[Music] the next special sense is Vision so as I mentioned before vision is probably the most important special sense to to humans all right we rely on Vision more than any other special sense that we have now all the special senses are important we um they're very useful to us but we tend to rely on Vision more than any of the others so in terms of vision of course you have your eyeballs and in your eyeballs those contain the visual receptors that are able to detect light and transmit that information to our brains so we can see what we're looking at right in addition to your eyeball we also have what we call Accessory structures of the eye itself so accessory structures in addition to the eye or the eyeball ACC structures do things like help protect the eye helps lubricate the eye so it doesn't dry out and get all you know hard to move around when you're looking around and helps kind of support support the eye and keep it in place and hold it in place so we're actually going to start off with discussing the accessory structures of the eye so as I mentioned accessory structures protect the eye lubricate the eye and help support the eye the accessory structures include your eyelids which are also known as the palpa so your palpa are your upper and lower eyelids it includes superficial epithelium of the eye superficial right closer to the surface epithelium is a covering so we have these layers the covering layers on the outer layer of the eye superficial epithelium and then we have something called the lacrimal apparatus okay so these pictures here just kind of show you the differ areas of the eye okay again besides the eyeball it includes the lids okay the lacal apparatus is underneath here so you can't see it and then superficial epithelium is kind of clear so it's it's transparent you can't see that either but I'll show you pictures of it and we'll talk about it all right let's first start with the palpa all right your palpa here again those are your eyelids it's basically just your skin it's a continuation of your skin so the skin and and the eyebrow going down it just turns into an eyelid and so from below the eye the skin there goes up and then it turns into the lower eyelid or the lower palpa so why do we have palpa again it's going to protect your eyes because if they're closed it's covering the eye so we do have a extra layer of protection over the eye when your eyes are closed and then also by opening and closing the palpe or BL blinking that's going to help kind of run tears over the front of your eye to wash off any kind of dust and debris that might have landed on your eye and because blinking also moves around your tears it's going to help kind of move them around your eyeball to keep it lubricated all right so I've highlighted the different parts of your your palpa all right so of course coming out of the lids we have eyelashes so these are just hairs but they're you know pretty thick hair so the eyelashes are there to help try to catch and filter out foreign matter from reaching the surface of the eye when your eye when your when your eye is open there's going to be a gap between the upper and lower eyelid that Gap is called the palpal fissure the palpal fissure so when your eyes are closed then that palpal fissure is gone right because there's no Gap but when your eyes is open open it reappears and that's the palpa fissure all right sort of the the corner of your eye medially so your nose is over here okay so this corner the medial corner of the eye closest to the nose is what's known as the medial angle that's where the upper and lower eyelids connect on the medial side and then on the far side closer to your ear that's what we call the lateral angle where the upper and lower Lids connect on the lateral Al side the you know the away from the midline the lateral side of the eye all right so eyeball lower lid okay we have various types of glands in your eyelids both upper and lower eyelids so one type of gland that we see in the lids or the palpe would be your tarsal glands so tarsel glands are type of sebaceous gland sebaceous glands produce seum are very kind of an oily secretion right that's what sebaceous glands do they produce sebum which is a very oily secretion so tarso glands are type of sebaceous gland these these these kind of oily secretions coming out of them and you can see them down here being squeezed out all right they're really important for help helping to prevent keeping those those eyelids from sticking together okay so that is one function of the tarso glands they mix in with your with your tears and they help keep the eyelids from sticking together they also mix with your tears and form an oily kind of like an oil slick over the tears that cover your eye and that's going to help keep those tears from spilling out of the eye okay and it's going to help reduce the evaporation of the tear as well because of that oil slick right from the tarsel glands over your eye that's going to really reduce evaporation of the tears and so they don't dry out quite as quickly okay now if you do have dry eyes a very common reason that you might is because these tarsel glands aren't secreting enough of their secretions out and so if there's not enough this oily stuff there then the water evaporates a lot faster and your eyes just are a lot drier okay so that's a common cause of dry eyes you have several other types of glands in the lids so a lot of