hello and welcome to Insight of thermology I am Dr Amrit welcoming you to another lecture in refraction today we are going to discuss about the variable tests of accommodation and in this video we shall be focusing on the range of accommodation and the amplitude of accommodation and how do we measure them before we start you should know what exactly is accommodation it's a process by which ouri adjusts its Optical power to maintain a clear focus on objects Presence at a near distance dist this is achieved basically by contraction of the celery muscle which causes relaxation of the celery zal and therefore the lens can now assume a more globular shape increasing the power of the eye this entire thing is known as accommodation if you're interested in knowing what is accommodation it's highly recommended you visit this video title what is accommodation and the link to this video will be provided in the description box before we start we have to understand certain important terms so these terms are the near point and the Far Point first of all let us discuss what exactly is meant by far point also known as punctum rotum so basically the farthest distance at which the small objects can be seen clearly is known as the Far Point of the eye or punctum rotum now this is going to vary with the static refraction of the eye I'll talk about that in a while then we have what is known as a near point also known as the punctum proximum and this is the closest distance at which the small objects can be seen clearly and this near point will basically um uh vary with age and this near Point basically recedes as we AG all right now so I was talking about the refractive status of the eye so in a normal eye or an emit Tropic eye the Far Point is present at infinity and the near point will basically uh be variable able usually the near point is at about 33 cm or 40 cm or at the Harmon's distance so I'll talk about Harmon's distance right now in case of hypermetropic eye which is also known as farsightedness here the Far Point is actually virtual and it lies Bas sorry it it's virtual and it lies behind the retina the ne point however varies with age again in myopic eye the power of the eye is more and therefore the race gets converged more and there therefore the Far Point is real and it lies in front of the retina whereas the near Point can again be different based on the degree of myopia for example if the patient is highly myopic it is seen that the near point is present more closer to the eye compared to an ametropic eye all right so let us discuss about these variable tests which are available for accommodation so we have total six things to measure when we talk about accommodation these are number one we have the range of accommodation the amplitude of accommodation the accommodative response accommodative facility relative accommodation in which we have positive relative accommodation and negative relative accommodation then we have the lead and lag of accommodation the lead and lag basically are a subcomponent of accommodative response so first of all let us talk about the range of accommodation now I hope you understood what exactly is near point and what exactly is Far Point okay so if the near point and Far Point is known we can clear we can very easily calculate the range of accommodation right the difference between the near point and the Far Point will basically give you what is known as the range of accommodation then we have what is known as the amplitude of accommodation now the range is just a simple uh difference between the near point and the Far Point in centim however if the difference is calculated in terms of the dioptric power or the difference in dioptric power which is needed to focus at a near point and at the Far Point that difference in diopters is known as the amplitude of accommodation so it's given by the formula amplitude a so amplitude of accommodation can be abbreviated as a A or it can also be abbreviated as a a AO okay amplitude a o a amplitude of accommodation right so it's given by the formula P that is the dioptric power needed to focus at the near Point minus the dioptric power needed to focus at the Far Point okay so the range is just the difference whereas the amplitude of accommodation is the difference in dioptric power let us take an example suppose this is a patient data given to you the near point for the patient is about at it is at about 25 cm now in meters it will be 0.25 M the Far Point of the patient is at around 50 cm so in met it will be 0.5 M we know 1 m is equal to 100 cm okay now how do we calculate the range of accommodation and the amplitude of accommodation in this case what did I tell you the range of accommodation is just the difference so you take the near point and the Far Point and you subtract the near point from the far point so 50 cm minus 25 cm gives you 25 cm okay so this is the range of Clear Vision for the patient so between this range of 25 cm the patient would be able to see clearly that is known as the range of accommodation now if you convert this 50 cm and 25 cm in terms of diopters and we know that power is equal to 1 / by distance or focal length in meters right and that is the reason why we can converted 25 cm and 50 cm in me right so 1 / 0.25 is four diopters that is the near Point power and the Far Point power is 1 / 0.5 that is two de opter so the amplitude now will be 4 de opter minus two diopters so that gives you two diopters so the amplitude of accommodation in this case would be about two diopters all right so this is how you calculate the amplitude of accommodation all right so once you have calculated the amplitude of accommodation how do you really know whether it is normal for the patient's age right and that can be uh estimated using the Hof formula so according to this Hof formula the maximum amplitude of accommodation is given by this formula 25- 0.4 into age of the patient minimum is 15us 0.25 into age and average is 18. 