[Music] hello and welcome to Insight Opthalmology this is Dr Amrit welcoming you to another lecture today we are studying amopa also called the lazy eye so without any delay let's get started so what is meant by amblyopia amblyopia literally means means dullness of vision and that is the reason commonly it is called The Lazy ey also now W graphy is said to have defined amblyopia as a condition in which the Observer that is the doctor will see nothing wrong with the patient but the patient will see very little so it can prove to be a very confusing diagnosis or very difficult to diagnose am lopia so how do you define amblyopia amblyopia is actually defined as decrease in the visual Equity of one eye when caused by abnormal binocular interaction okay so it can occur in one eye or both High also as a result of pattern Vision deprivation during the visual immaturity so what I mean to say over here is that as the common uh belief goes that amblyopia is usually unilateral that means it it affects only single eye however what I mean to say here is that amblyopia can affect both eyes also in certain conditions that means we can have bilateral amblyopia also so the lazy eye need not be always one single eye the lazy eyes could be even two eyes even both the eyes could be lazy or both the eyes could be Amic okay yeah and one third point in the definition of amopa is usually there will no cause that can be detected during the physical examination of the eye and here by no cause I mean to say that there will be no pathology in the retina of the patient okay the layer which is present in the back of the eye so there will usually be no abnormality in the retina of the patient and amblyopia in appropriate cases is reversible by therapeutic measures up to a certain age and that age is called the critical period of amblyopia so what is the clinical definition of the amblyopia according to doctors clinically for diagnosis amopa is defined as difference of two or more lines on the snellen's visual Equity chart in case of unilateral amop or in case of bilateral anopia the visual equity in both eyes should be of 612 or Worse okay so what I mean to say is we already know that we have this snellin chart like this okay so in this snellin chart if there is a difference of two or more lines okay so we know top one top one is 6X 60 and then we have 6X 36 6X 24 6x8 okay so on and so forth and if one I is reading 6X 60 and the other I is reading say 6X 24 there's a difference of about two lines 6x8 sorry so there's difference of about two lines so two or more lines difference okay between two eyes in case of unilateral anopia or if both the eyes are not able to read better than 612 okay or is it worse than 612 then it is called bilateral amblyopia so this is the commonly used diagnostic criteria for amblyopia now uh this uh criteria is actually not very short short it varies from the doctor to doctor and from various Publications also but this is the one that we use so uh amopa can also be classified based upon the sity of the visual Equity so in that mild amopa is defined as 6X 9 to 6x2 okay and moderate anopia is 612 to 624 so what I mean to say is the person is not able to improve Beyond 6x9 visual Equity or 6x12 visual equity and in moderate mopia is not improving Beyond 612 or 624 and severe amopa the vision is less than 6X 24 and it is not improving further so I hope at this point it is very clear to you what is meant by unilateral lopia and what is bilateral lopia and what exactly is the definition of amblyopia so amblyopia as such is a visual equity which does not improve right because of some uh abnormality during the visual immaturity period or of life that is from birth to approximately 7 to 8 years of life so usually what happens is both the eyes have to interact together and then the visual pathway will mature in the brain and this occurs up to 6 7 to 8 years of age and if there is any problem in this uh period of visual maturity then we develop some condition which is called amopa okay and usually the doctor will not be able to see any abnormality in the retina of the patient and this condition of amblyopia if detected early is actually reversible by certain therapeutic measures next I will explain to you what is meant by the critical period of visual development okay so the critical period of visual development is from birth to about 7 to 8 years of age why is it called critical it is called critical because our visual pathway will develop during this time so on my video on pupilary reflexes and Light refle flexes and visual pathway I have told you that the visual pathway consist of the retina of both eyes which are going into the optic nerve and then we have the optic chayms then we have optic tracts okay so these optic tracts are finally reaching uh your uh brain in the brain we have the visual cortex which is located in the oxy put of the brain okay so in the occipital low so this entire thing is the visual pathway right and these neurons are uh the optic nerve and the various neurons which are present in this visual pathway they're reaching the occipital cortex and they undergoing a process of maturation okay and all this is occurring from birth to about 7 to 8 years of age during this time if there is any abnormality that happens in the vision okay because the visual development starts right from the level of the eye and then it goes behind towards the brain if there's any problem that happens during this age group then this visual path will not develop in that particular side of the brain and that will cause amblyopia so that is the reason why this 7 to 8 years up to 7 to 8 years of age is actually called the critical period of visual development so how do you actually suspect amblyopia so in small kids uh usually amopa can occur in children and even in young adults and it's a leading cause of visual impairment and how do you actually suspect amblyopia is so usually there will be visual equity which is decreased and which is not improving as I already told you in the clinical definition of amop and uh when