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Arteries and veins of the eye.
Hello everyone! My name is Megan from Kenhub, and welcome to our tutorial on the blood vessels of the eyeball. During this tutorial, we will look at some of the arteries and veins that constitute the blood supply of the eyeball then at the end of the tutorial, we will briefly go through some clinical notes.
Before we have a look at the blood vessels, let me give you a brief overview of the function of the eye. As you all probably know, the main function of the eyes is the perception of vision. The eyes essentially convert information contained in visible light into electrochemical impulses, which then travel to our brain via the optic nerve. This information is then processed by our brain mostly by the visual cortex which then builds a representation of our surrounding environment.
From external to internal, I'm going to highlight some key components of the eye in this image on the right. I'm just going to do this so when we talk about the structures that blood vessels supply, you'll have some context. So, most externally, we can see the conjunctiva here, then we can see the cornea which is continuous with the sclera, and then the ciliary body which is continuous with the choroid. This yellow layer here represents the retina and here we can see the fovea and the optic nerve. We can also see the iris here. For more detail on these structures and their function, have a look at our tutorial on the eyeball which is on our website.
So now that I've given a brief introduction on the structure and function of the eye, we can now move on to looking at the blood vessels. The first thing that you have to remember is that the artery that supplies the structure of the orbit is the ophthalmic artery which is highlighted here in green. This vessel is the first branch of the internal carotid artery which is this artery here. As we can see in this image, the ophthalmic artery passes through the optic canal into the orbit and is accompanied by the optic nerve. In the next image, we can see branches coming off the ophthalmic artery.
The branches of the ophthalmic artery are grouped into orbital branches and ocular branches. In this tutorial, we will only focus on the ocular branches. The ocular branches can be grouped into three categories. These are the central retinal artery, the muscular branches of the ophthalmic artery and, finally, the ciliary branches of the ophthalmic artery. So, now, let's further discuss each of these branch groups.
The first ocular branch of the ophthalmic artery is shown here in green and is called the central retinal artery. As we can see in this image, the central retinal artery runs inferior to the optic nerve before taking a turn superiorly and penetrating the optic nerve. This artery supplies the inner layers of the retina. The ophthalmic artery also gives off numerous muscular branches, which as their name suggests, supply the extraorbital muscles. These arteries are quite variable in their origin and number and they reach and supply the muscles that move the eyeball. An example of this can clearly be seen in the image on the right, where one of these branches is supplying the inferior oblique muscle.
The ophthalmic artery gives off three distinct categories of ciliary branches. These are the anterior ciliary arteries, the short posterior ciliary arteries and, finally, the long posterior ciliary arteries. We will now talk about each of these groups in further detail.
The muscular branches of the ophthalmic artery give off some small arteries which are called the anterior ciliary arteries and are highlighted in green in this image. These arteries supply the conjunctiva, the sclera, and the superior, inferior, medial and lateral rectus muscles. So, as I showed you earlier, here we can see the conjunctiva and here we can see the sclera. We can also see two of the rectus muscles – here and here. Because this is a superior view of the right eye, this is the medial rectus muscle and this is the lateral rectus muscle.
So now let's move on to look at the short posterior ciliary arteries. These arise from the ophthalmic artery as it crosses the optic nerve. There are usually six to twelve of these arteries in each eye and they supply the choroid and the ciliary processes which are inward foldings of the choroid. So, again, in this image, we can see the ciliary body with the ciliary processes which is continuous with the choroid. The choroid is better represented here where the retina has been removed.
As the ophthalmic artery crosses the optic nerve, it also gives off the long posterior ciliary arteries and they are usually two of these in each eye. They run between the sclera and the choroid to the ciliary muscle. Here, they divide into two arterial circles which we will soon have a look at. The long posterior ciliary arteries supply the iris, the ciliary body and the choroid.
So now let's move on to look at these two arterial circles which are derived from the long posterior ciliary arteries. The first arterial circle is called the major arterial circle of the iris or the circulus arteriosus major. It is formed by the anastomosis of the long posterior ciliary arteries and the anterior ciliary arteries. Part of the circle is highlighted in green here and it runs the entire circumference of the iris. The other arterial circle formed by the long posterior ciliary arteries is the minor arterial circle of the iris or the circulus arteriosus minor. In contrast to the major arterial circle, this is an incomplete circle that runs around the pupillary margin. We can see part of this structure highlighted in green.
So now we're going to move on to look at the veins of the eyeball – the vorticose veins. These veins are known clinically as the vortex veins and they drain the ocular choroid. The number of vortex veins varies from four to eight with over half of the normal population having four or five and, in most cases, there is at least one vortex vein in each quadrant of the eye. These veins drain into the superior and inferior ophthalmic veins.
As we can see in the next image, the vortex veins run posteriorly within the sclera. They also exit the eye posterior to the equator which is an imaginary line equidistant between the anterior and posterior poles. If we zoom in slightly, we are able to see this dilation of the vorticose vein here which is referred to as the bulb of the vorticose vein.
So to end this tutorial, let's go over a few clinical notes which are relevant to the blood vessels of the eyeball. The ophthalmic artery or its branches can become occluded and this can produce pathologies or conditions which can threaten eyesight. A visit to the ophthalmologist is recommended for those who experience changes in their vision. Severe and immediate changes are often signs of a more serious health condition. Painless loss of monocular vision or vision in one eye is the usual presenting symptom of retinal artery occlusion and this is an ophthalmologic emergency.
Ocular stroke is commonly caused by embolism of the retinal artery. Emboli can travel to distal branches of the retinal artery and can cause loss of vision in only a small area of the visual field. Delay in treatment may result in permanent loss of vision while immediate attention can improve the chances of vision recovery although the prognosis is still poor. Ophthalmoscopy or fundoscopy is a test that help professionals use to look at structures in the eye including blood vessels. This is done using an instrument called an ophthalmoscope or a fundoscope. When performing an optical fundus exam, the arteries appear brighter red and narrower than the veins so this is a good way to differentiate between them.
And that concludes our tutorial on the blood vessels of the eye. I hope you enjoyed it and thank you for listening.
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Now, good luck everyone, and I will see you next time.