![]() ![]() The monocular cues, which some claim are still present, are much harder to detect under these circumstances. Being able to correctly identify the nearer circle is a good sign. In each of the circles are four circles, three of which are pushed inward behind the plane of the test and one of which is shifted out closer to the observer by the same amount the other three are inset. Depending on the direction of shift, the person will perceive the dots forming the figure, circles in this instance, as shifting closer or further than the plane of the test. If you are truly binocular, when figures appear, the dots in that area will shift right in one eye and left in the other, relative to the unshifted dots in the background. The background shows the same dots in the same place to both eyes. Global stereo targets, on the other hand, are all done with random dot patterns ( Figure 4). You can guess well down to 70 seconds of arc without really having good binocularity or, therefore, good stereopsis. Put the glasses on, cover one eye-or suppress the central vision through one eye-and now one of the circles has shifted slightly. Of the three circles, one clearly looks blurred without the stereo glasses. Here again, the monocular cues are easily discernible. In one, the Wirt circles lie on top of the random dot pattern background ( Figure 3). Then came random dot tests, of which there are two different kinds. Measures up to 70 seconds of arc may or may not be actual measures of binocular stereopsis and may represent excellent use of monocular cues.įig. These monocular cues to depth tend to work well until about 70 seconds of arc on the Wirt circle test. With the stereo glasses on, only one of the two circles shifts to the right or left, depending on which eye the person is looking through centrally. The lower circles in the diamond with the “1” in the center look fuzzy or appear in twos when viewed without the stereo glasses ( Figure 2). When conducting the Wirt circle test, few of us concern ourselves with monocular cues to depth. Fun times! But the real test was the Wirt circles. We all remember telling our patients to “pinch the wings” and watching as they recoiled from the image jumping off the page. Show it to people for the first time and watch their reaction. Stereo tests have evolved from the good old days when clinicians didn’t know the difference between local and global stereo-all we knew was the Stereo Fly ( Figure 1). The full Stereo Fly test book with Wirt circles on the left. If it did, then you should feel confident the new prescription will benefit the patient. One way to optimize your patient’s needs is to perform refraction with their habitual prescription and then with their new prescription to see if stereo improved. If stereo is present, we know the patient is using the information flowing through both of their eyes. The response to stereo testing indicates how well a patient’s binocular system is functioning. ![]()
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