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Biomedical subjects

E H Roth

Publications and source records attributed to E H Roth.

3 recordsLinked to original sources

[Retinoscopy. A multi-media teaching program on CD].

INTRODUCTION: Retinoscopy is a classical method to determine the refraction of the eye by observing the dynamics of reflexes and varying the experimental parameters until a specific reflex (neutralisation point) is observed. Until now photographs and geometrical drawings of the different ray tracings have been commonly used to visualise the pathways. We intend to use new media such as video and CD to offer the students a better understanding of retinoscopy. METHODS: With the aid of appropriate experimental devices, retinoscopal reflexes of artificial and human eyes are recorded on video. The video sequences are converted in computer files and together with computer animations of the geometrical ray tracings, text files and audio sequences, they are stored in a suitable CBT-programme. RESULTS: The systematically prepared computer compatible contents offer a modern individually controllable method to perform the instruction programme by multimedia. The CBT-program and the specific files are stored on CDs or can be distributed on the internet. A collection of retinoscopy records of patients, some with extraordinary reflex phenomena is also available. DISCUSSION: Video and animation procedures are more suitable for matching the dynamic phenomena on retinoscopy than photographs or drawings as they offer a more direct basis for understanding of the sometimes difficult processes of retinoscopy. The collection of recorded reflexes also offers the direct visualised experience of particular patient findings such as the appearance in context of implanted spherical and aspherical intraocular lenses or the irregularities of the optic system of eyes with keratokonus.

Computer-Assisted Instruction↗

[Image properties of spherical as aspheric intraocular lenses].

BACKGROUND: One reason for the problems that pseudophakic patients have with their mesopic vision is the spherical aberration of the implanted intraocular lens (IOL). Therefore we developed an aspheric IOL that will minimize this aberration. Starting with a 22 diopter lens we checked whether it is possible to keep the aspheric surface of the lens constant while changing the second radius to cover a larger range of needed refractive power. Afterwards we also checked whether the theoretical results correspond to the practically tested image quality. METHODS: We analyzed the image quality of the aspheric lenses theoretically by calculating the optimal defocused geometrical spot size. For the ray tracing we used the Gullstrand schematic eye model with an aspheric cornea. The calculated spot sizes were compared to those of a spherical IOL. Subsequently we compared the quality of both lenses by imaging an USAF-test target through a model eye. RESULTS: We were able to design an aspherical IOL to improve the optical performance up to the limit of diffraction. When the second radius was changed, the spot size enlarged as we expected, but it was considerable smaller than that of the respective spherical IOL. The image quality that we tested with the model eye was considerably better with the aspherical lens than with the spherical lens. CONCLUSIONS: It is possible to improve the optical performance of intraocular lenses by aspherization. The production procedure can be kept simple by aspherizing only one side of the lens. The refractive power can be changed by varying the radius of the spherical side. In our opinion aspheric IOL's should be used especially for cataract patients with a pupil size of 5 mm and more.

Adolescent↗

[In vivo measurement of the distribution of the refractive index of the human lens using a Scheimpflug photo of the anterior eye segment and a helium-neon laser beam].

The distribution of the refractive index of the human lens in vivo is measured by taking a Scheimpflug photograph of the anterior segment while simultaneously passing a HeNe laser beam through these structures. The refractive index can be evaluated simply by using the Snellens formula for refraction on the course of the beam after reevaluating the Scheimpflug photograph for distortion. It is possible to perform this measurement during accommodation and in the relaxed lens.

Humans↗