Hello and welcome to Insight ophthalmology. This is Dr Amrit, welcoming you to another lecture Today we are studying the exotropia classification. In our previous video we talked about what are the causes of exotropia in which we discuss seven theories that leads to the exotropia development .In this video on classification, we shall be studying first about certain important terminologies then we shall be understanding certain important Concepts .These will be regarding the convergence ,what is vergence after effect? or tonic fusional convergence and ultimately understanding these Concepts will help us to understand what exactly is the burian's classification and the kushner classification .So now let's get started now basically the classification of exotropia,usually we have two classifications we have the Burian or you can call it as the burianss classification and then we have the kushners or kushners classification.iFirst let us try to understand some important uh terminologies so here we know that we have something known as primary exotropia then we have something known as secondary exotropia consecutive exotropia and residual exotropia .So let us first understand what is meant by primary exotropia the primary exotropia or primary exodeviation it basically refers, uh, to an outward deviation of the eyes, which is known as exotropia, and this usually occurs without any underlying secondary or adaptive cause, so this means that the exodeviation is the main or the initial problem in the alignment of the eye, and the exotropia over here is not a result of any other ocular or systemic condition like injury or anything like that. Okay, so here the exotropia is the primary problem or the initial problem in the alignment of the eye. Right? Now, this primary exotropia can be of two types. It can be intermittent or it can be constant now intermittent exotropia means that the exodeviation is not manifest all the times okay? so it is present for some period of time and then it's not present and mostly it is seen in children and typically it is present whenever the child faces fatigue or during the periods of in attention .right? constant EXO deviation means that the deviation is present at all the times all right the next one the next terminology is that of the secondary exodeviation. Now secondary exodeviation is again an outward deviation of the eye but over here it occurs as a result of an underlying condition that disrupts the normal binocular single vision. Okay so this exodeviation develops because of a primarily sensory or a structural issue in the eye rather than just being the primary alignment dissolve da itself okay so it could be anything it could be because the child has poor vision or there is some sensory loss in one eye now this could be because of various pathologies the child might have amblyopia or you know there might be a cataract in the patient or there might be a retinal disease or an optic nerve damage so anything that is damaging the sensory pathway of the eye right so it can ultimately lead to deviation of the eye and leads to development of the secondary exotropia okay now it could also be sometimes a mechanical cause like post trauma or other post any surgery which can lead to development of exotropia and such exodeviations are known as secondary exodeviations right now if you want to really know how these uh lead to exodeviation I would suggest that you visit our first video on the seven theories of exodeviation causation all right next we have something known as the consecutive exotropia now as a name suggests consecutive exotropia means that this is an exodeviation that is developing after you do a surgery for esotropia so normally in esotropia the eye is going to be inverts and then certain surgery is going to be taken over so that you laterally deviate the eye and make it orthotropic however if there's any over correction in this esotropia surgery esotropia correction surgery the eye is going to now uh the eye will now be sitting in a lateral position leading to development of consecutive exotropia right so consecutive exotropia is nothing but it develops after surgery for esotropia and basically when the when there is overcorrection in the esotropia surgery All right next we have the residual exotropia, so what is residual exotropia? Something similar over here: you have under correction post surgery, so when you're treating an exodeviation, suppose the patient has about 40 prism diopters of exodeviation, okay, or exotropia, and now you want to correct this patient, so ideally the patient should be corrected for 40, but sometimes there might be under correction, say the patient is only corrected by 30 prism diopters, so the patient still has 10 prism diopter of exotropia now this remaining exotropia is known as the residual exotropia okay so I hope you understood all these important terminology now in a previous video I have explained to you in detail regarding what exactly is exophoria what is intermittent exotropia and what is constant exotropia and how they progress from one stage to another right so this is the video in which it is clearly uh explained all right the link to this video is going to be provided in the description box now let us understand some important Concepts in order to understand the classification of exotropia so uh first of all we must understand regard regarding the convergence it's very important okay so what are the various types of convergences which are present in the eye so we have tonic convergence we have accommodative convergence fusional convergence and then we have something known as the proximal convergence so let us try to understand all of these one by one the first one is the tonic convergence so what exactly is tonic convergence tonic convergence basically is the Baseline convergence that is actually going to maintain the eye in the Straight