| Abstract |
Ocular rigidity is a macroscopic mechanic parameter which expresses the flexible attributes of eye. Using mathematics it is defined as the change of pressure via the change of volume of eye. Friedenwald himself described the coefficient of ocular rigidity as a "measure of the resistance, which the eye exerts to distending forces". The development of techniques of measurement but also the wider study of coefficient of ocular rigidity is subject of international research, after publications that connect the value of the coefficient with the appearance and the development of ocular diseases such as macular degeneration and kearatokonus.
In the past it was developed by the researching team of V.E.I.C (IG Pallikaris, GD Kymionis, HS Ginis, GA Kounis and MK Tsilimbaris) a device which is interfered between the column of balanced salt solution and the eye, whereby the coefficient of ocular rigidity can be measured invasive. That was achieved by injecting a balanced salt solution through the limbus in the anterior chamber, while monitoring continually the intraocular pressure with a transducer. However despite the precision of this device, the measurement of the coefficient of ocular rigidity based on that method, is rendered difficult and feasible only during intraocular surgery. For that reason at the same time a second device was developed, whereby is possible the non invasive measurement of the coefficient of ocular rigidity.
The principle operation of this device is based on removing volume from the anterior chamber, using an optical element which comes in contact and deform the corneal surface. During the contact, a light beam of a LED is propagated through the optical system and cornea. The partial refractive index matching at the area of contact modulates the back-reflected intensity of the beam according to the size of the applanated corneal zone. The beam is propagated through the optical head in a set of four photodiodes, which they record the intensity of the back-reflected light beam. This opto-electronic sensor is mounted on a force sensor recording the applanation force. The whole system is mounted on a slit lamp and is operated in a manner similar to a Goldmann tonometer. After calibrating the system and using a nomogram this device is able to measure the not only the intraocular pressure, but also the coefficient of ocular rigidity.
Aim of this thesis is constituting the optimisation and the wider study of the non invasive elastometer. Specifically objective target of this work is the calibration of four photodiodes and the force sensor. Also it will be presented the experimental process that was used for the nomogram’s determination. At the end of this study a comparison is presented between the nomogram that was calculated using rabbit eyes and the theoretical model of linear approach.
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Μη επεμβατική μέτρηση των μακροσκοπικών μηχανικών ιδιοτήτων του οφθαλμικού τοιχώματος
