so what is an exod deviation exod deviation or exotropia is basically a form of squint or strabismus where one or both the eyes will deviate basically outwards this means that the eye is actually deviating away from the nose here in this picture you can see that the left eye is deviating away from the nose that is we are looking at a left exod deviation now another important point that I want you to know is regarding the nature of exod deviation now the exod deviation or exotropia can be actually uh be constant in one eye that means it can be present all the time or it can be alternative in nature that means times it can be present in the right eye and sometimes it can present in the left eye now the alternate exotropia or exod deviation can also show sometimes preferences it means that the right ey for example you have uh alternate exotropia with right eye preference it means that although the exotropia alternates between the right eye and the left eye still the patient has preference for the right eye that means the right eye is deviating much more compared to the left eye similarly if there's a left ey uh left eye preference of exotropia it means that although both the eyes are alternating the left eye is deviating more number of times compared to the right eye also the exod deviation sometimes might be present only for a limited duration of the time and rest of the time the patient would actually be having straight gaze or orthotropia now such an deviation is known as intermittent and in exod deviation it is known as intermittent exod deviation now exotropia or exod deviations can also be associated with vertical deviations like hypertropia or hypotropia apart from that your exod deviations can also be ass associated with patterns like the a pattern and the W pattern or the X and Y patterns all right now before we proceed it is very important to know some terminology and here we shall be talking about what is meant by exophoria intermittent exotropia and exotropia so first let us discuss what exactly is meant by the exophoria so as you can see over here exophoria basically is a term used when the outward deviation is never seen in a manifest State okay so when you see a patient of exophoria the patient is going to look exactly U absolutely normal to you with straight eyes okay it's only when you do the alternate cover test that you're going to see the inward movements of the eyes Okay so that is known as a Foria state or and and when the eyes are actually moving inwards under the alternate cover test that is known as the exophoria okay now next is the the intermittent exotropia as a name suggests here the outward deviation is seen sometimes uh but it can actually be controlled by Fusion or accommodation or convergence okay so what I mean to say is that sometimes the patient is going to be orthotropic that means the times when the patient is able to control or maintain the straight gaze by his Fusion or accommodative or convergence facility and other time suppose the patient is really fatigued or had some illness viral illness or something like that in those cases the patient will not be able to maintain that fusion and usually in the late hours of the day that time the patient will have very obvious outward deviation of the eye now such an exotropia is known as intermittent exotropia which appears only during certain times of the day for example late during the day when the patient is tired or the patient has read for longer duration of time or there's any fatigue or viral illness or immediately after waking up so that is known as intermittent exotropia all right then we have constant exotropia where the deviation is seen all the time right so it's seen constantly and in other words it's also known as Manifest exotropia because the deviation has manifested itself all the times now let's talk about the prevalence now when we talk about the exotropia in the exotropia it is the intermittent exotropia which is the most common type of stabismus seen in children as well as also the adults okay especially it is seen in the Asian and South Asian population and regions which are closer to the Equator they have higher prevalence of the exort deviations and it is more common in women and when we are talking about the Asian and South Asian population here the preference of exotropia is about 7 to 18.5 times higher than that of esotropia as well and as I told you the most common type of exod deviation that we see is the intermittent exotropia accounting for about 63% of the cases now you might be thinking what exactly is this x bracket T okay so we'll talk about the symbols in a while now completing the prevalence the exotropia can also start at Birth okay but what happens is that at the time of birth the child um or you can say in infancy or in childhood the kids usually have a great deal of fusion accommodation and a really robust um convergence right so often if you ask the parents if the exotropia or outward deviation uh was present since birth they wouldn't really be able to answer as it was taken care of by the robust or strong convergence in the childhood right later on in life as that decompensates or what I mean to say is as the fusion weakens or the convergence weakens you know then the E then the exod deviation becomes more apparent and more um constant and that is something we call as a manifest squint or manifest exod deviation right so basically you're not going to see an exod deviation right at the birth although the process starts at Birth now so if there's a child that has exotropia right from the childhood which is also known as the kidal exotropia now it basically means that the child is going to do