We present a method for calculating the ideal toric lens to implant in astigmatic patients following cataract surgery. We show that the online calculators provided by major toric IOL manufacturers are insufficient for both theoretical and practical reasons. We reveal important theoretical shortcomings in their approach, illustrated by a number of cases which demonstrate how the approach can lead to errors in lens selection. Our approach combines the spherical and cylindrical power calculations into one, and allows for lens data from any manufacturer to be used, eliminating the reliance on multiple programs.
We propose a method that allows an inexperienced observer, through the examination of the digital fundus image of a retina on a computer screen, to simply determine the presence of a cataract and the necessity to refer the patient for further evaluation. To do so, fundus photos obtained with a non-mydriatic camera were presented to an inexperienced observer that was briefly instructed on fundus imaging, nature of cataracts and their probable effect on the image of the retina and the use of a computer program presenting fundus image pairs. Preliminary results of pair testing indicate the method is very effective.
We present a symbolic approach based on matrix methods that allows for the analysis and computation of intraocular lens power following cataract surgery. We extend the basic matrix approach corresponding to paraxial optics to include astigmatism and other aberrations. The symbolic approach allows for a refined analysis of the potential sources of errors (“refractive surprises”). We demonstrate the computation of lens powers including toric lenses that correct for both defocus (myopia, hyperopia) and astigmatism. A specific implementation in Mathematica allows an elegant and powerful method for the design and analysis of these intraocular lenses.
Accurate diagnosis and treatment of disease is a function of how well the pathology can be imaged. Coregistering images from different modalities can offer significant advantages. Multi-modal imaging is finding its place in Ophthalmology and we illustrate and analyze its use in macular disease. New technologies have provided the ability to simultaneously capture FA and OCT images, allowing dynamic analysis at the exact point of interest. We establish that the combined imaging protocol is easier and faster for both patient and technician, and ultimately and most importantly more capable of guiding the physician to a diagnosis and treatment.
Breast cancer-related lymphedema (BCRL) can be irreversible with profound negative impact on patients' quality of life. Programs that provide screening and active surveillance for BCRL are essential to determine whether early detection and intervention influences the course of lymphedema development. Established methods of quantitatively assessing lymphedema at early stages include "volume" methods such as perometry and bioimpedance spectroscopy. Here we demonstrate 1) Use of topographical techniques analogous to those used in corneal topography 2) Development of point-of-care lymphedema detection and characterization based on off-the-shelf hardward 3) The role of subsurface imaging 4) Multimodal diagnostics and integration yielding higher sensitivity/ specificity.
Refractive surgeons and cataract surgeons need accurate measurements of corneal curvature/power. Increased expectations of patients, the increasing number of patients having undergone prior surgeries and patients with corneal pathologies dictate the need for reliable curvature measurements to enhance the predictability and the quality of surgical outcomes. Eye movements can negatively influence these measurements. We present a model of eye movements based on peak saccade velocities and formulate criteria for obtaining OCT topography within ¼ of a diopter. Using these criteria we illustrate how next generation MHz systems will allow full corneal OCT topography in both healthy and pathological corneas
Commercial OCT systems provide pachymetry measurements. Full corneal topographic information of anterior and
posterior corneal surfaces for use in cataract surgery and refractive procedures is a desirable goal and would add to
the usefulness of anterior and posterior segment evaluation. While substantial progress has been made towards
obtaining "average" central corneal power (D Huang), power in different meridians and topography are still missing.
This is usually reported to be due to eye movement. We analyze the role of centration, eye movements and develop
a model that allows for the formulation of criteria for obtaining reliable topographic data within ¼ diopter.
We evaluated the efficacy, safety, and stability of femtosecond laser intrastromal refractive procedures in ex vivo and in vivo models. When compared with longer pulsewidth nanosecond or picosecond laser pulses, femtosecond laser-tissue interactions are characterized by significantly smaller and more deterministic photodisruptive energy thresholds, as well as reduced shock waves and smaller cavitation bubbles. We utilized a highly reliable, all-solid-state femtosecond laser system for all studies to demonstrate clinical practicality. Contiguous tissue effects were achieved by scanning a 5 μm focused laser spot below the corneal surface at pulse energies of approximately 2 - 4 microjoules. A variety of scanning patterns was used to perform three prototype procedures in animal eyes; corneal flap cutting, keratomileusis, and intrastromal vision correction. Superior dissection and surface quality results were obtained for lamellar procedures (corneal flap cutting and keratomileusis). Preliminary in vivo evaluation of intrastromal vision correction in a rabbit model revealed consistent and stable pachymetry changes, without significant inflammation or loss of corneal transparency. We conclude that femtosecond laser technology may be able to perform a variety of corneal refractive procedures with high precision, offering advantages over current mechanical and laser devices and techniques.
