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We present in vivo noninvasive retinal and choroidal perfusion maps with phase-variance optical coherence tomography (pvOCT). We acquired a pvOCT volumetric data set of a normal subject and visualized blood circulation in the retina and the choroid. En face projection views of the retina as well as the choroid were generated from a manually segmented volumetric data set. In addition, the processed pvOCT images were compared to current standard imaging modalities used for retinal and choroidal vasculature visualization in clinical settings, including fluorescein angiography (FA) and indocyanine green angiography (ICGA).

Purpose. To estimate changes in surface shape and gradient refractive index (GRIN) profile in primate lenses as a function of accommodation. To quantify the contribution of surface shape and GRIN to spherical aberration changes with accommodation. Methods. Crystalline lenses from 15 cynomolgus monkeys were studied in vitro under different levels of accommodation produced by a stretching system. Lens shape was obtained from optical coherence tomography (OCT) cross-sectional images. The GRIN was reconstructed with a search algorithm using the optical path measured from OCT images and the measured back focal length. The spherical aberration of the lens was estimated as a function of accommodation using the reconstructed GRIN and a homogeneous refractive index. Results. The lens anterior and posterior radii of curvature decreased with increasing lens power. Both surfaces exhibited negative asphericities in the unaccommodated state. The anterior surface conic constant shifted toward less negative values with accommodation, while the value of the posterior remained constant. GRIN parameters remained constant with accommodation. The lens spherical aberration with GRIN distribution was negative and higher in magnitude than that with a homogeneous equivalent refractive index (by 29% and 53% in the unaccommodated and fully accommodated states, respectively). Spherical aberration with the equivalent refractive index shifted with accommodation toward negative values (-0.070 lm/diopter [D]), but the reconstructed GRIN shifted it farther (-0.124 lm/ D). Conclusions. When compared with the lens with the homogeneous equivalent refractive index, the reconstructed GRIN lens has more negative spherical aberration and a larger shift toward more negative values with accommodation. © 2013 The Association for Research in Vision and Ophthalmology, Inc.

Progress in biomedical optics and imaging, vol. 12, No. 3

We present recent developments from a phase variance based motion contrast method of retinal vascular OCT imaging, called phase variance contrast optical coherence tomography (PV-OCT). Using a 25 kHz spectral domain optical coherence tomography (SDOCT) system, the vascular visualization capabilities of this contrast method are demonstrated with composite images created from multiple data sets. Wide field vascular images extending over the fovea and optic nerve head are presented as well as microvascular retinal images over the fovea to demonstrate the trade-offs between imaging speed and vascular visualization.

An investigation was carried out with the aim of reconstructing the gradient index (GRIN) profile of human crystalline lenses ex-vivo using optical coherence tomography (OCT) imaging with an optimization technique and to study the dependence of the GRIN profile with age. Cross-sectional images of nine isolated human crystalline lenses with ages ranging from 6 to 72 (post-mortem time 1 to 4 days) were obtained using a custom-made OCT system. Lenses were extracted from whole cadaver globes and placed in a measurement chamber filled with preservation medium (DMEM). Lenses were imaged with the anterior surface up and then flipped over and imaged again, to obtain posterior lens surface profiles both undistorted and distorted by the refraction through the anterior crystalline lens and GRIN. The GRIN distribution of the lens was described with three variables by means of power function, with variables being the nucleus and surface index, and a power coefficient that describes the decay of the refractive index from the nucleus to the surface. An optimization method was used to search for the parameters that produced the best match of the distorted posterior surface. The distorted surface was simulated with accuracy around the resolution of the OCT system (under 15 mm). The reconstructed refractive index values ranged from 1.356 to 1.388 for the surface, and from 1.396 to 1.434 for the nucleus. The power coefficient ranged between 3 and 18. The power coefficient increased significantly with age, at a rate of 0.24 per year. Optical coherence tomography allowed optical, non-invasive measurement of the 2D gradient index profile of the isolated human crystalline lens ex vivo. The age-dependent variation of the changes is consistent with previous data using magnetic resonance imaging, and the progressive formation of a refractive index plateau.

Implantation of an intraocular lens (IOL) has become a standard procedure for vision correction following cataract surgery. Continually rising demand for perfect long-term post-operative vision has led to a proliferation of novel IOL designs. Though a standard monofocal or single-vision IOL affords near perfect vision for a fixed viewing distance, a patient may yet require supplementary optical devices for comfortable near vision.The quest for restoration of accommodative ability in pseudophakic eyes have led to number of advancement in the technology including the development of accommodating intraocular lenses. Translating-optics accommodating intraocular lenses is a rapidly emerging class of implant devices which has debatably gained increasing popularity among scientists and practitioners within a short period of time. A large variety of accommodating intraocular lenses, prominently represented by single-element and two-element designs, has been proposed. These devices work under the principle of changing effective power by shifting axial position of the optical element within the eye which is brought about by complex opto-mechanical arrangements.Earlier studies on accommodating intraocular lenses are primarily focused on their accommodative capacity. A comprehensive theoretical design analysis and evaluation of their performance is lacking. Virtually no report exists investigating other important aspects of their optical performance such as magnification, aberrations and optimization of retinal image quality. This thesis, using paraxial optical principles, undertakes a systematic development of the optical principles involved in the evaluation of design and performance of translating optics accommodating intraocular lenses and applies the results to seek superior performance.In the thesis, it is demonstrated that an appropriate design of accommodating intraocular lens may enhance performance overcoming a long-standing unmet visual need of pseudophakic presbyopi

We quantify the posterior surface distortions in optical coherence tomography (OCT) images of isolated crystalline lenses. The posterior radius of curvature and asphericity obtained from OCT images acquired with the beam incident first on the anterior, and then the posterior, surface were compared. The results were compared with predictions of a ray-tracing model which includes the index gradient. The results show that the error in the radius of curvature is within the measurement reproducibility and that it can be corrected by assuming a uniform refractive index. However, accurate asphericity values require a correction algorithm that takes into account the gradient.