coming to small children there will be decreased contrast sensitivity so as we all know that contrast sensitivity uh is the ability to differentiate different patterns basically so that will be reduced in small kids okay and uh there will be poor hand ey coordination hand ey coordination is how well the child is responding and going and reaching the toys especially if you talk about Toddlers and all so that is called looking at an object and reaching for it and that is called hand eye coordination which occurs if both the eyes are functioning properly however in amblyopia or lazy eyes since one eye is not functioning properly the child will be using only one single eye and because of that his binocularity that means the proper usage of two eyes would be affected and he will have poor hand eye coordination so he might he or she might not be able to reach the objects very well they might be actually under reaching or overreaching the target object then there will be a difficulty in the depth perception so this depth perception the ability to talk about the uh depth that is a height of an object also comes from using the two eyes together properly as you can see in uh in this picture the child might not be able to assess that the uh the time might not be able to tell that the table is actually ending here or uh so such kids might have frequent history of Falls because they're not able to actually make out the depth very well so that is called depth perception now children with amblyopia usually will suffer with a blurred vision or from the lazy eye and because of that blood Vision coming from this eye they prefer to actually close this eye so they will often give history of closing one eye and uh sometimes they might even rub that eye uh rub the lazy eye to suppress that image which is coming from the lazy eye which is often not very clear then uh sometimes they will have this history of squinting because we know that Squints are usually associated with amblyopia and some of them might even show a certain sort of head tilting uh pattern also okay so that is how you suspect amop in kids so coming to the classification of amopa and this classification I'm going to tell you based upon the ethology of the amopa that is what causes the amblyopia So based on the iology of amblyopia amopa can be classified into strabismic amblyopia refractive amblyopia visual deprivation amblyopia also called the sensory deprivation amblyopia organic amblyopia reverse amblyopia and idiopathic am lopia so let me explain to you in detail what is meant by each of these am mopas number one is the strabismic amblyopia strabismic amblyopia occurs when the patient has stabismus which is nothing but squint in the uh General sense it is called squint squint is nothing but normally the eyes are looking straight okay so that's a normal um position of the eyes however whenever the eyes will have abnormal positioning like in esotropia the eye will look inwards in exotropia the ey is looking outward in hypertropia the eye is upwards and in hypotropia the eye is downwards now what happens is that in a normal POS in a normal eye when the eyes are looking straight forward in both the retinas the image will be actually formed onto the phobia of the patient okay onto the phobia of the patient okay in both the eyes and therefore both the eyes will have equally cleared uh image in the brain however in e exotropia exotropia hypertropia or hypotropia when the position of the eye is changed the phobia that means uh the phobia will not receive the image and some other point on the retina is going to receive the uh image that the patient is seeing and the other eye which is normalized going to focus on the fobia now as we know that the fobia is the point where we have the Maxum visual equity and any other point of the retina if stimulated by the object will form a less uh clear image okay so the eye which is strabismic or the eye which is squinting will always form a blurred image in the brain and the child will actually prefer to suppress this blurred image to avoid confusion and use only the better eye resulting in lazy eye or amopa in the squinting eye okay so this is the principle behind the strabismic alopias and moreover it is the most common type of amblyopia it occurs when the child favors one eye for fixation and I told you why do they favor that normal eye for fixation and it usually occurs when the patient has unilateral amblyopia rather than the um alternating fixation patterns so what is meant by this alternating fixation patterns now sometimes in few people what happens is that this alternating fixation pattern is usually common in exotropia so either of the eyes will go outward so sometimes it's a left eye which is looking outward and sometime it's a right eye which is looking outward so there is an alternation of the squint between two eyes and in such a case what happens is that both the eyes are abnormal and the child will not develop uh any favism for any particular eye since both of them are equally abnormal so in such conditions development of amop is rare however if the patient has constant am constant squint in one eye then there will be a strong favism towards the normal eye and the patient will have amopa in the squinting eye now another point which is important is that strabismic amblyopia is more common in esotropia that means in the inward deviation of the eye compared to the outward deviation of the eye now why do esotropia has more amblyopia so what I mean to say is this child over here he is looking nicely okay right so this child who is having esotropia because of the inward deviation is going to be more amop compared to this child who is having exotropia he might or might not have amblyopia and the reason is that in esotropia the phobia of the deviating eye has to compete with the strong temporal hemifield that is nasal retina of the fellow eye so what I mean to say is as the child is actually deviating inward this child is going to see the image over here that means towards the other eye that is towards the temporal