Effect of changes in intraocular pressure on the retinal microcirculation.

The development of fluorescein angiography has stimulated a great deal of interest in the vascular physiology of the retina and choroid by providing a method for examining different aspects of the ocular circulation in vivo.Of particular interest is the role of the blood supply to the optic disc in the production of field defects in glaucoma, and its relationship to pathological disc cupping (Hayreh, I969, 1970; Blumenthal, Best, Galin, and Toyofuku, 1971; Goldmann and Blok, 197I).A number of experiments in animals and man have been carried out to demonstrate the influence of acute and chronic rises in the intraocular pressure on the choroidal supply to the disc and peripapillary region (Blumenthal, Gitter, Best, and Galin, I970; Swietliczko and David, 1970; Blumen- thal, Best, and Galin, 197I).In these conditions of high intraocular pressure, whether pathological or experimental, several observations have been made on the accompanying reduction of blood velocity in the retinal arteries but, apart from the studies by Dollery, Henkind, Kohner, and Paterson (I968), little quantitative data exists on this relationship between altered perfusion pressure and retinal blood flow.The present series of experiments was designed as an extension of the work of Dollery and his co-workers to investigate the changes in retinal blood flow velocity and retinal blood flow at different intraocular pressures, and to study the effects of measures used to treat retinal artery obstructions in man. MethodStudies were carried out on nine young pigs aged between 6 and I 2 weeks with weights ranging from I 3 to 28 kg.The experimental procedure described in a previous publication (ffytche, Bulpitt, Archer, Kohner, and Dollery, I973) was followed.Anaesthesia was induced with intravenous 5 per cent.sodium thiopentone and continued after tracheal intubation by further thiopentone injections through a leg vein catheter.Ventilation was maintained using a Palmer pump and continuous recordings of the pulse and blood pressure were obtained through a P6o catheter inserted into the aorta via the femoral artery and connected to a Devices M 4 recorder.Arterial PO2, pC02, and pH were monitored throughout the experiments.