welcome to today's lecture entitled the gross anatomy of vision my name is Carlos Andres aresquian I am the author of this work and will narrate it for you let's start by listing the census touch taste smell hearing and vision a deficit in any of the senses generates significant issues to a patient I contend however that if you were to ask anyone which sense it would least likely wish to lose it would be sight yes since July 26 1990 when the American with Disabilities Act was signed into law it is possible to argue that life has become marginally better for the disabled now do the following tape your eyes shut and try to go by your daily business es may not be able to discriminate against you but is that any consolation life remains quite difficult for the blind simply put we live in a world where sight is required and loosen this sentence becomes an issue no wonder so much research goes into helping to maintain sight for individuals the objectives of the lecture are listed here we will cover the following the location of the orbit within the skull what makes up the Bony walls of the orbit and understand why one is more likely to fracture than the other the surface anatomy of the eye the extrinsic muscles of the eyes and how they move the eye and position it to see what we want to see the nerves had moved the muscles of the eye but also the nerves it allows to accommodate our eyes to see near and far and finally the blood supply to the eye let's move to the Bony orbit to discuss their location and content the Bony orbit sockets contain the eyeballs that is clear but there are also seven muscles nerves vessels and quite a bit of fat as seen in the slide you'll be amazed at the amount of fat in our orbits and it's the type of fat that is not lost until final stages of starvation diets when this fat finally starts to disappear the eyes begin to pierce sunken in precisely because fat has been lost here's an image of volunteer who participated in a 1944 University Minnesota starvation experiment for 13 months note how sunken the eyes appear as you probably are aware there are worse images of sunken eyes in the web of individuals who have been subjected to even more devastating diet restrictions continuing with the orbits each orbit is pyramidal in shape the base of the orbit is the orbital margin the Apex is at the optic canal note how the medial walls are parallel to one another in approximately 25 millimeters apart half an inch the lateral walls are right angles to each other now look at the eyeball and realize that it only occupies about half of the length of the orbit as we saw in the first slide and again we'll see in the laboratory the posterior half of the orbit is filled with muscles and lose fatty tissue finally the eyeball is not as wide as it is deep note the width is approximately only 40 millimeters now why go into all these details about the orbit because the properties of the orbit dictate how ophthalmologists must enter the orbit to minimize the risk of damaging the contents of the orbit based simply on the geometry of the orbits note how the medial wall extends farther anteriorly than the lateral wall hence the lateral wall is more exposed than the medial wall of the eyeball and the preferred side in which to enter the orbit when surgical procedures are required in this area let's now focus on the orbital cavity as it relates to other regions of the skull in the drawing the orbital cavities indicated in a skull that has been sectioned the coronal plane the crystal Galley of the ethmoid bone and the nasal septum are labeled for orientation what is clear from the drawing is that the orbital cavity is surrounded by other cavities and each can impact on the respect of adjacent cavity as follows if a sharp object is pushed through the roof of the orbit it will enter the anterior cranial fossa if an object is pushed through the floor of the orbit it will enter the large maxillary sinus and if an object is pushed through the paper-thin medial wall it will enter the ethmoidal sinuses now you might be thinking gee where does Dr Suarez live that he's always talking about sharp objects piercing bone or trauma Etc let me assure you that I am quite safe where I live the point of discussing these issues is that accidents can and do happen so we must be aware of possible Downstream effects of injuries here are two examples from the recent literature with nail gun mishaps the individual on the left described it as feeling a slight headache and the individual in the middle even stopped to have his picture taken by a friend with the nail through his eye before being driven to the hospital finally there's the extraordinate case of Phineas Gage who had a blasting cap go off and the ramming stick was pushed through his temporal region orbit and frontal cerebral hemisphere he lost his sight on his eye and under one personality changes but lived an additional 12 years to the age of 47 not an uncommon lifespan in the early 19th century again expect accidents because they happen the final relationship of the orbit I want to point out is the posterior one if he pushed an object in the anterior posterior Direction it will enter the middle cranial fossa and this one is unlikely to be survived by the patient indeed