[Music] hello and welcome to insight of thermology this is dr amrit and today we are discussing jackson cross cylinder also called the cross cylinder the jcc or the jackson cross cylinder is a method of subjective verification of refraction it is actually a spherical cylinder or we can say a sphero cylinder combination in which the spherical component is actually half of the cylindrical component and it is of opposite sign the cross lender will be identified however by the strength of the cylindrical component acc or the jackson cross cylinder consists of an instrument shown over here which has a circular structure like this with a handle the handle is usually present at an angle of 45 degrees to the to the meridians which are marked on the jcc as i already told you that the jcc is a sphero cylindrical combination that means it has a spherical component and a cylindrical component and the sphere is half of the cylinder component with a sign opposite to that of the cylindrical component now have a look at this type of jcc over here we can see the red color markings okay and these red color marking indicates the axis of the minus cylinder of the jcc that means about minus 0.5 and over here we can see plus 0.50 written in the vertical axis right that means this is the axis of the plus 0.5 cylinder and therefore the power will be acting where the power will be acting horizontal if you would remember from the video on astigmatism in a case of cylinder the axis and power of the cylinder are perpendicular to each other and if the axis is at 180 the power will be at 90 degree and vice versa so similarly in this jcc since the red color markings or the negative cylinder is written on the along the horizontal meridian the power is acting along the vertical meridian so in a jcc we can also define jcc as a combination of two cylinders which are of equal power but of different sign acting at perpendicular to each other okay so the first question is do you think this jcc can be represented in two form yes this jcc of plus 0.50 can be written as a power cross like this that is a combination of two cylinders or it can also be written in a sphero cylindrical form that is a prescription form as shown over here that is minus 0.50 diopter spherical derived from here and writing the extra cylinder that is minus 1 cylinder into 180 degrees so both these representations are correct for the jcc in a jcc the handle of the jcc will always be at an angle of 45 degrees to the meridian switchama the minus marking will indicate the axis of the minus cylinder and the white dots will indicate the axis of the plus cylinder cross cylinder can be used in order to discover the astigmatism that means if astigmatism is present or not second if we know that the astigmatism is present in the prescription we can actually check the axis of the cylinder or we can refine the axis of the cylinder that we find that we found out initially and the third thing is we can also check or refine the power of that cylinder in the prescription right so in order to discover the astigmatism in order to refine the axis of the astigmatism and finally to check the power of the cylinder in that astigmatism these three things we can use jcc before i go and explain you how do we do those three applications of jcc i want you to be thorough again with this term sconoid i cannot stress enough the importance of storms connoit in refraction so if you are not seen my video on storms conor you can find it in the link and you can actually i would suggest that you go visit and clear your concepts on this term sconoid in storms connoit we saw that if this was the toric surface the convergence of the vertical meridian which is having more power say compared to the horizontal meridian actually gave us a horizontal line right and the convergence of the horizontal meridian or the horizontal rays of light which were having less power gave us a vertical line and these two were called our anterior focal plane and the posterior focal plane and in between them what we had was a circle of least confusion so the whole idea of refraction is to bring this circle of least confusion on to the retina and in the process to collapse this term sconoid that means to bring the horizontal line onto the vertical line but what happens in refraction is whenever we are introducing the lenses in front of the story surface we are trying to bring this anterior focal line and the posterior focal line close to each other right so the anterior focal line and posterior focal line when they come close to each other what is happening the storms of the storms connoit is actually come becoming shorter and shorter right but sometimes we might introduce the wrong lenses and then what will happen the anterior focal line and the posterior focal line will actually move away from each other and this terms interval will actually increase and the patient will see blur vision so that's the basic concept behind the jcc now let us try to understand this in detail suppose in front of this eye we will introduce a jcc now this eye as you can see there is a horizontal image which is formed and this horizontal image is actually from from the vertical meridian and a vertical image which is formed which is formed from the horizontal meridian right and the circle of least confusion is actually present on to the retina now this is our jcc and we can see that the negative negative axis or the red axis over here indicates the axis of the negative part of the cylinder okay and if the axis is marked like this where will the power of the negative cylinder act it will act along the horizontal meridian right that is we are actually giving this about minus 0.25 diopters along the horizontal meridian the horizontal meridian is