Ahead position now over here the eyes do not need any specific visual stimulus okay it's just present at rest now it is going to counteract the natural tendency of the eyes to drift outwards now if you would remember in a previous video I told you what exactly is the position of rest for our eyeballs right it's slightly in a Divergence position so tonic convergence basically counteracts that position of rest and maintains the eyeballs in a parallel state or in an orthophoric state right so that is known as tonic convergence and for Tonic convergence to act we don't need any stimulus it is just present all the time then we have something known as the accommodative convergence now this type of convergence is basically linked to the process of accommodation and over here it is going to kick in whenever the eyes are going to focus on a near object and the cedary muscles are going to contract and change the shape of the lens for a Clear Vision right so accommodative convergence basically kicks in whenever you accommodate to look at a near object because whenever there's accommodation there's going to be convergence and there's also going to be miosis right constriction of the pupil so along with accommodation you will have this accommodative convergence and over here I would just like to mention that uh there is one thing uh ratio that you can measure uh to calculate the Accommodative convergence and that is called AC by a ratio and this was also explained in the previous video we'll be talking about that again in this video as well all right the next one is the fusional convergence so as the name suggests the fusional convergence is basically something that is going to actually help to maintain the binocular single Vision right so fusional convergence basically corrects any misalignment even a minor misalignment of the visual axis so fusional convergence occurs to maintain the binocular single Vision whenever an object is moving closer or when there's a slight misalignment between the eyes right so it compensates for any misalignment of the visual axis to fuse the two slightly different images into a single image and this is something that the brain is doing okay so whenever you are looking from say you looking at 10 cm and suddenly you look at 11 cm or 12 CM there's going to be a slight misalignment and the brain is going to take care of that misalignment as and is going to correct those axis so that Fusion can take place in the brain so this can happen through motor Fusion or sensory Fusion all those terms I've explained in my previous videos on orthoptics all right so that is referred to as the fusional convergence which makes sure that fusion occurs at every point and there is binocular single Vision all right the fourth one is the proximal convergence now proximal convergence is the convergence which kicks in & triggered just by the awareness of an object being near so what I mean to say is if something is present close to you are aware that there is something close to you and you're supposed to look at it and therefore the eyes are going to begin to converge as a reflex when the object comes within that closed range okay so just an awareness of an object being near is going to trigger a convergence and this convergence is known as the proximal convergence okay so over here if you should know fusional convergence basically helps in alignment and proximal convergence gives uh Clarity to the object accommodative convergence also aarts uh sorry imparts the uh Clarity to the object and tonic convergence is something uh which basically helps an alignment of the axis again okay so that was regarding the convergences now the question is why do we really need to know about these convergences it's very important because in exodeviation what are we dealing with we we are dealing with the outward deviation of the eye right now if these convergences kick in like in some patients there might be excess convergence at near this might be anything this might be an excess tonic convergence this might be an excess accommodative convergence this might be an excess fusional convergence or proximal convergence we don't know okay so there might be some component of convergence that might be excessive and these convergences we know that they basically are working at a near distance so what happens is that this this AIS this excess convergence is going to basically counteract the Divergence at near and these patients are going to have less exodeviation at near compared to the exodeviation at a far distance so what I mean to say is that if there's a patient of exodeviation or exotropia and the patient is looking say at far distance that is 6 me M the patient will have more Divergence compared to the Divergence that the patient is going to have at a near distance say of about 33 cm so for example this patient might have 60 prism de opter exotropia at far and at near because the convergence is taking care of it the exodeviation might just be say 20 prism de Ops right so here the convergence are masking the true near deviation the true near deviation patient here might be say about 40 50 or who knows even 60 prism diopters but the patient is exhibiting just 20 prism diopters because he has these really robust convergence mechanism all right a very very important point that you must remember okay so here I would like to introduce you to another concept and that is the virgins after effect or virgins after adaptation now at this point I would like you to have some break maybe eat something maybe you know revise whatever we have learned by now okay so that you can understand this clearly okay so virgins after effect what exactly is meant by virgin after effect now uh virgins after effect or adaptation basically occurs gradually over time to help maintain the eyes alignment especially after a prolonged convergence effect right so it's