posterior float, and the distance of the apex from the central corneal point and compared the location of the cone apex with postoperative change in the above variables
An average reduction in spherical equivalent of 1.54 diopters was seen in our patient population. Postoperative dK was reduced by 1.93 diopters, Kmin was reduced by 0.54 diopters and Kmax was reduced by an average of 3.06 diopters on topography. A mean improvement of 2.74D was seen in postoperative cylindrical error. As preoperative magnitude of cylinder increased, the postoperative improvement in cylinder correction increased. Patients with a preoperative cylinder of ?4D had a median improvement in postoperative cylinder of 1.0 D, those with preoperative cylinder of 4 8D had a median improvement of 3.5 D and those with cylinder >8D preoperatively had a median increase of 6.5D. No positive correlation was noted between cone location preoperatively and postoperative changes in visual acuity, Ksim, dK or refractive error
Keraring implantation with femtosecond laser is an effective tool for correcting astigmatism associated with keratoconus. Patients presenting with a higher preoperative cylinder show the greatest improvement in magnitude of cylinder postoperatively. Despite suspicion of central cone location being a predictor of poor outcome, no correlation of cone location with postoperative outcomes was seen in our study.