May 11, 2020 · The central retinal artery supplies the inner two-thirds of the retina. Meaning that the central retinal artery nourishes all the retina except for the photoreceptor layer, this is supplied by choriocapillaris from the choroid. Upon entering the nerve fiber layer of the retina, the central retinal artery divides into two branches; the superior branch and the inferior branch.
Its course can be divided into three distinct parts: (1) intraorbital (lying below the optic nerve (ON) – ( Figure 2 )), (2) intravaginal (lying in the space between the ON and its sheath), and (3) intraneural (lying in the ON) ( Figure 3 ). It enters the ON about 10 mm posterior to the eyeball ( Figures 2 and 3 ).
According to Michaelson, there are two layers of retinal capillaries: (i) the superficial network in the nerve fiber and ganglion cell layers and (ii) the deep network in the inner nuclear layer. The superficial network has an average diameter of 65 μm (16–150 μm), and the deep network has an average diameter of 50 μm (15–130 μm).
The retina is supplied by the central retinal artery and the short posterior ciliary arteries. The central retinal artery travels in or beside the optic nerve as it pierces the sclera then branches to supply the layers of the inner retina (i.e., the layers closest to the vitreous compartment).
In humans, the CRA is the first branch of the ophthalmic artery (from internal carotid artery) and enters the ventromedial aspect of the optic nerve about 1.2 cm from the globe. As the CRA emerges from the optic nerve, it divides into superior and inferior branches, which further divide into temporal and nasal vessels.
tenThe retina is a layered structure with ten distinct layers of neurons interconnected by synapses.Aug 11, 2021
Anatomical terminology The central retinal artery (retinal artery) branches off the ophthalmic artery, running inferior to the optic nerve within its dural sheath to the eyeball.
superior ophthalmic veinThe central retinal vein (retinal vein) is a short vein in the retina of the eye. It travels through the optic nerve to drain into either the superior ophthalmic vein or the cavernous sinus. It drains blood from the retina.
The cellular layers of the retina are as follows: 1) The pigmented epithelium, which is adjacent to the choroid, absorbs light to reduce back reflection of light onto the retina, 2) the photoreceptor layer contains photosensitive outer segments of rods and cones, 3) the outer nuclear layer contains cell bodies of the ...
It is primarily made up of three layers of nerve cells, these are ganglion cells, bipolar cells and photoreceptor cells.
The center of the macula is called the fovea. The inner surface of the retina is adjacent to the vitreous of the eye. The outermost layer of the retina, the retinal pigment epithelium, is tightly attached to the choroid.Dec 7, 2017
The central retinal artery is a blood vessel inside the eye. It provides essential nutrients to the retina. The retina lines at the back of the eye and is full of cone cells and rods, which transmit messages to the occipital lobe in the brain's cerebral cortex.
The retina is supplied by the central retinal artery and the short posterior ciliary arteries (Fig 2.3). The central retinal artery travels in or beside the optic nerve as it pierces the sclera then branches to supply the layers of the inner retina (i.e., the layers closest to the vitreous compartment).
Capillaries are found running through all parts of the retina from the nerve fibre layer to the outer plexiform layer and even occasionally as high as in the outer nuclear layer.May 1, 2005
The retina consists of two layers: the sensory retina, which contains nerve cells that process visual information and send it to the brain; and the retinal pigment epithelium (RPE), which lies between the sensory retina and the wall of the eye.
Cornea: The outer, transparent structure at the front of the eye that covers the iris, pupil and anterior chamber; it is the eye's primary light-focusing structure.Jan 26, 2022
A capillary-free zone exists around the retinal arteries and arterioles because of high oxygen concentration in these vessels. In 25% of humans, a cilioretinal artery (from posterior ciliary arteries) comes out of the temporal aspect of the optic nerve head and supplies the macula.
Blood vessels enter and exit the retina at the optic disc (nerve head), located nasally and slightly superiorly from the geometric midpoint of the eyeball. The macula is located temporally and slightly inferiorly from this midpoint.