you've ever spent any time reading crime novels you may know that a favorite tool of Assassins is this stiletto knife a long pointed knife similar to an ice pick I always wonder why this was so until I took anatomy and realized that someone must have taught assassins their Anatomy too the internal carotid artery runs right smack in the middle cranial fossa and it's at risk of damage in these types of injuries now you might think this is Dr suartis being melodramatic telling accounts of Assassins but I did meet a retired CIA agent ones who had spent a lot of time overseas and did confirm to me at least years ago that agents do receive training with a stiletto dagger and the eye was definitely a choice point for attack okay back to anatomy and now we discuss the bunny walls of the orbit remember we already know that it's shaped like a pyramid and now you know it is made up of six bones let's identify them which conveniently they're color-coded in the image the frontal the sphenoid the psychomatic the maxillary the lacrimal and the ethmoid the bones are not of equal strength the lateral wall of style whereas a medial wall made up of the ethmoid is paper thin indeed it is called the lamina paparisha to denote this it is the reason that most rules calls have their medial walls missing instead of grabbing this call from the outside we tend to stick our fingers into the orbits and pinch the medial wall with our thumb and finger and quickly destroy the paper-thin medial wall if you have a skull and I wonder if it's real if it is missing the medial orbital wall it is real the relative weakness of the medial wall is also the anatomical reason for how the lesion known as a blowout fracture presents in a patient look at the bulging right eye known as an exothermus in the MRI the air is pointing to the damaged medial wall blowout fractures occur from increased pressure in the orbit and can result in an endothermus or posterior displacement of the eyeball or exothermus as shown in this image here's another example of exothermals this time you're looking at the blowout fracture from above the white material indicated by the arrow in the MRI is the inflammation resulting from the injury and here two CT images of blowout fractures note the clear demonstration of the medial damage in both in the coronal plane left image and in the axial plane right image however don't go thinking that exothalamus is only exhibited in blowout fractures apparently exothalamus is also manifested in the autoimmune disease called Graves disease Marty Feldman was a well-known comedian in the 1950s and 60s and was one of the stars in the classic comedy Young Frankenstein we now move to the surface anatomy of the eye and here it is now I'm sure given us importance in literature you have a favorite saying about the eyes here's some of mine the eyes have it unfortunately that has nothing to do with the eyes or dot your eyes and again nothing to do with the eyes but here's one by Charlotte Bronte the soul fortunately has an interpreter often and unconscious but still a faithful interpreter in the eye they say novelists are great observers and I've always found that quote telling with respect to the surface anatomy of the eye we need to spend a little bit of time presenting definitions and here they are the opening between the upper and lower eyelids is known as the palpebral fissure where the upper and lower eyelids meet medially and laterally to form joints are known as a lateral and medial poppybral commissures and the commissures by coming together form angles these angles are known as the kanthi plural of canthus ancient grief or corner of the eye let's now look at the surface anatomy the eye itself I'm sure you know these but let's review them here anyways the cornea is a transparent anterior 1 6 of the outer coat of the eyeball the iris is a varied color diaphragm seen through the cornea the pupil is the aperture at the center of the iris and the sclera is the whitish opaque posterior 5 6 of the outer coat of the eyeball looking now at a satchel view the eye let's label the structures we just named to see how they appear from this angle and here we see the sclera cornea pupil and Iris but in addition we now see the lens you'll get more information in a separate lecture in how these structures contribute to sight if we now focus on the outside of the eyeball we observe the palpebral conjunctiva mucosa that covers the posterior surface of the eyelid the conjunctiva turns back on itself at a region called a conjunctival fornix and becomes continuous to the ball but conjunctiva covering the anterior part of the sclera fornix simply means Archway in Latin finally the potential space between the eyeball and the eyelids is given the name of the conjunctival sac the surface anatomy of the eyelid is the last structure to consider and given how thin these are it is surprising how much there is inside the eyelids first thing you must understand about the eyelid however is that the artists of this drawing had to disproportionately draw it so they could fit all the structures found within the eyelid having stated as such let's add some labels the Tarsus are semilunar plates made up of dense connective tissue and are located between the palpebral conjunctiva