Visual Suppression Of Caloric Nystagmus Research Articles

Differential diagnosis of cerebellar and brain stem lesions by means of a visual suppression test

Visual suppression is one method of demonstrating the function of visual fixation. Visual suppression is calculated by measuring the slow phase velocity of caloric nystagmus with eyes covered in darkness and that with eyes open, fixed in light.Visual suppression was 54±12% in 52 normal adults.Clinical cases of typical and localized lesions in the cerebellum or brain stem were selected and tested. Visual suppression of caloric nystagmus towards the lesion side was reduced or abolished in cases of cerebellar (especially flocculus or nodulus) lesions. Visual suppression of caloric nystagmus towards both sides was reduced or abolished in cases of diffuse or bilateral cerebellar lesions. Visual suppression of caloric nystagmus towards the lesioned side was strongly abolished and even augmentation of caloric nystagmus in light with eyes fixed was seen in cases of brain stem (especially pontine) lesions.Thus, with this visual suppression test it can be determined whether the lesions are in the cerebellum or in the brain stem.

Visual suppression test

Visual suppression of caloric nystagmus was studied in normal adults and in 98 clinical cases in order to justify the application of the procedure as a clinical test. The maximum slow phase velocity during ten seconds in darkness and the slow phase velocity during ten seconds in light were taken from the recordings and measured. The mean values of these slow phase velocities were calculated and the mean slow phase velocity in darkness was assigned a value of 100%. The value which the slow phase velocity in light subtracts from the slow phase velocity in darkness, represents the visual suppression. It was determined that visual suppression of the slow phase velocity of caloric nystagmus was 48 +/- 10% in 22 normal adults. This was caused by the visual fixation mechanisms. Cases in which lesions were diagnosed in the cerebellum, such as spinocerebellar degeneration and cerebelitis, showed reduced or abolished visual suppression. The lesion side can be determined by this test. Compensation following unilateral sudden loss of inner ear function can be measured by the visual suppression test.

Visual Suppression Test

Visual suppression of caloric nystagmus was studied in normal adults and in 98 clinical cases in order to justify the application of the procedure as a clinical test. The maximum slow phase velocity during ten seconds in darkness and the slow phase velocity during ten seconds in light were taken from the recordings and measured. The mean values of these slow phase velocities were calculated and the mean slow phase velocity in darkness was assigned a value of 100%. The value which the slow phase velocity in light subtracts from the slow phase velocity in darkness, represents the visual suppression. It was determined that visual suppression of the slow phase velocity of caloric nystagmus was 48 +/- 10% in 22 normal adults. This was caused by the visual fixation mechanisms. Cases in which lesions were diagnosed in the cerebellum, such as spinocerebellar degeneration and cerebelitis, showed reduced or abolished visual suppression. The lesion side can be determined by this test. Compensation following unilateral sudden loss of inner ear function can be measured by the visual suppression test.

Clinical significance of visual fixation upon caloric nystagmus-caloric pattern test- (author's transl)

The effect of opening of the eyes and of ocular fixation upon caloric nystagmus has been routinely tested in our neurotological assessment of patients since 1974. All cases who showed a sign of FFS (Failure of Fixation-Suppression of Caloric Nystagmus) were found to have central nervous 'system '.lesions, especially posterior fossa lesions. From an analysis of caloric nystagmus with the sign of FFS, patterns of FFS were classified into the following three types. Type I Visual fixation failed to suppress caloric nystagmus to both directions. In this type, diffuse involvement of the central nervous system such as cerebellar degeneration, organic mercurials intoxication and myoclonus epilepsy was included. Type II : Visual suppression of caloric nystagmus could not be observed on either side regard-less of water temperature applied as caloric' stimuli. In this type, cerebellopontine angle syndrome such as acoustic tumor, meningioma, epidermoid and arachnoiditis was included. Type III: Visual fixation failed to suppress caloric nystagmus to either direction depending upon caloric stimuli. In this type, vascular disorder, head trauma and unilaterally located tumor of the cerebellar hemisphere were included. On the basis of our clinical data classified above, underlying neuroanatomical mechanism was discussed.

Loss of visual suppression of vestibular nystagmus after flocculus lesions

Eye movements of rhesus monkeys were studied after flocculus and paraflocculus lesions. Positional nystagmus, gaze nystagmus, optokinetic nystagmus (OKN) and visual suppression of caloric nystagmus was present to the operated side after bilateral flocculus lesions. Gaze nystagmus was present to the operated side after unilateral flocculus removal, and in all directions after bilateral lesions. Optokinetic nystagmus (OKN) was altered after unilateral and bilateral flocculus destruction. Animals were unable to follow OKN drum rotation at velocities higher than 45°/sec after bilateral flocculectomy. Caloric nystagmus in darkness was unaffected by floccular destruction. Initially after unilateral flocculus removal there was ipsilateral directional preponderance but this later disappeared. Visual suppression of caloric nystagmus, a reproducible phenomenon in the monkey, was lost or significantly reduced by flocculus destruction. After unilateral flocculus removal visual suppression of caloric nystagmus was lost or reduced when quick phases were directed to the ipsilateral side. After bilateral flocculus destruction suppression of caloric nystagmus was lost or reduced in both directions. Suppression of spontaneous nystagmus and PAN was also reduced after flocculus destruction. These data suggest that the flocculus exerts an inhibitory influence on mechanisms responsible for production of nystagmus with ipsilateral quick phases and contralateral slow phases. They support the hypothesis that the flocculus is a medium through which the visual system can alter or modify vestibular reflexes.