Programm & Abstracts                 "Innovationen in der Augenheilkunde"

Aktuelle Tagungsinformationen
   News and Updates

Anmeldung zur Tagung
   Hotel Registration
   Welcome address
Beteiligte Gesellschaften
   Societies involved
Eröffnung des Kongresses
   Opening Ceremony
Wissenschaftliches Programm
   Scientific program
   Poster Presentation
Begleitende Veranstaltungen
   Collateral Events
   Social program
   Jubilee Party
DOG Information
   DOG Information
Allgemeine Informationen
   General Information
   Index of Authors
   Registration fees

DOG Homepage

In Vivo Observation of IOP-dependent Reactions of the Episcleral Venous Plexus in the Rabbit

1Selbach J. M., 1Kremmer S., 2Steuhl K. P., 3Lütjen-Drecoll E.,
1Universität-Gesamthochschule Essen, Zentrum für Augenheilkunde (Essen)
2Universität-Gesamthochschule Essen, Zentrum für Augenheilkunde, Abt. für Erkrankungen des vorderen Augenabschnitts (Essen)
3Friedrich-Alexander-Universität Erlangen-Nürnberg, Anatomisches Institut LS II (Erlangen)

Purpose: To investigate the episcleral vascular network and its reactions to changes in intraocular pressure (IOP), which might play a role in aqueous humour outflow regulation.
Methods: For in vivo observation of the episcleral vasculature the microendoscopic technique as described by Funk and Rohen (1989; Ophthalmic Res. 21, 8-17) was applied. The endoscope together with a camera and a magnifier were attached to a micromanipulator. In 10 anesthetized New Zealand rabbits the episcleral vasculature was studied. IOP was monitored by a transducer connected to an anterior chamber needle. Mean arterial pressure was monitored, too. After an initial period of 10-15 min to reach steady state conditions IOP was raised or lowered by means of a hydrostatic reservoir and vascular reactions were observed for 15 min. The microendoscopic images were recorded continuously on a video recorder. Vessel diameters were analyzed at definite time intervals before (control) and after changing intraocular pressure with an image analysis software.
Results: At an IOP of 15 mmHg the plexus of the anterior episclera drains aqueous humor in aqueous veins which are either devoid of blood or show a typical lamellation of blood and aqueous. There is no predominant flow direction. After a stepwise experimental elevation of IOP from 20 to 60 mmHg, a 30-50% dilation of the veins and venules can be observed after 2-3 minutes. At high IOP levels the veins are mainly blood filled with a rapid flow from anterior to posterior. Reduction of IOP down to 5 mmHg is followed by a constriction of arteries and veins (up to 40%) after 3-6 minutes. No reflux of blood into the most anterior aqueous veins (loops) is observed. Topical application of sodium nitroprusside leads to a slight initial IOP increase (1.5 mmHg) followed by a marked decrease of IOP (4.3 mmHg) after 2 minutes which parallels a 30-40% dilation of the episcleral veins.
Conclusions: The results indicate that their might be an interaction between intraocular pressure and the densely innervated aqueous draining episcleral venous plexus which probably allows a subtle modulation of reflux of blood into the outflow pathways and presumably of aqueous humor outflow.