and The Superficial fascia the borders of the free margins of the eyelid and the Tarsus attach the medial and lateral walls of the orbit via the medial and lateral upheaval ligaments the tarsal glands are modified sebaceous glands within a Tarsus ducts open on free margins of the eyelid and their oily secretions form a surface film to reduce evaporation of Tears the tarsal muscles are smooth muscles within the tendon of the levator Papyrus superioris the tarsal muscles attach the Tarsus to the upper eyelid they receive sympathetic innervation from internal carotid plexus and contract reflexely to elevate the upper eyelid the orbital septum is a fibrous membrane extending from the orbital margin to the Tarsus it is continuous of the pericranium on a clinical note think of the orbital septum acting as a firewall by preventing the spread of infection from The Superficial fosh of the eyelids to the interior aspect of the orbit remember also that within the eyelids we have muscles of facial expression the orbicularis oculi hence note that distinct innervation between the levator palpebri muscle cranial nerve 3 from the orbicularis oculae by cranial nerve seven of course we also have eyelashes called cilia and these are associated with ciliary glands that can become infected and blocked in reality both the ciliary gland and the tarsal glands can be blocked and they present in similar fashion But realize that the blockage is a totally different origin a blocked torso gland is known as a calasian some books will describe it as a black meibomian gland which will cause dry eyes because tier of operation now occurs more rapidly and the condition can be exacerbated by eye makeup in contrast a bloxiliary gland is known as a hordeolum or stye and represents an infection which should be treated with antibiotics I injuries 2 are expressed as a function of surface anatomy periorbital ecchymosis block eye for example is nothing more than trauma to the header phase which causes bleeding beneath the skin when the small blood vessels beneath the skin break blood leaks into the surrounding tissue causing the discoloration being hit in the top of the head can also lead to a black eye the thick and tight aponeurosis of the scalp prevents the migration of the small bleeds except on the path of least resistance which is often the orbit in such cases a black eye May develop over a period of days even though the face did not sustain the injury a subconjunctival hemorrhage is also the result of a trauma and although it looks horrible when you see it it is often the result of a relatively benign condition something as trivial as an increase in blood pressure that can resolve from heavy lifting coughing sneezing laughing and constipation may lead to the condition the last structure we need to consider when discussing surface anatomy is a lack of apparatus as can be observed in the slide the LACMA gland is located on the lateral margin of the orbit and our tears travel from lateral to medial when we blink the tears are collected by the lacrum apparatus and ultimately drains the inferioris the nasal cavity precisely why we need to blow our noses when we cry the next topic for discussion becomes the muscles of the eye and their innervation let's start naming them the first muscle we see when we move the orbital plate of the frontal bone and enter the orbit from above is the levator palpeaver Superior auras the muscle will not act on the eyeball because it does not attach to the eyeball instead it raises the eyelid but is specifically not a muscle facial expression hence it is not innervated by the facial nerve but instead it is innervated by the oculomotor nerve cranial nerve three we next move to the six muscles that move the eyeball here they are four straight muscles hence there's suffixes end with rectus and the prefix of their name relates to their location let's look at the recti muscles as they appear on the eyeballs are from the front they are the superior rectus the medial rectus the inferior rectus and rounding out the circle the lateral rectus we now look from the back and observe two oblique muscles the superior and inferior obliques and remember what is keep up muscles you must know their innervation as well but this is straightforward for the six eye muscles by remembering the following formula lr6 so4 all others by three now we need to understand how these muscles direct eye movement and that may take some more effort to grasp what we need to do first is simply look at the actions performed by the eyeballs and here they are eyes can look toward the nose that is adduction eyes can look to the periphery that movement is known as abduction eyes can look upwards elevation or downwards depression and eyeballs can partially turn inwards that is known as in torsion or turn outwards which is known as extortion the axis of rotation is through the pupil and optic nerve clearly for normal vision the muscles we have just described must work in synchrony to move the eyeball in the direction we wish to move it shortly I will describe the specific actions of each muscle but first I want to describe some conditions in which the patients can tell that something is not as it should be and generally it is apparent that notices that