a phenomenon for example let me try to explain it to you in simple language so it's a phenomenon where your eyes get used to looking at something up close for a eyes for example you're looking at an object placed at 33 cm and you are converging right so the eyes will get used to looking at that object for a while now even when you stop looking at that object your eyes might feel like they are still in that position for a bit of time making it harder to quickly focus on something else far away right so this residual convergence effect that persists after a prolonged use of fusional convergence this is known as a virgin after effect okay and some of the scientists like kushners they called it even as uh tonic fusional convergence or slow to dissipate convergences because this convergence dissipates really slowly okay after a prolonged use of fusional convergence okay so this is known as vergnece after effect or adaptation now the question is why is it important it is important because it's also a type of convergence mechanism and this is again going to mask your true exodeviation at near and especially in people after prolonged extended near works right so this is known as virgins after effect and specifically we talking about this in exotropia because patients with intermittent exotropia they really have these high vergence after effect or high residual fusional conversion this is something that we need to really take care of right and therefore we also need some test in order to get rid of this virgins after effect or excessive convergence mechanism because it is only then that we will be able to reveal the total or the real extent of exotropia that the patient is having at near and how do we do that we do that by using a mono occlusion test of scobee and Burian okay so we'll talk about this test in a while okay meanwhile now let us come to our main topic of discussion today and that is the bans and the kushner classification okay so all that background conceptual knowledge was really really important for you okay so first we'll be discussing about the buran's classification now intermittent exotropia has been divided into four groups according to the classification system proposed by burian and this system is basically based upon the concept of fusional convergence and Divergence and it actually relies on the measurements of distance and near exotropic deviation right so what you're going to do over here for to classify a patient into burian classification is that we will be measuring the distance exo deviation then we will be measuring the near exoeviation then we are going to compare uh these two deviation the distance and near and if there is any difference between the near and the distance exo deviation we are going to do a test called as the monocular occlusion test or mono occlusion test and why do we do it we do it to bring out the real near deviation for the exotropic patient all right now at this point if any of you uh if anyone is not sure about how do we really measure the deviations in these patients so I'm going to give a link in the description box because I've explained to you about that in the prism cover test video so you can check out that video all right so burin basically classified this into four categories so we have four categories over here we have a Divergence excess category then we have basic intermittent exotropia then we have convergence insufficiency exotropia and pseudo Divergence excess or simulated Divergence excess exotropia okay so don't get scared let me try to explain it to you it's very very easy the Divergence excess also sometimes people like to call it as true Divergence excess here the DV devation is going to be larger and when I'm saying deviation I'm talking about exotropia because that is what is the topic right so here in Divergence excess the exotropic deviation is going to be larger at distance compared to the exotropic deviation at near okay so patients over here will typically maintain a good control at near obviously because they don't have that much squint at a near deviation but their deviation is going to increase when they are viewing an object at a distance distance okay say about 6 M right so Divergence excess means that they are going to have larger deviation at a distance compared to the deviation at near then what is basic basic intermittent exotropia basic exotropia is when your exotropic values or measurements are almost equal at near and distance convergence insufficiency is when the exotropic deviation is larger at the near distance compared to the distance uh measured ments right so such patients are going to actually have difficulty maintaining their binocular vision during the closed task example reading why because they have more squint present at a near distance right and then we have a fourth category that we'll discuss in detail and that is known as the Pseudo Divergence excess or simulated Divergence excess that means these patients are going to behave like the true Divergence excess but after you do certain tests you will figure out that there's something fishy going on there is something that is masking the true near deviation in these patients and that is the reason why we call it pseudo Divergence or simulated Divergence excess okay we'll talk about that but over here one more thing you should remember is that the difference between the deviations whether it is Divergence excess or convergence insufficiency where we are saying that in Divergence excess the distance deviation is more than the near in convergence in sufficiency it is the near deviation which is more than the distance deviation the significant difference between the two should be at least 10 prism diopter okay so what I mean to say is if distance deviation is 30 prism de opter the near should be about 20 prism de opter okay or it should be less if it is anything more