Slow Eye Research Articles

Effect of off-vertical tilt and macular ablation on postrotatory nystagmus in the squirrel monkey.

The slow phase eye velocity (SPEV) and duration of post-rotatory nystagmus (PRN) were studied in squirrel monkeys (Saimiri sciureus) after a ramp speed rotation (0-200 degrees/sec, with 1 degree/sec2 angular acceleration). When the results were compared between straight upright vertical rotation, 9 degrees tilt rotation, and 18 degrees tilt rotation, faster decay both in SPEV and in duration was found in the tilt rotation situations. Difference in nystagmic decay curves by tilting rotation axis could be from the convergence of macula-semicircular canal inputs. Subsequently bilateral macular ablation (two-stage) was performed. The difference in nystagmus decay curves between three different rotations was reduced; therefore, the change of gravity direction perceived through gravity receptors other than macular endorgans was minimal and did not produce a difference in three different rotations.

Changes in the Rat Electrocorticogram following Administration of Two Dihydrogenated Ergot Derivatives

Dihydroergotoxine mesylate (DHET; active substance of Hydergine) and dihydro-beta-ergosine altered the sleep-wakefulness cycle of the rat by increasing wakefulness and decreasing slow wave and rapid eye movement sleep. In addition, power spectrum analysis indicated that, in comparison with placebo, DHET increased total power. Dihydro-beta-ergosine increased relative power in the theta-(4--8 Hz) and in the fast beta-(30--40 Hz) bands of ther electrocorticogram. The alterations in the sleep-wakefulness cycle and in the distribution of power in the rat electrocorticogram are discussed as possible indices of changes in alertness and attention.

Effect of otolith end organ ablation on pendular rotation nystagmus in squirrel monkeys

Damped pendular rotation nystagmus was studied in squirrel monkeys before and after otolith end organ ablation (two-stage operations). After each operation, the nystagmic slow phase eye speed toward the operated side was reduced (to about 73% of that before the operation) and that to the non-operated side did not show any marked change. A few subjects showed spontaneous nystagmus with amphetamine administration but only in dark (could not be found in light) immediately after the operation, and it disappeared rapidly. Therefore, this post-ablative reduction of the slow phase eye speed is considered to result from the loss of inputs from the otolith end organs.

MITNYS-II--a digital program for on-line analysis of nystagmus.

A digital computer program, MITNYS-II, has been developed for on-line analysis of nystagmus which results from visual, vestibular or caloric stimulation. The program accepts sampled records of eye position and yields cumulative slow phase position, slow phase velocity, instantaneous fast phase frequency and other parameters in 25 ms. In this paper the algorithms by which fast phases are detected, and by which slow phase cumulative eye position is extrapolated across the fast phase interval are described. Extensive tests with vestibular, optokinetic and caloric nystagmus yield reliability figures of the order of 2% for false identification of fast phases and missed fast phases. MITNYS-II has been successfully employed to interpret clinical EOG records, examples of which are presented.

Parametric study of postrotatory nystagmus in normal squirrel monkeys.

In order to find the most consistent nystagmic parameter following rotation, 16 healthy young adult squirrel monkeys were rotated from 0 to 200 degrees/sec with 1 degrees/sec2 constant angular acceleration and then abruptly stopped. This centric horizontal rotation was performed in a dark room without the eyes being covered. Horizontal eye movement of the postrotatory nystagmic response was recorded: maximum slow and quick phase eye speeds, nystagmic duration, amplitude, number of beats, and maximum average frequencies were studied. The maximum frequency of the nystagmic beats was statistically confirmed at the least variable parameter among the seven parameters. The importance of baseline establishment in the animal nystagmus experiment was emphasized.

Value of rotational tests in the diagnosis of vestibular disease.

Caloric irrigation of the external ear canal represents an inadequate vestibular stimulus because the method is not physiologic and the canal irrigation and the heat transfer to the inner ear cannot be well controlled. In rotational testing an accurate acceleration profile can be applied with an appropriate rotating device. A test procedure is presently being used, which consists of constant acceleration at 3°/sec2 for 50 seconds, hold at constant velocity for 240 seconds, followed by a similar deceleration (equivalent to acceleration in the revelse direction) and hold. On-line data reduction of the nystagmus response is accomplished automatically using a simple analog technique. This technique provides a concise presentation (on a standard size sheet of paper) of the total slow phase eye displacement resulting from the primary and secondary responses and enables comparison of the results for both directions of acceleration. Experience with the routine use of rotational testing in a vestibular clinic and the significance of various paterns of response with special emphasis on vestibular adaptation function are discussed.