TEAR FILM

Tear filam of Eye

 

we have the eye and in the upper outer corner we have a gland called the lacrimal gland it's job is to produce a watery salty solution that is poured onto the eye and then washes the eye and performs some very important functions which we're gonna list here so firstly it will pour through these ducts you can see it has multiple ducts that drain into the eye and when you blink you actually spread this watery salty solution over the eye now what does that do well for one it keeps the eye from drying out so prevents dehydration that's very important because if that is dehydrated you will actually not be able to see clearly another thing it does is it will wash dirt away so your eyes always open it's exposed to dust and whatever else is in the air so it will wash that away and it actually protects the surface of the eye from viruses bacteria well mainly bacteria and any kind of microbes that might be in the air how does it do that well this water solution actually has many anti bacterial proteins in there like lysozymes etc and what these do is they function like they're antibiotic so they will kill any bacteria that land on the surface of the eye thus keeping the eye free of infection and again helping you to see because if you have infection in the eye you're going to have inflammation blood vessels will form you will have a lot of swelling and fluid collection in the eye and you will not be able to see so everything in the eye is directed at allowing you to see really clearly and really well now another amazing thing this watery solution does is you can see this kind of transparent layer we call this the cornea this is what allows light into the eye now the cornea does not have any blood vessels and so the cells in there still need a source of oxygen and they need a kind of fluid to take the waste from the cells away which is this is usually the function of blood since we don't have blood vessels in the cornea the watery solution poured in from the lacrimal gland does this function it dissolves oxygen from the air and it gives it to these cells here and then it washes away their waste as well and then when you blink what you're doing actually apart from spreading the water from this gland across the eye you're actually pushing it into this drainage system now let's look at this which system in a bit more detail so in the inner corner of the eye here we have two holes one hole on top and one hole under we call these the puncta now the Punkt are basically the opening onto these small canals so you have what we call a canaliculi on top and then a canal under as well and this drains the dirty water out so when you blink you push the dirty water through these punks or through the holes into these little canals and then the water is drained into this sack which we call the nasolacrimal sack and this drains into the nose so a great question would be does the water on the surface of the eye from this gland does that evaporate well it would evaporate but we have another layer on top that takes us to our second gland so if we just go back here these this row of glands on the top and we actually should have a row bottom at the bottom as well these are called the meibomian glands you have about 25 to 30 of these glands on top arranged in parallel you can think of them as a row of kind of eye droppers sitting on top of the eye and what they do is they produce an oily liquid or oily secretion. and again this oil is spread over the i/os pushed out over the eye when you blink now what's the purpose of this oily solution well for one it prevents the water you lay under it from evaporating which is amazing spamela and another thing it does is it seals your eyelids.

