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M. Tang, Y. Li, D. Huang; Corneal Topography and Power Measurement With Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5791.
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To measure anterior, posterior and total corneal power with optical coherence tomography (OCT).
A commercially available Fourier-domain OCT system (RTVue, Optovue Inc.) with a speed of 26,000 axial scans per second and axial resolution of 5 microns in tissue was used. A corneal adaptor module (CAM), which includes an adaptor lens and special software, was attached to the retinal scanner in order to image the cornea. The corneal mapping scan pattern consisted of 6-mm line scans on 8 meridians centered on the pupil completed in 0.32 second. Five consecutive scans were recorded in each measurement set and the power measurement was averaged from the most consistent 3 scans. Corneal surfaces were identified by the built-in software and anterior and posterior corneal power was calculated from a spherical fit over the central 3mm diameter area. The study included 39 eyes from 20 normal subjects, each measured 3 times during one visit. The reproducibility was evaluated by the pooled standard deviation of repeat measurements. The OCT measurements were compared with Orbscan II Sim-K (Bausch & Lomb), which is based on Placido ring reflections.
The repeatability of OCT anterior, posterior and total corneal power measurement were 0.24, 0.04 and 0.24 D respectively. The OCT and Orbscan II derived anterior and total corneal powers are shown in the table. There was no statistically significant (p > 0.05) difference between the two instruments.
OCT corneal power measurement can have precision and accuracy that are similar to those of Placido-ring topography. Unlike Placido-ring technology, however, OCT is capable of measuring both anterior and posterior corneal powers, and does not depend on specular reflection from a smooth tear film. Thus it may be a more robust method for measuring corneal power in postoperative corneas and irregular corneas.
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