than that then it will classify into the basic intermittent exotropia variety so I hope that is clear the difference is important over here should be at least 10 prism diopter all right now as promised let us discuss about what is meant by by pseudo Divergence excess or simulated Divergence excess now at this point I believe that all of you really understood what exactly is meant by convergence after effect right so if you understood that understanding Pseudo divergence excess becomes really really simple so Pseudo Divergence excess or simulated Divergence excess is something that patients are going to behave like true Divergence excess that means they are going to have this deviation or exotropia which is larger at a distance compared to the exotropia at a near distance but their near deviation is going to increase within the 10 prism opter of distance deviation after a period of monocular occlusion and that period is 30 to 60 Minutes of monocular occlusion right and why is it happening it's happening because they have those really difficult to dissipate or really thick uh convergence after effect which some people like to call it increased tonic fusional convergence at near mechanism and this excessive convergence is basically masking their true deviation at near and therefore we need some test to dissipate this excess convergence after effect to reveal the latent exo deviation at near and that test is the oclusion test of Scooby buriannow don't get confused this is the same monoc occlusion so you can call it as monocular occlusion test or you can call it as mono occlusion test as well right so burian basically found out that if you you Aude one eye if you patch one eye for 30 to 45 minutes you will be actually uh masking the fusional convergence and therefore in these patients the true Divergence or the true exotropia at near distance will be revealed after you occlude the patient for 30 to 45 minutes right so why exactly you have to occlude for near distance the reason was whenever we are looking at the near object we we have a stronger fusional stimulus okay A near stimulus is always a stronger fusional stimulus compared to the distance then an object which is present close Okay that's called the proximity of the object the size of the object is also going to be more because the object is nearer to you so extending a greater angle the brightness of the object is also going to be more something which is coming like the Rays coming from too close to the eye obviously the object is going to appear brighter right so therefore the stimulus for Fusion is going to be more from the near objects compared from the distance object and therefore occlusion for near testing is really really important and this is something which Buran said right okay now why are we really covering one eye now this is done to temporarily stop them from working together so basically normally the eyes are going to try really hard to stay aligned through something which is called fusional convergence that we discussed right and this fusional convergence is actually like a teamwork between the eyes and when we are covering one eye for about 30 to 45 minutes we are basically turning off that team work so patients with intermittent exotropia they're often controlling their deviation more effectively at near than at distance because of the stronger fusional stimulus at near because of the stronger convergence after effect or some like to call it tenacious proximal Fusion and the something called Scooby phenomena also so hang up for uh just hold your horses for a while we'll talk about that as well there so many mechanisms working at near right so this occlusion disrupts this mechanic mechanism allowing the true near deviation to manifest and that is why we occlude thepatient now at this point it's very important that you don't allow the two eyes to see together even when you're removing the patch you make sure that the fellow eyes is covered first with the cluder because if you're going to just remove the patch the patient is going to start seeing binocularly and the fusional mechanism is going to kick in again and then the entire purpose of doing a test would be futile right so always remove the patch cover the uh first occlude the felli and then remove the patch and then start doing your cover uncover test to measure the deviation right so in this patient if the near deviation now increases to almost approximate the distance deviation or comes within the 10 prism diopter value after uniocular occlusion then we say that the patient is actually having what is known as the Pseudo divergence excess or simulated Divergence excess okay so let me give you an example for example say this patient was there and at uh say this patient okay at uh distance the patient had a measurement of about 40 prism diopter and at near the measurement was 20 prism diopter of exotropia now after monocular occlusion say now what happens is that the deviation now becomes 35 prism diopter at near and distance it becomes 40 PR deop now before occlusion what category are you going to put the patient into the the difference between the distance and near deviation here is about 20 prism de opter it is definitely more than 20 prism de opter difference and therefore the patient would come into the Divergence excess category however post occlusion you can see that the difference over here has become just five prism de opter so the patient has now landed into the basic exotropia variety right and this is how the occlusion test basically actually uh uh this is how the the occlusion test basically works and therefore you can say that this patient was actually having a pseudo Divergence excess all right so that was your burian classification of intermittent exotropia so we had Divergence excess basic intermittent exotropia convergence insufficiency and pseudo Divergence excess