really poorly later on okay so there's going to be poor prognosis of conal exotropia why is that so it's because the child who has had this deviation right from the start of the childhood will actually have no orthotropic periods okay uh this child will never have had any straight eyes right and therefore would not have gotten any chance for normal binocular single Vision development that means they are going to have really poor binocular single vision and that's the reason why conal exotropia has poor prognosis okay so if the parents tell you that the deviation was present right since birth or right since 6 months of age it means it's poor prognosis okay now if you want to know more about the binocular single Vision you can refer to the video on our channel the link is going to be provided in the description box all right now let's talk about some of these symbols okay so I hope you understood what exactly is meant by exophoria and exophoria is basically represented uh like this okay so you can see over here how an exophoria is represented so it's represented like this and then you have the intermittent exotropia where you use brackets around the T and in exotropia you simply write XT and then sometimes we also use this dention uh this symbol which is known as bi okay base in and also use Divergent squint DS now the question is why exactly are we using this bi and Divergence squint okay so for example you can see over here and if you would remember the video on the prism cover test and the cover test second part so you would know how do we actually carry out a prism uh prism bar cover test or the loose prism test the prisms uh that we use for measuring the deviation usually are presented to the patient or they are put in front of the patient in such a way that the Apex points towards the deviation so when we talking about the exotropia the deviation is outside right and therefore the Apex is also going to be directed away from the nose and automatically the base is going to be towards inside that is towards the nose and that is the reason why the prism that we use uh in case of exotropia is referred to as a base in prism all right now uh such a patient when they are me being measured with prism cover test for example this patient okay over here say with 40 prism diopter of Bas and prism there is no redressal movement on cover test we say that the patient has left eye exotropia of about 40 prism diopters base in or we can also refer to it as as 40 prism diopter bi or 40 prism diopter XT okay so it means a manifest squint or a constant squint okay so remember exophoria has that small apostrophe on top of that intermittent exotropia has the brackets around the t exotropia is just written as XD bi is Basin used for the exotropia and similarly for esotropia we would be using what base out b o is a Deno okay and Divergent squint also because it's a diverging kind of squint okay so you can refer to these videos the links are going to be given in the description box and now let's try to discuss exactly what exactly causes EXO deviation now unfortunately so many scientists and so many causes there isn't really a consensus and one single cause as to what causes exotropia and that is the reason why I decided to make a detail video so that you can understand the pathophysiology in detail and we should try to simplify all of that for you so now let us uh begin we totally have around seven causes of exod deviation that we shall be discussing in this video the first one was actually given by danan okay and it referred uh he referred it to as the innovational theory uh based on the innovational factor so what does this Innovation means to you Innovation means that it has something to do with the nerve supply of the muscles right so we know that during conver it is the Mr which will get the nerve Innovation and both the eyes are going to move inwards whereas in the case of Divergence both the eyes are going to move outwards and The Innovation goes to LR right so there's kind of a tug of war going between the convergence and Divergence now ideally you might be thinking that there must be some equilibrium but that really doesn't happen right okay so you should know that during the normal uh whenever we do some near task it is the normal conversion that takes U the dominance right and what exactly is meant by normal Divergence normal Divergence basically refers to the ability of the eye to move outwards away from each other in a very coordinated Manner and actually speaking this outward movement is required when you're Shifting The Gaze from a near object to a distant one and this allows the eyes to maintain a proper alignment and focus on that distant object right now over here in exod deviation there's actually an imbalance between the convergence and Divergence mechanism now obviously it's a no-brainer that the Divergence is much more in exod deviation compared to the convergence but mind you that I'm not talking about the normal diverent Divergence okay so what we are talking about over here is the tonic Divergence okay so in exod deviation they have what is known as hyperactive tonic Divergence which is causing an outward drift now you might be thinking what exactly is meant by this tonic hyp ER Divergence okay now the normal Divergence that we talked about was U basically in response to a visual stimulus that means that distance object that you wanted to look at right but over here the tonic Divergence refers to that Baseline level of Divergence which is present even when there's no active visual stimulus that means even when the eyes are at rest okay so it is thought to result from tonic constant activity of the Divergence system