side of this eye and as we know that the temporal Hemi field is represented onto the nasal retina so if you consider this to be the right eye and the left eye now the left eye nasal hemifield as we know is uh the nasal retina or the temporal hemifield as we know is more stronger that means the right eye is now competing with the left eye nasal retina and obviously this left eye nasal retina is more stronger and therefore this right eye is actually going to lose and it is going to be suppressed and therefore in esotropia we have more mopia however in exotropia what happens is that the exotropia the eyes looking outwards and it is looking towards the temporal field of its own and the nasil this that temporal Hemi field of this left eye is going to correspond to the nasal Hemi field of the right eye which is focusing on the temporal retina of the right eye and now we know that the temporal retina is not as strong as the nasal retina uh because the temporal hemifield is stronger and the nasal retina is stronger and therefore which eye is going to win the left eye is going to win and the right eye is going to lose and therefore what happens is that in exotropia amblyopia and suppression is not that common and that is what I mean to say by in exotropia the phobia competes with the weaker counter lateral nasal hemifield or the temporal retina so let us see that in a little bit more details I'll try to uh explain it to you so what happens is that that if this is the normal eyeballs which are looking straight ahead and this is the forway uh this is an object of attention and here we have the two foras so both the uh eyes are actually projecting this object onto to the fobia and since they're looking straight now what happens in esotropia is that the eye is going to move inwards like this so this is a normal eye and this eye is now looking here so this eye is now looking at an object object here because of its inward deviation and the same object is now going to project where onto the nasal retina of the normal eye and what do we know the nasal retina of the normal eye is more stronger and since it is more stronger what will happen the this eye will win and this eye will be suppressed now because the eye which is squinting which is esotropic or inward deviating is squinting we are going to have amblyopia okay in esotropia however what happens in exotropia in exotropia the eye is actually looking outwards and the normaliz is looking straight ahead now what happens it is looking towards its same side and projecting the image onto the nasal retina of its side right so nasal retina we know is stronger whereas the other eye has look toward the same field of the squinting eye where will it project the image the image will be projected on its temporal retina right now which retina is stronger it's a nasal retina which is stronger so as a nasal retina is stronger this eye will win and suppression chances of this EXO I will be much less and therefore in exod deviation we will not have that much of amopa compared to the eso deviation so at this point I will uh uh tell you the reference this is from the textbook of Von Nan and this is the explanation that that is given in the textbook and I have taken the explanation from there as to why amopa is more common in ESO deviation compared to the exod deviation next let us talk about the refractive am lopia so till now we have talked about the strabismic amblyopia now we are going to talk about the refractive amblyopia that means amblyopia occurring secondary to the refractive errors so there are three types an Isom metropic ISO Tropic and meridional amblyopia so what is meant by anisometropic amblyopia anisometropic amopa means that two eyes have dissimilar refractive errors so when the two eyes are having similar Powers the image that is formed is equal in both the eyes however when there is refractive error which is present and one eye has different Power compared to the other eye the image size will be different in both the eyes and whenever there's a difference in the sizes of the image whenever there's a difference in the uh what do you say the clarity of the image then we know what happens the brain will suppress the one image which is not good for it the one image which is not clear enough the one image which is defocused and that will lead to am Opia so such a dissimilar refractive error condition is called an Isom metropia and that will lead to anisometropic amopa so how how much difference do you need in a case of hyperopia in case of hyperopia which is also called the long-sightedness the difference between the two eyes should be 1.5 diopters in case of myopia the difference should be more than three diopters what I mean to say is if one eye has a error of about say three diopters minus three diopters and the other eye has a power of about say - 6.5 de Ops what is the difference between the two the difference is about 3.5 de Ops and this is amenic okay so the ey which is having minus 6.5 de opas will develop amblyopia coming to aniso astigmatism that means when the astigmatic error in both eyes and the difference between them is more than two that will lead to amblyopia and that is amop genic so all these readings are according to the American academic of oftalmology okay so all of them are reliable coming to the second type of refractive amblyopia it is ISO ametropic amblyopia in ISO ametropic amblyopia it is mean it means that there is a bilateral decrease in the visual Equity so in anisometropic I told you that the reflective error in both the eyes were actually different but in ISO ametropic amblyopia both the eyes have equal refractive error but this refractive error is large okay it is equal large and uncorrected refractive error in the two eyes Okay so these three things are important large refractive error equal in size in both the eyes and uncorrected okay and since it occurs in both the eyes it's also called bilateral emit Tropic mopia so for myopia the uh cut off is 5 to six diopters and for hyperopia it is 4 to five diopters so if the patient has