[Vision measurement in candelas: description of a psychophysical technique to quantify luminous intensity].

Purpose: To develop a method and a device for vision measurement in candela (cd). Vision measurement studies are important to all visual sciences.

Methods: It is a theoretical and experimental study.

[Preliminary results of an algorithm for customized soft contact lens ablation].

Purpose: To develop a computer simulation for customized soft contact lenses in order to correct aberrations of higher order.

Methods: Using real data from a patient diagnosed with keratoconus, which were measured using a Hartmann-Shack wavefront sensor, the thickness of the contact lenses that compensate these aberrations as well the numbers of pulses required to ablate the lenses were specifically determined for the patient.

Results: The maps of correction are presented and the numbers of pulses are calculated, using a 0.

[Development and preliminary results of a chromatic illumination system for indirect ophthalmoscopes].

Purpose: Chromatic contrast is a technique used in some areas of medicine to provide better visualization of biological tissues. Based on principles of color composition, a new illumination system was constructed using colored emitting diodes to reproduce the spectral range of visible light. This technique was devised to be used in indirect ophthalmoscopes to improve the visualization of the posterior segment of the eye.

[Preliminary results of a computerized and stereoscopic system for in vivo pupillometry].

Purpose: We developed a digital system with accommodation capacities for measurement of the diameter and shape of the in vivo pupil for 10 different levels of illumination intensity, varying from mesopic to photopic.

Methods: An optical system for conjugating images from an infrared and white light illuminated pupil was designed and mounted using an ophthalmoscope helmet and a typical diving mask as support for a high-resolution and sensitivity CCD. Using an IBM compatible computer sequences of video in AVI format were digitized for several seconds at a mean rate of 30 Hz.

Neural networks and statistical analysis for classification of corneal videokeratography maps based on Zernike coefficients: a quantitative comparison.

Purpose: The main goal of this study was to develop and compare two different techniques for classification of specific types of corneal shapes when Zernike coefficients are used as inputs. A feed-forward artificial Neural Network (NN) and discriminant analysis (DA) techniques were used.

Methods: The inputs both for the NN and DA were the first 15 standard Zernike coefficients for 80 previously classified corneal elevation data files from an Eyesys System 2000 Videokeratograph (VK), installed at the Departamento de Oftalmologia of the Escola Paulista de Medicina, São Paulo.

[Preliminary results of a wide-angle corneal topography system for Placido-based videokeratographers].

Purpose: To develop the instrumentation and software for wide-angle corneal topography using a Placido-based videokeratographer. The objective is to allow the measurement of a greater area of the cornea using a simple adaptation to the Placido mire.

Methods: Using the traditional Placido disc of a commercial corneal topographer, 9 LEDs (Light Emitting Diodes) were installed on the conic mire so that the voluntary patient could gaze in different directions.

[Vision measurement and psychophysical tests].

Vision measurement is the basis for the study and standardization of visual sciences. Measurement of visual acuity has great value for research and for clinical practice. This paper (1) reviews the fundamental concepts to understand visual sense and the measuring units; (2) presents the fundamental limits to visual performance and the principles of aberration measurement of the eye; and (3) discusses methods for measuring and classifying vision with new technologies.

[Computational simulation of customized photorefractive surgery and precision of correction related to different order aberrations].

Purpose: To develop and implement an algorithm for simulation of photorefractive surgery. It is well known that many flying-spot lasers in the market have limitations in correcting higher order aberrations, but there is little quantitative information about errors related to aberration complexity.

Methods: By applying known surfaces described by Zernike polynomials of different orders it was possible to simulate several target surfaces that may well resemble in vivo cases of refractive surgery candidates.

Mumford-Shah algorithm applied to videokeratography image processing and consequences to refractive power values.

There are many corneal diseases that can be detected using an eye-care device called videokeratograph. The videokeratograph is based on the principle of an apparatus called Placido disc and is used to precisely measure the anterior surface of the cornea. This disc contains rings alternately white and black, which are reflected on the patient's cornea during the examination.

[Measuring the refractive power of customized soft contact lenses].

Purpose: Soft contact lenses with spherical base curves have been used for many years. The computation of the refractive powers of these lenses is easy, requiring only that one uses the lens maker equation for thick lenses. Nevertheless, for customized contact lenses, there is yet no reliable method for measuring the higher order optical aberrations.

[Different techniques for Plácido image analysis may improve precision of videokeratography].

Purpose: Videokeratography (VK) has been a widespread technology for corneal surface analysis since the mid-80s. The objective of this study was to develop different techniques for Plácido image edge detection and compare the results of each algorithm in terms of the consequences for axial curvature computations.

Methods: Plácido images from an Eyesys system 2000 were captured for 4 different spherical surfaces.

Spatial and frequency domain techniques for segmentation of Placido images and accuracy implications for videokeratography.

Objective: Videokeratography (VK) has been a widespread technology for corneal surface analysis since the mid 1980s. Most manufactures use personal computers attached to a Placido disc apparatus in order to capture and process digital images. Although precision reported by most manufactures are within very good limits, none of them have disclosed, probably due to proprietary reasons, the nature of the algorithm used in their image-processing phase.

[Techniques for facilitating in vivo corneal topography diagnosis].

Purpose: The videokeratoscope is one of the most widely used instruments for the diagnosis of the human cornea. Results are usually plotted in the form of color-coded maps where each color is associated with a specific range of curvatures or elevations. Nevertheless there has been no thorough study in the literature demonstrating the advantages or disadvantages of different visualization techniques applied to the videokeratoscope.