Abstract
Custom high-resolution high-speed anterior segment spectral domain optical coherence tomography (OCT) was used to characterize three-dimensionally (3-D) the human crystalline lens in vivo. The system was provided with custom algorithms for denoising and segmentation of the images, as well as for fan (scanning) and optical (refraction) distortion correction, to provide fully quantitative images of the anterior and posterior crystalline lens surfaces. The method was tested on an artificial eye with known surfaces geometry and on a human lens in vitro, and demonstrated on three human lenses in vivo. Not correcting for distortion overestimated the anterior lens radius by 25% and the posterior lens radius by more than 65%. In vivo lens surfaces were fitted by biconicoids and Zernike polynomials after distortion correction. The anterior lens radii of curvature ranged from 10.27 to 14.14 mm, and the posterior lens radii of curvature ranged from 6.12 to 7.54 mm. Surface asphericities ranged from −0.04 to −1.96. The lens surfaces were well fitted by quadrics (with variation smaller than 2%, for 5-mm pupils), with low amounts of high order terms. Surface lens astigmatism was significant, with the anterior lens typically showing horizontal astigmatism ( ranging from −11 to −1 µm) and the posterior lens showing vertical astigmatism ( ranging from 6 to 10 µm).
Highlights
The optical quality of the human eye is mainly determined by the geometrical and optical properties of two elements, cornea and crystalline lens
To quantify the effect of optical distortion from preceding surfaces on the crystalline lens shape, we evaluated difference maps, obtained as the subtraction of the elevation map estimated after full optical correction from the map obtained after fan distortion correction and a simple division of the optical distances by the refractive indices, both for the anterior and posterior lens surface
We provided the first report of lens surface shapes in vivo from optical coherence tomography (OCT) upon correction of optical distortion, we did not considered a Gradient Index (GRIN) in the lens
Summary
The optical quality of the human eye is mainly determined by the geometrical and optical properties of two elements, cornea and crystalline lens. Scheimpflug imaging allows acquisition of cross-sectional images of the crystalline lens, and with proper correction of the geometrical and optical distortions, the radii of curvature and asphericity of the lens surfaces can be obtained [16,17,18,23,24]. These non-optical techniques allow visualization of the entire crystalline lens and its neighboring ocular structures These are either invasive or time-consuming imaging methods, with significantly lower resolution than optical techniques, which impose major problems (low acquisition speed, motion artifacts or low sampling density) which prevent quantifying the crystalline lens geometry with high accuracy
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