forming which image it is forming the vertical image so what will be the effect of giving minus power to this for to this horizontal meridian the image will actually shift behind okay the image will shift behind right so whenever we are giving minus power we are making the eye weaker so the image will shift behind now what will be the effect of giving a plus power to the vertical meridian this image will shift even more further right so when we are giving plus we are increasing the convergence so the image will move forward so what is happening when we are putting a cylinder when we are giving the jcc to this eye both the images are actually moving away from each other and the storms connoit is actually expanding right so the patient will not be happy with the prescription or with the jcc on in this position right however what is happening to the circle of least confusion nothing circle of least confusion is remaining as it is on to the retina so that's the amazing thing about jcc that it will actually shift the two anterior focal plane and the posterior focal planes right so relatively there will be a shift in their position however the circle of least confusion will always remain on to the retina now let us see what will happen if we actually flip this jcc into this new position now as you can see that the meridians will totally change what do we have at the vertical meridian now we are actually having the axis of 0.25 cylinder if the axis of the 0.25 cylinder is on the vertical what is mean where is the power the power is along the horizontal and therefore the minus cylinder is acting on the vertical right so is this clear yeah so now let us see that what uh what will happen when we put this jcc in front of this eye so this image initially is actually formed from the vertical meridian and along the vertical meridian what are we giving we are giving a minus power along the vertical meridian a minus power will always shift the image behind right so this image will now be will be shifted in a backward direction right that means towards the retina now what will happen if we are giving this plus 0.25 along the horizontal meridian where is the horizontal meridian image the image is this one right so now we are giving a plus 0.25 to the horizontal meridian image so because whenever we give plus the image will move forward so what will in turn happen to this term sconoid both the anterior focal image and the posterior focal image are actually moving towards each other so this terms of conoid is becoming smaller the circle of least confusion is remaining at the same place but this term's interval is decreasing and therefore the patient will see clearer than the first jccc that we had put right so now in this position the patient will be actually happy so this is the concept of sturm's connoisseur whenever we are decreasing the storm's interval the patient will see clearer whenever we are increasing the storm's interval by putting the jcc the patient will see blurred image and he will not be happy okay and always he will prefer the position of jcc where he seemed clearer because at that point this terms interval is decreasing now let us see how can we actually discover astigmatism in a patient let us consider this patient to actually have myopia of about -2 diopters now after doing the subjective refraction we find out that he needs a sphere of minus two diopter spherical now if this person does not have any cylinder uh cylindrical error what it means is that with minus two diopter spherical we will have the focal point actually on to the retina that means there is no sperm skenoid present in this patient who does not have astigmatism right so now in front of this patient if we actually put the jackson cross cylinder in any orientation first we'll put it in the 90 and 180 degree orientation and then again we will check the 45 degrees and the 135 degree meridian right so when we are going to put it in these orientations we will find that the patient will have no difference in the vision that means he will see clearly in whether it is horizontally placed or vertically placed or the jcc is placed obliquely also so when the patient is not having any difference or any preference of the jcc position it means that the image is on to the retina and there is no astigmatism that we need to correct right however if there was a patient who actually had astigmatism like this patient so in in case of this patient if we are going to introduce the jcc in front of this eye okay what will happen is that either this terms conoroid will decrease in its interval or in one position it will be increase in its interval right so as i have explained to you in the concept of jcc right so the patient is going to now prefer the position of jcc in which the two images at the two focal points are actually going to move towards each other and the interval will decrease okay and he will be very unhappy with the position in which the terms interval is actually increasing because the images are going away from each other right so in such a case whenever we have done a spherical correction we are going to check by putting this term sonoid in the two principal meridians that is vertical and horizontal and then we are going to check two oblique meridians that is 35 and 145 degrees right sorry 45 and 135 degrees right and if the patient has preference for one meridian it tells us that there is astigmatism present because the the jcc is actually altering the stern scholoid inter after we have discovered that the astigmatism is present in the person now we are going to refine the axis always remember that the axis is refined first before refining the power right so in this case first we will put the cylindrical lens which we discovered during