Page 35 - Practical-Refraction-English

Subjective Refraction Binocular Vision Screening At this stage of the examination, it is important to check the patient’s binocular vision; more precisely, it is important to confirm that the patient has good simultaneous vision and that the images perceived by both eyes are fused without difficulty. To evaluate this, the patient’s binocular vision must be dissociated in order to check that: 1) there is not total or partial suppression of the vision in one eye, by ensuring the permanent presence of two © Essilor International images 2) there is not potential deviation or significant pho- ria, by checking the alignment of the two images. Figure 32: Dissociation by Prisms Note that simultaneous vision may already have been - Conversely, if the image seen by the right eye is to observed during the binocular balance test. the left and the image seen by the left eye is to the right, there is exophoria. Depending on whether binocular vision is dissociated by - Most people have some degree of heterophoria. means of prisms, red-green filters or polarized filters, for This poses a problem only if compensation for it proves example, one of the following tests could be carried out: difficult, for example. Dissociation by coloured filters (Schober test): Dissociation by prisms (Von Graefe method) This test is comprised of a red cross and 2 green circles Its principle is to dissociate binocular vision by means of seen through red and green filters by the right and left vertical prism. The patient looks at a line of letters, first eyes. The eye fitted with the red filter sees the red cross; vertical then horizontal. Proceed as follows: the eye fitted with the green filter sees the green circles. a) Place a 6 base down prism in front of the right Proceed as follows: eye (or 3 BDR and 3 BUL). a) Place a red filter over one eye and a green filter over the other. b) Check that the patient sees two images simulta- b) Ask the patient what they see: neously, one high (the right), the other low (the left) (the a. If both the cross and the circles are seen, image is moved towards the prism’s apex). If only one there is simultaneous vision. image is seen, one eye is suppressed. b. If only the cross or only the circles are seen, there is suppression in one eye. c) Have the patient assess the horizontal separation c) Ask the subject to identify the location of the of the two vertical lines (or measure by means of prisms) cross relative to the circles: a. If the cross is seen in the centre of the circles, a. If the two lines are aligned, there is ortho- phoria. there is orthophoria. b. If the cross is seen as off-centre, there is b. If the two lines are offset, there is (horizontal) heterophoria. heterophoria. (Combined horizontal and vertical phoria, or cyclophoria, may also be revealed with this test). Normally the patient should see both the red cross and the green circles. The cross should lie within the green circles. d) Now perform the test by dissociating the eyes by using a horizontal prism of 10 to 15 base in over one eye and by having the patient look at a horizontal line of letters; two images should be seen separated horizon- tally; any vertical heterophoria may be demonstrated and measured. Remember that for all dissociation tests: - If the image seen by the right eye is to the right and © Essilor International the image seen by the left eye is to the left, there is eso- phoria. Figure 33: The Schober Test 35 Copyright © 2008 ESSILOR ACADEMY EUROPE, 13 rue Moreau, 75012 Paris, France - All rights reserved – Do not copy or distribute.