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 preoperative videokeratoscopic values, posterior axial length (PAL), and trephine disparity with postoperative refractive outcomes.

SETTING

Hôtel-Dieu, University of Paris, France.

METHODS

This randomized clinical trial comprised 18 keratoconus patients who had PKP. After computerized videokeratoscopic analysis, patients were randomly assigned to a test or control group with matching for midperipheral corneal keratoscopic criteria. One surgeon performed all grafts using the same technique (except for donor button punching with an 8.00 or 8.25 mm blade, depending 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 surface) was measured by applanation ultrasonography. Refraction and videokeratoscopic analysis were done 18 months postoperatively (6 months after suture removal).

RESULTS

The mean deviation from emmetropia corrected for PAL in test group patients who had trephine sizing based on the hypothesis that preoperative videokeratoscopy is a useful determining 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). The test group had uncorrected visual acuities of 20/50 or better. Postoperative spherical equivalent was affected by PAL (P = .0001), preoperative keratoscopy (P = .0001), and trephine disparity (P = .01). Central corneal power after grafting was influenced by keratoscopy (P = .0001) and trephine disparity (P = .002). Uncorrected visual acuity was affected by PAL (P = .001) and keratoscopic data (P = .01).

CONCLUSIONS

Parameters for reducing ametropia after grafting of keratoconus patients can be developed for each surgeon based on trephine disparity dependent on preoperative keratoscopic values of the recipient midperipheral cornea and PAL. If the PAL is between 19.0 and 21.0 mm, preoperative 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 technique.