the retinoscopy in the trial frame on the spherical lens now we are going to occlude one eye and ask the patient to focus on the line that is clearest with the other eye and now we are going to hold the jcc with the handle parallel to the axis of the cylinder in the frame so what i mean to say is that if we discovered that suppose this was the prescription one diopter spherical and minus one cylinder at 90 degrees so the axis of the cylinder is 90 and therefore our jcc also we are going to place in such a way that the handle is actually parallel to the axis of the cylinder that we are going to put okay so this will be our position one now we are going to flip it to the another position and ask the patient for this for his preference of images if there is no difference between the two positions that is position one and position two it means that the axis of the corrective cylinder that we have chosen in the trial frame is correct okay however if there is visual improvement in one position it means that there is a need to refine the axis now how do we refine the axis is that we will rotate the minus correcting cylinder in the direction of the minus cylindrical component of the cross cylinder so what i mean to say is that if this is our correcting cylinder and the axis is 90 and we have placed our jackson cross cylinder on top of this straddling in such a way that this is the red mark which indicates a minus and this is the white mark which indicates the plus cylinder component of the jcc now considering that this is actually a minus cylinder that is minus 1 at 90 degree axis so which component are we going to focus in the jcc the red component because the red component is the minus component now suppose the patient actually prefers this position we are going to rotate this towards this minus component of the jcc because we are dealing with a minus cylinder now let us see the cylinder was actually plus cylinder at 90 degree axis then what will you do if the patient is preferring this position we are going to rotate it towards the white line that is the white component or the plus component of the cross cylinder because we are dealing with a plus correcting cylinder so the plus collecting cylinder should be rotated in the direction of the plus component that is the wide of the cross cylinder and we have to keep on repeating this test till the neutral point is reached what is meant by the neutral point the neutral point means that the patient now no longer has any preference so what i mean to say suppose this is the cylinder at 90 degrees is the axis and this is a minus cylinder first the patient prefers a position so we will rotate it towards the red line now again we are going to put the jcc with the handle parallel to this axis where we have put our correcting lens again we are going to ask suppose again he prefers this again we are going to rotate now suppose he prefers the flip position and the red mark now reaches on to the other side now we are going to rotate it backwards so we keep on rotating front and back till we get the neutral point let us assume that our patient is actually after retinoscopy we find out that this is the uh prescription that is minus two diopter spherical minus one cylinder and the axis is at 180 degrees right so what i mean to say is that the axis is at 180 degree that is the horizontal now in order to refine the axis we will be introducing our jcc with the handle parallel to this axis so if this is the handle of the jcc this handle will be oriented parallel to the axis of the cylinder that is 180 degree now what happens is that the two axis of this jcc will now be straddling this axis okay the axis that we have to test so here we are testing 180 degree and we can see that here this is the white mark which indicates that this will be the plus component of the jcc and this is a red mark which will be the minus component of the jcc so what we do is in the first position we will introduce jcc like this so that the the red mark okay is present on the right side and this is present on the left side right one very important rule that we have to follow while refining the axis is to take into consideration the sign of the cylinder that we are refining now here we are trying to refine this minus one cylinder right so as we are refining this minus one cylinder we have to take into consideration the minus component of the jcc that is the red component of the jcc so in the position one we can see that the red component is present on the right side of the handle right or we can say on the right side of the 180 degree line 0 and 180 degree meridian right now we are going to flip the cylinder and bring the cylinder bring the jcc into the position 2 okay and what is the position 2 we can see that in the position 2 the red component has now come to the left hand side of the handle right so have a look at this diagram so this is our connecting cylinder that we have introduced and the 180 degree was the axis that we found okay so 100 degree was the axis that we found now in the position one we know that the red component is over here where is it present it is present on the right hand side okay so always if there is a minus cylinder we have to always consider the red component and if we are dealing with a plus cylinder we have to consider the white component of the jcc right now suppose the patient actually prefers right suppose the patient is preferring this position that is position one okay so if the patient prefers the position one we are going to rotate our jcc in such a way that our axis of the cylinder will rotate towards this minus cylinder so have a look okay so we had our correcting cylinder like this place at 180 degree now since the patient is preferring the position one