hello and welcome to Insight Ophthalmology this is Dr Amrit welcoming you to another lecture today we are studying the cover test under the squint series so why do we need these cover tests now basically sometimes what happens is that your inspection alone will not always be sufficient to determine whether you're looking at a manifest misalignment or manifest squint or not right sometimes an epicanthus a facial asymmetry or a wide angle Kappa can also simulate a deviation right so basically what I'm trying to tell you is that sometimes in examination it becomes difficult just by inspection to differentiate whether we are dealing with a pseudostravismus or a true star business so in that case your cover tests become very very handy but what is the idea behind these cover tests so covering one eye of a patient with a cover basically disrupts or interrupts the normal binocular Fusion right so that's the idea of doing a cover test so as we are doing a cover test what we are doing is we are basically disrupting this Fusion so what uh what do we basically need to carry out these cover tests so we need basically some fixation targets right because the cover test should be done at near and distance okay now for near uh the distance is usually about 33 centimeters and we need to have these correct fixation targets for use example you know shown in this picture so your your fixation targets can also have these numbers and you know they can also serve very well as accommodative targets now for distance however how much distance you choose usually it's about 6 meters and the smallest letters however that can be seen clearly with the eye with the porous vision is chosen as your fixation point for example if there's a patient in whom you want to carry out the cover test say the right high as a vision of 612 and the left eye has a vision of 618 so which I is now the I with poor vision it is the eye with 618 Vision right so in such a patient you are going to choose a Target of 618 for distance fixation and to carry out the cover test at distance right now what about kids we know that kids do not have a very good attention span so they did what usually you know fixate very easily so for them you can use a fixed toy which is uh which is also having some sort of added oratory stimulus or sometimes you can use some remote control mobile toys or videos you know to achieve fixation in case of pediatric population apart from that what do you need you need basically needs covers to carry out the cover test so the most common one that is used is a black paddle occluder as shown over here however you also have some sort of occluder which is translucent you know made up of a rigid non-reflective plastic which actually allows you to assess the eye position behind the occluder as shown here in this picture right so this is called a spielman's occluda now the patient's view is definitely reduced to some sort of investing blur okay so definitely using a translucent occluder also you are breaking down the fusion and you also minimize the accommodation however when you talk about uh the efficacy of a translucent occluder or a total black occluder definitely your paddle occludo that is a black occluder will be more dissociating compared to your translucent spielmann's occluda now this is an important clinical Point here you know that Spielman secluder is actually used to diagnose your dissociated vertical deviation now and dissociate vertical deviation what happens is as you put the eye under cover the eye basically behind the cover will very slowly drift in an upward and outwards direction right and that is called dissociated vertical deviation and the phenomena is called the belchowski phenomena and here the occluder that we use is the same spielman's occluda right because you can very easily you know observe the movement of the eye behind this translucent occluda now what are the types of cover tests so basically we'll be discussing cover tests under three headings and there are three types of cover tests so these are the normal direct cover test or the cover test then we have an uncover test also called cover uncover test then we have an alternate cover test first let us talk about the cover test or the direct cover test so how do we do cover test now basically cover test is done usually in cases where we have an already apparent squint or a manifest squid for example this patient has a right eye exotropia right now here the normal eye or the fixating eye is a left eye so what are we going to do we are going to place cover in front of the left eye and now we are going to observe the right eye for its corrective movement now as you covered the fixating eye which is the left eye the right eye is now going to take fixation right so if the writer is going to take fixation it has to basically come from these rabbistic position towards the center now here the right eye was actually present outwardly deviated and therefore in order to take fixation it is supposed to move towards the left side that means inside right now as we know the herring's law of equal Innovation says that there will be a corresponding movement in the left eye as well and therefore the left eye is also going to move towards the left side example you can see there is actually a translucent occluder here and as you can see as you've put a transmission occluded in front of the left eye the left eye has also moved towards the left side although what I want you to remember here is that in cover test you are going to observe the movement of the eye which is not under the cover okay you're going to observe the movement of the eye which was initially strabismic so here the movement of the right eye which was traditional before which