Corneal power changes with Scheimpflug rotating camera after hyperopic LASIK

Abstract

To evaluate surgically induced refractive change (SIRC) by manifest refraction and corneal power changes using an automated keratometer and Scheimpflug rotating camera, and to find the best keratometric measurements reflecting SIRC after hyperopic laser-assisted in situ keratomileusis (LASIK).This retrospective study included 18 eyes of 18 patients undergoing hyperopic LASIK using the Schwind Amaris 750S excimer laser. All measurements were performed preoperatively and 12 months postoperatively. Cycloplegic manifest refractions were performed and keratometric measurements were obtained via an RK-5 automated keratometer and a Pentacam rotating Scheimpflug camera. Sim K, true net power (TNP), and total corneal refractive power (TCRP) at 2.0 to 5.0 mm were analyzed using a Scheimpflug camera.The mean manifest refractive changes in the spherical equivalent (SE) at the corneal plane were 2.32 ± 1.65 D at 12 months postoperatively. The refractive power changes by the automated keratometer and Sim K were significantly less than SIRC (P = .043 and P = .048, respectively). Both TNP and the TCRP in the 5.0 mm zone produced lesser mean differences with SIRC (0.05 D and 0.06 D) and showed closer agreements with SIRC on Bland-Altman plots and higher correlation coefficients with SIRC.Corneal power measured on the anterior corneal surface underestimated SIRC. TCRP at the 5.0 mm zone provided by a Pentacam Scheimpflug camera reflected the SIRC accurately and precisely, and would be applicable for prediction of intraocular power before cataract surgery and follow-up measurement of corneal refractive power.

Comparison of Corneal Power Difference Maps with Achieved Myopic Correction Using Scheimpflug Tomography After LASIK, PRK, and SMILE

“… 2 , 27 , 28 Whang et al preferred centration over the apex, given that the center of the pupil may change as the pupil changes shape. 19 Qian et al 8 and Savini et al 10 opted for centration over the pupil. Naeser et al found there to be no significant difference in centration over pupil or apex.…”

Scheimpflug analysis of corneal power changes after hyperopic small incision lenticule extraction

“…All of them have come to the conclusion that TCRP is more suitable for actual refractive changes than only analyzing the axial refractive power of corneal surface [ 12 , 14 ]. In hyperopic LASIK [ 14 , 15 ], the TCRP 4.0 mm/5.0 mm zone calculation was proved to best predicted the surgically induced change in manifest refraction. Though their comparison standard is sphere equivalent change, not CHM in present study.…”

“…Different from myopia, hyperopia is corrected by increasing the central refractive power and reducing the peripheral refractive power. There are a few studies about cornea power change after hyperopic surgery, and most of them focused on hyperopic LASIK [11,[14][15][16][17]. Hyperopic LASIK used excimer laser to ablate midperiphery cornea area.…”

Evaluation of the B/F Ratio Distribution of Cataract Patients Without Corneal Abnormalities and Its Effect on Ocular Parameters

“…Recently, the TNP and TCRP (total corneal refractive power) have attracted greater attention because they take into account the true refractive index of the anterior and posterior surface curvature and the directly measured radius of the posterior surface curvature. In contrast, TCRP also reflects the true corneal thickness and corneal asphericity value [27,28]. The difference between TNP and simK lies only in the true refractive indexes of the anterior and posterior surfaces of the cornea and the posterior surface curvature radius.…”