Correlation of changes in refraction and corneal topography after photorefractive keratectomy.
OBJECTIVE
To establish which corneal power evaluation measured with corneal topography correlates best with refractive changes after photorefractive keratectomy (PRK) for myopia.


METHODS
Two hundred fifty-one consecutive eyes of 171 patients who had PRK for myopia ranging from -14.80 to -0.50 D (mean -5.43 +/- 2.978 D), calculated at the corneal plane, were included in the analysis. Data included preoperative and postoperative (1, 3, and 6-mo) subjective refraction and videokeratography with a Keratron Scout (Optikon 2000). Statistical analysis was performed to determine the correlation between the change in subjective refraction at the corneal plane and changes in six corneal power measurements: best fit sphere, simulated keratometry (Sim K), corneal apex, and center of the pupil (last two evaluated for axial and meridional curvatures).


RESULTS
The closest correlation between subjective refraction change and corneal power measurement during the three follow-up evaluations was found with Sim K (R2 = 0.904; 0.889; 0.854) and best fit sphere (R2 = 0.919; 0.909; 0.872), whereas the other measurements showed poor correlation with the different curvatures.


CONCLUSIONS
The best fit sphere corneal topography parameter correlated best with the refractive changes, primarily for low treatment amounts, whereas it showed a clear-cut underestimation in eyes that had undergone high dioptric treatments.
Rosa
Nicola
N
Department of Ophthalmology, 2nd University of Naples, Naples, Italy. nicola.rosa@unina2.it
Furgiuele
Dario
D
Lanza
Michele
M
Capasso
Luigi
L
Romano
Antonio
A
D000328:Adult; D019781:Corneal Topography; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D054018:Lasers, Excimer; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000175:diagnosis / Q000503:physiopathology* / Q000601:surgery*; D018903:Photorefractive Keratectomy; D011184:Postoperative Period; D012029:Refraction, Ocular