Confocal microscopy evaluation of stromal ablation depth after myopic laser in situ keratomileusis and photorefractive keratectomy.
OBJECTIVE
To compare the measured ablation depth after myopic laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) with the predicted ablation depth.


METHODS
Mayo Clinic, Rochester, Minnesota, USA.


METHODS
Twenty-five eyes of 15 patients had PRK and 25 eyes of 15 patients had LASIK to correct refractive errors between -1.50 diopters (D) and -11.00 D. The corneas were examined by in vivo confocal microscopy before and 1 month after both procedures. Thickness measurements were obtained from digital-image analysis of confocal scans. The measured ablation depth, an estimate of the actual photoablation depth, was obtained as the surgically induced stromal thinning between the preoperative and the 1-month post-PRK or post-LASIK central stromal thickness. The predicted ablation depth was recorded from the laser's software program.


RESULTS
In LASIK, the measured ablation depth (81 microm +/- 34 [SD]) was 25% greater than the predicted ablation depth (65 +/- 13 microm, P =.007) and the difference between the measured and predicted ablation depths was positively associated with the mean ablation depth (r = 0.81, P<.001). In PRK, there was no difference between the measured ablation depth (48 +/- 19 microm) and the predicted ablation depth (47 +/- 18 microm, P =.84).


CONCLUSIONS
Significantly more tissue than predicted was removed by LASIK than by PRK excimer photoablation with the laser system used in this study.
Erie
Jay C
JC
Department of Ophthalmology, Mayo Clinic, Rochester, MN 55905, USA. erie.jay@mayo.edu
Hodge
David O
DO
Bourne
William M
WM
D000328:Adult; D001837:Body Weights and Measures; D003319:Corneal Stroma / Q000473:pathology / Q000601:surgery*; D005260:Female; D006801:Humans; D020731:Keratomileusis, Laser In Situ / Q000592:standards*; D054018:Lasers, Excimer; D008297:Male; D018613:Microscopy, Confocal; D008875:Middle Aged; D009216:Myopia / Q000601:surgery*; D018903:Photorefractive Keratectomy / Q000592:standards*; D011446:Prospective Studies