Purpose To evaluate the agreement of central corneal thickness (CCT) measurement between Scheimpflug imaging and ultrasound (U/S) pachymetry in keratoconic eyes, and investigate factors that affect the agreement.
Methods This post hoc analysis within a prospective, observational non-randomised study preformed at the Kensington Eye Institute, Toronto, Ontario, Canada, included crosslinking candidates with progressive keratoconus (KC). Main outcome measures were the agreement of CCT measurement between Scheimpflug imaging (Pentacam Oculus, Wetzlar, Germany) and U/S pachymetry (PachPen 24–5100, Accutome Inc., Malvern, Pennsylvania, USA), and factors that affect the agreement.
Results A total of 794 keratoconic eyes of 456 subjects with a mean age of 27.6±8.0 years (69.7% males and 49.6% right eyes) were included. Agreement between devices was moderate (intraclass correlation coefficient: 74.9%, Bland–Altman limits of agreement: −48.5 μm to +62.5 μm). In a multivariable analysis, cone decentration (p<0.001, coefficient +10.13 [+6.73 to +13.53 95% CIs]) and Kmax (p<0.001, coefficient +0.68 [+0.46 to +0.90 95% CIs]) were significantly associated (both clinically and statistically) with the level of agreement between the devices; the discrepancy in CCT between the devices increased on average by 10.13 μm for every mm of cone decentration, and by 6.8 μm for every 10D of Kmax. Age, corneal astigmatism and spherical equivalent were statistically but not clinically significant factors affecting agreement.
Conclusion The agreement of CCT measurement between Scheimpflug imaging and U/S pachymetry in KC was moderate. To ensure the safety of crosslinking in keratoconic corneas, Scheimpflug and U/S CCT measurements should not be used interchangeably, especially in steep corneas and corneas with decentred cones.
- Diagnostic tests/Investigation
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NS and WH contributed equally to the manuscript.
Contributors Nir Sorkin, NS and WH contributed to design, data acquisition, analysis, interpretation, drafting and revising of the work. AO contributed to data acquisition and revising of the work. HJ contributed to design, data acquisition, analysis and revising of the work. LH, LS and MM contributed to the design, interpretation of data and revising of the work. Vera Stiuso and Ann Whelan contributed to data collection.
Funding Kensington Research Institute, Toronto, Ontario, Canada (Grant #57). The data were part of an initiative by the Kensington Eye Institute to report on the efficacy and safety of crosslinking, crosslinking with intrastromal ring segments, and crosslinking with topography-guided photorefractive keratectomy in Ontario, Canada.
Competing interests MM is a paid consultant for Eye Yon Medical and Lapidot Medical. CC has received support from Alcon Laboratories Inc, Allergan, Bausch & Lomb, Santen, Shire, Tearlab, Labtician Thea, and Johnson & Johnson. AS has been a paid consultant for Abbott Medical Optics, AbbVie, Alcon Laboratories Inc, Allergan, Bausch & Lomb, Santen Inc, Shire, Acqueous, and Labtician Thea. DR has received support from Alcon Laboratories Inc and Johnson & Johnson. TR has been a paid consultant for Alcon Laboratories Inc, Johnson & Johnson, and AbbVie.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement No data are available.