Correlation between vestibulo-ocular reflex and optokinetic afternystagmus in normal subjects and in patients with vestibular system disorders.

Optokinetic afternystagmus follows optokinetic nystagmus as an expression of the central velocity storage integrator discharge and its fast phase is beating in the same direction as the previous optokinetic nystagmus. We investigated the correlation between vestibulo-ocular reflex and optokinetic afternystagmus in normal subjects and in patients with bilateral vestibular disorders. The aim of this study was to determine the possible role of optokinetic afternystagmus as a diagnostic test for identifying functional vestibular disorders. The subjects were examined by electronystagmography and vestibulo-ocular reflex, optokinetic nystagmus stare type as well as optokinetic afternystagmus were recorded. They were restrained in a rotatory drum chair, both the chair and the drum could be rotated, independently or coupled. For vestibulo-ocular reflex analysis, we studied post-rotatory-nystagmus from a velocity of 90 degrees s. Optokinetic nystagmus was recorded at a drum velocity of 30 degrees s and the registration continued in total darkness, after the illumination was switched off, to study optokinetic afternystagmus. We considered vestibulo-ocular reflex and optokinetic nystagmus gain, vestibulo-ocular reflex and optokinetic afternystagmus constant of time (tc) defined as the time necessary for the slow phase eye velocity to be reduced to 37% of its initial value. Results demonstrated that vestibulo-ocular reflex gain and ct showed a significant difference only in patients with reduced vestibular reflexia, while optokinetic nystagmus gain was greater only in patients with increased reflexia; optokinetic afternystagmus ct was different from the control group only in patients with hyporeflexia. In conclusion, our results suggest that vestibulo-ocular reflex and optokinetic afternystagmus ct are clinically more useful than the gain alone in testing vestibular disorders with hyporeflexia. On the other hand, we propose a new mathematical and statistical approach to study the temporal evolution of more parameters of the nystagmus.

Static and dynamic posturography in patients with asymptomatic HIV-1 infection and AIDS.

Alterations of the vestibulo-ocular reflex, optokinetic nystagmus, and visuo-vestibular-ocular reflex, have already been described in patients with AIDS and HIV-1 positive asymptomatic subjects. The introduction to the clinical practice of posturographic techniques allows us to study, with precision, postural perturbation that may be present when performing Romberg's test and to study the vestibulo-spinal reflex as a component of the vestibular system. The relative lack of studies on posturography and AIDS, encouraged us to continue our research on the vestibular system both in asymptomatic HIV-1 seropositive patients and in patients with AIDS (IV stage according to the classification proposed by the Centre for Disease Control). Recordings were made in group 1 (control group, 55 normal subjects), in group 2 (15 asymptomatic HIV-positive subjects), and in group 3 (15 patients with AIDS stage IV). Static and dynamic posturography were carried out using Tonnies platform system (Tonnies GmbH & Co., Wurzburg, Germany) and the data were analysed with Tonnies Posturographic Tübingen (TPOST) software vers. 5.19. In asymptomatic HIV+ subjects, we observed an increase in RW, RA and M3 reflex latency. AIDS patients (stage IV) exhibited significant alterations in almost all the posturographic parameters and the electromyographic potentials. Our results validate static and dynamic posturography as a method for otoneurological investigation and appear to confirm that the entire vestibular system is involved since the earliest stages of the HIV infection. In the HIV+ subjects, a variable dysfunction in the reflex control to long latency was observed, which is correlated with the alteration of the central dopaminergic system; in AIDS patients, the central nervous system damage appears more important, globally distributed and correlated also with immunosuppression.

[Optokinetic nystagmus and visual-vestibular interaction in subjects with "whiplash injuries"]. / Il nistagmo otticocinetico e d'interazione ottico vestibolare in soggetti con "colpo di frusta cervicale".

We studied the behaviour of Vestibular Nystagmus (VOR), of Optokinetic Nystagmus (OKN) and of Visuo-Vestibular-Ocular-Reflex (VVOR) in seven normal subjects and in thirty-two patients who had undergone cervical trauma in an automobile accident with the so called "whiplash mechanism". Thirteen subjects underwent examination within the first three months after the accident (first group), six subjects between the third and the sixth months (third group). Ocular movements was recorded according to the usual method by means of a Tonnies electronystagmograph with eight channels. The subjects, head blocked, sat on a Tonnies rotatory chair Pro model which was placed in the middle of a rotatory cylindrical chamber 2 metres in diameter and 1.9 metres in height. The width internal area was covered with thirty-two black vertical contrast. The rotatory cylinder was lighted from above by a 100 W bulb and was driven by a direct current engine which turned it clockwise and counterclockwise up to 200 degrees/sec., maximum speed, with preset acceleration ranging from 1 degree to 2 degrees/sec. All the subjects underwent to Rotatory Vestibular Stimulation by Stop test from a constant angular velocity of 90 degrees/sec. with clockwise and counterclockwise rotation, "stare type" Optokinetic stimulation with a cylinder rotation velocity of 30 degrees/sec. for 60 seconds and to contemporary Rotatory Vestibular and Optokinetic Stimulation (VVOR) so that OKN was VOR counterdirectional. The results of our experience show a statistically significative mean gain decrease of VOR and VVOR nystagmus (beating OKN direction) calculated on the first three beats in the patients of the first group and a significative increase of OKN mean gain in all the patients of the three groups. Furthermore, in sixteen out of thirty-two patients (seven in the first group, two in the second and seven in the third) we observed (during VVOR examination, immediately after stop) a nystagmus beating VOR direction lasting from 3 to 15 seconds.