Comparison of total keratometry with corneal power measured by optical low-coherence reflectometry and placido-dual Scheimpflug system

Abstract

Purpose: To compare the total keratometry (TK) and astigmatism measurements in eyes with cataract using automated keratometry of swept-source optical coherence tomography (ss-OCT), optical low-coherence reflectometry (OLCR), simulated keratometry (SimK), and total corneal power (TCP) of combined placido-dual Scheimpflug imaging system. Setting: The study was conducted at LV Prasad Eye Institute, Hyderabad, India. Design: Retrospective evaluation of electronic medical records of patients who were evaluated for cataract surgery Methods: Twenty-eight eyes of 28 patients were included in the study. All patients evaluated for cataract surgery underwent corneal power measurements using three devices: ssOCT, OLCR, and combined placido-dual Scheimpflug imaging were included in the study. Vector analysis was performed to evaluate corneal astigmatism and Bland-Altman analysis was conducted to evaluate the limits of agreement of similar parameters among devices. Results: The mean TK was statistically significantly different from the keratometry obtained from optical biometers and values measured by the Scheimpflug imaging system. The magnitude of mean difference was greater between TK and TCP (0.75 ± 0.25) compared to other variables. The mean difference in astigmatism between TK, ss-OCT-K (0.09 ± 0.12, p = 0.48), OCLR-K (0.10 ± 0.48, p = 0.91), and TCP (0.09 ± 0.47, p = 0.31) was not statistically significant but was statistically significant between TK and SimK values (0.23D ± 0.49D). The axis of orientation (<20°) of astigmatism was comparable (100%, 28 eyes) between two keratometry variables measured by ss-OCT. Conclusion: There appears to be a greater correlation of automated keratometry, and TK values obtained from ss-OCT compared to other variables studied. The measurements from TK, Simk, and TCP cannot be used interchangeably.

Evaluation of corneal power from an AS-OCT thick lens model and ray tracing: reliability of the keratometer index

“…1 With the new generation of corneal tomographers, based on either slit projection techniques (Scheimpflug tomography) or optical coherence tomography (OCT), the shape of the corneal front and back surfaces can be evaluated together with the corneal thickness profile in a large central zone of more than 8 mm. [13][14][15][16][17][18][19] This measurement technique is not restricted to situations with an intact tear film of good reflectivity. All tomographers provide information on the radius of curvature of the flat and steep meridians together with the orientations of the respective axes for the corneal front and back surfaces.…”