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A new ophthalmodynamometer for assessment of ocular perfusion pressure and outflow facility
E. Rumberger, J. Draeger
Introduction: The ocular perfusion pressure (PP) as the difference between pressure in retinal artery (PAR) and the intraocular pressure (IOP) is an important factor of sufficient oxygen supply of retinal tissue. Constant or intermittent reduction of PP either by elevation of IOP or by decreasing of PAR may be the essential cause of glaucoma. A decisive cause of elevation of IOP may be decreasing facility of outflow (FO). Measuring of IOP is an ophthalmologic standard procedure, but assessments of PAR and FO are more complicated methods. Early diagnosis of glaucoma may be improved by easy and simultaneous assessment of PAR, IOP and FO.
Method: We developed a new instrument which allows tonometry, tonography and ophthalmodynamometry. The instrument is based on the principle of applanation tonometry. An electric motor moves an applanation body against the eye, the cornea is applanated and thus IOP is successively elevated. A sensor in the centre of the applanation area registers continuously the actual IOP. A second force sensor positioned between the motor and the applanation body registers the force necessary to produce a given applanation area. The quotient force/actual IOP allows to assess the applanation area. The actual values of force and pressure are evaluated to drive or stop the
motor.
Tonometry: The IOP measured at a applanation area with a diameter of 3,06 mm.
Tonography: The alteration of applanation area produced by given movements of applanation body allows calculation of displaced
volume.
Ophthalmodynamometry: The motor moves the applanation body forward to increase IOP until retinal artery collapses. The sensor in the applanation area registers the actual IOP and oscillations. The maximal applanation diameter of 9 mm induces an IOP of 160 mmHg.
Department of Ophthalmology and Department of Physiology, University of Hamburg, Martinistraße 52, D-20246 Hamburg