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### 15 Cards in this Set

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• Back
 What is the purpose of the clock dial? To get a gross estimate of the astigmatic correction (in other words, a tentative axis and power) What will the clock dial look like if there is no astigmatic error? All spokes will look alike (fuzzy). No one spoke will stick will be more distinct. Assuming the CLC is on the retina, which focal line will appear the clearest. -the line closest to the retina -if the patient is fogged, the most posterior line will be the clearest Assuming the patient is fogged, which focal line will move with the addition of minus lenses? - the anterior focal line What happens to the interval of sturm when cylinder lenses are added? -the I/S is decreased -the focal lines move closer -the focal lines become smaller (shorter) What happens to the focal lines when too much cylinder is added? The interval of Sturm flips (what was clear vertical lines are now clear horizontal lines) Describe the set up for the clock dial. -occlude the non tested eye and remove all cylinder lenses from the phoropter -fog the patient (if after ret., don't take out your working distance) -NO first best sphere, because you want the patient fogged -confirm that all lines are equally blurred Describe the method. -while decreasing plus, ask the patient to tell you when one or some of the lines appear clearer than others What do you set the axis to on the phoropter? Multiply their answer by 30, this is the AXIS. Why do you make sure that the lines on either side of the axis are equally dark? you want the lines on either side of the axis to be equally dark. If one side is darker, then you need to shift the axis away from that side. How do you know that you added enough cylinder lenses? When all lines appear equally dark. If you add too much, the opposite line becomes darker and clearer. Why would the clock dial fail? -fogged too much -not enough fog to stablize accommodation -patient accommodative instability -uncooperative or unresponsive patient -cylinder too high for patient to respond How do you perform the clock dial using a plus cylinder phoropter? -set the axis opposite to what they say -adding plus cyl. will move the posterior focal line -this will make it foggy, therefore, you must add minus SPHERE to compensate Can you perform the clock dial on an absolute presbyope who is overminused? -Yes, add minus cyl, with plus sphere clicked in (can not be done with a plus cylinder phoropter) What are the intervals between lines for the clock dial and the Lancaster-Regan (sunburst)? clock dial=30 Lancaster-Regan=10