DEPISTEO VT1 Series User Manual
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Contents
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This document is the property of DEPISTEO. Its contents cannot be reproduced or divulged without the company's approvalPage 56 / 78V04.07.00March 20185.4. Astigmatism test5.4.1. PurposeAstigmatism is an important source of eye strain, particularly in intense conditions or poor lighting (screen workor night driving with glare from oncoming vehicle lights).5.4.2. DefinitionThe astigmatism test is composed of an astigmatic dial with 7 branches numbered from 1 to 7.5.4.3. PrerequisiteThis test should be performed in monocular mode.The operator should look at each of the branches consecutively.5.4.4. Patient instructionsAre some of the lines blacker or clearer?” Note the responses on the response form.5.4.5. Expected responsesIf the patient perceives some branches less clear, or greyer, than others, the eye is probably astigmatic.Normally all the branches should be perceived in the same way. A branch that is clearer in direction 4 indicatesvertical or direct astigmatism. On the contrary, if the branches are clearer in directions 1 and 7, this indicateshorizontal or inverse astigmatism. These directions indicate different optical strength in the particular meridian,as the corneal astigmatism is toric, rather than perfectly spherical.A ‘clearer in directions 1, 4 and 7’ response is thus impossible, and the VT1 operator is alerted by a questionmark. Generally, in these cases, after repeating the test with clear instructions, the response would beinterpreted as ‘identical’.“Oblique” astigmatism also exists and is more difficult to correct, sometimes persisting despite correction. Inthis case, the response would be given in either the 2 or 3 meridian, or the 5 and 6. A simultaneous response: 2,3, 5, 6 is impossible.Sometimes a meridian astigmatism is only detected by varying focal length. Astigmatism could thus be tested innear vision, or after addition of the hyperopia lens in far vision. Of course, detection for astigmatism in near orintermediate vision is useless, if it is present in far vision.Lastly, this device only screens “regular” astigmatisms. Other, “irregular” astigmatisms, notably on corneal scars,are screened by ophthalmologists.5.4.6. Perception example |
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