or simulated Divergence excess and over here the focus was on the fusional mechanism and the distance and near deviations and the difference between them now Kushner came and he said that actually 60% of the patients with divergence excess will actually have a high AC by a ratio and 40% will have a normal AC by a ratio that means questioner was suggesting that there were greater uh there were far more other mechanisms associated with convergence which were responsible for masking of the near deviation than just the fusional convergences right and therefore kushners came up with his new classification in which he classified exotropia as follows right now this might look a little bit daunting but uh first we'll try to understand what is meant by a plus three diopter test after we have understood this plus three diopter test this classification of kushners will become much more easier to understand so kushners was focusing at this time on the importance of accommodative convergence right so AC by a ratio basically actually measures the accommodative convergence and its role in exotropia AC by a ratio was explained in detail in the previous video it is nothing but it is change in the convergence or accommodative convergence per unit change in accommodation and here the length that we are using for measurement of near AC by a is+ 3 diopter lens okay so remember that plus lenses basically relax accommodation and minus lenses basically uh stimulate accommodation so if you want to carry out AC by ratio normally the lens which is recommended is about min-2 diopters okay so a by ratio basically is measured using the lens gradient method and the formula is near deviation change with the lens in place and here the lens will be plus 3 opter minus the near deviation without the lens and then you divide it with the power of the lens which will be+ three and that will give you the AC by a ratio according to the lens gradient method and the sign convention that you follow is for esophoria is Plus for exophoria it is minus what I mean to say is if you get 20 prism diopters of exotropia it has to be written as minus 20 prism diopter exotropia and then you carry out the algebraic calculations all right so here the lens that we use is the plus3 de opter spherical lens the plus the de opter is basically used to relax accommodation and if you relax or suspend the accommodation the effect of accommodative convergence will also be removed at near and this will reveal how much exactly the eyes are relying on the accommodative convergence to control the exotropia at near now the question is how do you really interpret this test so you carry out this plus three diopter test and then if the patient has a low AC by a ratio it means that the near deviation will increase only slightly when measured with plus three diopter lenses and this means that the accommodative convergence is not really playing a significant role in this patient in maintaining the alignment at the near fixation okay now on the contrary if the calculation that you get is really of high ACB ratio it means that the patient is majorly relying on his accommodative convergence to control the near deviation and it means that the near exotropia after you put that 3-day opter lens to relax accommodation the convergence is going to come down and therefore the near deviation increase uh near deviation will increase substantially when you carry out this plus three de opter lens test okay it means that the patient is relying heavily on accommodative convergence to control the near deviation okay so that was regarding the AC by a ratio so to summarize we basically have this primary exotropia and classified into intermittent and Conant then intermittent is again classified into Divergence excess then we have basic and convergence insufficiency this is all based on the near and distance disparity of the deviation then Divergence excess is again classified into the simulated and true Divergence excess so what I mean to say over here is that the near deviation if it increases to approximate the distance deviation after uniocular occlusion and the patient has normal AC by a ratio or sometimes the patient can have a higher AC by a ratio and that happens when the near deviation increases to approximate distance deviation when measured with a plus three diopter lens okay but it's not so much affected by the occlusion okay so at this point it should be very clear what exactly true intermittent distance exotropia true intermittent distance exotropia means that the exotropia is more at distance compared to the exotropia at near and here there's no significant increase in the near deviation after unior reclusion or even after a plus three de opter lens used to relax accommodation what does it mean it means that the patient doesn't have those excess convergence mechanism masking the near deviation and whatever deviation you are measuring is a true near deviation right so that is known as the true Divergence excess exotropia okay so basically in intermittent exotropia you go ahead and do a 1 hour of monocle occlusion if there is uh a change in the angle that means if the near angle uh changes to approximate the distance angle or it reaches within the 10 diopters of the distance angle it means that the patient had an excessive fusional convergence or you can cause it cause it uh sorry or you can call it tonic fusional convergence or there might be vergence after effect that is taking uh place over there and therefore here this is called sto Divergence excess and usually this patient if you carry out AC by ratio and the AC by by ratio is normal it means that only the fusional convergence is basically the convergence mechanism which is masking the near deviation so this is called Sur Divergence exes with normal AC by a ratio however sometimes after monocular occlusion also there will be no change