http://s.click.aliexpress.com/e/8jCEJrS?dp=219231038

The Anatomy and The Function of the Nasolacrimal apparatus

 The Anatomy and The Function of the         Nasolacrimal apparatus

The nasolacrimal apparatus and that's a fancy way of saying we're gonna talk about tiers we're gonna talk about what they're for how they're produced and how they're drained now every human being on the face of the earth at some point has cried we all do it we all have done it even the Prince of all Saiyans has cried at some point in his life the only human being that hasn't cried is of course Chuck Norris he's the only man alive that can make onions cry but assuming that you're not Chuck Norris assuming that you're any other regular human being I don't care how tough of a guy you are you've cried and there's a lot of stimulus for to your production sadness joy overwhelming and motion irritation of the eye and of course onions so first of all what is the purpose of the tears the purpose of tears is to coat the surface of the eyeball and protect it so if for whatever reason you didn't have tears on the surface of your eyeball then your cornea is going to be more susceptible to physical damage and we can't have physical damage of the cornea so you keep the tears on there to lubricate it which help protect it from physical damage but there's another purpose of the tears and it has to do with bacteria so bacteria if you don't kill them and don't control the growth of bacteria you can end up with overgrowth so suppose you had a situation where you didn't have any tears on your eyeball you'd be first of all really itchy that's for sure but you'd have a lot of bacterial growth on your eye and they might even penetrate deeper into the eye socket the reason tears prevent this from happening is because tears contain antimicrobial substances for example they contain a substance called lysozyme this is an enzyme that's present in a lot of léa secretions but in any case what it does is it breaks down bacterial cell walls specifically the peptidoglycan in the bacterial cell walls and then it renders them more susceptible to our immune defenses our innate immune defenses I should say one of the other major antimicrobial properties of tears  is that they are salty I think we all know that that if you've ever tasted your own tears what you think everybody's done at some point they're salty and that salt content actually helps inhibit the growth of a lot of species of bacteria so the major thing about the tears other than providing physical protection is they also provide antimicrobial protection to the eyeball okay now how our tears produced how did they get across the eye and then how do we get rid of them because in any biological system if we've got a way to make something we also have to wait have a way to get rid of it so to produce the tears we have this thing that sits on the lateral superior surface of the eyeball a little bit back it's called the lacrimal gland and of course we can't see this from the surface it's deep a little bit but it is above the eye and on the lateral side so if we didn't have a face here to help us we would know this as a right eyeball because the lacrimal gland has to be on the lateral side of the eye okay and so if it's on the lateral side of the eye this would make this the right eyeball in any case the lacrimal gland is going to make the tears it's going to secrete them onto the surface of the eye by moving them through these excretory lacrimal Dunn's okay and there's going to be several of those that allow the tears to move through the lacrimal gland and onto the surface of the eye Hey and of course these tears are going to help lubricate the eye they're gonna help protect it and so on and so forth and then eventually those tears are gonna make their way over here to something called the lacrimal lake and associated with the lacrimal lake.

UVEAL TRACT

Clinical anatomy of uvl tract

We discussing the anatomy of iris ciliary body and choroid to makethings easier.

we will start with the anatomy of choroid and then everything will make sense so the outermost layer of the choroid is the suprachoroidal lamina this black layer that we are seeing this is the suprachoroidal lamina now there is a space between the suprachoroidal lamina and the sclera that is a suprachoroidal space whereas the posterior ciliary artery and nerves okay we'll discuss about this in another time so the first layer is suprachoroidal layer after this we have stroma the stroma mainly consists of the bulk of vessels and these vessels are arranged according to their size the largest one known as heller layer is the outermost the moderate size one known as settler layer and the innermost the choreo capillaries which are smallest in size and these choreocapillaries are important because they nourish the outer part of the retina means our retinal pigment epithelium and rods and cones means this is the part of retina which is not being supplied by the central retinal artery but by these choreocapillaries this makes it important now we have a basal lamina of our stroma that is the brooks membrane and finally we have retinal pigment epithelium which is separated by a small space between from brooks membrane so the three layers we studied are suprachoroidal layer the stroma and the brooks membrane and finally we have retinal pigment epithelium that is a part of retina okay so now let's make thing easy that this suprachoroidal lamina will continue as supraciliary lamina so the first layer of ciliary body will be supraclearly lamina and then there will be stroma and this stroma will consist of ciliaris muscle the ciliaris muscle is important for accommodation and for uv scleral outflow we have three types of fiber in the cellulose muscle these are longitudinal fiber as you may see there are oblique fibers and there are circular fibers in this room of ciliary body now the longitudinal fiber and the oblique fiber help in the outflow of the aqueous means uv scleral outflow and the circular fiber are the one which help in accommodation the third layer in the ciliary body is the pigment epithelial layer okay now this pigment epithelial layer is the continuation of retinal pigment epithelium um due to paucity of space this is a simatic diagram so just try to understand i have just drawn an arrow that retinal pigment epithelium is the one which contributes to the pigment epithelium of the chloride then we have a non-pigment epithelial layer and this non-pigment epithelial layer is the one which is derived from sensory retina means the layer which will be more inside this will derive the non-pigment epithelium okay so these were the four layers in four important layers of ciliary body the supra ciliary lamina stroma the pigment epithelium derived from retinal pigment epithelium the non-pigment epithelium derived from sensory retina going on with iris will make things more easy the supraciliary lamina continues forward forming interior limiting layer now this interior limiting layer is the one which contains fibroblast and pigment cell and this decides the color of the iris means if this layer is thickened it will result in a dark iris and if this layer is thin there will be a blue iris moreover it also depends on the amount of pigment the second layer as we see is the continuation of is the stroma and this trauma is important because it contains two important muscles sphincter pupillae and dilated papillae also nelson vessels the sphincter papillary being the cause of active meiosis is supplied by um supplied by parasympathetic innervation and are dilated people pupillae being the one which causes active meduses located in the peripheral part of the stroma is one which is responsible for uh which is supplied by a sympathetic innervation the third layer is the interior epitheli

