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D Dursun, V Fernandez, SH Yoo, W Feuer, RW Knighton; Birefringence Properties of the Central Cornea After LASIK . Invest. Ophthalmol. Vis. Sci. 2002;43(13):173.
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Purpose: To determine the changes in corneal birefringence that result from ablation of collagen fibrils in the corneal stroma by laser in situ keratomileusis (LASIK). Methods: Corneal birefringence was measured with a corneal polarimeter (Knighton & Huang, IOVS, in press) that illuminated the eye with a yellow (585 nm) light emitting diode and provided a view of the fourth Purkinje image through crossed polarizers and a variable waveplate. Using the waveplate to extinguish the image yielded values for the axis and retardance of the corneal birefringence. Measurements before the surgery were compared to those at postoperative day 7. Results: 39 eyes(18 OD and 21 OS ) of 38 patients that underwent LASIK surgery were evaluated. Preoperative retardance measurements in the right eyes (left eyes) ranged from 29 to 214 (3 to 140) nm. One week postoperative measurements were within 20 nm of the preoperative value in 60% (53%) of eyes. Forty percent of both right and left eye measurements were within 10% of their preoperative values. However 11% (11%) changed by more than 30 nm. Conclusion: The majority of eyes did not demonstrate substantial change in retardance following LASIK; however about 10% of eyes did demonstrate large changes.
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