in the angle in those patients if you carry out a plus three diopter lens okay what will happen to the near angle near angle might show no change or it might again change to uh approximate the distance angle or reach within the 10 prism theop of the distance angle in that case it is called pseudoo divergence excess with high AC by a ratio or when there is no change in angle then you can call it a true Divergence excess when there is no accommodative convergence excess or there is no excess tutional convergence as well so often when we read our textbooks for exotropia we come across so many of these terms which are really really confusing right so let us just try to summarize them so the term tonic fusional convergence was given by burian and it basically means that there is a resting it basically applies to the resting alignment of the I without any visual Target then tential proximal Fusion was given by kushners and it is basically referring to the persistent Fusion effect at near that doesn't let go so easily and that is the reason why tenacious proximal Fusion was also referred to as the slow to dissipate virgins mechanism right and on the similar lines we have something called convergence after effect which basically applies to the same thing it's like holding on to a close alignment even after shifting from near to a far Target this was given by Scooby and burin then later kushners gave another term and that is called as the Scooby phenomena okay I'm so sorry for the spelling It's s c o b e e okay so what exactly is meant by the Scooby phenomena scoy phenomena according to kushners is nothing but later on in his papers in 2015 kushners said that it's not really the tenacious proximal Fusion which is responsible for the change in the near angle after monocular occlusion and he said that there's something else that is working over there so let me not just call it tenacious proximal Fusion rather I would call it as Scooby phenomena okay and he said that it is basically because of the difference in the retinal disparity when we look at a near object or when we look at a far object so what exactly happens over here is that when we looking at a far object usually the rays are going to fall on the temporal retina so if this is the phobia these are the nasal retina and these are the temporal retina the rays are falling on the temporal retina when we looking at far and this is going to lead to a crossed localization okay a crossed localization what exactly is crossed localization cross localization means that if the object is falling on the temporal retina the image is going going to fall on the other side over here on the nasal aspect of the visual field similarly the the image for this eye is going to fall on the other side this is like crossed it is going to lead to a cross localization when we looking at a far object and what diplopia sorry and what squint is a cross squint it is the exotropia which is a uh cross squint and therefore when we looking at a distance it is causing a cross localization and therefore it leads to exaggeration of a cross Quint that is exotropic however when we look at a near object say somewhere here the rays are going to fall on the nasal retina and the image is going to be formed on the temporal side of the uh two eyes right and this is what is known as uncrossed localization and therefore this is going to cause uncrossed diplopia or uncrossed squint and which one is the uncrossed squint it is esotropia okay I hope I know it's very confusing but just uh hang on for a while so what sco is told was that because there's uncross localization similar to uncross diplopia or esotropia so therefore these patients are going to have less exotropia at near compared to distance and this is called as the basal retinal uncross disparity and it is this preponderance of this basal retinal uncross disparity that leads to masking of the near exotropia I know another mechanism for masking of the near deviation in intermittent exoor okay as if we didn't have too many to understand so that is known as the Scooby phenomena all right so that brings us to the kushner's classification so what exactly are you going to do for krishna's classification again we will measure the distance measurement we will carry out the near measurement and then we will see if there's any disparity between the distance and the near measurement if there is a disparity AC by a ratio will be obtained and this will be obtained using the lens gradient method and using the lens gradient method you are going to basically be uh understanding regarding the uh accommodative convergence apart from that in patients who really are going to get this near deviation greater than the far deviation and if their AC by a ratio is normal in those patients you are going to carry out something known as the convergence fusional amplitude Okay so remember this we will uh we will actually have a look at it at the end of the video so this is the kushners classification it divides the exotropia into to about seven categories the first category is the basic exotropia very similar to the basic category of the Burian here the deviation at far and deviation at near are almost equal and the percentage of exotropes in this category are 37 then is a category of Tenacious proximal Fusion tenacious proximal Fusion very similar to convergence after effect and therefore the test which is going to detect the tenacious proximal Fusion is the 60 Minutes of monocular occlusion and according to kushner the category over here are those exotropes where the distance measurement will initially exceed the near measurement but after you do a monocular occlusion the near measurement is going to increase so this is the category of Tenacious proximal Fusion and the percentage of exotropes falling over here is 40% then we have those where you want to check the accommodative