HOW TO PRESCRIBE PRISM GLASSES

 Prescribing Prism

Both phorias and tropias can be accurately measured using prism and cover tests. Initially a cover test is performed to determine the fixing eye and estimate the deviation. This is followed by the prism and alternating cover test, with adjustment of prism strength until refixation movement of the eyes is neutralized.

Phorias

Although most normal individuals have at least some phoria, the vast majority are asymptomatic. If a deviation is uncovered on routine testing in an asymptomatic patient, no treatment is necessary. If a patient is complaining of asthenopia and a deviation is discovered during testing, one must first ensure that there are no coexisting issues prior to attributing the symptoms to a phoria. There are a number of causes for asthenopic symptoms that should be ruled out. Some of these causes are summarized in Table 1. To be sure, some of the refractive causes of asthenopia are via induced phorias.

Once other causes for symptoms are ruled out, phorias should be investigated, and, in certain cases, may benefit from partial prism correction. One indication that the patient will benefit from prisms is minimal prism adaptation during a 15- to 20-minute trial with prisms in the waiting area. Otherwise, if there is a significant adaptation to the prisms, the patient’s symptoms will probably not be improved through the use of prisms, and other therapies, including surgery, should be considered.

Esophoria

As soon as the cover/uncover test identifies an esophoria, the next step is to obtain an accurate cycloplegic refraction because many cases of esophoria are “accommodative,” due to uncorrected or undercorrected hyperopia. It is wise to perform the cover/uncover test for esophoria at both distance and near, for the deviation may be larger at one distance than the other.

After refracting the patient and ensuring that there is no uncorrected hyperopia, one may wish to try a small amount of plus sphere to decrease the accommodative demand, as some cases of esophoria are due to accommodative excess. Such intervention is often enough to treat the condition, but base-out prism may be necessary if refractive methods fail. In situations that require the use of prisms, base-out prism should be prescribed with only the minimum amount of power required to eliminate the symptoms.

Exophoria

Again, careful refraction of the patient can help the management of many cases of exophoria. With refractive correction in place, if any, cover tests should be performed, and accommodation should be evaluated by push-up measurement of accommodative amplitude, or, especially in children, by dynamic retinoscopy. Divergence excess (in contrast to convergence insufficiency) manifests as an increased angle of exophoria in the distance.

In exophoria, correcting both myopia and hyperopia can help improve symptoms, but additional cautions should be taken when correcting hyperopia, as full correction of hyperopia may worsen the symptoms. A several-minute test with hyperopic correction should be attempted to see if exophoric symptoms improve because of clearer imagery or worsen by relaxing accommodation. If they worsen, prescribe the largest correction possible to treat the hyperopia while avoiding exophoric symptoms. A good starting point is one-third of the spherical error. Just as plus lenses can be helpful for esophoria, decreased-power plus lenses or even minus lenses can improve exophoria.

Base-in prisms may also be helpful for the treatment of exophoria. As with esophoria, the least amount of prism that eliminates exophoric symptoms should be used. The cover test should provide an estimate of the power of the prism to be used. Additionally, treating a minor hyperphoria with vertical prisms can allow the patient to compensate for exophoria with no need for horizontal prisms (see below). If divergence excess is found to be the cause of the exophoria, prisms should be avoided. In this situation, base-in prism can cause esophoria at near, which patients do not tolerate well.

Hyperphoria

Both the measurement and treatment for hyperphoria are similar to those for the horizontal heterophorias. One important point regarding hyperphorias is that they often coexist with horizontal heterophorias, and the treatment of one may improve or eliminate the other condition. Therefore if either a horizontal heterophoria or a vertical heterophoria is found, it is important to investigate whether the other is present. Initial attempts at treatment should be focused on the primary phoria with the intention of treating both.