little small mucus glands that produce mucus other types of sebaceous glands in those eyelids they are often found on the inner surface of the lids producing mucus and and sebum all right so if you look here on their lower left eyelid this is what is known as a calasian a calasian is a cyst that forms in an eyelid when one of those tarsal glands gets blocked or infected so the the base of the gland that produces the the secretions farther in that eyelid right it carries the secretions through a duct to the surface so if that duct again is either blocked or an infection happens and the infection also causes it to be blocked these tarso glands can really fill up and you get a CST that forms and it it comes out all right and you can see it bulging out like this this is a calasian if you get a sebaceous gland sort of on the inside here that that gets infected this is what's known as a sty all right so usually with a sty what's going to happen is when one of these other kinds of sebaceous glands a smaller one tends to get infected and the infection it causes it to bulge out and swell up and everything and so that'll be a sty all right so generally it's going to be one of those glands that are connected to one of the hair follicles of an eyelash okay all right so that's everything you ever wanted to know about the palpe the next category of accessory structure includes the superficial epithelium of the eye so let's take a look at what I mean when I say superficial epithelium of the eye that includes two different types of structures that includes what we call the lacol caruncle and the conjuctiva so in this picture right here you can see the lacrimal corle I do not mean the median angle right here all right the median angle is just the area where the two lids come together but this right here is the lacal coron okay so the function of the lacro unle it's pretty soft tissue right there it contains glands that produce a pretty thick secretion and you it's most well known for the forming that sleep in your eyes when you wake up right you go to sleep you wake up and sometimes you have that that gritty kind of thick crusty stuff in the corners of your eye that's when the the secretions of this lacrimal corle sort of dry out when you're sleeping overnight and it gets that what we call sleep for those deposits okay but that usually means that you had a good night's sleep now we also have what we call the conjuctiva all right so the conjuctiva we have two types we have the palpal conjuctiva and the bulber conjuctiva now that's going to be this layer here in pink okay so you see it right this is a lateral or side view of the eye so we're going up here and this pink layer here is the conjuctiva okay so the part of the conjuctiva that lines the inner surface of the palra or the eye the eyelid that's the palpal conjuctiva because it covers the inner surface of the eyelid and then it's continuous but it loops around and then comes back down to cover part of the front surface of your eyeball that's called the bulber conjuctiva okay it covers we could say the anterior surface so the front surface of your eye all the way up to where it bulges all the way up to the cornea the part here where it bulges out right so it goes bulber conjuctiva all the way down here down down down down down until we hit the conjug or the um the uh the cornea and then it dwindles down and it ends so conri TAA is most famously talked talked about when you get an eye infection and when you get an eye infection all right not always but often the part of your eye that gets infected is the conjuctiva okay so another name for uh so what we call this is conjunctivitis itis means inflammation so an inflammation of the conjuctiva is conjunctive itis commonly referred to as pink eye all right now if you get hit in the eye that could also cause some damage and you can get some inflammation and conjunctivitis due to damage to the eye but very very very often pink eye or conjunctivitis is caused by an infection so this is where maybe somebody doesn't wash their hands really well so they they they go to the bathroom they don't wash their hands they rub their eye and they transfer some bacteria from the unwashed hand to the eye you get an infection you get pink eye really common in kids because you know we always have to harp on kids to wash their hands all the time and they they might not so it um it's also highly contagious so even if you wash your hands if somebody else has conjunctivitis and you're you're you touch them and then you touch your eye again you could get pink eye right so that's the superficial epithelium of the eye the last component of the acccessory structures of your eye include the is the lacrimal apparatus so lacal apparatus basically the function of the lacal apparatus is to produce tear and for the teers to travel over the surface of your eye all right so this is the lacrimal apparatus produces tears now the reason we have tears are is severalfold tears basically are there to help keep the the front of the eye moist to keep it lubricated and to wash away debris any kinds of germs or anything like that to keep it all nice and clean all right so I it's essentially like the um uh windshield washer fluid of a car right you to you spray the windshield and then the wiper blades kind of wash over the windshield kind of cleans up right these what tiers do so um there are several different components to teers all