The central retinal artery is the sole blood supply to the inner two-thirds of the retina. The terminal branches of the central retinal artery are end arteries, meaning that a proximal occlusion will completely cut off blood supply to that portion of the retina.
The retina is supplied by the central retinal artery that enters the optic nerve just distal to the point at which the artery branches from the ophthalmic artery. If external pressure is applied to the eye, the intraocular pressure can be increased to the point at which it exceeds the pressure in the central retinal artery. Blood flow through the artery then ceases, and retinal ischemia results. Approximately 4 minutes of ischemia to the retina can result in retinal blindness from ischemic necrosis of the light-sensing cells.
Despite preinjection paracentesis, the central retinal artery sometimes closes after gas injection. Several studies suggest that the retina can tolerate 60 minutes without blood flow as a result of elevated pressure.26,61–65 If the artery does not reopen within about 10 minutes, intraocular pressure should be lowered by repeat paracentesis.
The central retinal artery and its branches supply blood to the retina. This arterial system, derived from the ophthalmic artery (the first branch off the internal carotid artery), is commonly the first site where ischemic or embolic events (transient ischemic attacks) herald the presence of serious vascular disease and high risk for a future stroke. Ciliary arteries supply the middle vascular tunic, which also contributes partial blood supply to the retina; this component of blood supply can be disrupted by a detached retina. Blood vessels enter and exit the retina at the optic disc (nerve head), located nasally and slightly superiorly from the geometric midpoint of the eyeball. The macula is located temporally and slightly inferiorly from this midpoint.
If the retina becomes detached, it may be separated from part of its blood supply from the ciliary arteries in the middle vascular tunic, which also results in loss of vision. View chapter Purchase book.
The central retinal artery and its branches supply blood to the retina. This arterial system, derived from the ophthalmic artery (the first branch off the internal carotid artery), is commonly the first site where ischemic or embolic events (transient ischemic attacks) herald the presence of serious vascular disease and high risk for a future stroke. Ciliary arteries supply the middle vascular tunic, which also contributes partial blood supply to the retina; this component of blood supply can be disrupted by a detached retina. Blood vessels enter and exit the retina at the optic disc (nerve head), located nasally and slightly superiorly from the geometric midpoint of the eyeball. The macula is located temporally and slightly inferiorly from this midpoint.
The retina is supplied by the central retinal artery that enters the optic nerve just distal to the point at which the artery branches from the ophthalmic artery. If external pressure is applied to the eye, the intraocular pressure can be increased to the point at which it exceeds the pressure in the central retinal artery. Blood flow through the artery then ceases, and retinal ischemia results. Approximately 4 minutes of ischemia to the retina can result in retinal blindness from ischemic necrosis of the light-sensing cells.
The ocular branches include the central retinal artery, the anterior ciliary arteries, the lateral and medial posterior ciliary arteries, and small collateral branches to the optic nerve. The central retinal artery is typically the first branch of the ophthalmic artery. It runs along the inferior aspect of the optic nerve before piercing the optic nerve sheath 5–15 mm posterior to the globe. Once the artery has entered the neural sheath, it makes its way to the center of the optic nerve substance, supplying blood to the surrounding nerve as it courses toward the optic nerve head where its terminal branches divide to supply the inner retina. The central retinal artery is the sole blood supply to the inner two-thirds of the retina. The terminal branches of the central retinal artery are end arteries, meaning that a proximal occlusion will completely cut off blood supply to that portion of the retina. More distal occlusions can lead to segmental retinal ischemia.
