lecture 10

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Optometry Dep. Al Nasser Eye Hospital 10th BY DR. AMER ISMAIL ABU IMARA JORDANIAN BOARD OF OPHTHALMOLOGY I.C.O. PALESTINIAN BOARD IN OPHTHALMOLOGY STRABISMUS

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1- BASE-OUT PRISM Base-out prism is a quick and easy method for detecting fusion in children . The test is performed by placing a 20 ∆ base-out prism in front of one eye ( in the following example in front of the right eye ) . This displaces the retinal image temporally with resultant diplopia . The examiner observes corrective eye movements as follows : TESTS FOR BINOCULAR FUSION IN INFANTS WITHOUT MANIFEST SQUINT

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There will be a shift of the right eye to the left to resume fixation ( right adduction ) with a corresponding shift of the left eye to the left ( left abduction ) in accordance with Hering law . The left eye will then make a corrective refixational saccade to the right ( left re-adduction ) . On removal of the prism both eyes move to the right . The left eye then makes an outward fusional movement .

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Most children with good BSV should be able to overcome a 20 ∆ prism from the age of 6 months ; if not weaker prisms ( 16 ∆ or 12 ∆ ) may be tried but the response is harder to observe . 2- BINOCULAR CONVERGECE Simple convergence to an interesting target can be demonstrated from 3-4 months . Both eyes should follow the approaching target symmetrically to the nose . Over-convergence in the infant may indicate an incipient esotropia . Divergence may reflect a tendency to divergence or lack of interest in the target .

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WORTH FOUR-DOT This is a dissociation test which can be used with both distance and near fixation , and differentiates between BSV, or ARC and suppression . Results can only be interpreted if the presence or absence of a manifest squint is known at time of testing . 1- procedure : The patient wears a green lens in front of the right eye , which filters out all colours except green , and a red lens in front of the left eye which will filter out all colours except red . The patient then views a box with four lights ; one red , two green and one white . TESTS FOR SENSORY ANOMALIES

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If BSV is present all four lights are seen. If all four lights are seen in the presence of a manifest deviation , harmonious ARC is present . If two red lights are seen , right suppression is present . If three green lights are seen , left suppression is present . If two red and three green lights are seen , diplopia is present . If the green and red lights alternate , alternating suppression is present . 2- results

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BAGOLINI STRIATED GLASSES This is a test for detecting BSV , ARC or suppression . Each lens have fine striations which convert a point source of light into a line , as with the Maddox rod . 1- procedure The two lenses are placed at 45°and 135° in front of each eye and the patient fixates a small light source . Each eye perceives an oblique line of light , perpendicular to that perceived by the fellow eye. Dissimilar images are thus presented to each eye under binocular viewing conditions .

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Cannot be interpreted correctly unless it is known whether or not strabismus is present : If the two streaks intersect at their centers in the form of an oblique cross ( an X ) , the patient has BSV if the eyes are straight , or harmonious ARC in the presence of manifest strabismus . If the two lines are seen but they do not form a cross , diplopia is present . If only one streak is seen , there is no simultaneous perception and suppression is present . 2- results

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In theory , if a small gap is seen in one of the streaks , a central suppression scotoma ( as found in microtropia ) is present . In practice this is often difficult to demonstrate and the patient describes a cross . The scotoma can be confirmed with the 4 ∆ test .

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4∆ TEST This test differentiates bifoveal fixation ( normal BSV ) from a central suppression scotoma in microtropia and employs the principle described in the 20 ∆ test ( Hering law ) and convergence to overcome diplopia . 1- in bifoveal fixation : the response is as follows : The prism is placed base-out in front of the right eye with deviation of the image temporally and movement of both eyes to the left . The left eye converges to fuse the images .

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2- in left microtropia with CSS : the response is as follows : - The patient fixates a distance target with both eyes open and a 4 ∆ prism is placed base-out in front of the left eye with suspected CSS . The image is moved temporally in the left eye but falls within the CSS and no movement of either eye is observed . The prism is then moved to the right eye which adducts to maintain fixation ; the left eye similarly moves to the left ( Hering ) , but the second image falls within the CSS and no refixation movement is seen .

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