something is just not normal with a child's eye I list here some common questions that parents will raise when they start bringing their child in for checkups why is my child cross-eyed is this going to be permanent will he need surgery what the parent has observed is strabismus a condition in which the eyes are not properly aligned with each other when looking at an object the eye that is focused on an object can alternate the condition may be present occasionally or constantly if present during a large part of childhood it may result in amblyopia or loss of death perception the word is derived from the Greek strabismuth which means squinting the opposite of strabismus is orthophoria exact ocular balance instruments can be considered latent in which case it is termed heterophoria or it is Manifest in which case a proper term to use is heterotropia Auburn tracking of the eyeball also occurs to the eye being in an inward deviated position a conditioned term esotropia or outward deviation called exotropia and are now on the image on the right it is easy to observe the esotropia but not sure anyone would notice the exotropia but now cover the aberrant eye in both children you can clearly see that the left eye of the little girl was focusing on The Examiner vertical deviation can also be an issue and the vertical deviation can be either hypertropia as shown here or hypotropia pseudoesotropia can be difficult to confirm as in this child again we cover the ah that is not tracking correctly in the Gaze of the children focus on the examiner is not clear as a review here's a drawing of possible various forms of strabismus let's now go back to the muscles and gain an understanding of what each individual muscle attached to the eyeball does the inductors are the medial Superior and inferior rectus the abductors are the superior and inferior obliques in the lateral rectus the elevators are the superior rectus and the inferior bleak the depressors are the inferior rectus in the superior oblique turning to the rotators the lateral rotators the ones that cause extortion are the inferior rectus and the inferior bleak whereas a medial rotators those causing in torsion are the superior rectus and the superior oblique as a review I show how each individual muscle is capable of moving the eyeball let's look at this left eye that has the six eye muscles attached we start with a superior bleak the superior rectus the lateral rectus the inferior rectus the inferior oblique and the medial rectus knowing what the muscles do allows you to isolate an action of a particular muscle to test whether the nerve innervating the muscle remains intact for example look at the eye and the arrows to test for the action of the lateral rectus one only needs to ask the patient to abduct their eye however to test the action of the superior rectus one needs to first ask the patient to abduct the eye then have them elevated why is this the explanation is in this set of drawings on the bottom panel look at the axis of the superior rectus muscle the axis of the eyeball in superior rectus muscle are not parallel therefore the superior rectus muscle cannot be isolated however once the eyeball has been abducted the eyeball now is parallel with the superior rectus muscle therefore only the superior rectus muscle can Elevate the eye let's do one more muscle this time the superior oblique when we look at the axis of the eyeball and that of the superior oblique muscle we know that they're not parallel therefore the superior Bleak muscle cannot be isolated in contrast once the eyeball has been adducted the eyeball now is parallel with a superior Bleak muscle therefore only the superior oblique muscle can depress the eye a detailed description of how to test for all six muscles of the eye is presented in this YouTube video please visit the site if you wish to gain additional information we now move to the nurse supply of the eye and we have discussed these previously the nerves of the eyes are listed here the optic oculomotor trochlear ophthalmic division of five and the abducens let's go in order and describe what they do the optic nerve is actually not a nerve but an extension of the brain that is covered by meninges it emerges from the posterior aspect of the eye courses posteriorly within the retrobulver space and exits through the optic canal the mechanism of how light is converted into Vision will be presented in a separate lecture I did present the visual pathway in the cranial nerve lecture however and you will be expected to follow it I will not describe it again here in this lecture except to remind you that it is the temporal visual field that crosses over but the temporal retina fibers do not look closely at the image to appreciate why this statement is correct also review again the direct and consensual pupillary reflex and understand why they occur and why they are used in emergency situations to assess patient status remember however more details about these Pathways will be provided in neuroscience next we move to the oculomotor nerve shown here in the drawing entering the orbit through the superior orbital fissure and splitting into a superior and inferior division the details that you need to know for this nerve are listed in the slide