5 - 0.3 into AG let's take an example suppose the age of the patient is 40 years so you're going to put 40 in all these formulas and then you can calculate the accommodation the maximum acceptable amplitude of accommodation for this patient will be nine diopters the least would be five diopters and average for uh this patient would be 6.5 de opter so what does it mean it means that anyone who is 40 years of age should have have an average amplitude of accommodation of about 6.5 if not this at least five doops so if you have a patient and you calculate the amplitude of accommodation and it comes around say three diopters you know that it is definitely less than the minimum amplitude of uh accommodation acceptable for that age and therefore this patient is suffering from accommodative insufficiency okay so that is the purpose of calculation of accommodative amplitude all right now the amplitude of accommodation can also be given uh by this daers table so you can go through this table however uh otherwise you can just remember these formulas H status formulas and calculate it and H status formulas are more precise uh they give more precise amplitude of accommodation so now let us see how what exactly are the methods uh that we use for calculating the amplitude of accommodation so there are basically four methods that we use three are subjective tests and one is an objective test okay the subjective test means that it is going to rely on the patient's response whereas objective test basically relies on us okay so we can U look at the result and we can estimate the result on our own so that is what is meant by objective test right so the first three tests which are subjective are the pushup method pull away method and the minus lens method and the OB objective one is the dynamic retinoscopy now all of these tests are usually going to be done at a comfortable near distance for the patient or the reading distance now this distance could be 33 cm or it could be 40 cm however there's another distance known as Harmon's distance now 40 cm is for adults but what about kids what about pediatric population so there we cannot generalize 40 cm as a near point for everyone right so the com aable near distance near point or reading distance can be calculated using this Harmon distance Harmon distance is nothing but it is the distance between a distance calculated from the elbow to the middle knuckle of the patient okay okay now before we go on and understand all these methods it is very important for us to understand the RAF rule because three of these methods are actually going to use this instrument for the calculation of the near point of Ecom ation all right so the RAF rule basically here RAF stands for Royal Air Force and as you can see it consists of this graduated scale which is marked in centim or diopters and it is mounted on a steel rod and on top of that so basically the length of this is about 50 cm long on top of that you can see this Cube okay and this is known as a sliding Target because you can move it up and down on this uh graduated scale or the metal rod of the royal Air Force rule apart from that over here this what you see is known as the wing like support this is going to fit over the nose of the patient and these parts are going to rest on the lower orbital margins of the patient okay now this instrument the RAF rule is can actually be used to calculate both the near point of convergence and the near point of accommodation all right so let's go a little bit into more details so the the sliding Target actually has these rotatable drums so you can see different targets are available so on one side we have the reduced nellons chart and then on another surface we are going to have a section of General post office telephone directory so you just have these um names here and the telephone numbers and then on one face we are going to have this times Roman type face and those um N5 N8 n 10 and N2 letters and finally we have a DOT on a single line now the first three ones are basically used to calculate the near point of accommodation in accommodation we want the patient to see to read something and to clear these things you know so when you tell the patient to look at these targets you have to make sure that the patient is able to read all these things because only when the patient is able to read it you can be assured of the fact that the patient is using e accommodation that is the reason why the first three of the target drums will be used to calculate the near point of accommodation however the dot on a line will be used to calculate basically the near point of convergence and that is not something that we are going to talk today all right okay so when we're talking about this just a second yeah when talking about this metal rod this also has about four surfaces so on each surface so basically you take that RF Rule and you rotate the metal rod and you you will basically find different markings on one side you will find a CM scale with about 2 cm increments on the other side you will find an equivalent dioptric power scale okay and on the out of the surface you will find the expected age scale according to that uh distance or dioptric power and on the other side you will find something indicating the convergence whether it is normal or abnormal convergence okay so this was about the RAF scale now all these tests that we are going to discuss you can measure the amplitude of accommodation monocularly and also binocularly the whole idea of doing it in this way is that when you are calculating the amplitude monocularly you are just calcul you are basically purely calculating the accommodative ability of the eye okay and this will reflect the maximum dioptric power of accommodation without any interference from the convergence now you should know that meosis convergence and accommodation they basically form a part of the near reflex so when you look at a near object the when accommodation kicks in usually the convergence will also kicks in Kick in and also the construction of pupil okay so to prevent the convergence from coming in we basically check only uh we basically check amplitude of accommodation monocularly so whenever you are testing monocularly you are going to measure only the pure accommodative ability of the eye however when we are testing binocularly convergence is also going to kick in and because of that convergence also there will be some amount of accommodation so the amplitude that you're going to get would actually be contaminated because of the convergence however