Ocular Blood Supply PDF

Blood Supply to Eye and Adnexa Lacrimal apparatus Conjunctiva Eyelids Eyebrows Extraocular muscles Retina, ciliary body, iris, choroid, sclera Further reading: Remington: Clinical Anatomy of the Visual System Blood Supply to Eye and Adnexa Functions: Provide oxygen, nutrients and water Remove carbon...

Blood Supply to Eye and Adnexa Lacrimal apparatus Conjunctiva Eyelids Eyebrows Extraocular muscles Retina, ciliary body, iris, choroid, sclera Further reading: Remington: Clinical Anatomy of the Visual System Blood Supply to Eye and Adnexa Functions: Provide oxygen, nutrients and water Remove carbon dioxide and metabolic wastes Transport or hormones Mediate immune system response Maintain constant pH, temperature Source of pressure Blood supply to the head and neck Arch of aorta → brachiocephalic trunk + left common carotid right subclavian + right common carotid Blood Supply to the Head and Neck Left and right common carotid arteries, each of them divides into: - Internal carotid (structures internal to the skull) - External carotid (external to the skull including a small portion of the ocular adnexa) Common carotid External Carotid (9 branches) Supplies: Exterior of the head, neck and face including thyroid gland, throat, tongue, face, ears Meningeal branches to dura mater External carotid Branches of the external carotid artery that supply the ocular adnexa Circle of Willis = cerebral arterial circle Vertebral arteries Circle of Willis Equal blood pressure Alternative routes for blood flow (clot) Internal Carotid Ophthalmic artery Internal carotid Internal carotid Ophthalmic Artery Several branches: Central retinal artery Lacrimal artery Posterior ciliary arteries: short and long Muscular arteries give branches forming anterior ciliary arteries Ethmoid arteries Supraorbital artery Medial palpebral arteries Supratrochlear artery Dorsonasal artery Central retinal artery Central retinal artery - Arises from the ophthalmic artery - Pierces the optic nerve behind the eye - Accompanied by central retinal vein - Pierces the optic disc centrally Collateral branches of central retinal artery provide blood supply to the optic nerve and pia matter Branching of central retinal artery: - subdivides into superior and inferior branches - subdivides into nasal and temporal branches Branching of arteries and veins within nerve fibre layer Retinal Circulation – Blood-Retina Barrier Tight junctions (zonula occludens): - RPE - Endothelial cells of retinal capillaries Retinal Circulation Autoregulation to maintain constant blood flow despite changes in intraocular pressure (IOP) and systemic blood pressure Controlled by metabolic needs (O2, pH, CO2) Retinal Circulation – Age-Related Changes Aging changes similar to those found elsewhere in the body (arteriosclerosis - formation of Loss of Blood-Retina Barrier plaques of cholesterol, platelets, fibrin, and other substances on the arterial walls, and leads to progressive degrees of blockage of the arterial circulation) Loss of cells at the capillaries: typically endothelial cells maintain a one-to-one relationship with pericytes. With age there is a loss of endothelial cells followed by a loss of pericytes, leading in some cases to an acellular vascular channel Retinal Circulation – Age-Related Changes Cell loss Thickening of the pericyte basement membrane Narrowing of vascular lumens Diminished retinal microcirculatory flow and thus tissue perfusion Macula: blood flow may decline as much as 20% in people > 50 years old A decrease in total capillary number in the macula with age, corresponds with an increase in size of the foveal capillary-free zone Light Neural retina Retinal pigment epithelium (RPE) Bruch’s membrane Choroid Age-Related Changes in Bruch’s membrane: Thickening Decreased permeability RPE/Bruch’s membrane Extracellular debris: Basal linear deposit Drusen Basal laminar deposit NET FLUID FLOW HYDROPHOBIC BARRIER DRUSEN and AMD - Large drusen – predictor of age-related macular degeneration (AMD), especially its atrophic form (dry AMD) - Laser-induced photocoagulation may induce drusen regression but causes choroidal neovascularisation (CNV; wet AMD) Posterior ciliary arteries supply the choroid Choroid: Short posterior ciliary arteries Long posterior ciliary artery Choroid: vascular bed fenestrated Choroid Cilioretinal artery (in about 15-50% of populations) Choroid Central Retinal artery Artery and Posterior Ciliary Arteries Dorsonasal provide blood supply to the retina Long posterior ciliary artery Short posterior ciliary artery Central retinal artery Long posterior ciliary artery Ophthalmic artery Internal carotid artery Dual Retinal blood supply iris ciliary body conjunctiva anterior ciliary arteries muscular artery to lateral rectus (LR) → ciliary body anterior ciliary arteries anastomose with the branches of the long posterior ciliary arteries → major circle of iris Long posterior ciliary arteries → ciliary body and anterior choroid anastomose with anterior ciliary arteries to supply the iris → major arterial circle of iris Posterior Ciliary Arteries Two branches arise beneath the optic nerve to produce 10-20 branches Most are short posterior ciliary arteries: pierce the eyeball to supply choroid, optic nerve and pia Two are long posterior ciliary arteries: pierce the sclera to supply the ciliary body and the anterior choroid; their branches anastomose with anterior ciliary arteries to supply the iris → major arterial circle of iris Anterior Ciliary Arteries Branch from the arteries supplying recti muscles Exit the recti near their insertions Send branches into the conjunctiva, forming a network of vessels in the limbal conjunctiva Pierce the sclera just outer to the limbus, several braches → ciliary body → anastomose with the branches o the long posterior ciliary arteries → major circle of iris Extraocular Muscles Medial Rectus Lateral Rectus Superior Rectus Inferior Rectus Inferior Oblique Superior Oblique Levator palpebrae superioris Muscular Arteries: Lateral-superior artery supplies: - lateral rectus, superior rectus, superior oblique and levator muscle Medial-inferior artery supplies: - medial rectus, inferior rectus, inferior oblique Trochlea pulley lies in the trochlea fossa which is just behind the orbital margin of the frontal bone Blood supply to extraocular muscles Lacrimal Gland Lacrimal artery Lacrimal Artery Supplies branches to LR muscle, recurrent meningeal artery, zygomatic arteries, lateral palpebral arteries Branches on the lateral side of optic nerve and runs forward to the lacrimal gland Lacrimal Artery Passes through or lateral to the lacrimal gland which supplies Supply also the conjunctiva and the lids (anastomose with medial palpebral arteries to form palpebral arcades) Medial palpebral arteries Supply eyelids, anastomose with branches from the lacrimal artery to form palpebral arcades Dorsonasal artery Supplies the lacrimal sac, anastomose with the angular artery from the external carotid Supratrochlear artery Supplies the skin of the forehead and scalp and the forehead muscles; Anastomoses with supraorbital artery and anterior temporal artery Internal carotidcarotid artery of the external Ethmoid arteries Posterior ethmoid artery supplies - sinuses (posterior ethmoid sinus, sphenoid sinus) - nasal cavity (upper part of nasal mucosa) Anterior ethmoid artery supplies - sinuses (anterior ethmoid sinus, middle ethmoid sinus, sphenoid sinus, the frontal sinus) - nasal cavity - skin of the nose Supraorbital artery Supply skin and muscles of forehead and scalp, SR, SO, levator muscle and periorbita Veins draining the globe and orbit No valves!