it is motor to five muscles it will provide preganglionic parasympathetic fibers to the ciliary ganglion you know be responsible for constricting the pupil and accommodating the lens of the eye if damage it could simply prevent mitosis or droop your eyelids because the nerve innervates elevator palpeva Superior auras we again look at the trochlear and abduces nerves and these are straightforward each is only motor to one muscle the trochlear to the superior oblique the abducens to the lateral rectus also understand why double vision ensues if these nerves are damaged here we see an isolated trochlear nerve policy which are rather rare given what you now know about the superior oblique muscle it should be clear why the lesion results in diplopia and inability to rotate the eye in an inferior laterally Direction due to the paralysis of the muscle on the same side the idv8 upward and slightly inwards but the contralateral eye is unaffected a person suffering from such a lesion will have difficulty in walking downstairs unless they cover the affected eye if you ask the patient to look downwards towards the opposite side of the lesion it will lead to diplopia isolated abducens nerve injuries are also quite rare isolated abducens nerve leads to medial Squints with an inability to direct the effect that I laterally due to the unopposed action of the medial rectus diplopia will always be present except when looking opposite the side of the lesion the last individual nerve we need to discuss is the ophthalmic division of cranial nerve five once a nerve enters the orbit it splits into the various components now indicated the frontal lacrimal and nasaciliary the frontal will continue as a super orbital once it exits the skull remember all these branches are sensory all of the lacrimal nerve will ultimately be joined by post ganglionic fibers from the tegopolitan ganglion via psychomatic nerves let's again review the ciliary ganglion which you have seen previously for this particular ganglion we need to discuss his General sensory contribution its preganglionic parasympathetic contribution and it's postganglionic sympathetic contribution the sensory components of the ciliary ganglion are derived from the ophthalmic division of the trigeminal nerve fibers from V1 will travel to the ganglion then pass right through to reach the eyeball and the cornea via the short ciliary nerves in addition note that fibers from V1 will bypass the ciliary ganglion and travel directly to the back of the eyeball by fibers known as long ciliary nerves the preganglionic parasympathetic fibers to the ganglion will arrive there from the oculomotor nerve once there the fibers will synapse at the ciliary ganglion and exit the ganglion as postganglionic fibers via the short ciliary fibers to constrict the pupil and accommodate the lens finally postganglionic sympathetic fibers traveling with the internal carotid artery will jump to the ganglion or directly to the eyeball and provide sympathetic innervation of the eye these are the nerves for fight or flight and will lead to pupillary dilation next we consider the corneal reflex the afferent pathway will be by V1 that is if our corneus or touch we blink given that the muscle responsible for blinking of the eyelid is the orbicularis oculate a muscle facial expression the pharyn pathway will be enacted by the facial nerve cranial nerve seven before leaving the nerves let's discuss Horner syndrome and understand its signs is a cervical sympathetic trunk is somehow disrupted for example as a result of trauma or secondary to surgery the manifestations are an absence of ipsilateral sympathetic stimulation and the signs of Horner syndrome may include meiosis ptosis and anhidrosis the meiosis will result because a sympathetic innervation to the pupils interrupted the pupil being constant state of constriction even in the dark as shown on the image the drooping of the eyelid is because the tarsal muscles within the eyelid are not receiving innervation and the absence of sweating is because again the patch of skin on the face is missing sympathetic innervation and cannot respond to stress individuals also lose the ability to become flush and the reason for why some individuals choose selective surgery to abolish their excessive Flushing the last topic for the day is a blood supply to the orbit and this is quite straightforward all the arterial supplied to the orbit is from the ophthalmic artery a branch of the internal carotid the ophthalmic artery is also the source of the central artery of the retina understand why any perturbation in the soil artery will result in loss of vision in that eye there's no Second Source the vein is returned as you have not heard on various lectures link some meninges to the danger sound of the face infection in the face can trial by way of the venous system to the cavernous sinus meaning to severe meningitis as well on rare occasions a fistula may result in the internal carotid artery mixing arterial and venous blood and a pulsation of the eyeball will be observed a pulsating eyeball can also be the result of A congenital condition where this phenoid bone is missing check out the indicated video on YouTube that's not concludes this video on the gross anatomy of vision