which is present in the brain brain stem okay and it is this tonic Divergence which is going to actually help set the resting position of the eyes and this is known as the physiological position of the rest okay and the physiological position of the rest is actually slightly Divergent okay so that is one point that you must remember okay so in normal functioning eyes the tonic Divergence is just going to help the eyes maintain the alignment and avoid that excessive drifting of the eyeball outwards whenever the visual system is not really engaged in a task right however if the patient has this excessive tonic Divergence it can contribute to exod deviation where the eyes are going to deviate outwards so I hope you understood that all right now in childhood what happens is that the convergence is pretty strong and that can actually mask the deviation present at near okay so we know that convergence comes into play during the near task and in childhood they actually have a really strong robust convergence and and therefore whenever the child is going to look at near object the exod deviation is going to automatically disappear right and that is something which I wanted you to know apart from that there's another entity which is known as infantile exotropia now infantile exotropia is a very rare form of strabismus which is actually characterized by uh this deviation outward deviation of one eye or both the eyes that is going to appear shortly after birth or within the first 6 months of life okay so remember the time period it's shortly after birth or within the first 6 months of the life okay now there are certain characteristics of infantile exotropia that we shall enumerate now itself so number one is early onset usually detected in the first 6 months of Life Second is really large angle deviation the exotropia is often large with deviation of 30 to 50 prism diopters or even more and what did I tell you the binocular vision is going to be really poor associated with almost absent binocular vision and little to no potential for fusion and stereopsis okay and apart from that they will have Associated ocular neurological abnormalities they will have developmental delays compared to other type of exotropia and such kids usually need early surgical intervention because conservative treatments like patching and glasses are not going to work in them right so over here let me remind you that it's very important that you understand what exactly is binocular single Vision before you jump into these topics of squint and therefore I would highly recommend that you visit our video on bsv all right now the second theory was given by Bel chowski Theory and this Theory basically says that it's not just the innovational factors but it's also the mechanical factors which are responsible for the development of exotropia so it could be the shape and orientation of the orbit for example um you take the variation in the size shape and orientation of the orbit that means the sockets can actually affect how exactly the eyes are positioned and how exactly the eyes are going to move inside that socket okay for instance if someone has a really wide socket or more horizontally aligned it is going to make it easier for the eyeball to drift outward okay so that is how the shape of the orbit is going to decide the position of the eye similarly the size the elasticity of the muscle and the insertion point of the muscle is really going to impact how exactly the muscles are going to control the movement of the eye for example a the later rectus muscle which is actually responsible for the outward movement say is overacting what exactly is going to happen okay or what I mean to say suppose the later reective muscle is more elastic for example what is going to happen it is going to have this tendency to move the eyeball outwards leading to exotropia similarly if the medial rectus is really you know um what do you say Banky or long and without any elasticity what is going to happen it is not going to be able to pull the eye towards the midline and therefore again it is going to cause exod deviation so definitely again a mechanical Factor over here similarly the surrounding tissues also is going to play a role in the uh determination of whether the patient is going to develop exotropia or not okay the volume the viscosity of the retr balar tissue what I mean to say is the orbital fat so what exactly is present behind the eye it is the orbital fat and other tissues right so whenever there's an increase or decrease in the volume of the retr balar tissue behind the eye including the fat that can cause mechanical displacement of the eye okay for example uh suppose uh the tissue is increased Suppose there is some tumor over here in the retral area what is going to happen that is going to push the eyeball outwards and also slightly you know away from the nose leading to exotropia right similarly Scar Tissue fibrosis all these things are going can actually cause mechan they can actually cause development of squint and exod deviation right so you know this is why we actually uh do our for suction test because we want to rule out disc scar tissues and fibrosis so what happens is that if there's any Scar Tissue which has fibr blast around that extraocular muscles or surrounding the orbital tissues it can actually mechanically restrict the normal eye movements potentially leading to exotropia right so what for example this is later rectus and you have some surgery around the later rectus before or around the orbit what happens is there's a fibrous growth near this later rectus which is going to prevent the relaxation of the latal rectus so what will happen this