so we have to consider the red component because it's a minus cylinder the red component is present towards the right side and therefore we will be rotating our correcting cylinder towards the right side and this is what we get now let us consider that the retinoscopic prescription that we get from this retinoscopy is this right now in this case the cylinder is actually a plus cylinder right so we need to know where is the plus component of the jcc present in the preferred position now in this case the patient is preferring the position one right and because we are dealing with a plus cylinder we will consider the white mark on the jcc the white mark is located on the left side of the handle and therefore we will actually rotate our correcting cylinder also towards the left hand side so this would be our rotation and why we have rotated it towards the white part because we are dealing with the plus cylinder in this now let us assume that the patient actually prefers the position b now in the position b of the jcc we can see that the red component is present on to the left side okay or we can say above the handle and the white component which is the plus component is actually present on to the right side of the handle right or below the handle now as we are dealing with the minus cylinder say in this condition where are we going to rotate our jcc we are going to rotate it towards this minus component okay because minus is always rotated towards the left hand uh towards the red so this is what we are going to get so from from this we have rotated it to this right y the patient was actually using the minus cylinder now suppose in this condition we are actually dealing with a prescription like -2 diopter spherical but the cylinder is however a plus cylinder at 180 degree axis and the patient is preferring position b now as the patient is position preferring this position b where are we supposed to rotate this jcc we are supposed to rotate it towards the wide mark of the jcc so what are we going to get we are going to get something like this right and since we were dealing with the plus cylinder at 180 degree we are considering the white mark of the jcc the white mark in the preferred position is present on to the right side and therefore from the previous position we have rotated it towards this side so this table over here actually represents how much rotation we have to do so if we are dealing with the uh cylinders of lesser power usually the amount of rotation that we do is more about 30 degrees 15 degrees 10 degrees and as the cylinder power is going to increase the amount of rotation is very less about five three two one okay also the rotation that we do in each in the initial steps of refinement will be more and later especially when we are going back towards that rotation in the say in the opposite direction usually it will be less let us first go through the steps of refining the power of the cylinder and then with an example i will explain it to you the first step is we are going to put the cylindrical lens that we found in retinoscopy along with the spherical correction in the trial frame then ask the patient to focus on a distant object next is we are going to introduce the jcc now if you would remember from the refinement of the cylinder the handle of the jcc was actually parallel to the axis of the cylinder right so what i mean to say is if you would remember that trial frame the axis of the cylinder that we chose was about 180 degrees and the jcc also was introduced in such a way that the handle was actually parallel to the axis such that these axis of the jcc that means the red and the white marks were actually straddling the handle or straddling the axis that we were checking to refine it right however when we are refining the power of the cylinder we have to place the jcc in such a way that the axis of the jcc will be parallel to the axis of the cylinder so what i mean to say is we are going to place it in such a way that if this is the axis of the correcting cylinder 180 our jcc also will be placed in such a way that at least one of the axis that means either the red mark axis or the white mark axis are perpendicular parallel to that axis of cylinder okay or are superimposing with the axis of the cylinder right yeah the third step is we are going to flip the jcc to see that if there is any preference uh in the vision seen by the patient right so ask patient about any improvement in the position then if the patient notices that there is no difference between the two position the inference is that the power of the correcting cylinder in the trial frame is actually correct however if there is visual improvement attained in one position then we have to give the corresponding correction of the cylinder and finally we are also going to adjust the spherical correction in such a way that the least confusion circle does not move away from the retina now let us try to refine the power of the collecting correcting cylinder using the jcc as already i told you that whenever we are correcting the power of the cylinder whenever we are refining the power of cylinder using the jcc it is the axis of the jcc which should be parallel to the axis of correcting cylinder and not the handle so we can see that in position 1 it is the white marks which are a parallel to the 180 degree meridian and in position 2 it is the red marks which are parallel to the 180 meridians and let me remind you that the plus marks indicate the axis of the plus cylinder of the jcc and the minus marks indicate the axis of the minus cylinder of the jcc and their power will be acting perpendicular to their axis now let us consider this position one in this position one we can see that the retinoscopy that we found for this patient