Page 36 - Practical-Refraction-English

Subjective Refraction 4 Dissociation by polarized tests (Polarized Cross Test): Stereopsis The polarized cross is available in the majority of projec- To assess the subject's stereoscopic vision, use a test tors charts. Proceed as follows: that enables two separate images to be presented to the On procède comme suit : subject. These images are almost identical but slightly a) Place the polarized filters in front of both eyes. offset relative to one other so that they create a percep- b) Ask the patient if both branches of the cross are tion of relief (that is, three dimensional vision) when they clearly visible: merge. These tests achieve dissociation by means of red a. If the full cross is clearly visible, there is and green filters (Brock technique) or polarized filters simultaneous vision. (for example, polarized rack test). They involve checking b. If only one branch is visible (or one branch that a part of the image is perceived by the patient as tends to disappear and re-appear), there is (full or inter- being closer or further than the rest of the image. The mittent) suppression of one eye. principle is that when the two eyes fuse, if the image c) Ask the patient if both branches of the cross are seen by the right eye is slightly offset to the right and perfectly centred or if one of them seems offset relative that seen by the left eye is slightly offset to the left, the to the other: patient has the impression that the plane of the test a. If the branches are centred, there is ortho- recedes; conversely, if the image seen by the right eye is phoria. slightly offset to the left and that seen by the left eye is b. If they are offset, horizontally and/or vertically, slightly offset to the right, the patient has the impression there is heterophoria. that the plane of the test advances. The presence of even a slight degree of stereoscopy implies a very good level of binocular vision. © Essilor International © Essilor International Figure 34: Polarized Cross Test Figure 35: Brock Rings Test © Essilor International Figure 36: Polarized Bar Test If a binocular vision anomaly is detected, proceed to a more detailed evaluation such as that described below in the Chapter ‘Binocular Vision Evaluation’. 36 Copyright © 2008 ESSILOR ACADEMY EUROPE, 13 rue Moreau, 75012 Paris, France - All rights reserved – Do not copy or distribute.