fibrotic tissue is going to constantly pull on the later rectus tug on the lat rectors and also pull the eyeball laterally right this is how a scar tissue or fibrosis can cause the development of EXO deviation right so mechanical factors do play a role along with the innovational factor that was the second theory and example of this is the cruson and eper syndrome you know High prevalence of exod deviation is seen in these patients they have this cranofacial dyis okay premature Fusion of their sutures so that leads to development of really shallow and laterally directed orbits and because of that even the eyeballs which are sitting inside the orbits will seem to be as if they're laterally directed okay that is what is meant by that is what is called as exotropia all right now let us talk about the third theory that basically is based on the role of defective Fusion in the development of exod deviation now what exactly is meant by Fusion now in our previous videos also I told you that the fusion by the eyes basically refers to the brain's ability to combine the images which are coming from both eyes into a single unified image allowing us to have that depth perception and binocular single Vision okay so normally what's going to happen the right eye is going to see one image the left is going to see one image both these images are going to fall on the phobia of the two eyes considering that they are orthotropic okay and these two images are going to be fused together into a single image by whom by brain right and this is known as Fusion faculty usually if the fusion faculty is good the patient is going to have a good control of exotropia and usually will be in the initial pathophysiology that means in the EXO foric state or exophoria however if the fusion is poor then the patient is going to actually progress in the um pathogenesis of the exotropia and can actually become intermittent exotropic or can have even more worse thing which is known as the constant exotropia okay so in our previous video we talked about what exactly is meant by sensory fusion and motor fusion and to understand uh it's very important to understand these two concepts in order to understand why effective Fusion leads to progression of exotropia okay so as I told you in simple language unification of those two visual excitations or two visual images that are coming from both the eyes because these images are falling on the corresponding points on the retina okay that unification is known as fusion and it is simply done by our brain okay so that is what is known as sensory Fusion however what exactly is Mota Fusion now Mota Fusion is something which is the ability for the of the eyes to align themselves in such a way that the sensory Fusion can actually takes place okay so motor Fusion basically depends on the extra fobal retinal periphery okay it depends upon what exactly is the retino motar value of the retinal elements okay so don't get scared we have all of this covered in our video on binocular single Vision you can go and check out that video and come back to this video okay so basically what I mean to say is that in exotropia or in esotropia when the eyes are deviated the rays are not going to fall on the phobia instead they're going to fall on an extra fobi element okay and the eyes also know that that they are actually forming the image on a wrong part of the retina and therefore the eyes are actually going to make a corrective movement to align themselves okay now this happens to certain degree and this is known as Mota Fusion okay so sensory Fusion is something that happens at the level of the brain whereas motor Fusion basically Bally happens at the level of the eyes Okay so motar Fusion is something what our eyes do okay so you can talk you can actually U know about this in detail in the first part of binocular single vision and in the second part which is confusion versus diplopia you can actually figure out um about the other things as well all right so this so we talking about the sensitive Fusion Mota Fusion taking care of everything aligning the eyes but everything happens to a certain limit right there's a limit to everything and how long will the brain or how long will the eyes actually compensate and try to keep them straight so what happens over here is that in the normal conditions under normal conditions when the patient has normal sensory Fusion Mota Fusion that means normal brain and normal eyes okay which are able to align well okay so at that time the patient might just have a latent outward deviation which is known as exophoria why is it latent because the patient can use their fusional reserves that is a fusional convergence to keep their eyes aligned right now these reserves are actually an extra effort the brain and the eye muscles are using to pull the eyes inwards and maintaining the proper alignment all right now when that uh fusional Reserve becomes insufficient or they fail now they can fail because of variety of reasons either the medal rectus becomes weaker for some reason or the patient is constantly using fusions the patient is getting tired or something like that you know fatigue so what happens now the deviation will now start getting manifested for long duration of time and that is known as intermittent exotropia and when the fusion capacity becomes even more worse what exactly is going to happen then the patient is going to have something which is known as constant exotropia that means the deviation is manif uh deviation is actually manifest all the time that means in such patients you would be actually able to see clearcut deviation all the time all right now let's talk about the fourth reason uh