hello and welcome to inside of filmology this is Dr Amrit welcoming you to this Quinn Series today we are going to discuss about some very important and basic aspects of squint examination first we shall be studying about the hershberg's corneal reflex first of all what is strabismus or squint now strabismus is basically a condition in which the visual axis of the eye are not parallel right now at this time you should know what is meant by visual access Visual axis is an axis which is drawn from the point of fixation that means where you are looking at to the phobia okay so if you draw a line from the which from the point of fixation to the phobia that is called visual access now if both the eyes have similar visual access parallel visual access if both the eyes are looking straight forward that is called an orthotropia okay so these terms are also very very important so what is orthotropia orthotropia is when both the eyes are actually looking straight forward which is a normal physiological condition right however if one or the other eye is either deviated to one side maybe divided towards left right up or down now such a condition will lead to the visual axis being directed in different directions okay they're not leading to one single fixation point now such a condition is called heterotropia right so the term hetero means that the two visual axises are not coinciding on a single visual Point okay and this is what is known as strabismus or squint so I hope that is clear now squint austrobismus is basically a deviation of one eye right so if the eye is diverted towards outside deviated towards outside that is called exodaviation right so you can remember it as x x means exterior right so if the eye is deviated outside it is called exoderation if the eye is deviated towards the nose that is inside it is called ESO deviation if the eye is deviated upwards it is called hyper deviation if the eye is deviated downwards that is called hypo deviation now as I told you that the term hetero means that both the eyes are not looking straight forward their visual axis is not directed together towards a fixation point but what is meant by heterophoria and heterotropia that means there is some difference between four years and tropia so heterophoria is that a person who has a tendency of developing squint or who has a tendency of deviation of one eye is still looking orthotropic to you and why is he looking autotropic to you he's looking orthotropic because he is taking control of that squint by using his Fusion right so using this capability of fusion is still able to look straight ahead now such a condition where the fusion is taking care of the squint and the squint is not apparent to you such a condition is called a heterophoria right however if the strawberry space become too large or the squint becomes too large the fusion will not be able to take care of that large angle of strabismus and in those conditions what will happen is you will be actually able to see the squint the squint will become manifest okay it will be quite apparent now such a constant pres constantly present squint is called a trophy okay or heterotropia now let us have a look at this in the first picture you can see that the child is uh using both her eyes to look at an object that means this is a binocular condition right so a binocular condition means the patient is using both uh both his or her eyes right so in this binocular condition you can see that both eye seems to be parallel the visual axis seems to be parallel right in the second picture however now what have we done we have put a translucent occluder in front of one eye and what can we see that we can see behind that translator the eye has actually rotated inwards right now what have we done basically here is by placing a occluder in front of the eye we have changed this binocular condition to basically a uniocular condition right and you should know that the fusion will always work under a binocular condition only a fusion is a binocular faculty right so if you make the patient uniocular the patient will not be be able to use now it's his or her Fusion right this is also called as dissociation so we have basically dissociated the uh the two eyes or we have disrupted the patient's Fusion now as we disrupt distribution or as we dissociate the 2i what will happen the underlying tendency of these eyes to actually squint or deviate will now come out okay and therefore again as you can see in the third picture as well as as you place the translucent occluder in front of the left eye the left eye is again deviating inwards what does it tell you it tells us that this child actually has a Fourier that means the child actually has a tendency to squint and the child is taking care of that squinting tendency by his by his or her Fusion right now it's only a matter of fact that when the fusion goes away the Fourier will now become tropia and now if the child would have tropia you will actually see deviating eye right in the first picture itself right so I hope that is clear so this condition is nothing but it is a Fourier where the fusion was taking care of it and now by putting an occluder we have actually disrupted or dissociated both the eyes so now Fusion cannot take place and therefore that we can see that the eyes are actually now deviating under the under those translucent occluda so this was a Fourier in this series we are going to discuss about how do we first detect that squint is present or not after we know that squint is present how do we actually just you know estimate the angle of squint and estimate the squint and third is how you actually objectively measure that square so first let us talk about the detection of strabismus for the purpose of detection basically that means in your inspection okay you're going to observe the patient's appearance there are certain appearances which will tell you that this patient might have actually squint okay okay now second thing is you will observe the position of the corneal reflexes and that is what is called as the hershberg's corneal reflex and the third is the cover test now I don't want to make this video too heavy to understand and therefore the cover test will be included in a separate video first is You observe the patient's appearance as the patient comes to you or walks in the