Tropias

various types of tropias can be categorized in a number of ways. Broadly, they can be considered as comitant or incomitant. Surgery is generally the preferred treatment for tropias unless there is a reason not to perform surgery (see above). Therefore prisms for tropias are generally used as a temporizing measure until surgery can be performed.

In general, the measurement and treatment of tropias parallel those of phorias, as discussed above. A 30- to 45-minute patch test can be especially useful in uncovering the full deviation. When measuring incomitant deviations with prisms with each eye “fixing,” it is imperative to switch the prism to always be before the non-fixing eye. Otherwise the “fixing” eye behind the prism will not truly be looking in the intended direction, and major measurement errors can occur. For comitant strabismus, a prism adaptation test can be helpful to help determine treatment. For incomitant strabismus, prisms may be helpful to move an area of single vision to straight ahead.

Anisometropia

Often when patients with anisometropia receive a new pair of glasses, they will complain of double vision, particularly while reading. This double vision is due to the differential prismatic effects of the two lenses when the patient is looking off-center as when reading (as per Prentice’s Rule). In order to improve reading vision, vertical prism can be incorporated into the lower portion of one lens or the other to help compensate for the differential vertical prismatic effect and lessen or eliminate the double vision. These prisms are referred to as slab-off or reverse-slab prisms. The slab-off prism is placed on the more minus or less plus lens, more commonly on glass lenses, and in effect takes away base-down prism (adds base-up prism). The reverse-slab prism is placed on the more plus or less minus lens, most commonly on molded plastic lenses, and adds base-down prism.

Rather than a calculation of the amount of slab-off or reverse-slab prism to prescribe, trial-and-error measurements are preferred because one does not know how much the patient has already compensated to previous anisometropic glasses. Increasing the amount of prism handheld over the lower portion of one lens of the anisometropic correction until the patient can read comfortably is the most reliable way to determine the amount of slab-off or reverse-slab prism to prescribe. Up to 4∆ to 6∆ of slab-off or reverse-slab effect can be obtained when needed.

 Pitfalls in Measuring Deviations

When prisms are used to measure a strabismic deviation in a patient, several easily avoidable mistakes are commonly made.

Positioning

The position in which the prism is held can be critical when measuring a patient’s deviation. There are three intended positions for holding prisms: the Prentice position, the minimum deviation position, and the frontal plane position . Glass prisms are calibrated for the Prentice position and should be held in this manner when making measurements. Plastic prisms, including plastic prism bars, are generally calibrated for the minimum deviation position. As it is difficult to estimate accurately the minimum deviation position, the frontal plane position is a good approximation when using plastic prisms.

Adding Prisms

Stacking two prisms in the same direction, especially if one is of high power, can also lead to errors because of the same positioning issues mentioned above. If the two prisms are held in contact with each other, even if the first prism is held in the correct position, the second prism will not be in the correct position in relation to the light leaving the first prism. This will create a stronger prism effect than the sum of the two prisms, leading to a falsely low measurement. If the sum of the two prisms is prescribed, or surgery is based on the prism measurement, the patient will be left undercorrected. It is difficult to estimate accurately the correct position of the second prism in relation to the first, and it is therefore more accurate to simply stack the prisms together and use a conversion table to add their true effects.

Splitting Prisms Between the  Eyes

One might assume that one way to avoid the difficulties of stacking two prisms is to split the prisms between the two eyes and add the powers together. Although this may work for low prism powers, it becomes increasingly inaccurate with increasing prism power. Splitting prisms is preferred over stacking two prisms together in the same direction before one eye, but again using a table of summed prism values is preferred to avoid errors.

Method for Calculating Oblique Prism

There is a simple method to calculate oblique prism from combining a horizontal prism with a vertical prism that does not require trigonometric calculations and requires only a piece of paper, a ruler, a pen or pencil, and the protractor on a phoropter or trial frame.

First, sketch the vector addition of the two prism powers on polar coordinates to determine the approximate angle for the base direction of the oblique prism. Up is base-up, and right is base-in or base-out depending on which eye the prism is intended for.

