ASSESSMENT OF ABLATION ZONE CENTRATION AFTER PHOTOREFRACTIVE KERATECTOMY USING A VECTOR CENTER-OF-MASS FORMULA

BACKGROUND: Adequate centration of keratorefractive surgical procedure s is essential for a successful outcome, An accurate technique to math ematically describe the centration and topography of the ablation zone after photorefractive keratectomy (PRK) would be valuable in assessin g the effects of these variables on subsequent visual results, METHODS : A vector center of mass formula and computerized videokeratography w ere used to study the postoperative treatment zone centration and topo graphy of 17 consecutive highly myopic patients (-6.00 to 12.00 diopte rs [D]). Each had undergone PRK using either a single 6.0 mm (n=11) or three-stepped ablation zone (n=6), with good visual results, RESULTS: Calculations disclosed mean ablation zone decentration relative to th e pupil center for all patients to be 0.20 +/- 0.16 mm using the vecto r center of mass formula, Areas of uniform central corneal dioptric po wer (mean diameter 3.4 +/- 0.8 mm) and surrounding transition zones of declining dioptric power (mean slope 1.61 +/- 0.44 D/mm) were also de termined, CONCLUSION: A new vector center of dioptric power distributi on that analyzes centration and transition zone topography offers a ri gorous but straightforward means to assess the effects of refractive c orneal surgery procedures on central corneal topography.