was having exotropia is inwards right so here what happens is basically for example if a patient has esotropia when you put cover in front of the other normal eye this eye will actually move outside or temporarily to in order to take fixation right so that that actually confirms that what you're looking at is isotropia similarly if the eye was originally present outwards that means if originally there was exotropia the eye is going to move inwards in order to take fixation similarly if the eye was deviated upwards that is hypertropia when you place cover in front of the fixing eye the normal eye the eye has to move downwards and this indicates that the patient had hypertropia to start with similarly if the eye is moving upwards and placing the cover in front of fixating eye it means that the patient originally had hypotropia right so basically you place cover in front of the normal eye or the straight eye or the fixing eye and you look for the movement in the squinting eye and based on the movement you will tell whether it was esotropia exotropia hypertropia or hypotropia so I hope that is clear to you now now sometimes it's not really important that you carry out cover tests only if you have very large squint presence now sometimes you know you might be confused whether you are dealing with a proper squint or is it a pseudo squint now in those conditions also your cover test can come very handy can become very handy now suppose you do carry out a cover test basically in both the eyes so first you cover one eye and look at the movement of the other eye Suppose there is no movement in the fellow eye you cover the other eye and then look for the movement right so when there is no movement of the fellow eye when either of the eye is covered then you can you know with confidence you can say that there is no manifest reminisce at least present in this patient right so when there is no movement in either of the eye uncovering either of the eye that means if you cover the right eye there's no movement at the left eye if you cover the left eye there's no movement in the right eye it means that there is no manifest strabismus present in this patient okay so I hope that is clear so for example here you can see that the patient looks looking straight ahead in the first picture the second picture we have placed a cover in front of the left eye and what is happening to the right eye the right eye is the same there is no movement at the right eye now let us check for the left eye in the left eye for shaking the left eye we are putting a cover in front of the right eye and is there any movement in the left eye no there's no movement in the left eye so what does it indicate it indicates that this patient is orthophoric okay that means there is no manifestabismus present in this patient so so how do you interpret these results basically on covering the seemingly fixating eye the normal eye if there is no movement of the other eye it means that there is normal binocular fixation present that means there is no Manifesto business if there is a movement of redressal okay so that screen tie will come back to the center to take a fixation that is called a redressal movement so if there is a movement of redressal in the other eye it means that a manifest deviation was present before you have applied the cover so I hope that is very clear to you okay next we go to what is meant by indirect cover test now till now what you were talking about was a direct cover test now we go on to indirect cover test obviously a child when it comes to your clinic will not let you apply the cover so easily as an adult so in such a case you will actually apply your cover or occluder from a distance right so this test which is termed as indirect cover test it does not permit a full Interruption of fusion as in case of the direct cover test however it can be useful in case of infants and you know small children who have heterotropia and will give you will allow you to assess such kids so this is called indirect cover test so a very important clinical nugget in the same context is that of an infant who starts crying when you put cover on one of his fixating eye so what does it mean it means that the squint the eye which has Quint actually has very poor vision okay similarly sometimes when you put a patch what happens is the other eye will start developing some sort of searching or the stagmoid movements so such nystagmoid movements are indicative of the fact that the child actually has amblyopia so do you see that the cover test is so important it can actually estimate your and sometimes you know give you a diagnosis of amblyopia in case of infants now coming to the cover uncover test okay so what happens in case of Fourier or latent strabismus is that when you cover the fixating eye okay the eye which is not covered will not show any movement so in case of four years you are not going to see any movements right and the eye which is behind the cover however if it has any sort of Fourier it will show some sort of movement so here is a very important point that with cover test you can definitely eliminate a component of tropia but can you eliminate four years no you cannot eliminate Fourier or Laden strabismus by simply doing a cover test and observing the other eye you need to observe the eye under the cover to determine the presence of Fourier or latent strabismus and that is the principle behind doing a uncovered test okay so let us see how do you do a cover and cover test basically one and then the other eye is covered while the patient is maintaining a fixation so you give patient a fixating Target and now you start covering one eye and then the other eye but here the attention of the examiner is towards the