Abstract
Purpose:To compare the corneal power measurements obtained using different topographic instruments after myopic photorefractive keratectomy (PRK).Methods:Patients with myopia who were candidates for corneal refractive surgery were sequentially included. Pre-PRK and six months post-PRK corneal powers were measured using Javal manual keratometer, Orbscan II, Galilei, Tomey TMS4, and EyeSys 2000 topographers. Measured values were compared with those obtained using the clinical history method (CHM).Results:This study included 66 eyes of 33 patients. The lowest keratometric measurements were obtained using the Galilei topographer (42.98 ± 1.69 diopters, D) and the highest measurements were obtained using the Javal manual keratometer (43.96 ± 1.54 D) preoperatively. The same order was observed postoperatively. Effective refractive power (EffRP) measured using EyeSys was most similar to the values obtained using CHM (ICC, intraclass correlation coefficient = 0.951), followed by the total corneal power measured using the Galilei system (ICC = 0.943). The values obtained using the adjusted EffRP formula (EffRP – 0.015*Δ Refraction – 0.05) were more consistent with the values obtained using CHM (ICC = 0.954) compared to those obtained with the adjusted average central corneal power formula measured using the Tomey system (ICC = 0.919).Conclusion:Post-PRK corneal powers measured using the adjusted EffRP formula were the most similar to values obtained using CHM.
Highlights
Photorefractive keratectomy (PRK) is an approved method for application of excimer laser in corneal refractive surgery
A significant source of error is the fact that most keratometers measure the central corneal radius of curvature and assume a sphero‐cylindrical cornea, which is incorrect after myopic refractive surgery,[14] leading to overestimation of the corneal refractive power and hyperopic outcomes.[12,15]
Since the cornea becomes flattened after myopic laser surgery, the anterior chamber is incorrectly assumed to be shallow in the widely used third generation Intraocular lens (IOL) formulas, such as the Holladay, Hoffer Q, and SRK/T, while it has remained negligibly altered.[16]
Summary
Photorefractive keratectomy (PRK) is an approved method for application of excimer laser in corneal refractive surgery. It has been shown to be effective and safe in the correction of refractive errors.[1,2] there are still significant challenges including inaccurate measurement of corneal power and intraocular pressure after corneal laser refractive surgery.[3,4,5,6,7] Intraocular lens (IOL) power calculation
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