Comparison of corneal power obtained from VERION image-guided surgery system and four other devices

Abstract

Purpose: To assess the corneal keratometric values obtained using the VERION image-guided surgery system and other devices.

Methods: This study evaluated the right eyes of 115 cataract patients before intraocular lens (IOL) implantation through consecutive tests using 5 devices: VERION Reference Unit, Placido-based corneal topography (OPD-Scan III), monochromatic light-emitting diodes (LenStar LS900 and AL-Scan), and rotary prism technology (auto kerato-refractometer KR-8800). Analyzed parameters were corneal steep and flat keratometric values (Ks and Kf) and corneal astigmatism and axis. These parameters were evaluated using the one-sample two-tailed t-test and the 95% limits of agreement (95% LOAs) between the devices.

Results: The mean corneal cylinder value measurements were -0.97±0.63 D, -0.88±0.60 D, -0.90±0.69 D, -0.90±0.67 D, and -0.83±0.60 D with VERION, LenStar, AL-Scan (2.4 mm), OPD III, and KR-8800, respectively. Only KR-8800 showed a significant difference from VERION in the corneal cylinder value (P<0.05). The mean differences in the Kf and Ks of VERION compared to those of OPD III were 0.18±0.45 D and 0.17±0.38 D (P<0.05), respectively. The 95% LOAs of Bland-Altman analysis for the corneal astigmatism axis of the VERION with LenStar, AL-Scan (2.4 mm), OPD III, and KR-8800 were -26.25° to 58.71°, -20.61° to 47.44°, -25.03° to 58.98°, and -27.85° to 65.17°, respectively.

Conclusion: None of the VERION parameters were significantly different from those of AL-Scan and LenStar. AL-Scan (2.4 mm zone) was especially similar to VERION. Wide LOAs are potential contributors to axis error in patients with toric IOL implants.

Keywords: corneal astigmatism; image-guided surgery system; phacoemulsification; surgical induced astigmatism; toric IOL.

Figure 1

Examples of relative angle differences.

Figure 2

Bland–Altman plot comparing the corneal cylinder obtained with VERION Reference Unit and 4 other devices (LenStar, AL-Scan [2.4 mm], OPD III, and KR-8800). Notes: The 95% LOAs ranged from −0.32 D to 0.93 D, −0.28 D to 0.84 D, −0.22 D to 0.87 D, and −0.22 D to 0.81 D, respectively. Dotted lines ±1.96 SD. Abbreviations: LOAs, limits of agreement; SD, standard deviation.

Figure 3

Bland–Altman plot comparing the corneal astigmatic axis obtained using VERION Reference Unit and 4 other devices (LenStar, AL-Scan [2.4 mm], OPD III, and KR-8800). Notes: The 95% LOAs ranged from −26.25° to 58.71°, −20.61° to 47.44°, −25.03° to 58.98°, and −27.85° to 65.17°. Dotted lines ±1.96 SD. Abbreviations: LOAs, limits of agreement; Kf, flattest keratometry; SD, standard deviation.