Presbyopia is an age related, gradual loss of accommodation, mainly due to changes in the crystalline lens. As part of research efforts to understand and cure this condition, ex vivo, cross-sectional optical coherence tomography images of crystalline lenses were obtained by using the Ex-Vivo Accommodation Simulator (EVAS II) instrument and analyzed to extract their physical and optical properties. Various filters and edge detection methods were applied to isolate the edge contour. An ellipse is fitted to the lens outline to obtain central reference point for transforming the pixel data into the analysis coordinate system. This allows for the fitting of a high order equation to obtain a mathematical description of the edge contour, which obeys constraints of continuity as well as zero to infinite surface slopes from apex to equator. Geometrical parameters of the lens were determined for the lens images captured at different accommodative states. Various curve fitting functions were developed to mathematically describe the anterior and posterior surfaces of the lens. Their differences were evaluated and their suitability for extracting optical performance of the lens was assessed. The robustness of these algorithms was tested by analyzing the same images repeated times.
Presbyopia is the age related, gradual loss of accommodation, mainly due to changes in the crystalline lens.
As part of research efforts to understand and cure this condition, ex vivo, cross-sectional OCT images of
crystalline lenses were obtained and analyzed to extract their physical and optical properties. The raw OCT
images are distorted, as the probing beam passing through media of different refractive indices and
refraction on curved surfaces. In a first step, various filters, edge detection and pattern matching methods
are applied to isolate the edge contour. An ellipse is fitted to the lens outline to obtain central reference
point for transforming the pixel data into the analysis coordinate system. This allows for the fitting of high
order equation to obtain a mathematical description of the edge contour, which obeys constraints of
continuity as well as zero to infinite surface slopes from apex to equator. Robustness of these algorithms
are tested by analyzing the images at various contrast levels. Gradient refractive index of the lens is
determined and the physical shape is reconstructed. In a further refinement, the refraction on the curved
anterior surface is compensated to obtain the actual shape of the posterior surface. Once the physical shape
is fully reconstructed, the optical properties are determined by fitting conic sections to both surfaces and
calculating the power profile across the lens. The relative contribution of each of these refinement steps is
investigated by comparing their influence on the effective power of the lens.
Cataract surgery usually involves the replacement of the natural crystalline lens with a rigid or foldable intraocular
lens to restore clear vision for the patient. While great efforts have been placed on optimising the shape
and optical characteristics of IOLs, little is know about the mechanical properties of these devices and how
they interact with the capsular bag once implanted. Mechanical properties measurements were performed on 8
of the most commonly implanted IOLs using a custom build micro tensometer. Measurement data will be
presented for the stiffness of the haptic elements, the buckling resistance of foldable IOLs, the dynamic
behaviour of the different lens materials and the axial compressibility. The biggest difference between the lens
types was found between one-piece and 3-piece lenses with respect to the flexibility of the haptic elements
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