related to the exod deviation development and that is the sensory adaptations and suppression now we know that for example over here you can see this is the right eye of the patient and the right eye is showing exotropia now what exactly happens is that when the eye deviates outside or away from the nose you can see that the rays which were initially meant to fall on the fobia are now falling on the temporal retina and therefore the image which is supposed to be here overlapping with the black image which is coming from the left eye is now falling on the other side nasal to that black dot that means the patient is patient is experiencing something known as double vision or diplopia right and the type of diplopia that we see in case of exotropia is a crossed diplopia right now what exactly is brain going to do to deal with uh this diplopia or double vision very simple the brain is just going to suppress it right right so in cases where the fusion is deficient so what I mean to say is initially the eyes and the brains they try to basically do what is known as Fusion okay they try to fuse those two images but if that is not possible especially when the development of exotropia is later in the life okay that time the brain is trying a brain brain will actually try to suppress that extra image right so if the suppression is at the fob is know as Central suppression and the peripheral part of the retina is getting suppressed that is known as peripheral suppression now for this suppression to develop as well it is very important that the suppression uh it's very important that the exotropia develops within the critical period of time that is 6 to 7 years of age okay so if the patient develops exotropia Beyond this age and if his Fusion is not good then this patient is going to have double vision okay so that is the message that you must no coming to the fifth Theory related Theory given by nap and joli and that is the theory of hemir retinal suppression okay and you can guess over here which part of the retina is going to get suppressed it is the temporal retina why because the imagees because this image is falling on the temporal aspect of the retina because of the outward deviation of the eye so what happens exactly there is outward deviation therefore the patient is going to have diplopia or confusion and to deal with the diplopia what does the brain do it just does suppression so this is known as hemir retinal suppression because usually it is the temporal retina which gets suppressed by the brain and now as this suppression the patient is not going to see again double and therefore he's going to see single although not steroscopic Vision but there will be a single image coming from the other eye left eye in this case and therefore the deviation will now become tolerable that means the patient is not having any problem with the deviation no double vision and therefore deviation becomes tolerable now once the deviation becomes to Toler the brain has almost no incentive for motor Fusion no incentive for sensory Fusion right that means that because the patient is seeing only one single image and there's already suppression that has developed it means that this patient need not now move his eye inwards or you know try to converge the eyes bring back that outward deviated eye and that is what I mean by motor Fusion okay so there's no incentive for motor Fusion in this case and therefore there will be progression from EX Foria to exotropia all right so that's very important so in the foric stage eyes are well aligned okay and that allows fusion and good stereo equity and that's basically happening because of good Fusion right but in the trophic in the tropics phase basically the fusion detur rates and now it is on the suppression whether the patient has suppression or not ability to suppress or not that he will be taking care of his double vision Okay so andoria it is a fusion that takes care and prevents the progression of the uh exotropia but once the exotropia progresses it is uh basically it depends on the suppression whether the patient has suppression or not uh and that is going to decide whether the patient will have double vision or not all right so again I I'll just make it clear I'll repeat it so whether or not Fusion uh will occur or not it depends upon the amount of deviation as well okay so because sometimes if there small amount of deviation the eyes will be able to uh carry out motor Fusion the brain will be able to carry out motor Fusion they'll be able to converge and it's the amount of deviation that determines the fusion okay similarly the fusional reserve how good is the convergence fusional reserve of the patient that is going to determine whether Fusion will take place or not but when we talk about suppression it's not that in suppression it is a time of onset of exotropia that is going to decide whether suppression will occur or not for example in late onset exotropia what happens the critical period has already passed and therefore this patient will not be able to suppress and therefore this patient has lost the ability of suppression and therefore they will definitely have what is known as diplopia okay now let's talk about other sensory adaptations that you see so basically in foric phase of intermittent exotropia actually intermittent exotropia as I told you basically the most common type of exotropia and it has the sporic phase which is called exophoria then it has intermittent phase then it has the constant phase so in the foric phase eyes are perfectly aligned there's bobal Fusion because the fusion is good and since the fusion is good stero Equity is good between 40 to 60 seconds of AR okay