Glaucoma Group
Team Leader: PD Dr Plange
Team Members: Dr. Marion Kaup
Projects:
Dynamic Contour Tonometry
Several recent studies have underlined the shortcomings of applanation
Tonometry, mainly its dependence on the biomechanical properties of the
cornea. Goldmann Tonometry provides an estimate rather than a real measurement
of IOP. Classical Tonometry is based on the formula Dp = Df / A. Pressure
is always indirectly determined by the measuring a certain force. This means
that the eye must be distorted to a certain degree in order to determine
the force required for this given deformation. Any deformation of the cornea
may it be by applanation or by indentation (impression), interacts with
the biomechanical properties of the cornea, especially central corneal thickness,
radius and rigidity. Contour Tonometry determines pressure directly by means
of a pressure sensing element, integrated into a tonometer tip with a "contoured",
concave surface. It is a contact surface which comes as close as possible
to the shape which the cornea assumes if pressure within and outside the
eyeball were identical and if no forces were thus acting on the cornea.
If this condition is met, the pressure sensor in the tip measures true IOP
correctly.
Dynamic Contour Tonometry making it is easily possible to record the pressure
detected by the sensor not only once at a more or less arbitrary point in
time, but continuously at a high sampling rate of 100Hz. IOP is not a static
property of the eye but a dynamic quantity modulated by cardiac activity.
Ocular pulse amplitude (OPA) reflects the modulation of the intraocular
pressure (IOP) due to the heart beat. OPA is the difference between the
diastolic and systolic IOP. Currently we are investigating the correlation
between OPA and the velocity of the retrobulbar vessels.
| Working principle of the DCT: |
 |
| A: Ocular pulse amplitude messured by DCT B: Pulse curve of the aortic artery |
 |
Cooperation partners: TechnoMed
Colour Doppler Imaging
Retinal blood flow regulation may be compromised in a variety of diseases. For example Glaucomatous optic neuropathy appears to be accompanied by changes in blood flow in the optic nerve head, retina and choroid. Therefore, we investigate the retrobulbar hemodynamic using a colour Doppler imaging device (7.5 MHz linear phased-array transducer, Siemens Sonoline Sienna, Germany). Peak systolic velocities (PSV) and end-diastolic velocities (EDV) are obtained from the velocity waveforms of each artery. The resistive index, known as Pourcelot’s ratio, is calculated by theformula (PSV-EDV) / (PSV). It characterizes peripheral vascular resistance of the studied vessels. We investigate the retrobulbar velocity in glaucoma patients, in patients with anterior ischemic optic neuropathy and other vascular high risk patients.
Fig 1: A Colour Doppler imaging device Siemens Sonoline Siena, B 7.5 MHz linear phased-array transducer
Fig. 2: CDI Examination in patient.
Fig. 3: A Colour Doppler imaging curve of the ophthalmic artery showing PSV and EDV of the artery B CDI curve of the central retinal artery showing PSV and EDV of the artery and the vein.
Selected publications on CDI
- Harris A, Arend O, Chung HS, Kagemann L, Cantor L, Martin B A comparative study of betaxolol and dorzolamide effect on ocular circulation in normal-tension glaucoma patients. Ophthalmology. 2000 Mar;107(3):430-4.
- Arend O, Remky A, Plange N, Martin BJ, Harris A. Capillary density and retinal diameter measurements and their impact on altered retinal circulation in glaucoma: a digital fluorescein angiographic study. Br J Ophthalmol. 2002 Apr;86(4):429-33.
- Plange N, Remky A, Arend O .Colour Doppler imaging and fluorescein filling defects of the optic disc in normal tension glaucoma. Br J Ophthalmol. 2003 Jun;87(6):731-6.
- Huber K, Plange N, Remky A, Arend O. Comparison of colour Doppler imaging and retinal scanning laser fluorescein angiography in healthy volunteers and normal pressure glaucoma patients. Acta Ophthalmol Scand. 2004 Aug;82(4):426-31
- Kaup M, Plange N, Niegel M, Remky A, Arend O. Effects of brinzolamide on ocular haemodynamics in healthy volunteers. Br J Ophthalmol. 2004 Feb;88(2):257-62.
- Huber KK, Remky A. Effect of retrobulbar versus subconjunctival anesthesia on retrobulbar hemodynamics. Br J Ophthalmol. 2005 Jun;89(6):719-23.
- Huber KK, Remky A. Colour Doppler imaging before and after retrobulbar anaesthesia in patients undergoing cataract surgery Graefes Arch Clin Exp Ophthalmol. 2005 Jun 18; [Epub ahead of print]
- Huber KK, Remky A. Die Farbduplexsonographie weist auf eine verminderte okuläre Durchblutung bei Normaldruckglaukom Patienten hin. KliMo (accepted)
- Huber KK, Adams H, Remky A, Arend O. Retrobulbar hemodynamics and contrast sensitivity after CO2 breathing. Acta Ophthalmol Scand. (submitted)
- Kaup M, Plange N, Arend KO, Remky A. Retrobulbar haemodynamics in non-arteritic anterior ischaemic optic neuropathy. Br J Ophthalmol. 2006 Nov;90(11):1350-3.
Contact: Dr. Niklas Plange, Dr. Marion Kaup
Sorry, the rest of this chapter is still under construction