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Surgically-induced astigmatism after laser in situ keratomileusis for spherical myopia.

PURPOSE
To characterize the surgically-induced-astigmatism (SIA) associated with spherical LASIK.


METHODS
Refractive outcomes in 70 eyes that underwent primary myopic LASIK with purely spherical ablation were analyzed. The Summit Apex Plus excimer laser was used. The Bausch & Lomb Hansatome with the 180-microm plate was used to produce superiorly hinged flaps. The relationship between refractive astigmatism and corneal topographic astigmatism was analyzed using linear regression and vector analysis.


RESULTS
There was a statistically significant negative correlation (slope = -0.21) between refractive surgically-induced astigmatism and preoperative topographic cylinder. A 0.24-D with-the-rule shift was also found. Surgically-induced astigmatism was not correlated with the magnitude of laser ablation.


CONCLUSION
The lamellar keratotomy portion of LASIK reduces pre-existing corneal astigmatism and produces a relative steepening of the hinge meridian.