Liliane Ventura

Detection system for ocular refractive error measurement.

An automatic and objective system for measuring ocular refractive errors (myopia, hyperopia and astigmatism) was developed. The system consists of projecting a light target (a ring), using a diode laser (lambda = 850 nm), at the fundus of the patients eye. The light beams scattered from the retina are submitted to an optical system and are analysed with regard to their vergence by a CCD detector (matrix). This system uses the same basic principle for the projection of beams into the tested eye as some commercial refractors, but it is innovative regarding the ring-shaped measuring target for the projection system and the detection system where a matrix detector provides a wider range of measurement and a less complex system for the optical alignment. Also a dedicated electronic circuit was not necessary for treating the electronic signals from the detector (as the usual refractors do); instead a commercial frame grabber was used and software based on the heuristic search technique was developed. All the guiding equations that describe the system as well as the image processing procedure are presented in detail. Measurements in model eyes and in human eyes are in good agreement with retinoscopic measurements and they are also as precise as these kinds of measurements require (0.125D and 5 degrees).

Automatic measurements of the radius of curvature of the cornea in Slit Lamp

We have developed an automatic optical system attached to the Slit Lamp in order to provide automatic measurements of the radius of curvature of the cornea at low cost. The system consists of projecting a light ring as a target at the patients cornea and the further analysis of the deformation of the target in order to obtain the radius of curvature as well as the axis of the associated astigmatism. The reflected image of the target is displayed in a PCs monitor and a dedicated developed software performs the analysis of the image, that provides the corneal keratometry. Also, the system is able to measure irregular astigmatism and the clinician is able to understand the behavior of the corneas curvature radius in these regions by comparison of the graphical analysis of regular astigmatism that is generated by the software. There is no system commercially available which is able to measure irregular astigmatism, which is a very important feature for keratoconeous detection. The system is easy to use and it has a friendly software interface for the user. Measurements in volunteer patients have been made and the results that were obtained in the system, for the standard target ring, are in good agreement with commercial automatic and manual systems, presenting a correlation coefficient of 0,99347 and 0,97637, respectively regarding the radius of curvature and 0,96841 and 0,9568, respectively, regarding the axis. The systems precision is 0,005 mm for the curvature radius and 2* for the axis component.

Morphologic analysis of the endothelium corneal tissue using mathematical morphology

An effective method for the analysis of donated corneas consists in the evaluation of the indexes of cellular density, pleomorphism and polimegatism. We have developed a system attached to the slit lamp and dedicated software for image treating and analysis of the referred indexes using the mathematical morphology procedure. The results of automatic determination of the cellular density has a correlation coefficient of 0.95798 compared to measurements done by the interactive counting method and for the polimegatism and pleomorphism indexes the preliminary visual results are in good agreement with the presented processed image.

Automatic diagnostic system for measuring ocular refractive errors

Ocular refractive errors (myopia, hyperopia and astigmatism) are automatic and objectively determined by projecting a light target onto the retina using an infra-red (850 nm) diode laser. The light vergence which emerges from the eye (light scattered from the retina) is evaluated in order to determine the corresponding ametropia. The system basically consists of projecting a target (ring) onto the retina and analyzing the scattered light with a CCD camera. The light scattered by the eye is divided into six portions (3 meridians) by using a mask and a set of six prisms. The distance between the two images provided by each of the meridians, leads to the refractive error of the referred meridian. Hence, it is possible to determine the refractive error at three different meridians, which gives the exact solution for the eyes refractive error (spherical and cylindrical components and the axis of the astigmatism). The computational basis used for the image analysis is a heuristic search, which provides satisfactory calculation times for our purposes. The peculiar shape of the target, a ring, provides a wider range of measurement and also saves parts of the retina from unnecessary laser irradiation. Measurements were done in artificial and in vivo eyes (using cicloplegics) and the results were in good agreement with the retinoscopic measurements.

Availability of fluorescence spectroscopic in the accompaniment of formation of corneal cross-linking

The corneal cross-linking is a method that associates riboflavin and ultraviolet light to induce a larger mechanical resistance at cornea. This method has been used for the treatment of Keratoconus. Since cross-linking is recent as treatment, there is a need to verify the effectiveness of the method. Therefore, the viability of the fluorescence spectroscopy technique to follow the cross-linking formation at cornea was studied. Corneas were divided in two measuring procedures: M1 (cornea + riboflavin), and M2 (cornea + riboflavina + light irradiation, 365nm). For fluorescence measurements, a spectrofluorimeter was used, where several wavelengths were selected (between 320nm and 370nm) for cornea excitation. Several fluorescence spectra were collected, at 10 min-interval, during 60 min. Spectra allowed one to observe two very well defined bands of fluorescence: the first one at 400nm (collagen), and the second one at 520nm (riboflavin). After spectra analyses, a decrease of collagen fluorescence was observed for both groups. For riboflavin, on the other hand, there was a fluorescence increase for M1, and a decrease for M2. Thus, it is possible to conclude that it this technique is sensitive for the detection of tissue structural changes during cross-linking treatment, encouraging subsequent studies on quantification of cross-linking promotion in tissue.

