hi this is an instructional video on clinically measuring a patient's ACA and PCA ratios there are several different types of convergences these include accommodative convergence proximal convergence tonic convergence and fusional convergence the two main types of virgin C's that are mainly affected in concomitant strabismus include accommodative convergence and proximal convergence fusional convergence and tonic convergence are often very subtle and incomparable to their actions of accommodative and proximal convergences for this reason this video will only focus on calculating accommodative and proximal convergence before we get started on measuring these ratios what exactly are they and what values are we expecting what is accommodative convergence and ac/a ratio accommodative convergence is the degree of convergence induced by accommodation and therefore the ACA ratio is the total accommodative convergence induced by each diopter of accommodation the normal range for ACA ratio is within three to five prism diopters for every one diopter of accommodation what is proximal convergence and PCA ratio proximal convergence is the convergence that is stimulated by a sense of nearness the normal range for PCA ratio is within one to three prism diopters for every one diopter of accommodation let's have a look at a patient's a CA and PCA ratio is being measured thank God yeah thanks see how simply checking their worries today yeah my name is Abdul I'll be your student today today I'm just gonna be performing a couple of my examinations just to see how well the eyes are working together for measuring the ACA and the PCA ratio we essentially need three different PCT results one for distance one for Nia another one for either Mia or distance using plus or minus lenses okay then that charlatan distance for me I just kill you read the lost liner you can pxt eh eh he tried with the long you to be a the h xt good ask even look at that for me yeah okay keep looking at that that's all thank you the orthopedist found the PCT result for distance to be an EXO phoria of eight prism diopters whilst performing PCT especially when measuring the ACA ratio it is extremely important that the patient is accommodating in the distance therefore the patient must be encouraged to accommodate now another PCT is measured for Nia okay David I'll stay with the letters over here for me just read the lowest line that you can yep see I don't age and he trying to get any long a agency to ask you to look at the ER for me yep okay they are scared of all this familiar all the things my nose [Applause] thank you very much Damon the earth Optus found the PCT result for Nia to be an EXO forea of two prism diopters next another PCT measurement is required with either minus or plus lenses and this can be performed at either distance Anya if the PCT is performed at distance - lenses are used to induce accomodation if the PCT is performed at Nia plus lenses are used to relax the accomodation for the purposes of this video we'll be using - three lenses in the distance to induce accomodation it is vital that you ensure the patient is accommodating by checking if they can read through the - lenses usually - 3 is used to induce accomodation but if the patient is not accommodating through the lenses you may reduce down to 2.5 or - until the patient can see clearly through the lenses hey they must these trough rooms on you know now how does that feel so I feel good okay it's going to be poppy to lens in front of your eyes okay they're not feet look at that child and this this for me don't even tell me what's the last line you can read to you or you know HIV can try and go any lower [Music] our house we look at that Sheila Pinette that way for me yeah [Music] they are thought to surround the result for distance through the minus lenses to be an EXO forea of three prism diopters now that we have the PCT for distance with and without the minus three lenses and also a measurement for Nia we can use these values and plug them into a formula to get the results as shown in the formula there are two different methods of measuring a cm ratio the gradient method and the head chef Auria method previously the hetero foria method was used by itself to measure the ACN ratio but it was found that because the formula includes a PCT for distance and a PCT for Nia the different distances meant that the results were contaminated by proximal convergence this issue was rectified by using the gradient method where the distance used in the formula regardless of it being for distance or for Nia was kept consistent this eventually meant that the gradient method was used for calculating the ACA ratio and the hetero foreo method was used for calculating the PCA ratio and now when we use the gradient method the deviation when accommodating most is -3 the deviation when accommodating least is -8 the amount of accomodation the lens is used is minus 3 when we plug that into the equation as shown below we find that the HCA ratio using the gradient method to be 1.7 to 1 diopter which if you recall from the initial slides it is outside the normal range of 3 to 5 prism diopters for every diopter of accomodation so for this patient using the hetero for ian's method the deviation at Nia is minus 2 the deviation at far is minus 8 the intercalary distance is 6 this was measured by the earth up test and found to be 6 centimeters using the formula the final value comes to eight however in order to measure the PCA ratios it is vital that you subtract the gradient method from the hetero foreo method which equates to a PC a ratio of 6.3 diopters for every diopter of accomodation compared to the norms for the PCA as discussed previously this is higher than the normal range according to these results for the patient's any strabismus noticed in the patient can be potentially attributed to the anomaly in the PCA and ACA ratio however as for any diagnosis and treatment we must look at the patient holistically the ACA and PCA ratio on its own would not be enough to provide a complete diagnosis for the patient before we conclude in what instances do we measure the ACA and PCA ratios usually the indications for measuring the ACA ratio is when the strabismus or i-10 is greater at a certain distance and we are looking to find out if the reason for this increase is due to a variability and either the ACA or PCA ratio this will influence the differential diagnosis and the management of the specific classification of the strabismus thank you so much for listening this time have a seat actually yeah have a seat me did you see that