clinic there are certain Clues which will tell you that this person actually has squint now many a times obviously the patient will have very obvious tropias right so there will be a deviation there will be an exhibition or an ISO deviation the eye is up that is hyper or hypoderiation but sometimes the eyes will actually be orthotropic but still there will be complaints and such patients you can actually pick up uh to have business based on their appearance now the first thing that you're going to pick up in their appearance is the position of the head right and this is also called abnormal head posture or an abnormal head position now again here I will not go into the details of the ahp because that is again a very detailed topic but basically what you need to know is that we have three types of abnormal head posture we can either have chin up or chin down we can have face turn or head turn towards right or left or we can have a head built towards right or left okay so it's a symmetry of the face is usually very common you know in a congenital head example header which is associated with the vertical muscle pulses like the oblique muscle policies what you need to know at this level is that whenever a patient comes to you with chin up or chin down position it is basically the problems with your vertical movements okay that means elevation and depression now however if the person comes to you with some sort of face turns that that is the horizontal turns towards right or towards left it means that there's a problem with the horizontal movements and what are the horizontal movements horizontal movements are abduction and adduction if the patient has a tilting of the head towards the right or the left it means that it is the cyclotations that means some sort of your obliques which are associated with the cyclovertical movements you know those are basically affected example the head till that you see in Superior optic policy it is very very common this example in this child you can see that there's actually a head tilt towards the right side another thing that you should notice in your uh appearance is the presence of any sort of craniofacial abnormalities right so usually the patients who have some sort of craniosynostosis or craniofacial abnormalities they usually have anomalous position of the orbit and anomalous position of the globe that loss that will usually lead to strabismus right and here uh example that I would like to give you is that of the cruise on syndrome the one more thing they should see in the appearance is the eyelid shape and position many a Time the patients will have ptosis and you should know that ptosis is actually associated with lots of strabismus and sometimes ptosis might actually lead to pseudostropismus also okay that's again a topic of discussion for another video then again you should look at the Earth symmetry or abnormality of the palpable fissures which is quite characteristic of certain Okla motor disorders right okay so for example in this picture you can see the first picture in this or the center picture you can see that the patient seems to be looking straight forward however when you ask the patient to look towards the right side what do You observe You observe the palpable fissure height here okay this uh this palpable fissure and this palpable fissure so compare this this seems to be much narrowed down right and this position is called adduction so whenever you're seeing narrowing of the parable fissure in adduction that is quite a giveaway for your duan's attraction syndrome so now another fourth feature that you're going to see in patients you know in a pain patient's appearance in order to detect you know squint is sometimes these prominent ice that you see in graves orbitalopathy because we all know that orbital pithy or Gray's orbitalopathy is usually associated with the pro problems in the media rectus and in the inferior rectus right now because of that usually these patients will have esotropia and hypertropia esotropia is inward deviation and hypertrophia is downward deviation right so you should never miss such a such important changes in the patient's appearance because they often give you the clue towards the etiology of the squid now let us come to the proper topic of discussion that is the hershberg's corneal reflex test okay so what is this hershber's corneal reflex test in hershber's corneal reflex test basically we use a spotlight or a Torchlight and the distance between the torch and the patient is going to be about 33 centimeters the start is going to be shown on the patient's glabella and now the corner reflections of the starch will be observed with both the eyes open now we will see that if the patient actually has these reflexes falling right at the center of the pupil in both the eyes it means that the patient is actually orthotrophic now in this case the patient might also be having some sort of Fourier that you'll only know after you do your cover test but for the purpose of Simplicity we will say that the patient is orthotropic on hershberg's corneal reflex test that means there's no squint there's no manifest squint present at this point now if there was some manifest or apparent squint present in the patient example in this first picture as you can see the eye seems to be slightly deviated towards the nose in the right eye so this is what is called as ESO deviation here if you actually observe the corneal reflex if you see the coral reflex is slightly towards the temporal part of the pupil and not in the center so what do we observe we observe that the reflex is slightly shifted temporarily okay so in ESO deviation the reflex is shifted temporally now what about exor deviation in exodaviation the eyeball is shifted temporarily that is towards outside and what about the reflex the reflex is more on the inside that is nasally right so in exodaviation the reflex is shifted nasally now what about the vertical deviations in the first thing that you can see here is that the eyeball is rotated downwards or deviated downward now as the eyeball is divided downward The Reflex will be deviated towards the upper part of the pupil so in hypoderiation that is a deviation of the eye down eyeball downwards the reflex is shifted upwards in the pupils and totally opposite will happen in case of hyper