this gives you a more real life scenario here because in real life the patient is going to see binocularly so therefore typically also when you measure amplitude of accommodation via a binocular testing the amplitudes will be 0.20 to 0.60 deop higher than the monocular measurement and why is that so because these amplitudes are also coming from convergence all right so I hope you understood what exactly is monocular and binocular testing now let us start discussing all these tests one by one the first one that we are going to discuss is the push-up test okay so let let me just briefly tell you what these tests are so we are going to use the RAF rule in the first three so push-up means you are going to take a target the target is going to be the rotating drum of your RAF rule if you're going to put push that Target towards the patient that is called a push up test if you're going to move the target away from the patient that is called a pull away test and if you're going to keep the target stationary and instead put some lenses that is known as the minus lens and if you're going to observe the accommodative response during near fixation that is called Dynamic retinoscopy all right so we'll discuss about this in detail first let's talk about the push-up test so here the patient is going to be seated comfortably now in all these tests make sure that patient is wearing uh his or her refractive correction it's very very important because what did I tell you the amplitude of accommodation is the difference between the dioptric power for Far Point and dioptric power for near point now when you correct the patient for the Far Point that means when the patient is wearing their correction whether the patient is myopic he's going to wear concave glasses and if the patient is hyperopic he will be wearing plus glasses right and even astigmatism so when such patients are corrected for their Far Point their Far Point now will be at Infinity so 1 divided by Infinity will become zero so in these cases and in these tests what we are going to do is we are just going to measure the near point of accommodation and based on that near point of accommodation we are going to calculate the amplitude of accommodation why because the Far Point is already Infinity because the patient is wearing his refractive correction so make sure that the patient wears their corrective uh refractive correction and use an ambient source of light now over here what you do is make sure the patient is sitting comfortably and you explain the patient the procedure and ensure there's proper lighting ensure that the patient is wearing correct distance uh distance correction now you use the Target on the RF Rule and this target is going to be slowly moved closer to the patient's eye along this graduated scale okay and this movement is at a rate of about 5 cm/ Second right now you ask the patient to constantly read the target you have to ask the patient to focus on the target and the patient will then tell you the first time it becomes blur and it remains blurry okay and that is known as the first sustained blur okay sustained blur means that not just the uh not just uh the first point when the target becomes blurry but also at this point the patient is not able to use his or her accommodation to clear that Target and that is known as the first sustained blur after that what are you going to to do is you will measure from the patient spectacle plane the distance from the patient spectacle plane to this Target and that will become your near point of accommodation right and this near point of accommodation you convert it basically in meters right so this is known as your push-up method as so here basically are moving the target up towards the patient it is called up because although it is a horizontal scale it is slightly placed in this oblique thing we we don't place this scale parallel to the ground right so the normal value of near point of accommodation at 10 years of age is about 7 at 40ers it's 25 and at 45 it's about 33 cm now after you have measured the near point of accommodation what you will do you can calculate the amplitude of accommodation what was what was the formula formula was 1 ided by nearpoint of accommodation minus 1 divided far point of accommodation since the Far Point of accommodation near will be Infinity so it doesn't matter we'll just use the near point of accommodation and we will uh find the reciprocal of it and that will give us the amplitude in diopter for example if the near Point comes at about 10 cm you convert it into meters that is 0.1 and the amplitude will be 10 de Ops so I hope that is clear okay now the next method is the pull away method now over here again the patient is going to be seated nicely you can do the test monocular L and binocularly okay you can do that so here you present the Target first directly in front of the patient's eye close to the spectacle plane obviously at this point it is going to be blurred for the patient and now you slowly move the target away from the eye until the patient can clearly identify the stimulus so here you don't ask for the blur here you ask for the point when it is clearly identified by the patient and how do you know it is clear you ask the patient to read those letters right now at this point you will measure the distance from the target to the spectacle planes in meter so here since the target is being moved down it is called a pull away method Target is being pulled away right and then you're going to Simply calculate the near point of accommodation and from that you can use the same formula and calculate the accommodative amplitude so that is your pull away method then the third method is the minus lens method now at this point again you can use the RAF rule or you can actually do it without RF rule also the thing over here is what you have to remember is and I think I've talked about this in my previous videos as well if you regularly follow inside of thermology you would be aware of that that minus lenses also known as the concave lenses they usually stimulate accommodation whereas the plus lenses or the convex lenses they relax accommodation now over here first you carry out refraction you find the best visual Equity at near and suppose the patient