From the Guidelines
Optokinetic asymmetry signifies a neurological abnormality, typically indicating a lesion in the parietal lobe or parieto-occipital region of the brain, which can be further evaluated using imaging studies such as contrast-enhanced MRI of the orbits or brain, as recommended by the American College of Radiology 1. When testing optokinetic nystagmus (OKN), a normal person should show similar eye movements regardless of whether the stimulus moves from left to right or right to left. However, in patients with optokinetic asymmetry, the response is diminished or absent when the stimulus moves toward the side of the brain lesion. Some key points to consider in the evaluation of optokinetic asymmetry include:
- The parietal cortex is responsible for processing motion in the contralateral visual field, making optokinetic asymmetry a valuable tool in diagnosing parietal lesions 1.
- The asymmetry can help differentiate between central and peripheral causes of dizziness or balance disorders.
- Testing for optokinetic asymmetry is performed using an OKN drum or tape with alternating black and white stripes moved horizontally in both directions while observing the patient's eye movements. In terms of imaging, the American College of Radiology recommends the use of contrast-enhanced MRI of the orbits or brain to evaluate visual loss localized to the orbit or disease process involving the pre-chiasmatic optic nerve, which can be complementary to the evaluation of optokinetic asymmetry 1.
From the Research
Optokinetic Asymmetry Significance
- Optokinetic asymmetry is associated with disruption of early binocular visual development 2
- It can occur in patients with congenital esotropia who are aligned early and develop high-grade stereo acuity 2
- Even brief periods of strabismus during the early period of binocular motor development can result in persistent OKN asymmetry 2
- Unilateral lesions of the central nervous system may be associated with a reduction of the optokinetic nystagmus slow component in the direction of the lesion, leading to asymmetry 3
- OKN asymmetry can be a clinical sign of an insult to early binocular motor development 2
- Asymmetry in OKN response can also be observed in normal individuals, with a preference for upward stimulus motion 4, 5
Factors Influencing Optokinetic Asymmetry
- Target size, shape, contrast, and velocity can influence OKN gains 6
- Visual field defects can contribute to OKN asymmetry in patients with central nervous system lesions 3
- Binocular viewing conditions can affect OKN gain, with higher gain observed during binocular viewing compared to monocular viewing 4
- Stimulus velocity can impact the sustainability of vertical OKN responses, with velocities above 30 degrees s-1 leading to less sustained responses 5