deviation that is the deviation of the eyeball upwards in which the reflex is towards the downside of the pupil so I hope that is clear now the hershberg's corneal reflects is basically based on the concept of angle Kappa the angle Kappa is basically an angle which is formed between the pupillary axis and the visual axis now what is your pupillary axis the pupillary axis is an axis which passes through the center of the pupil and to the nodal point and then into the center of the posterior Pole or your fundus whereas the visual axis basically passes from the fixation point that is the point where you try what you are trying to look at right and the image is formed at the phobia so a line which is going to join your fixation point and the phobia is called the visual axis and the angle which is formed between the pupillary axis and the visual axis is called the angle Kappa now if you want to know more about angle Kappa and regarding the Angles and axes of the eye we have a video on the channel named as anglicapa now as I told you that this angle Kappa basically determines your hershberg's corneal reflex test and similarly you can also determine your angle Kappa based on the reflex now if it is centered right at the center of the pupil if your reflex is centered at the pupil the angle copper is said to be zero so that's a very hypothetical condition where your pupillary axis and your visual axis are supposed to coincide however that does not happen because we know that the phobia is definitely present temporally and not at the center of the posterior Pole right so that I will explain to you in a while but for now what I want you to focus here is that whenever the reflection is formed towards the nose that means on the nasal side of the pupil the angle Kappa is said to be positive and wherever the reflex is formed on the outside of the pupil that means of the temporal aspect the angle copper now becomes negative so this is a very important point to remember that the angle Kappa is positive towards the nose so that's the mnemonic that you can remember now so what I what was I telling you is that the pupillary axis and the visual axis if they were actually to coincide perfectly with each other you will actually have no angle Kappa right the angle Kappa will virtually become zero and at that time a perfect uh Cornell reflection will form right at the center of both the pupils however is that possible no it's not possible because your phobia is present slightly temporal to the posterior pole it's not present right at the center of the posterior pole it's present temporally right so if this is the location of the phobia so definitely there will be a difference between pupillary axis and the visual axis and definitely there will be an angle Kappa and if you can see over here that if this is your visual axis between the fixation point and the four wheel you can see that the visual axis is coming out from the nasal aspect of your cornea right so definitely where should be your corneal reflex form the corner reflex also will form slightly at the nasal aspect from the center of the pupil right and that angle will be your sorry and that angle will be your angle Kappa right so physiologically or normally in every patient basically you will have a normal positive angle Kappa of around 3 degrees okay in any orthotropic or Amy Tropic eye so therefore when we say a person is normal actually speaking it does not mean that the reflexes are formed right at the center of the pupil it basically means that the reflexes are actually formed slightly nasal to the pupil and this could be about three degrees nasal to the pupil okay so what is normal normal is a positive angle Kappa of about 3 degrees anything more than three degrees will be your pathology and anything less than 3 degrees will also be pathological okay so I hope this point is clear till now now so what is meant by a larger angle Kappa or a larger positive angle Kappa now here what if your phobia was to shift even more temporal even more to a temporal position now before we had our phobia Here and Now suppose the phobia has shifted even more temporally that is say here now obviously your visual axis will also change the visual axis will come out of the cornea more nasally so as the visual ax is coming out more nicely so where will the reflex form the reflex will also shift more nicely now as the reflex is Shifting more nicely what did I tell you as a reflex shift towards the nose the angle copper becomes more positive right so the angle Kappa here has become more positive right so in this case and one more point that I want you to remember that I told you before is that in hershberg's corneal reflects test whenever the reflexes nasal it means that the person has exodaviation right so if you were to see such a patient who has more positive angle Kappa and you shine a torch on his glabella and you'll learn you actually try to focus on his reflexes what will you notice you will notice that it reflects the form more nicely and obviously you will think that the patient has actually exotropia however this exotropia is because of a larger positive angle Kappa and not because of the squint per se right so therefore this is called pseudostrabismus or pseudo exotopia and it is sudo because it is because of the positive angle Kappa right now this is usually seen in case of hypermetropes okay however there are multiple other conditions also in which the macula can be dragged more temporarily and those are called ectopic macular conditions now these conditions could be retinopathy or prematurity toxic retinitis congenital retinal poles as well now these conditions will cause ectopia of the macula and therefore can cause pseudo EXO tropia right so here what did we talk about we talked about an excessive or larger positive angle couple leading to exotropia pseudo exotropia now what if we were actually uh to move this phobia more inferiorly that means more towards the nasal Point okay so this is a normal phobia which is present temporarily now what if in certain conditions the fovea shifts to move towards the nasal site okay so what will happen to your visual axis now the visual axis will get shifted in such a way that the reflex which is formed now from the hershberg's corneal reflex test will now perform more temporally right and the