Software for keratometry measurements using portable devices

In this work we present an image processing software for automatic astigmatism measurements developed for a hand held keratometer. The system projects 36 light spots, from LEDs, displayed in a precise circle at the lachrymal film of the examined cornea. The displacement, the size and deformation of the reflected image of these light spots are analyzed providing the keratometry. The purpose of this research is to develop a software that performs fast and precise calculations in mainstream mobile devices. In another words, a software that can be implemented in portable computer systems, which could be of low cost and easy to handle. This project allows portability for keratometers and is a previous work for a portable corneal topographer.

Surgical Device for Supporting Corneal Suturing

A system for ophthalmic surgery support has been developed in order to minimize the residual astigmatism due to the induced irregular shape of the cornea by corneal suture. The system projects 36 light spots, from LEDs, displayed in a precise circle at the lachrymal film of the examined cornea. The displacement, the size and deformation of the reflected image of these light spots are analyzed providing the keratometry and the circularity of the suture. Measurements in the range of 32D - 55D (up to 23D of astigmatism are possible to be obtained) and a self-calibration system has been designed in order to keep the system calibrated. Steel precision spheres have been submitted to the system and the results show 99% of correlation with the fabricants nominal values. The system has been tested in 13 persons in order to evaluate its clinical applicability and has been compared to a commercial keratometer Topcon OM-4. The correlation factors are 0,92 for the astigmatism and 0.99 for the associated axis. The system indicates that the surgeon should achieve circularity ≥98% in order to do not induce astigmatisms over 3D.

Automatic multidiagnosis system for slit lamp

We have developed a system for several automatic diagnose in Slit Lamp in order to provide 04 additional measurements to the biomicroscope: (1) counting of the endothelial cells of donated corneas; (2) automatic keratometry; (3) corneal ulcer evaluation; (4) measurement of linear distances and areas of the ocular image. The system consists in a Slit Lamp, a beam-splitter, some optical components, a CCD detector, a frame grabber and a PC. The optical components attached to the beam-splitter are the same for all the functions, except for 1. For function 1, we have developed an optical system that magnifies the image 290X and a software that counts the cells interactively and automatically. Results are in good agreement with commercial specular microscopes (correlation coefficient is 0,98081). The automatic keratometry function is able to measure cylinders over 30 di and also irregular astigmatisms. The system consists of projecting a light ring at the patients cornea and the further analysis of the deformation of the ring provides the radius of curvature as well as the axis of the astigmatism. The nominal precision is 0,005 mm for the curvature radius and 2 degree(s) for the axis component. The results are in good agreement with commercial systems (correlation coefficient of 0,99347). For function 3, the ulcer is isolated by the usual clinical ways and the image of the green area is automatically detected by the developed software in order to evaluate the evolution of the disease. Function 4 simply allows the clinician do any linear or area measurement of the ocular image. The system is a low cost multi evaluation equipment and it is being used in a public hospital in Brazil.

In-vitro corneal transparency measuring system

A system for measuring the average corneal transparency of preserved corneas has been developed in order to provide a more accurate and standard report of the corneal tissue. The donated cornea transparency is one of the features to be analyzed previously to its indication for the transplant. The small portable system consists of two main parts: the optical and the electronic parts. The optical system consists of a white light, lenses and pin-holes that collimate white light beams that illuminates the cornea in its preservative medium. The light that passes through the cornea is detected by a resistive detector and the average corneal transparency is shown in a display. In order to obtain just the tissue transparency, the electronic circuit was built in a way that there is a baseline input of the preservative medium, previous to the measurement of the corneal transparency. Manipulating the system consists of three steps: (1) Adjusting the zero percentage in the absence of light (at this time the detectors in the dark); (2) Placing the preservative medium in the system and adjusting the 100% value (this is the baseline input); (3) Preserving the cornea and placing it in the system. The system provides the tissue transparency. The system is connected to an endothelium evaluation system for Slit Lamp, that we have developed, and statistics about the relationship of the corneal transparency and density of the endothelial cells will be provided in the next years. The system is being used in a public Eye Bank in Brasil.

Automated system for keratometry in slit lamp

We have developed an automatic optical system attached to the Slit Lamp in order to provide automatic keratometry at low cost. The system consists of projecting a light ring as a target at the patients cornea and the further analysis of the deformation of the target in order to obtain the radius of curvature as well as the axis of the associated astigmatism. The reflected image of the target is displayed in a PCs monitor and a dedicated developed software performs the analysis of the image, that provides the corneal keratometry. Also, the projection of two additional targets provide information about two other regions of the cornea. The clinician is able to understand the behavior of the corneas curvature radius in these regions by the comparison of the graphical analysis of regular astigmatism that is generated by the software. Irregular astigmatisms measurements are possible in the developed system. The system is easy to use and it has a friendly software interface for the user. Measurements in volunteer patients have been made and the results that were obtained in the system, for the standard target ring are in good agreement with commercial automatic and manual systems, presenting a correlation coefficient of 0,99347 and 0,97637, respectively regarding the radius of curvature and 0,96841 and 0,9568, respectively, regarding the axis. The systems precision is 0,005 mm for the curvature radius and 2 degrees for the axis component.