so excellent bobal Fusion develops because the eyes are well aligned in early infancy when the critical binocular cortical connections are being established right very very important and next is what is known as the tropia phase in tropia Phase the exot ropia will become manifest for most of the patient and they will show these patients will now most of them will show Regional suppression of the temporal retina all right so some of them can have this hemir retinal suppression again depends upon when what is the onset of exotropia apart from that some people will develop this abnormal relationship between the fal and extra fovial point okay so I I told you that so what did I tell you so in exotropia suppose this is the normal I and the rays are falling on the fobia but in the I which is deviated outward the rays are going to fall somewhere on the tempo RNA so this point F this point is not corresponding to the fobia right so when there's a normal relationship or correspondence developing between the fovial and extra fobal point that is known as anomalous retinal correspondence that is present in the second that is something that I explained in the second video on binocular single Vision confusion versus diplopia all right so Arc can also develop in the tropia phase okay now a minor amount of a minority of patients with intermittent exotropia can also develop what is known as monofixation syndrome where they're going to develop a very small Central scotoma of the phobia right now a rare patient may even have significant amount of am lopia now let me tell you that amop is not very common in exotropia and it is actually more common in esotropia and I would like to know from you what do you think why as to why ex this amopa is more common in esotropia compared to exotropia okay so you can give the answers in the comment section all right so that was regarding the fusions sensory adaptations in exotropia I hope it made sense now let us move ahead and talk about the sixth Theory as to what is the role of AC by a ratio and exod deviation so what exactly is this AC by ratio we'll talk about that but the scientists like Kushner in 1988 they had this finding that 60% of the patient who patients who have Divergence exist exotropia they have high AC by a ratio and 40% have normal AC by a ratio now don't fret about this Divergence ex excess exotropia okay don't think about that we'll talk about that in the classifications of exotropia but just know that there is a role of AC by a ratio as well in very simple terms what exactly AC by a ratio means to you AC stands for accommodative convergence and a stands for accommodation so whenever there's a change of accommodation for example you're looking far and then you you suddenly start looking at a near object that means your accommodation is changing similarly you're looking at a near object and suddenly someone introduces a lens in front of your eye it could be a plus lens or it could be a minus lens now what in order to uh see the same object clearly you will have to accommodate okay so dep basically depends so if someone is using a minus lens in front of your eye that means they will be basically stimulating your accommodation so you will have to to accommodate more and if someone has introduced a plus lens in front of the eye now you will have to relax your accommodation because plus lenses basically relax accommodation and minus lenses stimulate accommodation all right okay so when the lenses are introduced in front of the eye someone is trying to change your accommodation and when the accommodation changes convergence also changes right so that is called change in convergence and basically if you would know from my video on accommodation during accommodation the medle rectors get stimulated and the eyes are going to converge okay so definitely when there's accommodation there has to be some amount of convergence as well and when you are measuring this change in convergence divided by change in accommodation that is referred to as the AC by a ratio now there are a lot of ways by which we can measure AC by ratio but the most common method with which we measure it is by the lens gradient method that means the examiner is going to introduce a certain sort of lens in front of your eye so AC by a ratio is basically change in convergence and by change in accommodation and we here we are going to talk about the lens graded method and the formula for lens graded method is change in deviation divided by the lens power and how do you calculate the change in deviation now over here the it is written near deviation but you can also do AC by a ratio for distance deviation as well for example say we are measuring the AC by a ratio for a near deviation that means we are carrying out the AC by a measurement at say about 30 C 33 C CM all right so we do our prism cover test and we find out that patient has about 40 prism diopters or Basin uh 40 prism diopters of exotropia now here the sign convention is that for exotropia you basically are going to take minus symbol okay so we say the original near deviation is minus 40 prism de opter and say we introduce plus two de opter lens in front of the eye now making uh keeping the distance same now a plus lens will basically relax the accommodation so if the accommodation goes down the convergence will also go down okay and now the new deviation is going to be somewhat less say the new deviation with lens in place is about minus 20 prism deop okay we're talking about exotropia right and therefore it's minus so according to this method the change in deviation will be the deviation with lens minus the deviation without lens so with lens is your Min - 20 