Clinical Study
Eye (2008) 22, 332–339; doi:10.1038/sj.eye.6702545; published online 25 August 2006
Risk factors for postoperative cylindrical prediction error after laser in situ keratomileusis for myopia and myopic astigmatism
R B Vajpayee1, D Ghate1, N Sharma1, R Tandon1, J S Titiyal1 and R M Pandey2
- 1Dr Rajendra Prasad Center for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India
- 2Department of Biostatistics, All India Institute of Medical Sciences, New Delhi, India
Correspondence: RB Vajpayee, Dr Rajendra Prasad Center for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi 110029, India. Tel: +91 11 26593192; Fax: +91 11 26588919; E-mail: rasikvajpayee@rediffmail.com
Received 8 August 2005; Revised 5 July 2006; Accepted 5 July 2006; Published online 25 August 2006.
Abstract
Purpose
To study the risk factors for the occurrence of cylindrical prediction error (PE) after laser in situkeratomileusis (LASIK) for myopia and myopic astigmatism.
Methods
The study was a nested case–control study. Five hundred eyes of 252 consecutive patients who underwent LASIK for myopia and myopic astigmatism on the Chiron Technolas 217C laser and completed 6 months of follow-up. There were 435 controls and 65 cases based on the postoperative refractive cylindrical PE. The probable risk factors studied included preoperative sphere and cylinder, keratometry, pachymetry, suction ring used, flap thickness, hinge centeration, optic zone, ablation depth, and intraoperative complications.
Results
By univariate analysis, the cylindrical PE was found to be associated with preoperative spherical equivalent higher than -6 D (
2=10.83; P=0.001), preoperative sphere higher than -6 D (2=6.15, P=0.013), preoperative cylinder more than -0.75 D (2=6.61; P-value=0.010), and an optic zone less than 5.5 mm (2=19.3; P=0.001). Risk factors for postoperative astigmatism by stepwise multivariate logistic regression analysis were an optic zone of less than 5.5 mm with an odds ratio (OR) of 2.81 (95% confidence interval (CI)=1.62–4.86) and preoperative cylinder more than -0.75 D with an OR of 1.60 (95% CI=0.92–2.77).
Conclusion
Postoperative astigmatism (as indicated by the cylindrical PE) is more likely to occur with an optic zone of less than 5.5 mm and a higher preoperative cylindrical error.
Keywords:
prediction error, myopic LASIK, surgically induced astigmatism
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