Choroidal vascular permeability in visually regulated eye growth

Area of Science:

• Ophthalmology
• Comparative Physiology
• Fluid Dynamics

Background:

• Choroidal thickness fluctuates diurnally and with visual input, potentially aiding retinal photoreceptor alignment during emmetropization.
• Understanding the sources of extravascular fluid in the choroid is crucial for comprehending these thickness changes.

Purpose of the Study:

• To investigate the origins of extravascular fluid in the chick choroid.
• To analyze how choroidal fluid dynamics are affected by experimentally induced myopia and recovery from myopia.

Main Methods:

• Chicks were subjected to form-deprivation myopia or recovery from myopia.
• Fluorescein dextran tracer was administered intravenously and intracameral to track fluid pathways.
• Suprachoroidal fluid, aqueous humor, and plasma were sampled for protein and tracer analysis.
• Sulfated glycosaminoglycans were assayed in choroidal tissues and fluid.

Main Results:

• Suprachoroidal fluid protein concentration decreased significantly in myopic eyes and increased markedly during recovery.
• Intravenous fluorescein dextran distribution mirrored protein levels, showing reduced uptake in myopic eyes and elevated levels in recovering eyes.
• Intracameral fluorescein dextran showed altered distribution in myopic and recovering eyes compared to controls.
• Sulfated glycosaminoglycan levels were largely unchanged in the choroid and fluid.

Conclusions:

• Chick suprachoroidal fluid is lymph-like and primarily derived from plasma.
• Sulfated glycosaminoglycans do not appear to regulate choroidal fluid content.
• Altered protein and tracer levels suggest significant changes in choroidal circulatory dynamics and capillary permeability during myopia and recovery.