was minus one diopter spherical minus 0.75 cylinder at 180 degree so our axis was at 180 degree now at this axis of 180 degree the plus component of the jcc is present that means the white marks and therefore the plus 1 cylinder is acting at the vertical meridian and the minus 1 is acting at the horizontal meridian similarly for position 2 we can see that the red marks are however aligned to the 180 degree axis and therefore the minus component of the jcc is acting along the vertical meridian and the plus component is actually acting along the horizontal meridian now let us understand the position 1 and position 2 in more depth using these terms conoy our patient over here who is having -1 diopter spherical and minus 0.75 cylinder at 180 degree actually is having compound myopic astigmatism compound myopic astimatism means that both the images that the anterior focal point and the posterior focal point as shown over here they are formed in front of the retina right now the first image that we see over here in red is actually being formed from the vertical meridian now when we are going to introduce this jcc and the power cross of the jcc is shown here along the vertical meridian what power are we giving we are giving about plus one diopter so plus one diopter will do what it will actually shift the image more anteriorly right because plus means adding more power more convergence to the vertical rays and they will converge even more ahead and therefore the image will move somewhere here right now what are we doing to the horizontal meridian to the horizontal meridian we are adding -1 diopter right that means we are making it more weaker so this image which is formed by the convergence of the horizontal rays will now move even more behind right image will be formed here so what is exactly happening in this case this terms interval is increasing now because this terms interval will increase the patient will not be happy with this position one now let us see that what happens in position two in position two it is the minus marks which are present uh parallel to the 180 degrees that means along the vertical meridian we are having the minus power right and along the horizontal we have the plus power of the jcc now in the same patient who was having the simple myopic astigmatism what are we giving along the vertical meridian we are giving the minus power okay that is a minus one diopter so what will happen to this image which is formed from the vertical median this image will be pushed behind okay now what are we giving to the horizontal meridian to the horizontal median we are giving plus one diopter right so that horizontal rays will shift will act on the image which is formed from the horizontal meridian right which is this image as we are giving plus one diopter to this what will happen the image will be formed in front okay to be found more ahead because the convergence of the horizontal we are increasing so what is happening in turn both the images are actually moving towards each other and this term sonoid is becoming smaller and smaller and therefore the patient will be now happy so what do you think which position the patient is going to prefer the patient would be preferring position two right so this is the funda of refinement of the power we give patients two positions of the jcc in one position we move the images away from each other and increases terms interval in the second position we will actually be decreasing this terms interval and the patient will prefer that position right so the position and the jcc that the patient accepts will be this one right now that we know that patient is actually accepting the position b let us see how do we adjust this prescription according to the position b now in the position b we know the power cross that we got was -1 diopter and plus one diopter okay along the horizontal and minus one was along the vertical right so now what do we do is that since the cylinder over here the axis is 180 the power is acting along the vertical meridian so we are going to take this vertical meridian power and add algebraically to this that means 0.75 diopter cylinder plus minus one diopter cylinder from the jcc okay and the axis will remain the same that is 180. so what do we get we will get minus 1.75 cylinder at 180 degrees right now this was the correction for our cylinder but what will happen to our spherical component okay what will happen to the spherical component now i already told you before that the sphere in the jcc is actually opposite sign and half of the cylinder so what cylinder are we adding here we are adding minus one diopter cylinder right and what is the uh what will be half of that cylinder it will be minus 0.5 right so the same minus 0.5 we are going to add here but with the opposite sign okay so it will become plus so the sphere that we get is -1 diopter spherical plus 0.5 that means it will come to about minus 0.5 diopter spherical and the cylinder is our minus 1.75 cylinder at 180 degree so this is going to be our final prescription so remember that whenever we get a preferred position that particular meridian along which the correcting cylinder is acting to that meridian algebraically we have to add the power of the jcc along that meridian and then we have to carefully adjust the sphere also according to this relationship so that our least circle of least confusion does not move from the retina right so after our final refinement the prescription that we get is this so this was it about the jcc i hope it was clear and you finally understood how to discover astigmatism how to refine the axis of cylinder and how to refine the power of cylinder in a jcc thank you and have a nice day if you like the videos kindly spread the knowledge [Music]