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OCULAR BLOOD FLOW IN GLAUCOMA
UPDATE YOUR CONSENSUS KNOWLEDGE
Anatomy and Physiology (of Ocular Blood Flow)
- Blood supply to the prelaminar and laminar portion of the optic nerve head comes from branches of the short posterior ciliary arteries.
Comment: These often form an incomplete vascular ring around the optic nerve head ('Vascular ring of Zinn and Haller'), before giving off branches into the tissue of the optic nerve head located inside of the peripapillary scleral ring of Elschnig. These vessels feature an anastomotic blood supply.
Clinical Measurement of Ocular Blood Flow
- At the present time, there is no single method for measuring all aspects of ocular blood flow and its regulation in glaucoma.
Comment: A comprehensive approach, ideally implemented in a single device, may be required to assess the relevant pathophysiology of glaucoma.
Clinical Relevance of Ocular Blood Flow Measurements
- Lower ocular perfusion pressure (OPP = blood pressure - intraocular pressure) is a risk factor for primary open-angle glaucoma.
- Ocular blood flow parameters measured with various methods are impaired in open-angle glaucoma, especially in normal-tension glaucoma, compared with healthy subjects.
Comment: Reduction of ocular blood flow with aging has been confirmed by various methods.
Comment: The optic nerve head blood flow may be reduced during the nocturnal period.
- Vascular disregulation may contribute to the pathogenesis of glaucoma, more likely in people with lower intraocular pressure.
Should Measurements of Ocular Blood Flow be Implemented into Clinical Practice?
- Although there is an association between measurements of ocular blood flow and glaucoma progression, no causal relationship has been established.
What do We Still Need to Know (about Ocular Blood Flow)?
- Longitudinal studies are necessary to confirm that blood flow abnormalities precede visual field defects and correlate with their severity.
- The hypothesis that treatment of ocular perfusion pressure, rather than intraocular pressure alone, is beneficial in glaucoma should be tested.
Selected from: Robert N. Weinreb and Alon Harris (eds.). Ocular Blood Flow in Glaucoma. Amsterdam: Kugler Publications 2009.
