Comparison of central corneal thickness measurement by scanning slit topography, infrared, and ultrasound pachymetry in
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ORIGINAL PAPER
Comparison of central corneal thickness measurement by scanning slit topography, infrared, and ultrasound pachymetry in normal and post-LASIK eyes Wing-cheung Ho . Philip Tsze-ho Lam . Thomas Yee-hang Chiu . Mandy Ching-man Yim . Fion Tung-ching Lau
Received: 9 March 2020 / Accepted: 20 June 2020 Ó Springer Nature B.V. 2020
Abstract Objectives To compare central corneal thickness (CCT) measurements by scanning slit topography (SST), infrared pachymetry (IRP), and ultrasound pachymetry (USP), and their agreement in normal and post-laser in situ keratomileusis (LASIK) eyes. Methods Sixty normal and 35 post-LASIK subjects were recruited. Only one eye from each subject was analyzed. Non-contact pachymetry was performed first, and the order for SST (Orbscan IIz) and IRP (Tonoref III) was randomized for each patient, to be followed by contact USP (Echoscan US-4000). Pearson’s correlation, paired t test, and Bland–Altman plots were used to investigate association, difference, and agreement among different instruments respectively. Results The measurements obtained with the instruments were highly correlated. Compared to CCT determined by USP (CCTUSP), CCT determined by SST (after correction with acoustic factor) (CCTSSTC) was thicker by 7 lm in normal eyes (P \ 0.001). There was no significant difference between CCTSSTC and CCTUSP (P = 0.128), but a thickness-dependent deviation in post-LASIK eyes (P = 0.003). The CCT
W. Ho P. T. Lam (&) T. Y. Chiu M. C. Yim F. T. Lau Eye Centre, Hong Kong Baptist Hospital, 222 Waterloo Road, Kowloon Tong, Hong Kong, People’s Republic of China e-mail: [email protected]
determined by IRP (CCTIRP) was thicker than CCTUSP in normal (P \ 0.001) and post-LASIK eyes (P \ 0.001) and demonstrated proportional overestimation with thinner corneas, with less predictable ultrasonic equivalent corneal thickness in normal eyes. Conversely, CCTIRP significantly underestimated CCT compared to CCTSST and showed increasing underestimation with thinner corneas in both normal and post-LASIK eyes (both P \ 0.001). Conclusion Central corneal thickness determined by SST, IRP and USP were not interchangeable or interconvertible, probably attributed to difference in methodologies. Compensation with algorithms may improve agreements amongst instruments. Keywords Central corneal thickness Orbscan Optical pachymetry Infrared pachymetry PostLASIK
Introduction Pachymetry plays a crucial role in the preoperative assessment for corneal surgery. In laser refractive surgery, estimation of the residual stromal thickness is necessary to reduce the risk of iatrogenic keratectasia [1]. In collagen crosslinking, by limiting ultraviolet light irradiation to the anterior stroma, the endothelium is protected from potential damage during treatment [2]. Central corneal thickness (CCT) is a
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risk factor (independent of intraocular pressure) associated with primary open-angle glaucoma [3]. It has become indispensable in risk str
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