has 2020 or uh basically use a 2030 Target or if the patient has visual Equity less than that you're going to use two lines below the patient's best visual Equity right then you position the target at a distance of 40 cm from the patient spectacle plane or you can use the harman distance as well right next what you're going to do is you're going to start testing and in this case you are going to start stimulating the accommodation and how do you do that you basically start adding minus lenses in 0.25 de opter step so what does it mean it means that you're putting minus 0.25 first and asking the patient is if the target is clear if the patient says that fine it is clear it means that the patient was able to accommodate for this minus 0 25 doops okay now you test again you increase it by 0.25 and now you add minus 0.50 and if the patient is able to still see it clearly you increase It Again by a step of about 0.25 so this you keep on doing till the patient reports the point of first sustained blur where the target can no longer be made clear okay so what exactly do you uh how exactly do you calculate the ampl amplitude of accommodation from this now what did I tell you the testing distance over here is 40 cm and you should know that for 40 cm the amount of accommodation that would be required would be 1 divided by 40 40 cm but the cmet you have to converted into meters right so that will be 100 divided 40 and that comes to about 2.5 diopters right so for 40 cm working distance the patient needs 2.5 deop apart from that the patient was able to tolerate for example minus 5 de opter at 40 cm so the total amplitude or the maximum amplitude that the patient has is amplitude of accommodation right so over here the patient has 5 + 2.5 so the amplitude of accommodation in this case would be 7.5 diopters I hope that is clear now don't get confused this is not always 2.5 okay so if you're carrying out your measurement say at about 50 CM then what will you do then it will be 100 divided by 50 so you will be adding two dectors okay so use common sense be very sure with your uh Concepts and then understand and then apply all right so this is known as the minus lens method now one more point you should understand is the minus lens amplitude of accommodation would be about two diopters less than the push-up test accom of accommodation so basically what I want to tell you is that when you do a minus lens method of calculation of accommodative amplitude the value that you get would be two de opter usually two de opter less than the value you get using the push-up test now this basically is an advanced Concept in refraction that I'm going to try to explain it to you now if you enjoying our video and if this video is really adding any value into your life don't forget to subscribe if you haven't already subscribed and also make sure that you share this video with your friends okay that really makes a huge difference for our channel so why does that happen in push-up test basically the target is going to be moved so what exactly do we do in push-up test right we are moving the target towards the patient's eye right so as the target is physically moved closer to the eye the size of the retinal image is also going to increase as the target gets nearer right so a larger Al image size will make it quite easier for the patient to detect and focus on the Target and this will lead to overestimation of the amplitude of accommodation in contrast when we using the minus lens therapy we are not moving the target closer to the patient the target is fixed right and instead we using the lenses to stimulate the closer distance Without Really changing the actual Target distance so the retinal image size will remain constant and therefore it will actually test the patient's real ability of accommodation and this makes it harder for the the patient to focus and that is the reason why the accommodative amplitude will be slightly less compared to the push-up test so that was the retinal image size second thing is the depth of focus now the depth of focus is the range of focus at which the object is going to appear clearer without the change in Focus right so in push-up test uh it basically relies on the patient subjective Judgment of blur now due to this depth of focus Concept in the eye the patient might tolerate even a small amount of blood uh before reporting it leading to an again overestimation of the accommodation however in a minus lens method the lenses will provide a more controlled and a precise way to measure accommodation and therefore they minimize the influence of depth of focus again in push-up uh method what happens is that you're physically moving the Target now this gives a proximal Q which is which is basically simply an awareness of the target getting closer this awareness also stimulates accommodation and that is the reason why again in push-up test you going to find greater amplitude of accommodation compared to the U minus lens method because this is again going to lack that physical movement of the Target and therefore it's going to lack those proximal cues as well okay so retinal image size depth of focus and proximal cues these are something which are responsible for giving greater amplitude of accommodation measurements in the push-up and test all right okay so finally we have the objective test now now in subjective test we are basically relying on the patient's response now this might be right or the patient might be mingary now but what if you need an objective test on which you can maybe rely on your skills and not on patient response so then we have what is known as Dynamic retinoscopy now this is a really big topic but I'm just going to limit for the purpose of this video on how to calculate accommodative amplitude using Dynamic retinoscopy all right so Dynamic retinoscopy you should know what exactly a static accomodation or static retinoscopy in static retinoscopy we are basically trying to measure the Far Point of the patient and here the accommodation is static or inactive and how is the accommodation static the accommodation is static because the patient is basically made to focus at a distance object okay so remember in our video on retinoscopy I told you that you ask the patient to look