Then measure off the number of prism diopters of the two component prisms on two adjacent edges of a piece of paper. (One can use any unit for this measurement, but the unit must be consistent. For example, if you have two prisms, one of 3∆ and the second 2∆, measure off 3 cm/inches/etc on one edge and 2 cm/inches/etc on the other edge). Connect the two measurement marks with a line, forming a triangle. Now measure the length of the connecting line you just drew, the hypotenuse of the triangle. This will give you the number of prism diopters for your oblique prism.

Then fold the paper along the hypotenuse, identify the acute angle of the triangle that you estimated using your polar coordinate plot, and measure this angle using the protractor on the phoropter or trial frame, giving you the base direction of the oblique prism.

Uncommon but Important Uses for Prisms Childhood Cranial Nerve Palsies (Third, Fourth, and Sixth Cranial Nerves)

For children with cranial nerve palsies, early treatment is important to prevent amblyopia. Prisms may be used for small, reasonably comitant deviations in order to maintain binocular function. A test with temporary plastic Fresnel prisms is recommended prior to grinding prisms into the child’s lenses. Treatment of a recognized underlying cause is essential, and if prism therapy fails, surgery should be considered.

Prisms for Enhancing Communication

For patients with no useful vision in the deviated eye, prisms can be extremely helpful in improving the appearance of the eyes and facilitating the patients’ communication and interaction with others by alleviating difficulties with eye contact. A prism held opposite the direction of a correcting prism can improve the apparent alignment of the eyes (ie, base-in for esotropia and base-out for exotropia). Expect approximately 1 mm of apparent eye shift for every 8∆ of prism power.

Homonymous hemianopia

Prisms (or mirrors) may be used in patients with homonymous hemianopia to bring images from an area within the visual field defect into the area with retained vision. Although this may be useful on occasion, generally very high prism powers are required, which can create cosmetic problems as well as a confusing visual environment in which objects may appear and disappear from view unexpectedly.

Hemispatial neglect

Patients who experience right hemisphere strokes often experience left hemispatial neglect. Recent studies have shown that yoked prisms which move both visual fields to the opposite side (to the right) improve function in these patients. The mechanism for this improvement is believed to be that in order to compensate for the shifted binocular visual field, the patient must remap his  sensorimotor coordinates leftward, and this has been shown to improve function on the neglected left side.

Nystagmus with head turn

Patients with a head turn to compensate for nystagmus can benefit from yoked prisms, but just as with patients with homonymous hemianopia, they will often require very high prism powers which may lead to decrease in visual acuity (especially with Fresnel prisms), chromatic aberration, heavy lenses, and cosmetic problems, as well as the visual disturbances described above. In spite of these problems, prescription of bilateral yoked prisms, with base in the same direction as the head turn, can keep the patient’s eyes in an eccentric null position while lessening the head turn.

Save 40.0% on select products from FooAeetom with promo code 40MWVYNE, through 5/15 while supplies last.Save 50% on select product(s) with promo code 50BQ4F6V on Amazon.com

The visual pathway

 The visual pathway so we're going to take how the light hits the retina and we're going to take it through the optic nerve and all the other different process if you guys have already watched our video on the phototransduction cascade that's going to be very very important that you do that before we get into this visual pathway because we already talked about exactly how those light rates got converted into chemical changes and then electrical changes and how they went down the axon to the ganglion cells which basically made up the optic nerve all right so now we're going to have two eyeballs right

