الفهرس 
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Abstract
Laser in situ keratomileusis (LASIK) is effective in treating a wide variety of refractive errors and has become the most commonly performed refractive procedure to correct myopia. There is, therefore, a need for greater understanding of the factors that directly affect visual function after this procedure.
After LASIK, a subset of patients reported night time visual disturbances; these symptoms may be a source of patient dissatisfaction.
A difference in opinions exists among refractive surgeons, concerning the role of pupil size in the appropriate selection of patients for refractive surgery. Its role as a risk factor of visual disturbances under low-light conditions remains controversial.
This work aims at investigating the effect of scotopic pupil diameter on contrast sensitivity after conventional laser in situ keratomileusis (LASIK) for myopia. This is an attempt to evaluate the effect of pupil size on the quality of vision after LASIK for myopia.
This clinical study included 99 eyes of patients undergoing laser in situ keratomileusis. The eyes included had a refractive error of myopia up to -10D and myopic astigmatism up to -3D. All patients were refractive surgery candidates for myopia and moypic astigmatism. None of patients had previous ocular surgery.
Patients are classified into two groups according to the degree of myopia, group (1) consisted of 74 myopic eyes between -1.0D and -6.0D and group (2) consisted of 25 myopic eyes between -6.25D and 10.0D.
Every patient was subjected to complete ophthalmologic examination; including UCVA and BSCVA, corneal topography, pentacam, ultrasonic pachymetry, scotopic contrast sensitivity using CSV 1000 (Vector Vision), scotopic pupil assessment using Colvard pupillometer for all patients and Wave Scan aberrometer for 83 eyes. LASIK was performed under topical anaesthesia (eye DROPs). VISX STAR 4 Excimer laser system (VISX, Santa Clara, CA) was used for the ablation, with 6.5mm ablation zone and 8mm transition zone.
Postoperatively, the patients were followed up at one day, one week, one month and three months. In each follow up visit the patient was examined regarding uncorrected and best corrected visual acuity, manifest refraction and slit lamp examination. Scotopic contrast sensitivity was done after one and three months.
A questionnaire was administered postoperatively at the first month visit after surgery. The questions were designed to assess the satisfaction with quality of vision and night vision.
Preoperative contrast sensitivity scores were compared between the two groups and compared to one and three months postoperative contrast sensitivity. Preoperatively the contrast sensitivity of group 1 (low myopia) is better than that of group 2 (moderate myopia); these differences persisted after 1 and 3 months.
One month postoperatively, there was a significant decrease on contrast sensitivity at 12 cpd only, which disappeared after 3 months.
Scotopic pupillary diameters were compared between the two groups preoperatively using both Colvard pupillometer and Wave Scan aberrometer, there was no significant difference between the 2 groups.
Scotopic pupillary diameters were compared with preoperative contrast sensitivity, one and three months postoperative contrast sensitivity. We found that the pupillary diameter does not affect contrast sensitivity preoperatively, but larger pupil diameter was accompanied by lower contrast sensitivity level at 3 cpd one month postoperatively and 12 cpd 3 months postoperatively.
Results of the questionnaire were compared using the Kruskal Wallis test. Comparisons between scotopic pupillary diameters were done. The quality of scotopic vision was not affected by the changes of pupillary diameter.