right it's not just like water or something like that there's all these different kinds of chemicals that we find in Tei so again tear are going to help reduce friction wash away debris tears besides like just water and salts tear also contain in different kinds of antibodies to kill different types of microbes TI also contain an enzyme called lme and lme is an enzyme that is does a pretty good job at killing bacteria now another major function besides kind of washing and cleaning your eyes and killing germs right those are the first three points here is that there's all sorts of good stuff dissolved in tears all sorts of nutrients Like Oxygen other kinds of nutrients in there as well and the nutrients in the tear are going to help feed the conjuctiva both types and the corne the front bulged part of your eye so let's take a look at the different parts of the lacrimal apparatus the lacrimal apparatus gets split up into lacrimal glands lacrimal canaliculi lacrimal sac and nasal lacrimal duct let's take a look at these one by one right so first of all let's start with the lacrimal gland lacrimal gland is it's a gland right so this is what's going to produce most of the chemicals that form your teeth tears all right so most of your tiar is produced by that lacrimal gland the laal Ducks are these little white ducks here and they're going to help deliver the tears from the lacrimal glands to this kind of front surface of the eye so when the lacrimal glands secrete tears through those lacrimal ducts it dumps it into this little pocket that you see up here one up here okay one down here this little pocket here is called the fornex fornex all right the pocket here's the fornex that's where the two types of conjuctiva Meet the palpal and the bulber when they meet together they make this little dip here that is the fornex that is where the tear first enter from that lacrimal gland through the Ducks but then from there as you're as you're blinking and the lids moving up and down that's going to help move the teers from up here here in the Forex down to wash over the surface of your eye generally when you're blinking the tears are going to go sort of diagonally from the lateral side to the medial side so from the ear side and up diagonally down toward it's lower and towards the nose over top of your eye all right so blinking is really important for doing this it not only helps move the tears in the in the right direction from ear side to to nose side from lateral to medial sides but it also has a chance to mix up the what's coming out of the lacal gland with the other secretions from the other glands in your eye like those tarsel glands for example right so it kind of mixes everything up we are going to produce about one milliliter of Tears per day that washes over the eye okay so one mill is not a lot it's a very small volume but it's such a thin layer over the eye that it's still enough to you know that 1 ml per day is plenty of volume because it's so thin to wash over that surface of the eye and keep it clean and lubricated all right so as the Tei are made and come out and wash over the surface of the eye towards the nose right they are going to be collected and drained from the eye through one of these two openings that you see here okay so these two little pores that you see here these are what we call the lacrimal puncta lacrimal puncta it's just these openings are pores and they're going to drain tears away from the eye so once the tears travel through the lacal Puna okay they're going to travel out through these two little openings right here called the lacrimal canaliculi can canaliculus or canaliculi is Italian for Canal right a canal like a like an opening or a Waterway so these two lacrimal canaliculi are connected to these Lac lacrimal puncta which will drain the tears out away from the eye now through the lacron puncta through the lacrimal canaliculi the tiers next travel to this swollen duct right here this is what is known as the lacrimal Sac okay the lacrimal Sac from the lacrimal Sac the tears will then travel to an area that tapers down a little bit known as the nasal lacrimal duct and then from the nasal lacrimal duct oops the tears will drain out into the nasal cavity so lacrimal gland where they're made through the lacrimal Ducks over the eye through the lacrimal Puna upper and lower right Superior inferior through the lacrimal canaliculi Superior inferior into the lacrimal Sac sack like it's bigger down to the nasal lacrimal duct through the opening into the nasal cavity so generally if it's just a normal amount of tiar that makes it into the nasal cavity that fluid will be like absorbed like kind of reabsorb back into the body and help keep the nasal cavity also nice and moist and humid if you produce more tier than what can be drained away so it's coming out faster than it's being drained away then you cry all right so that's all crying is well I mean you know there's different causes of course but crying happens when that tear release is greater than the removal into the nose so not only do your tears if there as a lot of tears coming out that back up they they overflow down the cheeks right but you also get a runny nose when you cry because you still do get excess tear draining into the nose it mixes with all the other the the mucus and stuff like that in the nose and it makes it really watery and your nose runs a whole lot when you cry for the same reason