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D. Huang, M. Tang; Corneal Power Measurement With Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3267.
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To measure anterior and posterior corneal topography and power with optical coherence tomography (OCT).
A commercially available Fourier-domain OCT system (RTVue, Optovue Inc.) capable of 26,000 axial scans per second was used in the study. An adaptor lens was attached to the scanning module in order to map the cornea. Corneal anterior and posterior elevation topographies were measured using a custom algorithm that accounts for refractive index transition. Total corneal power (sum of anterior and posterior corneal power) the over the central 3-mm circular area was calculated by curvature fitting. OCT scans were repeated 4 times during one visit. Reproducibility was evaluated by the pooled standard deviation of the repeat measurements. Normal, post-myopic LASIK and keratoconus subjects were recruited in an IRB-approved prospective study.
The average anterior and total corneal powers of post-LASIK and keratoconus groups were statistically different from the normal group (p < 0.01 for unpaired t-tests). The average posterior corneal power in the keratoconus group was more negative than normal eyes (p = 0.001). Post-LASIK and normal eyes had similar posterior powers (p = 0.45). The reproducibilities of the total corneal power measurement were 0.26D, 0.26D, and 0.70D for the normal, post-LASIK and keratoconus groups, respectively.
This is the first demonstration of OCT corneal power measurement that achieved a precision equivalent to Placido-ring topography. Unlike Placido-ring technology, OCT is capable of measuring both anterior and posterior corneal surfaces, and does not depend on specular reflection from a smooth tear film. Thus it may be a more robust method for measuring topography and power.
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