Microspheres method for ocular blood flow measurement in rats: size and dose optimization

Area of Science:

• Ophthalmology
• Biomedical Engineering
• Physiology

Background:

• Accurate measurement of ocular blood flow is crucial for diagnosing and managing various eye diseases.
• The microsphere method offers a potential approach for quantifying blood flow in ocular tissues.
• Optimization of microsphere (MS) parameters is necessary for reliable and reproducible results.

Purpose of the Study:

• To modify and optimize the microsphere method for accurate ocular blood flow measurement in rats.
• To determine the optimal size and dose of microspheres for quantifying blood flow in the retina, choroid, and optic nerve.
• To evaluate the distribution and systemic circulation reentry of different sized microspheres.

Main Methods:

• Fluorescent microspheres (6, 8, 10, or 15 microm diameter) were administered into the left ventricle of anesthetized rats.
• Microsphere doses varied (10^6, 5x10^6, or 10^7).
• The number of microspheres entrapped in the retina, choroid, and optic nerve (Ntissue) was quantified and analyzed based on size and dose.

Main Results:

• Eight-micrometer MS at a dose of 5x10^6 significantly increased Ntissue in the retina and optic nerve compared to other sizes.
• Ten-micrometer MS yielded the highest Ntissue in the choroid across different doses.
• Fifteen-micrometer MS were found to be inappropriate due to lodging in arterioles and causing blood pressure increases; no MS >= 8 microm reentered systemic circulation.

Conclusions:

• Eight-micrometer microspheres are optimal for retinal and optic nerve blood flow estimation.
• Ten-micrometer microspheres are optimal for choroidal blood flow estimation.
• Optimal doses were determined for each ocular tissue, and 15-micrometer microspheres were deemed unsuitable for ocular blood flow measurements in rats.