 I'm standing on the right side, this is the right eye and the camera person is also on the right side towards the head end. To bring you up to speed, we have removed the eyelid and the orbicularis oculi muscles. So we can see in the depth, the remaining part of the eyelid, upper eyelid with the palpable conjunctiva, the lower eyelid with the palpable conjunctiva, the bulbar conjunctiva and the cornea. This is the medial canthus, this is the lateral canthus. Now I'm going to lift this up and we can see the intraorbital structures with the eyeball inside too. We had to cut a couple of muscles just to get increased mobility and I will tell you as we go along which are the muscles we cut. This whole orbital structure was first covered by the periorbita which is the periosteum of the orbit and this periorbita gives expansion which is called the orbital septum above and below which continues as the superior and inferior tarsal plate. It also gives facial expansion to these muscles and it also forms a suspensory ligament of eyeball or the suspensory ligament of lockwood and it also forms a shear above the sclera which is known as the tenon's capsule and it is to the tenon's capsule that these muscles are inserted. Inside this cone of muscles was a bundle of fat which we have removed and that is referred to as the intraconal fat and outside these cone of muscles was yet another bundle of fat which is referred to as extraconal fat that also we have removed. So let's first start off with the extraocular eye muscles. We see this remnant of this muscle. This is the riveter palpable superioris LPS. It takes origin from the lesser ring of sphenoid and comes down and gets attached to the superior tarsal plate and as it comes down it splits the lacrimal gland in partial into two parts and we can see the part of the lacrimal gland here. The lacrimal gland on being split one portion remains attached to the eyeball and that is known as the bulbar part and the part is in relation to the two prolateral aspect of the roof of the orbit and that is known as the orbital part. So we can see part of the lacrimal gland that is the first muscle. As we know the riveter palpable superioris is responsible for elevating the upper eyelid. It is supplied by CN3. Now let's take a look at the extraocular eye muscles inside. We notice that these muscles they form a cone because all these muscles they take origin from a fibrous ring around the optic canal and from that fibrous ring we have the rect eye muscles coming out. So we can see these muscles are taking origin in a cone shaped fashion. This is the sedatal MRI of the orbit to show the eyeball and the extraocular eye muscles with the optic nerve in the middle. So let's identify the muscles. This is the muscle that we had to cut to get this increased mobility of the eyeball. This is the lateral rectus. This is one cut portion of the lateral rectus and this is the other cut portion of the lateral rectus and they were together like this. The lateral rectus as we know is supplied by CN6. Abyssin nerve which I'm going to show you a little later. The next muscle that we can see here is this one which I have lifted up. This is the superior rectus. This is supplied by CN3. This turns the eyeball up and medially. The next muscle is this one. This is the inferior rectus. This turns the eyeball down and medially. Both of these are supplied by CN3. Now let's come medially. We can see this muscle here. We can see one part of the muscle coming from inside the orbit from this phenoid bone and then it is making a curve around this fibrous structure. This is the pulley or the trochlea and the rest of the muscle is then coming and getting attached to the upper part of the eyeball. This is the superior oblique. This is supplied by CN4, the trochlea nerve. And if you watch closely, I'm going to exert traction on this muscle and you will see the eyeball turning down and out. So please focus on the cornea. We can see the eyeball has turned down and out. When I'm pulling on this muscle, you will see the eyeball is turning down and out. The eyeball has turned down and out. So this is the action of the superior oblique. The superior oblique is supplied by CN4. The next muscle that we can see here is this one. This is medial rectus, which is also supplied by CN3. What we cannot see here is the inferior oblique muscle, because the inferior oblique muscle was attaching the eyeball right to the floor of the orbit. The inferior oblique muscle, as we know, takes origin from the floor of the orbit and it goes under the inferior rectus and gets attached to the eyeball. And this is the remnant of the inferior oblique. We had to cut it again to get increased mobility of the eyeball. So therefore, to summarize muscles that we saw till now, this was the levator palpate superioris. This is the cut portion of lateral rectus. And this is the other cut portion of the lateral rectus. This is the inferior rectus. This is the superior rectus. This is the superior oblique proximal part. Superior oblique distal part. This is the medial rectus. The inferior oblique had to be removed to liberate the eyeball for free movement. Having mentioned these, now let's take a look at the neurovascular structures. We can see this structure here. This is the ophthalmic artery. The ophthalmic artery is the first branch of the internal carotid artery. It enters the orbit through the optic canal and this is the optic nerve. It comes into the optic canal with the optic nerve. Inside the orbit, the ophthalmic artery gives 10 branches. And one of that branch I will show you just now. The next structure that we can see is this. This is the abdicent nerve. CN6, which supplies the lateral rectus. The next structure is the one which I have picked up now. This is a branch of CN3, which supplies the medial rectus. Now I'll draw your attention to this structure here, running along the superior roof of the orbit. This is the supra-orbital nerve and the supra-orbital artery. This passes through the supra-orbital foremen. Sometimes it's a notch, sometimes it's a foremen and we can see it is passing here. Supra-orbital artery is a branch of the optic artery and the supra-orbital nerve is a branch of ophthalmic division of trigeminal nerve CN5B1. Supra-orbital nerve and the supra-orbital artery, both of them supply a large part of the scalp right up to the vertex. Then we can see these neurovascular structures here, which I have lifted up. We cannot see them here in the orbit because they run in the floor of the orbit. They come out through this infra-orbital foremen. This is the infra-orbital nerve, the infra-orbital artery and the infra-orbital vein. Infra-orbital nerve and the infra-orbital artery. They are branches of the CN5V2, maxillary nerve and it's a branch from the third part of the maxillary artery. So these are the structures that we can see here. Let's take a quick look at clinical correlations. Paralysis of the lateral rectus will produce medial strabismus due to unbalanced activity of the medial rectus, also referred to as esotropia. This is a clinical picture to show the left-sided CN6 parallelysis producing medial strabismus and esotropia. Likewise, paralysis of the medial rectus will produce lateral strabismus, also referred to as exotropia. This is a clinical picture of a patient with left-sided CN3 parallelysis producing lateral strabismus or exotropia. In either situation, the patient will have squint and the patient will have diplopia. Before I conclude, let me mention one more thing. Whenever we do an orbital surgery, the usual approach is from the lateral side because lateral margin of the orbit is more receding and that gives us approximately 2.5 centimeters extra axis and that is the approach that we have used in our dissection here also. So these are the points which I want to mention to you about the orbital structures and the eyeball in situ. Thank you very much for watching. Dr. Sanjay Sanyal, signing out. Please like and subscribe. If you have any questions or comments, please put them in the comment section below. Have a nice day.