Preliminary results of a high-resolution refractometer using the Hartmann-Shack wave-front sensor - Part I

In this project we are developing an instrument for measuring the wave-front aberrations of the human eye using the Hartmann-Shack sensor. A laser source is directed towards the eye and its diffuse reflection at the retina generates an approximately spherical wave-front inside the eye. This wave-front travels through the different components of the eye (vitreous humor, lens, aqueous humor, and cornea) and then leaves the eye carrying information about the aberrations caused by these components. Outside the eye there is an optical system composed of an array of microlenses and a CCD camera. The wave-front hits the microlens array and forms a pattern of spots at the CCD plane. Image processing algorithms detect the center of mass of each spot and this information is used to calculate the exact wave-front surface using least squares approximation by Zernike polynomials. We describe here the details of the first phase of this project, i. e., the construction of the first generation of prototype instruments and preliminary results for an artificial eye calibrated with different ametropias, i. e., myopia, hyperopia and astigmatism.

Videokeratograph (VKS) for monitoring corneal curvature during surgery

Purpose: We have developed an instrument for computerized surgical videokeratography. A corneal central region of approximately 7.00 mm in diameter may be analyzed, providing the surgeon with information of the power and the astigmatism. Methods: The system is based on a fiber optic Placido disc projecting cone, which is attached to the objective lens of aZeiss compatible surgical microscope. At the beam splitter we installed a monochromatic high resolution camera. A frame grabber is installed on a PC and images are digitized at a 480x640 resolution. Image processing is used for edge detection of rings. Results: Calibrating curves based on 4 spherical surfaces were generated and approximately 3600 points are calculated for each examination. Preliminary measurements on 10 healthy corneas were compared with those of an EyeSys System 2000 Corneal Topographer. Mean deviation was 0.05 for radius of curvature, 0.24 D for the power and 5.0 degrees for the cylinder. Conclusions: This surgical V KS, with some hardware and software improvements, may be used to reduce residual astigmatisms in conventional cataract and keratoplasty. It could also be used to gather preoperative data in corneal topography assisted LASIK.

Desenho ótico e mecânico do instrumento oftálmico: lâmpada de fenda / Optical and mechanical drawing of ophthalmic tool: slit lamp

Este trabalho tem por objetivo desenvolver uma linha de pesquisa bastante interessante dentro da área de Instrumentação Ótica, a parte da Ótica Técnica denominada de Desenho Ótico integrada à área de Oftalmologia, cujo o intuito é desenvolver um instrumento oftálmico muito utilizado na área oftálmica: a Lâmpada de Fenda. A Lâmpada de Fenda é um instrumento ótico bastante utilizado pelos oftalmologistas para a realização de exames da visão.

This work has been developed in an interesting line of research within the Optical Instrumentation area named Optical Design, associated to the Ophthalmology area, with the purpose of designing a widely used ophthalmic instrument: the Slit Lamp. The Slit Lamp is an optical instrument widely used by ophthalmologists for eye examination.