eye which is covered okay in the cover test we were looking at the other eye and not at the eye which was covered here we are looking at the same eye that we are covering with our cover okay so that is your cover and cover test if the patient has some sort of heterophoria the eye is going to deviate behind the cover okay in the direction of the heterophoric position so for example if a patient is there and he has a uh exophoria in right eye as you place cover in front of the right eye the right eye is going to deviate outward or that means towards the right side okay behind your cover so that indicates that the patient has a Fourier and as soon as you're going to remove the cover the eye is again going to become Center under the influence of fusion and therefore the eye is going to move inwards from its outward position right so that is very very important point for you to remember for example let us see this patient now this patient seems to be actually orthophoric both the eyes seems to be looking straight ahead now can this patient have a component of Fourier in him yes definitely so what do we do we carry out a cover uncover test so in cover uncover test you could either use your black occluder or if you want to simplify the process you can actually use a translucence payments occluder as shown here in this picture right so here you can see that as you have put the occluder in front of the right eye the eye under the cover has moved out so what does it indicate what did I tell you that whenever the patient has hydrophoria the eye will tend to move towards the heteroforic position behind the cover so here the eye is moving towards the outside that means behind the cover that means the patient has exophoria and as soon as you do the uncover test that means as soon as you remove the cover what do you see the right eyes moving back towards the center and in order to move to uh back toward the center it has to actually move from outwards to inwards in this direction right so if you have a translucent occluded like this you can do you can actually observe the eye behind the cover and then you can remove it and observe it ah observe the movement of the eye on uncovering as well however if you have just a paddle black color occluder you are going to basically look for the movement in the third picture right that is the redressal movement okay so basically your car cover and cover test is uh giving you a clue regarding the presence or absence of four years so that is very very important now let us see this now in the first picture you can see that when you cover the right eye and when you uncover the right eye because we're talking about the uncover test you see that there is no movement in the right eye right that means there is no Fourier in the writer now let us test the left eye in the picture B okay again you you remove the cover that means you have uncovered the left eye and you see that there is no movement in the left eye that means an uncover test in the left eye there is no movement that means there is no Fourier present in the left eye as well now what about this picture C in picture c as you uncover the left eye the eye seems to be moving outwards okay so what information does it give it to us it tells us that maybe the eye was inward behind the cover so here the eye is moving outwards that means the patient has esophoria in the D picture you can see that the eye when it is uncovered now it is moving inwards that means the patient had exophoria in the image e labeled as e you can see the eye is actually moving downwards that means it was originally upward behind your cover right so on uncover test the eye is moving downward it means that the patient has hyper Fourier now on uncovered as in scene as seen in this F labeled image the eye is moving upwards it means that the patient has hypophoria so I hope that is clear to you now so digest that information and next we go to the importance of the speed of recovery okay so all that eyes you know moving up down inwards outwards you know I told you that it's called redressal movements right so you also observe on cover test with what speed the eye is actually redressing backwards and why are these eyes moving backwards toward the center they're coming back toward the center to take fixation right so it gives you a clue regarding the fixation as well right so you basically observe the speed of recovery in case of these deviations specially in case of four years you check how rapidly the eye is moving towards the center is it a rapid redressal a moderator dresser a delayed redressal and sometimes the patient has to actually you know blink the eye yes um you know to bring the eye back towards the center right so as you place the cover the eye is going to move towards the heteroforid position and if you remove the cover you're not going to see any redressal movement that means eyes almost fixed there it is only a matter of fact when the patient will blink and then the eye is going to come toward the center right that may that actually tells you that the patient is having a very poor control of his Fourier and dysphoria is going to soon decompensate and the patient is now going to have you know a tropia or a manifest strabismus similarly sometimes these patients will also complain of diplopia before the redressal movement and this happens in delayed redresses or the redresses which actually need a blink you know for uh for it to recover now sometimes there will be no recovery at all or a very poor control heterophoria so as you can understand this is actually a spectrum so before first of all you will have a Fourier that Fourier is going to decompensate and now the squint will become you know more often it'll appear