ABSTRACT Background : Corneal wound healing and tissue response have been known to have an effect on the outcome in refractive procedures when comparing different refractive surgical modalities performed in different subjects. The purpose of this study was to compare the visual outcome, refraction and stability in the same subjects who were treated with excimer PRK in one eye and LASIK in the other.
Methods : Twelve subjects treated with excimer PRK in one eye and LASIK in the other for myopic correction were reviewed. Ten eyes in PRK group were treated with Aesculap-Meditec, MEL 60 Excimer Laser and the other two with Omnimed UV 200 LA Summit Excimer Laser. The Chiron automate microkeratome had been used to create a corneal flap and the Aesculap-Meditec, MEL 60 was applied for remodeling over the corneal bed in all LASIK treated eyes.
Results: PRK series : Five eyes (41.7%) had a myopic regression with the spherical equivalent refraction over - 2.0 D after first treatment and 4 eyes were retreated. One eye (8.3%) developed marked haze (grade 3) and loss of two lines of best corrected visual acuity.
LASIK series Eleven eyes (91.7%) achieved an uncorrected visual acuity of 20/40 or better by 1 month after surgery and this degree of visual acuity was maintained or improve at least 12 months after treatment. Two eyes were retreated due to initial overcorrection. Loss of two or more lines did not occur in any eye.
Conclusion LASIK seemed to be superior to PRK by using lamellar keratectomy to gain access the corneal stroma with anterior corneal flap and keep intact central Bowman's layer accompanied with the precision of the excimer laser ablation. Optimal visual result was obtained with rapid recovery. The post operative spherical equivalent refraction in LASIK group appeared to be nearly stable one month after the procedure in low myopic eye and had a minor change since 2 months after treatment in myopia over-6.0 D. Furthermore LASIK reduced or eliminated the problem concerning severe pain, delayed reepithelization and the complications assoicated with long term use of topical steroid.

Key words : excimer laser, photorefractive keratectomy (PRK), laser assisted in situ keratomi leusis (LASIK), microkeratome, spherical equivalent refraction (SE), best corrected visual acuity (BCVA), uncorrected visual acuity (UCVA)