Chirurgie oculaire | EPFL Graph Search

La chirurgie de l’œil, également connue sous le nom de chirurgie ophtalmologique ou chirurgie oculaire, est la chirurgie exécutée sur l'œil et ses annexes, généralement par un ophtalmologue. Bien que la plupart des interventions chirurgicales sur l'œil puissent être exécutés par n’importe quel ophtalmologue expérimenté, les procédures les plus complexes sont habituellement données à des médecins qualifiés et reconnus. L'œil est un organe sensible, qui requiert des soins extrêmement exigeants avant, pendant et après l’opération chirurgicale. Le chirurgien ophtalmologue qui intervient doit donc prendre toutes ses responsabilités et identifier les bonnes façons de procéder afin de mener son opération sans risque. Beaucoup de programmes universitaires aux États-Unis permettent à des patients d'indiquer s'ils acceptent d’être opérés par un interne ou alors s’ils refusent explicitement et veulent vraiment avoir affaire à un médecin qualifié. L'anesthésie est une nécessité pour n'importe quelle chirurgie d'œil. L'anesthésie locale est en règle générale la plus employée. Des techniques d’injection et d’infiltration de produit anesthésiant au niveau sous-cortical sont employées pour immobiliser les muscles extra-oculaires et éliminer la sensation de douleur. L'anesthésie locale emploie souvent des gels à base de lidocaïne qui est préférée pour les opérations rapides. Pour l’anesthésie locale, la coopération du patient est la meilleure chose pour une procédure se déroulant en douceur. L’anesthésie générale quant à elle, est recommandée pour les enfants, pour des lésions traumatiques de l’œil, pour la plus grande partie des orbitotomies et pour les patients ayant de l’appréhension. Une surveillance cardiovasculaire est préférable pendant l'anesthésie locale et est obligatoire pour l'anesthésie générale. Des précautions appropriées au niveau de la stérilité sont prises pour préparer la zone qui va subir l’opération, y compris par l'utilisation d’antiseptiques comme la bétadine. Être vêtus de blouses, et gants stériles est bien sûr obligatoire.

Optische Augenlängenmessung für klinische Anwendungen

Beate Möller

Cataract is the leading cause of blindness worldwide. The clouding of the human eye lens is called "Grauer Star" in German. In the industrialized countries this process of increased blindness is corrected by the surgical removal of the clouded lens and its replacement by a plastic lens (intraocular lens, IOL). Cataract surgery is the most frequent surgery worldwide. In Europe more than two million operations are performed annually. For the selection of an optimum replacement the refractive power of the lens is calculated from the radius of curvature of the cornea, the length of the eye and the anterior chamber depth. Therefore these data have to be measured before every surgery. Until now the length of the eye was measured exclusively by ultrasound in the clinical praxis. For this procedure the sound transducer has to be placed directly or via a water funnel onto the cornea. It was the aim of the work presented in this thesis to lay the framework for introducing into the clinical praxis a contact free optical length measurement of the eye. The basic parameters for the measurement were determined. Starting from the state of the art new solutions were found, implemented in a laboratory device, and tested clinically. A two-beam interferometer with light of short coherence length that had been developed at the University Vienna was analyzed and compared with the one-beam technique. Neglecting practical limitations due to the optical arrangement and assuming shot-noise limited detection the one-beam technique allows the measurement of reflected light that is a factor of two lower compared to the two-beam technique. From the point of view of detection both techniques are therefore equivalent. The advantage of the two-beam technique is its independence from the eye movement. Until now the two-beam technique utilizes for detection only 1 over 400 of the light reflected from the retina and 1 over 2500 to 1 over 4000 of the light reflected from the cornea. This causes the dynamic range to drop by 26 dB. Furthermore the noise of the electronics (excess noise) comes into play. In this work a novel concept for the optical configuration in the two-beam interferometer is presented. By using a diffractive lens cornea and retina are imaged simultaneously onto the detector and the losses of the light from the retina are minimized. The cornea is imaged with an efficiency of 5.6 per cent. In order to minimize the requirements on the patient the measuring time was shortened to 1 s. Therefore the scan speed was increased by a factor of four compared to the state of the art. In the laboratory device it fluctuated by 20 per cent. To keep the detection narrow band it was necessary to implement a signal processing that is largely independent of the scan speed. By using a synchronous demodulation of two 90 degrees phase-shifted channels that are added as vector quantities a filter with self-adjusting center frequency was created. Its bandwidth is 4 kHz with signal frequencies between 30 kHz and 90 kHz. This concept was realized as a compact slit-lamp head and tested clinically. A shot-noise limited detection with a dynamic range of 105 dB was achieved (input power 200 µW). On the healthy eye the signal-to-noise ratio was limited by the digitization range of 8 bit. On the eye with cataract the measuring was not limited by the degree of clouding any more. The optical lengths were determined along the line of sight. They agreed with the post operative results. In some cases refractive errors of more than 2 dpt would have been avoidable by determining the IOL from the measurement of the optical length of the eye. This technique allows a comfortable, contact free optical eye length measurement that works correctly in 95 per cent of all eyes with cataract. Additionally smaller post operative refractive errors can be achieved as compared with traditional techniques. These results were the basis for the development of the IOL-Master – a novel device for the cataract treatment – at the Carl Zeiss Jena GmbH. With this device all biometric data can be measured in a non-contact fashion and intraocular lenses can be calculated and selected.

EPFL2001

Optische Augenlängenmessung für klinische Anwendungen

Beate Möller

EPFL2001