In humans, the CRA is the first branch of the ophthalmic artery (from internal carotid artery) and enters the ventromedial aspect of the optic nerve about 1.2 cm from the globe. As the CRA emerges from the optic nerve, it divides into superior and inferior branches, which further divide into temporal and nasal vessels. Retinal vessels radiate from the optic nerve head supplying networks throughout the retina and stop short of the periphery and also spare the fovea. The retinal vessels are endarterial in nature and have no anastomoses with other vessels. Thus, occlusion of the CRA leads to complete loss of blood supply and death of retinal cells. All the four arterial branches of the CRA have the same structure of small arteries. Retinal arteries are unique and different from the muscular arteries of similar size in other parts of the body, as they lack an internal elastic lamina and muscularis. In the posterior part of the globe, the arterial wall contains five to seven layers of smooth muscle cells that become one to two layers in the periphery. Retinal veins also do not have elastic lamina and contain pericytes and abundant collagen fibers.
Despite preinjection paracentesis, the central retinal artery sometimes closes after gas injection. Several studies suggest that the retina can tolerate 60 minutes without blood flow as a result of elevated pressure.26,61–65 If the artery does not reopen within about 10 minutes, intraocular pressure should be lowered by repeat paracentesis.
The retina is pale and indistinct or cloudy due to oedema in the nerve-fibre layer. Only the macula retains its usual pink appearance because of the absence of nerve fibres in that area. By contrast with the milky colour of the fundus the macula comes to look redder than normal and is known as the cherry-red spot. After a few weeks the ischaemic oedema of the retina subsides and the cherry-red spot ‘fades’.
The pathophysiology is similar to that in CRVO. This is because, during the third month of intrauterine life, there are always two trunks of the CRV in the optic nerve, one on either side of the CRA. 53 The two trunks are united with each other by numerous anastomoses. As the two venous channels pass back from the eyeball, they approach one another and finally coalesce at a variable distance behind the optic disc into one – the main trunk of the CRV. One of the two trunks usually disappears before birth; however, in 20.5% of eyes a dual-trunked CRV persists as a congenital anomaly. 82 In HCRVO, usually only one of the two trunks of the CRV is involved by occlusion within the optic nerve 53; occasionally, however, both trunks may be involved, presumably because the site of occlusion is in the main trunk of the CRV after the union of the two trunks, or the two trunks may be involved independently, one after the other, and this would appear on routine examination to be ordinary CRVO; however, one can see two venous trunks entering the optic disc.
In contrast to thevertical orientation of the nerve fibers in the extrafoveal retina, the nerve fibers in this layer course obliquely & actually run parallel to the retinal surface. Also, in the central retina, every cone is interconnected with a single bipolar cell, which in turn synapses with a single ganglion cell.
The retina consists of 10 layers which include nine layers within the sensory retina and retinal pigment epithelium. Embryologically RPE is developed from the outer layer of the optic cup and photoreceptors are developed from the inner layer of the cup and there is a potential space between RPE and sensory retina, known subretinal space. Absence of specialized molecules like laminin and fibronectin, lack of junctional complexes between RPE cells and photoreceptors are responsible for this loose attachment of RPE cells to the photoreceptors. In retinal detachment, the sensory retina detaches from retinal pigment epithelium (RPE). RPE remains firmly attached to the choroid during retinal detachment.
The neurosensory retina is mainly made up of three groups of neurons: photoreceptors, bipolar cells, and ganglion cells. Other important neurons like amacrine cells, horizontal cells have supporting roles. The photoreceptor cells, bipolar cells, and ganglion cells carry the neural signal in a three-step pathway through the retina. Photoreceptors are sensory receptors. Bipolar cells are first-order cells and ganglion cells form second-order neurons. In this section, we will discuss the anatomy of the cells present in the retina.
The ora serrata represents the anterior limit of the neural retina. The retina is strongly adherent to the retinal pigment epithelium at the ora serrate, the reason retinal detachment rarely extends anterior to the ora serrata. Ora serrata has a scalloped appearance and is serrated much more nasally than temporally.
Human retina measures 32 mm from ora to ora along the horizontal meridian and t he total surface area of the retina in each eye is approximately 1,100 square mm.2 The average thickness of retina is 200 micrometers, it is slightly thicker near optic nerve head and near the macula and gradually thins out at the ora serrata and fovea.3 Broadly the retinal surface can be divided into the following areas:
With age, RPE gradually loses melanin granules, possibly related to effects of photooxidation. Each RPE cells show variation in pigmentations, the reason for characteristic coarse, granular appearance of fundus. Pigmentation of RPE cells usually increases in periphery of retina with old ages.