this is the we're going to say this the left eyeball and this is the right eyeball okay now first things first what I want us to try to imagine if we're gonna put a lot of different concepts together when you guys are looking you guys are like looking at anything around you we our eyes are so amazing that they can pick up different types of visual fields so for example this is the right visual field or the right visual field and this is the left eyes visual field okay so what is this one right here this is the right eyes visual field and this one over here is the left eyes visual field okay now with in the visual field you have two different components of this visual field we're going to say this is the nasal so since your you'd have your honker right there pretend this is your nose okay so pretend this structure here is your nose okay since this is the nose these two structures that are near the nasal region this is the nasal component of the visual field alright so this is the nasal component of the visual field and then this one over here would be near the temple so this is the temporal component of the visual field and this over here is going to be the temporal component of the visual field okay now to make it easy though now that we know that this is what it is it's nasal and the temporals these words are going to get interchanged a lot so I do not want to confuse you guys so what I'm going to do is for the sake of it is I'm going to switch nasal and since this is the right visual field this is what gets confusing the right visual field has a left visual field and a right visual field okay so the right eye has a left visual field and a right visual field so we're going to say this is the left visual field and this is the right visual field okay so I just want to make it as simple as I possibly can here this whole right eye is going to have two fields it's going to have the right visual field and last visual field same thing this left eye is going to have two visual fields it's going to have a left visual field and a right visual field okay simple as that now we're going to be able to kind of do this a lot easier now so instead of using the words nasal and tempore but understand those words because it's going to be important lesions okay let's say first off when we're looking out let's say that this part of the retina there's two parts of the retina so this is the right eye this part of the retina is closest to the Temple or the right temple right so we're going to call this part of the retina we're going to call this the temporal Hemi retina okay that's a temporal Hemi retina now here's what gets really funky the temporal Hemi retina is receiving light rays from the left visual field okay so from here this part here this left visual field is hitting this part of the retina okay so if light rays from the left visual field are hitting this part of the hit retina that temporal heavy right now but then the what is this one this one is close to the actual nose so since it's close to the nose this is called the nasal right Hemi retina so it's called the nasal hemorrhage now and it's called the temporal Hemi retina the nasal hemorrhage now is receiving light from the right visual field so the nasal Henry retina is getting hit with light from the right visual field .

RETINA

 The retina 

The retina which is the deepest layer of the eye remember that we have a fibrous tunic which consists of the sclera and cornea then we have the vascular tunic which contains the choroid and then the neural tunic which has a lot of neurons as you can see and that really is just the retina and we'll go to this image real quick just for a minute but when light enters your eye it's gonna go through the pupil obviously and it's gonna go through to the back of the eye and here's the retina and so in doing so in following that path the light's gonna have to pass through the cornea the anterior chamber the posterior chamber the lens and then through the vitreous chamber and then finally that light is gonna strike the retina at the back of the eye in which you can see a little bit more macroscopically in this picture right here and within the retina we have three cell types the first type is called the photoreceptor cells or just photoreceptors and these are the cells that initially detect the light and there are two subtypes of photoreceptor cells and those are rods and cones we're gonna have a separate video where we go over the major differences between these but I'll just say this for now rods detect non colored light so non color vision just bright and dark and cones detect color okay see four cones see four color then we also have bipolar cells and then we have ganglion cells which eventually become continuous with the optic nerve these are the three major cell types there's also a couple other cell types called amacrine cells and horizontal cells and we're not going to get into these very much most Anatomy courses don't but they just exist pretty much to find tune and regulate the functions of these cell types particularly bipolar cells and ganglion cells okay now before we go any further I want you to notice something so we've got light that we mentioned was passing through the eye okay like this in this direction and then it strikes the retina but what's interesting about the setup of this is it actually doesn't encounter the photoreceptors first actually if we follow the passage of light the photoreceptors are at the back of the eye they're there actually we could say superficial to the ganglion cells so actually the light has to travel through the ganglion cells and then through the

bipolar cell layer and then finally is

able to make contact with the

photoreceptors but it's the

photoreceptors that initially detect

that light and then the photoreceptors

will have an effect on the bipolar cells

which will then in turn have effects on

the ganglion cells and we're gonna look

at that now in this slide okay now to

really understand what happens here we

have to understand what's happening in

the dark so imagine a situation where it

is complete darkness okay

so let's first of all say it's night

it's dark out you're in your room

there's no night lights doors are closed

and you have blackout curtains so you

can't see anything all right so I have

the photoreceptor cells in blue now

interestingly in the dark the

photoreceptor cells are actually

depolarized okay so the photoreceptor

cells are actually D polarized and that

not may not now that probably doesn't

make a lot of sense because usually only

think of depolarization we think of

activating but trust me this is how it

is and it will make sense in the end so

in the dark photoreceptor cells rods and

cones are depolarized that being said

that means the photoreceptors are

activated and they activate the next

neuron in sequence which is called a

bipolar cell it's also worth mentioning

that the way that photoreceptors

activate the bipol