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Non-Organic Vision Loss
Published in Vivek Lal, A Clinical Approach to Neuro-Ophthalmic Disorders, 2023
Ashwini Kini, Mangayarkarasi Thandampallayam Ajjeya, Padmaja Sudhakar
The optokinetic drum is a drum with vertical stripes which can be rotated to elicit optokinetic nystagmus in the viewer's eye (pursuit with refixation saccade) (Figure 13.1). In a patient who claims to be unilaterally or bilaterally blind to the extent of no light perception (NLP), light perception (LP) or hand motions, eliciting a nystagmus with OKN drum establishes a vision of at least 20/400. In bilaterally blind, test is conducted with both eyes open and when unilateral, the test is started with both eyes open and the examiner introduces an occluder in front of the good eye during the course of the test to elicit nystagmus in the claimed blind eye (14).
When There Are Symptoms But it All Looks Totally Normal
Published in Amy-lee Shirodkar, Gwyn Samuel Williams, Bushra Thajudeen, Practical Emergency Ophthalmology Handbook, 2019
Optokinetic drum: This is a simple device made up of a rotating drum with vertical lines on its sides. Looking at the rotating lines will elicit fast and slow phases of nystagmus in patients with at least 6/60 vision. This is an involuntary response to the moving stimulus and is therefore a more objective test (see Figure 25.2). The mirror test is a similar variation on the same principle. A mirror rotating on the vertical axis is positioned in front of the patient. The moving image on the mirror will produce a similar involuntary response.
Mickey
Published in Walter J. Hendelman, Peter Humphreys, Christopher R. Skinner, The Integrated Nervous System, 2017
Walter J. Hendelman, Peter Humphreys, Christopher R. Skinner
General physical examination is normal; neurological exam is also normal except that she is unable to visually track an optokinetic drum (see Figure 13.9) when it rotates from left to right; no difficulty tracking from right to left.
Ophthalmoplegia: Definition and Clinical Diagnostic Techniques
Published in Journal of Binocular Vision and Ocular Motility, 2018
Saccades, or rapid eye movements, can sometimes be used to differentiate a restriction from a palsy. Saccades directed into the limited field of gaze are reduced in velocity if the limitation is due to a palsy,4 but of normal velocity (though reduced in amplitude) in a restriction. Saccades are tested by holding two similar targets, separated horizontally or vertically by no more than 30 cm. The patient is instructed to repeatedly switch fixation from one target to the other, without moving the head. Alternatively, the examiner may evaluate reflexive saccades by observing optokinetic nystagmus. Using the optokinetic drum or tape moving in a direction opposite to the gaze limitation, the velocity of saccades toward the limited gaze can be evaluated. A mild paresis may not reduce saccadic velocity enough to be detected by observation alone. In this case, the assistance of electro-oculography or eye-tracking devices may be necessary. In the absence of this specialized equipment, observation of saccades may still be useful when performed in conjunction with the other tests described above.
Congenital Nystagmus and Its Congeners
Published in Journal of Binocular Vision and Ocular Motility, 2020
When testing visual acuity in congenital nystagmus, the following examination strategies can be invoked to provide the most useful information: Make sure that the nystagmus stays horizontal in upgaze. This is the “moment of truth” maneuver that defines congenital nystagmus and tells you that this patient belongs in an ophthalmologist’s office and not a neurologist’s office.In an infant with congenital nystagmus, spin the optokinetic drum vertically to see if they can follow the targets (as indicated by the conversion of horizontal to diagonal nystagmus as the vectors summate). David Cogan is credited with recognizing that the ability to superimpose downward optokinetic responses on the nystagmus signifies that the child will develop fairly good vision and will likely be mainstreamed into the regular school system. Contrary to what Cogan believed, however, this maneuver cannot be used to rule out underlying sensory visual dysfunction, as many children with albinism and other sensory visual causes retain the ability to generate vertical optokinetic responses.Test distance and near acuity both monocularly and binocularly.20 Let the child maintain their habitual head posture during the examination.20Since congenital nystagmus may be accompanied by latent nystagmus, use a + 5.00 lens in place of monocular occlusion when assessing visual acuity, since this has been shown to minimize the superimposition of latent nystagmus.21In children with large head turns, observe the child for 2–4 minutes for a reversal of the head turn indicating periodic alternating nystagmus, a condition much more common in children with albinism.20,22In children with abnormal head positions, turn the head in the opposite direction to see if the nystagmus intensifies, in accordance with a true null position.