Sidney Julio Faria de Sousa

Corneal astigmatism measuring module for slit lamps

We have developed an automatic keratometer module for slit lamps that provides automatic measurements of the radii of the corneal curvature. The system projects 72 light spots displayed in a precise circle at the examined cornea. The displacement and deformation of the reflected image of these light spots are analysed providing the keratometry. Measurements in the range of 26.8-75 D can be obtained and a self-calibration system has been specially designed in order to keep the system calibrated. Infrared LEDs indicate automatically which eye is being examined. Volunteer patients (492) have been submitted to the system and the results show that our system has a high correlation factor with the commercially available manual keratometers and the keratometry measurements from a topographer. Our developed system is 95% in agreement with the corneal topographer (Humphrey--Atlas 995 CZM) and the manual keratometer (Topcon OM-4). The systems nominal precision is 0.05 mm for the radii of curvature and 1 degree for the associated axis.

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.

Optical system and image processing of endothelial cells of donated cornea

A magnifying optical system (250-400X) attached to a Slit Lamp has been developed in order to evaluate the endothelium of donated corneas. The images from the endothelium are captured by a CCD and displayed in a PC monitor. The cost of the system is relatively low compared to the specular microscopes that are on the market for donated corneas (66% less expensive). The system offers two kinds of computer evaluation: interactive and automatic. The interactive counting of the endothelial cells provides a window of any shape and size desired by the clinician, where the cells are clicked by the mouse and the developed software estimates the number of endothelial cells in the cornea as a whole. The automatic counting of the cells is done by an image processing, where the cells are recognized by the developed software, without any interference of the clinician, and counted automatically. The most important features of this system compared to most that are on the market are: there are two ways for the clinical to count the cells and both can be used simultaneously (the automatic provides a quick counting of the cells and the interactive provides a wanted clinical interference on the result); many parts of the cornea can be evaluated and an average counting is provided (usually just the central part of the cornea is analyzed); real time image is provided instead of just a static image, which allows the clinician to have more information about the cornea such as the evaluation of the cells in the snail tracks.

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.

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.

Automated specular microscopy in slit lamp

Oftenly the evaluation of a cornea is made using a Slit Lamp where the aspect of the cells is qualitatively observed, there are elaborated apparels and consequently much more expensive that accomplish a quantitative analysis of the endothelium cells. To overcome the limitations of subjective analysis, manipulation difficulties and high cost, we developed a system coupled to the Slit Lamp (that magnifies 290X the cells) exhibiting the image in a computer monitor and a software dedicated for identification and counting the endothelium cells to at a low cost standardizing the diagnosis for the donated corneas.

Automatic analysis of the corneal ulcer

A very common disease in agricultural countries is the corneal ulcer. Particularly in the public hospitals, several patients come every week presenting this kind of pathology. One of the most important features to diagnose the regression of the disease is the determination of the vanishing of the affected area. An automatic system (optical system and software), attached to a Slit Lamp, has been developed to determine automatically the area of the ulcer and to follow up its regression. The clinical procedure to isolate the ulcer is still done, but the measuring time is fast enough to not cause discomfort to the patient as the traditional evaluation does. The system has been used in the last 6 months in a hospital that has about 80 patients per week presenting corneal ulcer. The patients follow up (which is an indispensable criteria for the cure of the disease) has been improved by the system and has guaranteed the treatment success.

Low-cost endothelium cell counter for slit lamp

One of the optical ways to evaluate the donated cornea in order to provide a diagnostic regarding its indication for transplant is to count the number of the living endothelial cells (over 2000 cells/mm2), which are responsible for maintaining the corneal transparency. Specular Microscopes are equipments which are exclusively dedicated for this kind of evaluation. However they are of high cost and most of the Eye Banks are not provided by them. Hence, the usual evaluation is done in a Slit Lamp (SL) -- 40X magnification -- and just the aspect of the cells are subjectively observed. In order to overcome the limitations of subjective assessment and high cost, we have developed a system attached to the SL (optical system with 250X magnification image captured by a CCD detector which displays the image of the cells on a PC monitor and a dedicated software) which is able to count the endothelial cells providing a lower cost objective diagnostic of the donated cornea.