more commonly now but still it is intermittent it is not present all the time and gradually it will become a total manifest squint or a constantly present squint and that is called atropia right so Euphoria leading to intermittent deviation leading to a manifest or constant tropia or squint now the third type of test is the alternate cover test so what is this alternate cover test so as the name suggests alternate cover test means you are already going to alternatively cover one eye and the other and then look for the movement in the other eye for example here the patient seems to have exotropia in the left eye okay now you place the cover in front of right eye what is happening to the left eye is that the left eye is moving inwards right that means there was extra deviation in the right in the left eye now if you cover this left eye what is happening there's a regressive movement seen in the right eye the right eye is moving inwards now that means there's exotopia present in the right eye as well right so what you're dealing here is you are dealing here with is the alternating exotropia right so this is your alternate cover test so basically you have these cover uncover tests and the alternate cover test one point that you should remember is that the alternate cover test will fully dissociate your eyes compared to your cover and cover test okay so you can break the fusion much in a much better way with an alternate cover test compared to your cover and cover test and therefore an alternate cover test is of value is of Great Value in four years and in tropias regardless right so your entire deviation can be brought about you can get an exact estimation of the maximum deviation only by doing an alternate cover test so as we go ahead and discuss the prism bar cover test also you know you will realize that these tests are also done with an alternating cover test okay so whenever you try to measure the deviations you have to do it with an alternating cover test because alternating cover test will fully dissociate your eyes and bring out the maximum deviation or the true deviation however another important point is if you would have observed this alternating cover test is actually seems to be a mixture of your cover and uncovered test so as you are alternatively covering one eye and looking at the other eye you really do not get the exact information whether you're dealing with the latent or manifest deviation it could actually be a mixture of both right so it's useful for measuring however you can't put a label on it whether it is just a latent or a manifest deviation just by doing alternate cover test right and this is why it's very important to do all the three cover tests uh you know systematically so I hope you got it bye now so now let's summarize and see if he can jot down all the important uh aspects of the cover test so the cover test is a very important method by which you can differentiate Manifesto business latent strabismus you can know about the directional deviation whether it's a horizontal screen or it's a vertical squint right so horizontal I or EXO and ezos and vertical is your uh hyper and hypo deviation then you can also differentiate the different angles by doing cover test at near distance and cover test at distance fixation you can also study about the effect of accommodation and the patient refractive error by doing cover test which you will understand when you study esotropia in which we have accommodative isotropia okay where we actually give the patient refractive correction okay your convex classes and then do the cover test and look at the deviation angles obviously by doing cover tests you get to know whether you're dealing with Euphoria or a tropia sometimes it gives you information regarding whether it's a constant squint whether it is coming and going off whether it is unilateral or it is alternating kind of squid of course you get an estimation of visual Equity also as I told you in case of infants if there is nostalgamoid movements you get an idea what the patient has amblyopia also the speed of recovery in latent strabismus can tell you how good is the control how good is the fusion is the patient going to decompensate very soon from Fourier to tropia so therefore your speed of recovery is important again sometimes you can also judge the presence of latent or manifest latent nystagmus so latent nystagmus is a nystagmus which is usually absent but when you put a cover the eye starts showing uh oscillating right oscillations so that is called a latent nystagmus which appears only if you cover one eye manifest Latina stagmus is an estimate which is present but once you cover one eye the nystagmus is going to increase in its intensity or amplitude right so that is called a manifest latent nystagmus so here also your cover test comes very handy similarly you can find the latent component in case of infantile nystagmus and also as you go ahead in your squint examination you will find out that all these tests especially the alternating cover test we actually do it in all the directions of the Gaze you measure your deviation in all direction of the Gaze by making asking the patient to look towards the right left up down next to Elevation legal elevation depression okay simultaneously so if your angle of deviation is equal in all the direction of gazes it is called a combatant squid whereas if the deviation angle actually or if your exotropias or esotropia or in simple terms if the squint is variable in different direction of the case it's called incompetent squint right so your combatants and incompetence can also be found out by doing an alternate cover test okay so so that's all for today I hope it was useful thank you and have a nice day