PENETRATING KERATOPLASTY FOR KERATOCONUS - ROLE OF VIDEOKERATOSCOPY AND TREPHINE SIZING

Purpose: To evaluate whether determining graft-host trephine disparity on the basis of videokeratoscopic data of keratoconus patients having penetrating keratoplasty (PKP) reduces ametropia and to correlate pre operative videokeratoscopic values, posterior axial length (PAL), and trephine disparity with postoperative refractive outcomes. Setting: Ho tel-Dieu, University of Paris, France. Methods: This randomized clinic al trial comprised 18 keratoconus patients who had PKP. After computer ized videokeratoscopic analysis, patients were randomly assigned to a test or control group with matching for midperipheral corneal keratosc opic criteria. One surgeon performed all grafts using the same techniq ue (except for donor button punching with an 8.00 or 8.25 mm blade, de pending on preoperative keratoscopy) with suction trephination (8.00) and a running 10-0 nylon suture. The PAL (total axial length minus the distance from the anterior corneal surface to the anterior lens surfa ce) was measured by applanation ultrasonography. Refraction and videok eratoscopic analysis were done 18 months postoperatively (6 months aft er suture removal). Results: The mean deviation from emmetropia correc ted for PAL in test group patients who had trephine sizing based on th e hypothesis that preoperative videokeratoscopy is a useful determinin g factor was 1.12 diopters (D) +/- 0.74 (SD), which was significantly smaller (P = .005) than that in the control group (2.19 +/- 0.85 D). T he test group had uncorrected visual acuities of 20/50 or better. Post operative spherical equivalent was affected by PAL (P = .0001), preope rative keratoscopy (P = .0001), and trephine disparity (P = .01). Cent ral corneal power after grafting was influenced by keratoscopy (P = .0 001) and trephine disparity (P = .002). Uncorrected visual acuity was affected by PAL (P = .001) and keratoscopic data (P = .01). Conclusion s: Parameters for reducing ametropia after grafting of keratoconus pat ients can be developed for each surgeon based on trephine disparity de pendent on preoperative keratoscopic values of the recipient midperiph eral cornea and PAL. If the PAL is between 19.0 and 21.0 mm, preoperat ive midperipheral corneal videokeratoscopy to choose same-size or 0.25 mm different donor and recipient trephine blades is useful to achieve refractive results approximating emmetropia with the described techni que.