[Music] hello friends welcome to optometer rails do you know what ac by air issue is are you aware of its clinical use do you know how easy and quick this test can be stay with me till the end to learn the best and the easiest way to perform ac by e ratio as we know accommodation and conversions are interrelated and they develop together so that we see a single image accommodative convergence is the convergence which occurs when the eyes accommodate therefore the ratio of accommodative convergence over accommodation indicates the relationship between the stimulus of conversion and the amount of accommodations which produces that conversion and the ac by ratio is highly useful in diagnosing and managing the binocular vision anomalies there are various ways to measure ac by ratio but i will explain you the two easiest way to calculate it first will be gradient method and the second will be a calculated method in gradient method you just require a paint watch madox rod a trial frame and a modified thorington chart this modified thorington chart is a simple chart which indicates the various type of fouriers present in the eye through gradient method we can measure fourier in normal viewing condition by stimulating the accommodation with negative lengths either with -1 or -2 adapter sphere to perform this test place the madox rod on a trial frame and ask the patient to look straight at the center of the modified thorington chart which is kept at 40 centimeter the charge should be illuminated through the center and patient should be asked to look at the light please remember that madox rod contains a parallel plano convex lenses which reflect light rays so that a point source of light appears as a line or the stick of light and this line is seen perpendicular to the axis of the cylinder when madox rod is kept vertical it makes horizontal line and when it is kept horizontal it will make a vertical line which you can see clearly in this picture when medox rod is kept horizontally it is showing a vertical line while performing the test ask the patient to point the line seen by patient on a modified thorium chart the line seen on the chart is the fourier present in the eye here patient pointed on six exophoria now you need to stimulate accommodation with minus lenses either minus one or minus two diameter sphere to check the accommodative convergence here we use minus one diaper sphere and the stimulated fourier came out to be minus two exo the change in the fourier from without any lenses to minus one diameter sphere came out to be four since the minus one diameter was used therefore the ac by ratio was four is to one okay let's understand again with that new example what will be sc by ratio when fourier change from six xo to four iso with minus one diameter sphere on the modify thorington you can clearly see the change is at 10 hence ac by ratio will be 10 is to 1. again if you would have used 2 diopter as a stimulation it would have been 10 is to 2 or 5 is to 1 another way to find ac by ratio is calculated method this method requires some values like interpreter distance which should be in centimeter near fourier and distance fourier and these values need to be put in either of these given formulas in first formula ac by ratio can be obtained by adding ipd to difference of fourier from near to distance and dividing this with 2.5 here 2.5 is the accommodated demand for 40 centimeter for second formula also we require ipd and this ipd should be added to the difference of fourier from near to distance multiplied by near functional distance the near functional distance should be in meter and for 40 centimeter of the working distance it is 0.4 meter thus the calculated method for ac by ratio can be understood in the three steps step one is to measure the ipd in centimeter now perform cover uncover test to find out the type of fourier [Music] now use prisms to neutralize that fourier for easy deviation use base out prism for exodivation use pace in prism [Music] the third step is to measure the distance fourier again you need to check the type of fourier by performing cover and cover test and neutralize that fourier using the prism [Music] okay let's understand this with an example what will be ac by ratio if ipd is 6 centimeter near fourier is 5pd iso distance fourier is 10 exophoria considering the accommodated demand for 40 centimeters 2.5 if you put these values in formula 1 the ac by ratio will be 12 is to one again if you put this these values to the second formula by considering the near functional distance as 0.4 meter again the ac ratio will be 12 is to 1. thank you for watching till the end hope this video was informative and useful please like share and subscribe see you at the next video