prism deop and without lens is minus of minus 40 prism deop so it's basically an algebraic equation so it becomes minus of minus divided by the lens that you have used that is two deop plus lens so this become minus minus will become plus so this will become - 20 + 40 so you ultimately have + 20 / 2 so roughly about 10 okay so you get an AC by ratio of 10 right so that is how you calculate the AC by a ratio using the lens gradient method so let us just keep it very simple AC by a ratio basically is change in convergence by change in accommodation and normally this is about 3 2 5 is to 1 that is a normal so 3 is to 1 to 5 is to 1 is in uh within this range is the normal AC by a ratio okay so you're basically carrying out you're basically finding out how much is the convergence change with the change in accommodation right so if a patient has say low AC by a ratio so what does that mean so if a patient has low AC by a ratio it means that for a given amount of accommodation the eyes will not be able to converge sufficient uh sufficiently because what is AC by a it is accommodated convergence by accommodation so you're giving some amount of accommodation but the eyes are not able to converge very well that means low AC by a and definitely if the convergence or accommodative convergence is low it means that the are going to drift outwards and there will be exotropia and when will the accommodative convergence basically play into uh I mean come into role it basically comes at near work so such a patient whenever they're trying to do some near work like the SpongeBob over here okay they are going to basically have this deviation of the eyes outwards because the poor accommodative convergence and this causes exotropia at a near distance and this is known as near exotropia or convergence insufficiency exotropia okay we'll talk about this more don't worry about that but know that low ACP ratio can cause convergence in sufficiency and exotropia at near similarly what about a patient who has high AC by a ratio now over here a patient with high AC by a ratio means that the patient actually has more accommodative convergence per accommodation that means the eyes are going to converge much more than normal for a given amount of accommodation now this can cause the eyes to actually converge well for near task so near task are not going to be a problem the patient is going to maintain good orthotropia but the eyes are going to now over diverge for distant objects creating an outward drift during distance Vision task okay so such a patient is now going to have more exotropia for distance vision for example over your SpongeBob is trying to look past or away and that time his eyes are diverging okay so this is Divergence exist exotropia because of high AC by a ratio okay so simply to uh summarize low AC by ratio leads to convergence insufficiency exotropia or exotropia at neon and high AC by ratio is associated with Divergence excess exotropia or U exotropia being more at a distance fixation all right coming to the last Theory and that is the seventh Theory regarding the role of refractive errors and this was given by daers okay so some refractive errors can also cause the development of exotropia and in that we have myopia well this might actually be the reason why Asians have more chance I mean more prevalence of or high prevalence of exotropia because maybe they have high prevalence of myopia now what exactly happens in myopia in myopia the Rays of light are going to focus in front of the eye because the Far Point is located in front of the retina right so the rays are going to focus over here now such a patient is definitely not going to try to accommodate why because he if he tries to accommodate that means he's trying to increase the power of the lens and if he's increasing the power of the lens the power point is going to shift even more further so a patient who has myopia is not going to have good accommodative effort instead he's not going to try to accommodate and since he has low accommodative effort the accommodative convergence is also going to be reduced and since the convergence is less there's going to be Divergence leading to exod deviation okay this is how myopia causes exod deviation now what about high hypermetropia now we're talking about high hypermetropia and here the important term is high hyper metropia in hypermetropia basically the rays are focusing behind the eyeball and the Far Point is located behind the Rea right and now you might say that why not accommodate and bring these rays of light on the Rea right yes that does happen and that is what exactly is happening in latent hypermetropia and all but when the patient has really high hypermetropia no matter how much they accommodate they're not going to you know they're not being able to bring these rays of light on the retina and such patients they know it right and therefore such an i is not going to make an attempt to focus curely or bring the ra back on the retina okay so quite counterintuitive but still you know high hypermetropia it's really high power the eye think like I don't want to accommodate such for such a high power and therefore since there's no attempt to accommodate there's no accommodative convergence the AC by a ratio becomes smaller so there's going to be EXO deviation so those were the seven theories as to why exod deviation develops I really hope that this video was of value to you if it was kindly let us know in the comment section also don't forget to uh hit that like button and also subscribe and if you think that this video shall be useful to any of your friends kindly do share that's all for today thank you and have a nice day