Differences between Scheimpflug and optical coherence tomography in determining safety distances in eyes with an iris-fixating phakic intraocular lens

Abstract

Purpose To investigate the agreement and reliability of anterior segment optical coherence tomography (AS-OCT) and Scheimpflug imaging in measuring the distance from the anterior edge of an iris-fixated phakic intraocular lens (IF-pIOL) to the corneal endothelium. Methods Anterior segment configuration was assessed in a total of 62 eyes of which 25 hyperopic and 37 myopic eyes, all corrected with an IF-pIOL. Measurements were performed by two independent observers using AS-OCT (Visante, Model 1000, Carl Zeiss Meditec Inc.) and Scheimpflug imaging (Pentacam HR, Oculus Optikgerate). The distance from the anterior edge of the pIOL to the endothelium was measured in five different positions using both modalities with their corresponding pIOL software. The measurements as well as the inter-and intra-observer reliability of the two imaging modalities were then compared. Results Distance measurements for all positions performed by AS-OCT were found to be significantly larger than those performed by Scheimpflug imaging, with mean differences ranging from 0.11 to 0.22 mm. Both instruments exhibited good interand intra-observer reliability. Conclusion Anterior pIOL edge to endothelium distance measurements by AS-OCT and Scheimpflug imaging have good intraand inter-observer reliability. However, as AS-OCT provides larger measurements, these two modalities cannot be used interchangeably. Correction of this difference might be essential for proper decision-making during pre-operative screening for pIOL implantation and post-operative safety monitoring.

Correction Method for Optical Scaling of Fundoscopy Images: Development, Validation, and First Implementation

“…The proposed model relies on clinical measurements of the eye, which always have some uncertainties. 30 However, these uncertainties have limited impact on the calculated magnification, as is shown by increasing the axial length or corneal curvature by 0.1 mm or the RSE by 0.5 D, which resulted in respective 0.5%, 0.6%, and 3.3% changes in magnification for the Escudero-Sanz–Navarro eye model. As the exact optical properties of the lens, including curvature and spatially varying index of refraction, are not easily determined clinically, we fitted the curvature of the posterior lens surface so that the RSE of the eye model would match the clinically measured RSE.…”

“… 26 For the healthy eyes, these data had been acquired as part of earlier scientific studies. 24 , 27 – 30 For the uveal melanoma eyes, 48 consecutive patients treated with proton beam therapy who had given written informed consent for the retrospective use of their data were included. From these patients, 19 were excluded due to missing refraction data, six due to incomplete biometry data, and two due to astigmatism of >3 D. This resulted in 33 phakic, 29 pseudophakic, 11 pIOL, and 21 uveal melanoma subjects.…”

Diagnostic Techniques to Increase the Safety of Phakic Intraocular Lenses

“…Due to its longer wavelength than is used in Scheimpflug photography, it is less affected by opacities, can be used to examine deeper structures, and is better suited for the analysis of the iridocorneal angle [90,91]. AS-OCT has also been demonstrated to be suitable for the assessment of pIOL positioning [56,[92][93][94].…”

Current Developments in Corneal Topography and Tomography

“…One of the most threatened potential complications of any type of anterior segment surgery, and particularly after anterior chamber and iris-fixated IOLs, is accelerated endothelial cell loss [49,50]. This risk has been shown to be negatively correlated with the anterior chamber depth, and the position of these IOLs in the anterior chamber is one of the main safety parameters in both preoperative screening and follow-up [51]. Assessment of anterior chamber morphology is also critical for implantable collamer lens (ICL) assessment; if an inserted ICL is too large, it might bow anteriorly, causing anterior chamber shallowing and introducing a risk of pupillary block and angle-closure glaucoma [52,53] In contrast, if the ICL vault is insufficient, it might potentially result in contact between the ICL and the crystalline lens, causing subsequent cataract formation [54].…”