at 6 M distance so you are making sure that accommodation is inactive and also you are giving the patient cycloplegic drugs so that is going to paralyze your selary muscle as well in Dynamic retinoscopy however we are making the patient look at a near object and we are stimulating the accommodation and we are actually studying the components of accommodation it could be amplitude it could be response of accommodation we'll talk about this in detail in our next video also so that is known as Dynamic retinoscopy so the objective here is to use a retinoscope and observe the movement of the reflex as the patient patient is focusing on a near Target all right so let me just revise briefly uh the principles of retinoscopy so if this is your retinoscope and this is the patient and let us consider this to be the focal point I'm not talking about a distance focal point or a near focal point I'm just talking about a focal point right so if your retinoscope is conjugate with the focal point of the retina so what I mean to say is if the retinoscope is present at the focal point you are going to get a neutral reflex if your anoscope is present beyond the no beyond the focal point that means the Rays have already converged and now they are diverging as they're reaching you you are going to get an against movement if the retinoscope is present in front of the focal point that means the rays are still converging as they are reaching you in your retinoscope you will get a WID movement all right so we will use those three uh principles and we are going to use these magnetic fixation cards so you can use these cards and you can stick them on your retinoscopy now there used in mem method also we'll talk about all those variety of retinoscopes that we talk about whether it is Bells retinoscopy knots retinoscopy book retinoscopy don't worry about that we'll talk about that in the next video when we talk about accommodative response it's going it's all going to make sense okay so stay with me so in this video let's talk how to calculate the accommodative amplitude using the dynamic retinoscopy very simple you use your retinoscope uh stick on the fixation Target on the retinoscope what I showed you over here okay now you put your retinoscope at a distance of say about 40 cm again don't forget make your patient wear their distance correction make sure that the room is uh dimly lit there's a dim light in the room okay because you're going to observe the reflects and now what you're going to do is you are going to carry out your vertical streak retinoscopy and as the patient is reading the target on your retinal scope you're going to observe the reflex now usually what will happen is the Target that you give is the normal near uh the distance that you're going to choose will be the normal near distance say about 40 cm 33 cm or the Harmon distance so at this point you are going to get the neutral reflex now what you do is you keep on moving the retinoscope which is also having that fixation Target closer to the patient so just like the pushup method or the uh just like the pushup method basically you're going to take the retinoscope along with the fixation Target so in the push-up method what were what were we doing we were moving the target closer to the patient's ey similarly here we'll also move the rectoscope with the fixation Target closer to the patient and how long are we going to do it we going to do it till the neutral motion is observed okay so suppose you move it for example let me tell you you move your target here you find a neutral Mo neutral motion again you move it closer you find a neutral motion again you move forward see at this point now the uh the neutral motion is no longer seen and you start seeing a change in the motion mostly you what you're going to find is a WID motion now you know that the near point of accommodation of the patient is reached okay so at this distance you can measure the distance from the spectacle lens to the retinoscope point of neutrality okay the last point where you observe the neutral reflex and that will give you your near point of accommodation that is one way of calculating the near point of accommodation using dynamic retinoscopy so here this is an objective test why because you're not relying on the patient response whether that is a sustained bloodred distance or blurred Target okay you're relying on yourself and on your skills of observing The Reflex okay that's the reason why it is known as objective test okay all right another way of testing is you uh give the target to the patient and you tell them to place it as close as possible or the closest point at which they can read the Target and at that point you are going to do your anoscope and see if you can if you're able to see the neutral point or neutralization then you slowly move again closer to the patient and if the reflex changes to with the motion you know that with motion or uh you know that basically that the near point of accommodation has reached okay so I hope that is all making sense now once you have calculated that distance u in meters basically that's why it is 100 by CM over here you will be able to calculate the amplitude of accommodation in this patient right so for example if the reflex changes at 10 cm your accommodative amplitude will be 100 divided by 10 so that will be about 10 diopter now since the accommodation is changing constantly right so here there was some other com at this point the accommodation was different at this point accommodation will be more and this point accommodation will be Max and then if you move closer there will be no accommodation right the accommodation is changing from one point to another and that is the reason why it is known as Dynamic Ros scopy all right so there's a lot more to Dynamic roscopy don't think that we are summarizing it now but for your homework what I want you to do is go through this video on the concepts of retinoscopy I really want you to clear your basics in retinoscopy before we start discussing the accommodative response and the lead and lag of accommodation so these two are the things that we are going to discuss in our next video so if this video added any value don't forget to subscribe thank you for watching and have a nice day