| Summary: | 碩士 === 國立臺灣大學 === 臨床醫學研究所 === 94 === Laser refractive surgery is performed by using Ar-F excimer laser to disrupt the inter-molecular bonding of corneal tissue and ablate the cornea, thereby changing the curvature and refractive power of anterior corneal surface. However, as soon as the spherical and cylindrical refractive errors are corrected by laser, higher-order aberrations of anterior corneal surface also result. This is due to the irregular change of anterior corneal surface by wound healing process or the laser treatment itself.
The surgical and mechanical techniques of laser refractive surgery have been processing during the past decade. Photorefractive keratectomy (PRK) was preformed in the past, whereas laser in situ keratomileusis (LASIK) is used most often at present time. The laser beams also evolve from broad beams to flying spots and mixed spots. Since the laser refractive surgery itself induces the higher order aberrations of anterior corneal surface, these different surgical techniques and machines attribute differently to the higher-order aberration (HOA).
In this study, we calculate the HOAs of anterior corneal surface by computerized corneal topography and calculating software. We then analyze the affecting factors of HOA changes after surgery, including surgical techniques (PRK vs. LASIK), laser machines (Summit Apex Plus, Allegretto Wave, Bausch & Lomb Technolas 217z, and VISX S4), age, attempted sphere correction, attempted cylinder correction, optic zone size, and transitional zone size. Besides, we use questionnaires to evaluate the visual quality and the extent of satisfaction of patients, and analyze the relationships with corneal surface HOA changes.
As the result shows, all HOAs increased significantly after surgery by various techniques and machines. LASIK induced more trivial HOAs (the 5th and 6th orders) after surgery than PRK did. The diopters of spherical equivalent corrected were highly correlated with surgical-induced HOA changes. Patients with older ages had less HOA changes. The larger the treatment zone sizes (including optic zones and transitional zones), the less the surgical-induced HOA changes. Some flying-spot machines induced less coma-like aberrations, while no obvious differences of spherical-like aberrations and total HOAs between broad-beam machines and flying-spot ones were noted. The visual quality and the extent of satisfaction of patients correlated most strongly with spherical-like aberrations, then with total HOAs, and then with coma-like aberrations.
In the future, we can try to improve the surgical techniques and the preciseness of laser machines according to these results. We hope our efforts can contribute to more perfect visions of future patients!
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