angle Kappa will now decrease okay in its degrees and sometimes even become negative as shown over here right so if your phobia was present here there would be a visual access so visual access will be somewhat here and we know that the normal visual axis was here before so this was the initial angle Kappa say a and now because of the drifting of the phobia the next angle Kappa will be here say B obviously B is less than a right so as the phobia shifts downward what is happening the angle Kappa is decreasing right and sometimes if it crosses the center and reaches on the nasal side your angle copper has now shifted Above This Center and reached the temporal part of the cornea and that is called a negative angle copper right so now what will happen if you see a reflex on the temporal side you will feel that the eyes are shifted inwards that means the patient has esotropia right however you should know that this esotropia is not normal it is because of a negative angle Kappa and this is a pseudo esotropia right so a negative angle Kappa is usually very rare compared to a positive angle copper and it is seen in case of myopes so I hope that is clear now this is what I was talking about sodexitopia now here the first picture you can make out that the child actually seems to have an eye which is deviated outward right at the same time the pupil reflex also seems to be present more on the nasal side of the pupil compared to the center right so this will tell you that the patient actually has exotopia however if you put an occluder in front of this eye what is happening if this was normal exotropia if this was real lexotropia this I would actually take fixation and come in the center and the pupillary reflex also will come in the center but that does not happen in this condition this tells you that there's something wrong and maybe we are dealing with a you know very uh maybe we are dealing with a very large positive angle copper right so you go ahead and do a fundus examination and what do you find you find that the phobia which should happen somewhere here has actually been you know dragged more temporally in this condition right so this tells you that this is pseudo exotropia I when you are dealing with a large positive angled Kappa right this is seen in retinopathy or prematurity it can be seen in toxic or it could be seen in congenital retinal folds so all these folds will basically you know pull your phobia more temporally now this brings us to a very important clinical nugget now sometimes when you see an eye which is deviating and the reflex is also deviated either to the nasal side or the temporal side sometimes just by your hush pubs corneal reflex test and just by covering the eye which has a normal Central reflex you can get an idea of fixation you can get an idea whether the patient has a central fixation or the patient has an eccentric fixation if the patient has Central fixation in the eye which is deviated and Central fixation means that the image is formed at the phobia Okay then if you cover the eye which does not have squint or the eye which does not have deviation the deviated eye is going to move and come to the center okay however if you cover the normal eye and still the deviated eye does not come to the center it means that the image is not formed andophobia it means that the image is being formed somewhere eccentrically and the patient has eccentric fixation this is what we saw in this picture the eye was not moving towards the center even after occlusion of the left eye and therefore we said that the patient actually has a pseudo pseudo exotropia and not the true exotropia right so this eccentric fixation is however more common in esotropes now sometimes what will happen is the corneal deflection will be you know so mildly displaced example in very small angle strabismus that means sometimes the amount of strabismus will be as less as 10 prism diopters and even lesser than that so in those conditions you know with your naked eyes you'll not be able to pick up that there's any difference in the corneal reflexes and such sort of you know such sort of deviations are called microtropias why is it called micro it is called micro because the angle of strabismus is very less less than 10 prism diopters now at this point we have learned how to detect the presence of squint right now the question is can we actually you know get an estimate of the squint using your hershberg's corneal reflex test the answer is yes we can for every one millimeter displacement of the light reflects from the center it is equal to about seven degrees of squint on a globe and that'll be equal to 15 prism diopters so here what you should know is one degree is actually equal to two prism diopters roughly right so your seven degrees will come to about 15 prism they operate this 2 is approximate uh value right now another uh approximate way to assess the squint uh estimate the amount of squint which is present is uh was given basically by one Moodle so one wouldn't said that whenever it is present in the center it is called normal right and to be more specific it's not exactly in sentence slightly nasal three degrees nasal right now if the reflex is present at the margin of your pupil okay the amount of deviation is about 15 degrees right now it could be ET or it could be x t that means it could be isotropia it could be exotropia based on whether your reflex is present on the temporal edge of the pupil or on the nasal edge of the pupil if it is present on the temporal Edge it means that the eye is deviated inwards as in this condition and therefore we have written e t that is esotropia right now moving ahead so if the reflex is now present say not on the edge but in between the edge of the pupil and in between the limbus then the amount of deviation is almost 30 degrees right now if it is present at the limbus it is 45 degrees and if it is present beyond beyond the limbus then the amount of deviation is more than 45 degree so remember these three magical numbers given by vulnerable where 15 degrees is at the edge of the pupil 30 degrees is between the edge and the limbus 45 is at the limbus and Beyond the limbus is more than 45 degrees so that was about the hirschbox corneal reflects in particular I hope you found it useful that's all for today thank you and have a nice day