plus4 or plus4 in both the eyes they can have this Isom metropic amblyopia and if the myopia it is + 5 + 5 or more than + 5 + 5 to be exact they can have an Isom metropic ISO ametropic amblyopia and the reason is that they will have this blurred image in both the eyes projecting to the brain okay and the Brain will actually uh the neurons uh also will not develop subsequently because of that chronic blurred image and the Brain will get adjusted to that blurred image for a long period of time and that leads to isotropic amblyopia similar to the iso ametropic amblyopia when it occurs in a particular axis because of a particular astigmatism in a particular axis that is called meridional amopa since it occurs only in one particular Meridian that means a patient is going to develop amopa only in one single Meridian this is called meridional am lopia okay so it results from uncorrected bilateral astigmatism in early childhood leading to loss of resolving ability limited to the chronically blurred Meridian okay so here how much cylinder do you need more than two to three de opter of astigmatism in one axis will lead to meridional mopia and this should be present in both the eyes the third type of amop which is also a rare type of mopia but very easy to detect is the visual deprivation amblyopia it is also called amblyopia X anopsia the reason it is called this x anopsia is because the visual visual is the vision is actually deprived or the sensory stimulation is actually deprived in this kits so as we know that the uh visual axis for an image to be formed the light should pass through the cornea to the pupil to the lens Vitus humor to the vitus and finally reach our phobia on the retina if there is any abnormality on the uh on this visual axis it will interfere with the passage of light will interfere the perception the vision the sensory stimulation of the retina and therefore will cause visual deprivation mopia okay so this can happen if there's a problem in the lids eyelids so if the eyelids are closed chronically for a long time if there's an opacity on the cornea if there's a problem in the iris itself the IR if there's problem in the pupil if the lens is cataractous if there's blood in the vitus all these things can lead to am Opia due to visual deprivation so the common causes are congenital or early acquired cataract as you can see in this image okay blos spasm surgically sometimes the the patient lid will be closed okay unilateral complete tosis osis of this type can also lead to amblyopia opacity in the cornea because often that's the first medium through which the light passes Hemorrhage in the vitus because that will also prevent the light from reaching the phobia and will lead to the mopia after these three major types of amblyopia we have organic amblyopia often a very confusing uh topic for everyone what is meant by organic amblyopia so in organic amblyopia first three things that you should remember is we do not have uh any squint okay so it is not strabismic amblyopia we do not have any refractive error problem so it is not your refractive amblyopia third we do not have anything obstructing the visual axis so we do not have cataracts or anything like cornal opacities okay so it is not even your visual deprivation or sensory deprivation amblyopia so what is this organic amopa organic amblyopia happens when there is absence of any gross readily detectable anomalies in an eye with very subtle subop thalos scopic morphological retinal damage so there is some retinal damage but that retinal damage you cannot see with the normal opthalmoscope examination okay that's why it is called sub opthalmoscope morphological retinal damage so retinal is essentially normal on the examination uh but when you do certain other Advanced examinations like the electrophysiological test whether it is an ERG or a we in those cases we realize that okay fine there was some damage in the retina according to the results of these test but as such we do not have any very obvious retinal damage that we can detect by doing our fundoscopy or by doing any kind of opthalmoscope or uh test that's why it is called called sub opthalmoscope morphology and this is called this is known as the organic amopa then we have another entity which is called the reverse amblyopia so reverse amblyopia is a form of visual deprivation amopa only which occurs in the fellow eye as a result of patching so initially this eye was amblyopic but when we uh patch the other eye as we know that patching is a very common uh treatment given for amopa so when we patch the normal eye the normal eye after some time because of the visual deprivation for long periods of time can develop amopa and this is called reverse amblyopia since it's happening in the other eye which was previously normal then there's another amblyopia which is called idiopathic amblyopia for which the cause is unknown so apparently the patients will be normal they will have they will not have any history of stabismus there's no refractive errors there's no visual deprivation moreover there is no sub of thalos scopic abnormality in the retina that means there's it's not even organic amblyopia okay so organic amblyopia and idiopathic amblyopia they are both different so according to ju Nan he said that this happens uh because during infancy there might be some am amenic Factor like an anisometropia but that anisometropia was transient it got corrected but after that time also the uh inhibition that resulted because of this anisometropia actually assisted even though the original obstacle to the bobal fusion was no longer evident so if during that particular time we would have tested patient we would have gotten some uh cause for the amblyopia but that cause got resolved however amblyopia persist in such patients and when the patient comes to us we do not find any cause so that is called as the idiopathic amopa so I hope that was very clear to you and this was about the basics of mopia if you have any doubt you can post in the section and uh thank you for watching have a nice day [Music]