Between the neural retina and RPE, there is a potential space known as subretinal space . The adhesion between neural retina and RPE is relatively weak. The neural retina is firmly attached at its anterior termination, the ora serrata, and at the margins of the optic nerve head.
After a short intracranial course, the ophthalmic artery pierces the dura and enters the orbit through the optic foramen, traveling through the optic canal alongside the optic nerve. Within the optic canal, the ophthalmic artery begins its course lying inferolaterally to the optic nerve.
Origin and course. The ophthalmic artery most commonly arises as the first major branch of the internal carotid artery, directly after emerging from the carotid sinus. It arises from the C6 segment of the internal carotid artery, usually at the level of the anterior clinoid process of the sphenoid bone.
Central retinal artery occlusion occurs as the central retinal artery becomes blocked, usually due to ipsilateral carotid artery atherosclerosis.
Posterior ciliary arteries: consist of two sets of arteries; long and short posterior ciliary arteries. These arteries pierce the sclera on the posterior aspect of the eyeball, just lateral to the optic nerve, and go on to supply the sclera, choroid and anterior segment of the eyeball.
Along its course, the ophthalmic artery gives off 10 branches that supply all the structures of the orbit, the upper two-thirds of the nose, the nasal cavity, the frontal area of the scalp, the ethmoid and frontal sinuses and some parts of the meninges . The terminal branches of the ophthalmic artery establish extensive anastomoses with branches ...
Upon entering the cranial cavity, the anterior ethmoidal artery gives off the artery of falx cerebri, that supplies the falx and dura mater, and the nasal branches that descend into the nasal cavity through the cribriform plate to supply the middle and anterior ethmoidal cells, lateral wall of the nasal cavity and the nasal septum.
The long posterior ciliary arteries end near the sclerocorneal junction by joining the major arterial circle of the iris. Lacrimal artery: one of the largest branches of the ophthalmic artery. This artery arises just before the ophthalmic artery enters the orbit.
On entering the orbit, the central retinal artery leaves the ophthalmic artery and travels within the optic nerve, after which it enters the eye, where it is subjected to intraocular pressure changes. Approximately 15%-30% of the population has a cilioretinal artery, a branch of the short posterior ciliary artery.
The retina receives a dual blood supply, with the inner retina supplied by the central retinal artery and the outer retina supplied by the choroidal circulation via branches of the posterior ciliary arteries.
CRAO of arteritic etiology is mostly caused by giant cell arteritis, although other vasculitic disorders such as Susac syndrome, systemic lupus erythematosus, polyarteritis nodosa, and granulomatosis with polyangiitis have also been associated with retinal artery occlusion.
Central retinal artery occlusion (CRAO) is an ocular emergency. Patients typically present with profound, acute, painless monocular visual loss—with 80% of affected individuals having a final visual acuity of counting fingers or worse. CRAO is the ocular analogue of a cerebral stroke—and, as such, the clinical approach and management are relatively similar to the management of stroke, in which clinicians treat the acute event, identify the site of vascular occlusion, and try to prevent further occurrences. The incidence of CRAO is approximately 1 to 2 in 100,000, 1,2 with a male predominance and mean age of 60-65 years.
Approximately 15%-30% of the population has a cilioretinal artery, a branch of the short posterior ciliary artery. It supplies blood to part or all of the fovea. If a CRAO occurs in such eyes, the cilioretinal artery is spared, typically preserving visual acuity at 20/50 or better, although peripheral visual field is still severely impaired.
CRAO is a medical emergency. Prompt referral for stroke evaluation is necessary in order to minimize risk of secondary ischemic events such as cerebral or myocardial infarction. In the acute setting, therapy is directed at resolving the CRAO and maximizing visual outcome.
Subsequent retinal atrophy and thinning occurs after approximately 6 weeks.