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Corrected Scheimpflug crystalline lens/IOL imaging may drive clinical advances
J Refract Surg. 2009;25(5):421-428.
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Corrected anterior segment Scheimpflug imaging may provide insight into crystalline lens physiology comparable with those currently yielded by optical coherence tomography.
“Applications of corrected Scheimpflug crystalline lens/IOL in vivo imaging include customized eye modeling, studies of quantitative changes of crystalline lens morphology with accommodation, aging or disease, and assessment of new intraocular implants and surgical approaches for the correction of presbyopia,” the study authors said.
The authors used the Pentacam (Oculus) to obtain raw images of a model eye, with a PMMA contact lens simulating the cornea and a conventional spherical silicone IOL acting as the lens, and a normal human phakic eye. The Pentacam and Topcon SL-45 Scheimpflug camera were used to obtain raw images of the natural eye. Ray tracing algorithms were used to correct geometrical and optical distortion.
Anterior and posterior corneal radii, corneal thickness, anterior chamber depth, lens thickness and posterior lens radius were assessed.
Uncorrected raw images showed flatter surfaces and thinner ocular structures than corrected images. The largest discrepancy was between uncorrected and corrected images of the posterior lens radius of curvature (109% for the artificial eye and 59% for the natural eye).
Geometrical and optical distortion correction algorithms improved the accuracy of estimated anterior lens radii of curvature by 30% to 40%, and the posterior lens radii of curvature by 50% to 100%, the authors said.
“This is particularly relevant in current Scheimpflug imaging-based instruments available on the market, as the commercial software typically provides corrections for the anterior and posterior corneal surface, but not for the crystalline lens,” they said.
Optical imaging of intraocular structures must be corrected to account for distortions created by intermediary structures through which light passes. For example, an image of the posterior capsule of the lens is distorted by both surfaces of the cornea and the anterior surface of the lens. Correcting for these distortions creates a more accurate geometric description of the eye and may be critical for the development and application of innovative intraocular devices such as phakic refractive lenses and accommodative pseudophakic lenses.
– Mark Packer, MD, FACS
Drs. Fine,
Hoffmann and Packer Ophthalmologists, Eugene, Ore.