2007 Sep;23(7):677-80

Accuracy of Orbscan II in the assessment of posterior curvature in patients with myopic LASIK.

Cheng AC, Rao SK, Lam DS.

Department of Ophthalmology & Visual Sciences, The Chinese University of Hong Kong, Hong Kong Eye Hospital, Kowloon, Hong Kong. artcheng@netvigator.com

PURPOSE: To evaluate the accuracy of Orbscan II measurements in assessing posterior corneal curvature in patients undergoing myopic LASIK. METHODS: Using the Orbscan II, posterior corneal curvature was assessed pre- and postoperatively in 304 eyes that underwent myopic LASIK. The radius of curvature and corneal refractive power in diopters (D) were compared using the paired sample t test. RESULTS: The mean pre- and postoperative radius of posterior corneal curvature were 6.49 +/- 0.26 mm and 6.35 +/- 0.30 mm, respectively. Mean pre- and postoperative posterior corneal power were -6.17 +/- 0.25 D and -6.32 +/- 0.30 D, respectively, and the difference (0.14 +/- 0.14 D) was statistically significant (P < .01). CONCLUSIONS: Although the derived value for the power of the postoperative LASIK posterior corneal surface is overestimated using the Orbscan II, this small difference may not be clinically important. Orbscan II measurements can therefore be used (with caution) to measure posterior corneal curvature in patients with myopic LASIK for the assessment of intraocular lens power based on the Gaussian optics formula.