Alteration in choroidal blood flow produced by local pressure

Area of Science:

• Ophthalmology
• Vascular Biology
• Retinal Physiology

Background:

• Transient pressure applied to the retinal pigment epithelium (RPE) and choroid is a common occurrence in certain ophthalmic conditions.
• Understanding the impact of such pressure on choroidal blood flow is crucial for diagnosing and treating related pathologies.

Purpose of the Study:

• To investigate the effects of transient pressure on the RPE and choroid on choroidal blood flow in a rabbit model.
• To elucidate the mechanisms underlying changes in choroidal circulation following pressure application.

Main Methods:

• Indocyanine green (ICG) angiography was used to assess choroidal circulation in rabbits subjected to transient pressure.
• Histological examination of retinal and choroidal tissues was performed postmortem.
• A control group of rabbits without pressure indentation was included.

Main Results:

• Pressure application resulted in nonfluorescence in retinal vessels and reduced capillary fluorescence, creating a temporary "black region" on angiograms.
• Evidence of thrombotic-like material was found in choroidal arteries and veins at areas of reduced perfusion.
• Choroidal circulation recovery took approximately 24 hours, with partial reopening of vessels and hyperfluorescence at obstructed ends.

Conclusions:

• Brief pressure on the RPE and choroid induces immediate reduction in choroidal blood flow, potentially due to rapid local thrombosis.
• The slow resolution of these vascular changes may lead to retinal ischemia and contribute to the pathophysiology of pressure-induced choroidal insults.
• Neural reflexes causing vasoconstriction might also play a role in the observed circulatory changes.