We investigated three potential femtosecond laser ophthalmic procedures: intrastromal refractive surgery, transcleral photodisruptive glaucoma surgery and photodisruptive ultrasonic lens surgery. A highly reliable, all-solid-state system was used to investigate tissue effects and demonstrate clinical practicality. Compared with longer duration pulses, femtosecond laser-tissue interactions are characterized by smaller and more deterministic photodisruptive energy thresholds, smaller shock wave and cavitation bubble sizes. Scanning a 5 (mu) spot below the target tissue surface produced contiguous tissue effects. Various scanning patterns were used to evaluate the efficacy, safety, and stability of three intrastromal refractive procedures in animal eyes: corneal flap cutting, keratomileusis, and intrastromal vision correction (IVC). Superior dissection and surface quality results were obtained for the lamellar procedures. IVC in rabbits revealed consistent, stable pachymetric changes, without significant inflammation or corneal transparency degradation. Transcleral photodisruption was evaluated as a noninvasive method for creating partial thickness scleral channels to reduce elevated intraocular pressure associated with glaucoma. Photodisruption at the internal scleral surface was demonstrated by focusing through tissue in vitro without collateral damage. Femtosecond photodisruptions nucleated ultrasonically driven cavitation to demonstrate non-invasive destruction of in vitro lens tissue. We conclude that femtosecond lasers may enable practical novel ophthalmic procedures, offering advantages over current techniques.
We investigated refractive corneal surgery in vivo and in vitro by intrastromal photodisruption using a compact ultrafast femtosecond laser system. Ultrashort-pulsed lasers operating in the femtosecond time regime are associated with significantly smaller and deterministic threshold energies for photodisruption, as well as reduced shock waves and smaller cavitation bubbles than the nanosecond or picosecond lasers. Our reliable all-solid-state laser system was specifically designed for real world medical applications. By scanning the 5 micron focus spot of the laser below the corneal surface, the overlapping small ablation volumes of single pulses resulted in contiguous tissue cutting and vaporization. Pulse energies were typically in the order of a few microjoules. Combination of different scanning patterns enabled us to perform corneal flap cutting, femtosecond-LASIK, and femtosecond intrastromal keratectomy in porcine, rabbit, and primate eyes. The cuts proved to be highly precise and possessed superior dissection and surface quality. Preliminary studies show consistent refractive changes in the in vivo studies. We conclude that the technology is capable to perform a variety of corneal refractive procedures at high precision, offering advantages over current mechanical and laser devices and enabling entirely new approaches for refractive surgery.
As ultrafast laser technology advances, it is of importance to evaluate the potential of sub-100-fs laser pulses for laser surgery. We have extended the investigation of laser- induced optical breakdown on hard and soft tissues down to laser pulse widths of 20 fs. Powerful 20-fs to 100-ps pulses from a single Ti:sapphire oscillator/amplifier laser source at 800 nm were focused in vitro onto the surface of fresh human corneas and human enamel to a spot of 60 - 70 micron in diameter. The threshold for ablation was determined by increasing the pulse energy while monitoring scattered probe light at ejected ablation particles. Our experiments show a slower decrease of the threshold fluence in dependence of the pulse width in the femtosecond regime than in the picosecond regime. Unlike previously suggested, no saturation behavior could be observed at the shortest available pulse widths. For the shortest pulses with 20 fs width, we measured a threshold of 0.38 J/cm2 and 0.42 J/cm2 for cornea and enamel, respectively. For the longest pulses at 100 ps, the threshold fluence was 4.3 J/cm2 and 2.06 J/cm2, respectively. Comparison to theoretical models and to previous data determines the contribution of multi-photon and avalanche processes. Our results suggest an optimum laser pulse width of several hundred femtoseconds for most applications in ultrashort pulse laser surgery.
The theme is that of `inheritance' and the use of symbolic algebra to implement it. The notion of inheriting knowledge between networks is crucial since training a network can be exceedingly slow. Partial information acquired through long experience (learning epochs) should be `transferrable.' A technique using the notion of `gluing' networks has been pioneered by Alex Waibel of CMU. However, this technique cannot be considered true inheritance since the component networks are trained on similar but different subtasks that are later `concatenated.' The approach presented here is based on the observation that even when the problem is not separable, one can get a reasonable performance out of a 2 layer network. Its training is fast and its only minimum is often below that of many of the local minima of the corresponding multi-layer networks. After training such a net, if one can transfer the knowledge to a multi-layer net, not only would one have saved valuable training time, but one would have avoided many of the local minima associated with the multi-layer network. Training can then proceed with the task of the multi-layer net reduced to improving the performance of the 2-layer net, instead of having to start from scratch. Equations corresponding to this approach are derived. They can be written for specific topologies and solved exactly (toys) or approximately (larger problems) using symbolic algebra.
Pitch recognition and timbre discrimination for a string instrument is investigated using artificial neural networks. Pitch recognition, the easier task, is realized with a linear classifier while timbre discrimination is achieved with a multiple layer perceptron using gradient back propagation learning.