[Orbscan II-assisted intraocular lens power calculation after LASIK]

To evaluate the accuracy of keratometric value derived from one zone of Orbscan II mean power map after Laser in situ keratomileusis (LASIK) in combination with Holladay IOL Consultant software to calculate the intraocular lens (IOL) power.

A two-part study was conducted at a referral practice. Part 1 was a prospective study of 118 eyes undergoing LASIK. The changes in Orbscan II mean power maps at four central zones (1.5, 2.0, 2.5 and 3.0 mm) were compared with the cornea power calculated from pre-LASIK data to determine the optimum Orbscan II correlation zone. In Part 2, the power of optimum measured by Orbscan II after LASIK was applied to IOL calculations for 62 eyes undergoing LASIK. And the results were compared with the IOL power calculated by the pre-LASIK data.

(1) An analysis at the Orbscan II 1.5 mm measurement zone demonstrated an underestimation of net cornea power after LASIK while the 3.0 mm zones demonstrated an overestimation. The 2.0 mm and 2.5 mm zones best approximated the net cornea power calculated from pre-LASIK data; (2) The cornea power at 2.5 mm from Orbscan II was selected for IOL calculations in combination with Holladay IOL Consultant software Holladay II and HofferQ formula. The refractive error calculated by Holladay II and HofferQ formula were (0.47 ± 0.75) D and (0.52 ± 0.83) D versus the IOL power calculated by clinical history method. The refractive errors of two formula within ± 0.50 D were 48.4% and 43.5% and within ± 1.0 D 80.6% and 74.2%.

The cornea power from 2.5 mm Orbscan II zone after LASIK in combination with Holladay II or HofferQ formula can accurately predict the IOL power for cataract surgery.