convergence playing any role or not so you do a plus three deop test or you measure AC by ratio using the lens graded method so in these patients if if the AC by ratio is high they fall under the category of high AC by ratio it means that the distance measurement initially exceeds a near measurement and then they have a high AC by a ratio also present so this is the 5% of the exotropic population sorry then we have proximal convergence so these are the patients where the distance measurement will exceed the near measurement even after 60 Minutes of occlusion and the AC by ratio is also normal so it means that here neither the fusional mechanism that is neither the tenacious proximal Fusion nor the accommodative convergence is playing any role that means there's something else which is masking the near deviation and that is the proximal convergence now this Falls to 4% of the category then kushners comes to the uh part where the near measurement of the exo deviation might be exceeding the distant measurements okay so up till now the distant measurement was more than the near measurement but but here the near measurement is more than the distance okay so here the near measurement exceeds the distance measurement and the accommodative convergence and AC by a ratio is low so this is the low AC by a ratio right and then we have those where there is a actually fusional problem there's a fusional convergence in sufficiency here again the near measurement is exceeding the distance measurement that is near exotropia is more and why is that near exotropia more it is more because the patient have poor fusional convergence amplitudes okay less than and this is the less than 1% of the exotropic population then we have pseudo convergence ins sufficiency here the near measurement exceeds the distance measurement but the distance measurement is again going to increase after 60 Minutes of monocular occlusion something very similar to a pseudo Divergence excess again it forms less than 1% okay so now let us try to understand how do you really measure this that is the fusion convergence amplitude so fusional convergence amplitude is basic basically measured using the base out prism so the base out prisms are actually going to be placed you can actually use this prism bar and these are going to be placed in front of the patient eye and they will force the eye to turn inwards to maintain fusion and by keeping on adding the Prism Power you can actually measure the patient's ability to sustain convergence don't worry I'll explain it to you so you can see over here this is the eye and we have introduced a base in h base out prism this is the base this is the apex and since the base is towards the outside it is known as the base out prism now when you introduce this base out prism in front of this exotropic eye the Rays of Light which are coming like this so you can see this is the point from where they're coming the Ray are going to bend towards the base right that is what happens in prism and the image is shifted towards the Apex so to the eye it is going to see as if the image is coming from here right somewhere closer from from the original point of fixation and therefore in order to make that point clearer the patient has to converge now so you are basically by putting a base out prism you are forcing the patient to converge and by doing so you are actually testing how much the patient can converge and till what level the patient can actually keep on focusing on that Target and can actually clear out that Target right so that is known as the measuring of the fusional convergence amplitude so you start with the low power base art prism and then you increase the power in really small increments and while asking the patient to keep focusing on that single Target like a DOT or a letter so you do give the patient this target over the patient has to focus on that and make sure you ask the patient that they have to see that Target clearly all right so then there will be a break and Recovery points the point at which the patient is going to first report seeing double vision that is called the break point right so you keep on increasing your prism powers and at one point the patient would not be able to fuse it or see it clearly and there will be a diplopia and that is called a break point now after that what you do is you start decreasing the power now until again the patient can see a single vision and that is called a recovery point now what are the normal values these are important for distance the normal fusional convergence is about 15 to 20 prism de opter for break and 10 to 15 prism de Ops for recovery and for near it is 30 prism de Ops for break and Recovery for 10 to 25 prism doter so if your patient basically has near deviation greater than the far deviation and the AC by a ratio is also normal and there is no pseudo diver pseudo convergence insufficiency as well so in those patients you can actually measure the fusional amplitudes and the amplitudes Falls below these you know that it is the fusional amplitude which is responsible for the uh lesser for the excess deviation at far and lesser deviation at near so that that's all for the burian classification and the kushners classification I hope you understood it really well and I hope it becomes easier now for you to go through your squint textbooks and if this video was of any help to you do for don't forget to like the video and also share it with your friends it really helps us with the algorithm these videos really take a lot of effort to come uh to you and if you don't really if the number of views are not sufficient they get some they get lost in the huge huge pile of videos that we have on YouTube so make sure you share like and also subscribe so that these videos can stand out and reach all those who really need them that's all for today thank you and have a nice day