Visual functions before and after LASIK

Pao Yue-kong Library Electronic Theses Database

Visual functions before and after LASIK

 

Author: Chan, Wing-wo Jay
Title: Visual functions before and after LASIK
Degree: M.Phil.
Year: 2002
Subject: Hong Kong Polytechnic University -- Dissertations
LASIK (Eye surgery)
Eye -- Physiology
Vision
Department: Dept. of Optometry and Radiography
Pages: xvi, 223 leaves : ill. (some col.) ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1657703
URI: http://theses.lib.polyu.edu.hk/handle/200/2882
Abstract: Laser in situ keratomileusis (LASIK) is a relatively new technique to reduce refractive error, and many clinical studies have shown that the visual outcomes after LASIK are better than with previously-used procedures such as radial keratotomy (RK) and photorefractive keratectomy (PRK). Studies of LASIK outcomes have shown that corneal recovery time after LASIK is relatively short, nevertheless visual problems such as glare and halos, are reported by a small percentage of patients. The objective of this longitudinal study was to characterize the visual changes occurring within one year of LASIK treatment. Three aspects of visual function, contrast sensitivity, glare sensitivity and corneal clarity were investigated before and after LASIK treatment, so that by comparing the results the effects of LASIK on the visual functions were found and recovery time determined. In the contrast sensitivity study, a computer-base contrast sensitivity test was used. Subjects were asked to respond "yes" if the target was seen and "no" if it was not. Contrast sensitivity threshold values were determined using a staircase protocol. Contrast sensitivity was measured for seven spatial frequencies, prior to LASIK and one week, one month, three months, six months and one year post-LASIK. There was a general depression of contrast sensitivity after LASIK treatment and contrast sensitivity took at least six months to recover to the pre-operative level. This non-permanent depression is probably related to optical factors. In the glare sensitivity study, a glare tester was developed. Contrast sensitivity was measured with and without glare prior to LASIK and at the time intervals shown above. There was no statistically significant extra glare detected after LASIK treatment. This negative result may be because pupil miosis under glare condition reduced the diffracted and scattered light from the peripheral area of the LASIK treatment zone. Subjective glare sensation was experienced immediately post-operatively, however this had decreased just one day post-surgery. In the corneal clarity study, a new method to measure corneal clarity objectively and quantitatively was developed, and proved to be able to detect small amount of corneal clarity change. The color intensitity of a photograph of a carefully controlled slit lamp optic section of the cornea was measured and analyzed to provide a measure of corneal clarity. Corneal clarity decreased and returned to pre-treatment levels one month post-treatment. The haze noted was very subtle and would be unlikely to affect best-corrected visual acuity. LASIK is an effective surgical alternative for the reduction of moderate myopia. LASIK causes a temporary decrease in contrast sensitivity and corneal clarity, and a sensation of glare which usually subsides within a day of surgery.

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