Term
|
Definition
| represent the fastest eye movement in humans and primates which allow rapid refixation of objects. They exist because of fovea |
|
|
Term
| Abnormalities of fixation |
|
Definition
| slow drift, saccadic intrusions, nystagmus |
|
|
Term
|
Definition
| are irregular and slow fixation eye movement patterns typical found in functional amblyopia and has been observed in patients with macular scotomas |
|
|
Term
| How do slow drift affect vision |
|
Definition
| they cause the retinal image of a stationary target to impinge upon different retinal loci |
|
|
Term
| In patients with macular scotoma the velocity of drift tends |
|
Definition
| to increase as eccentric retinal locus increased. The condition may be assessed in visuoscopy. |
|
|
Term
|
Definition
| These represent abnormally large fixation saccades which can be seen as darting to-and-fro under the visuoscope and tend to occur when an attempt is made to fixate (foveate) a stationary target. |
|
|
Term
|
Definition
| Typically seen in patients with functional strabismus. They are sporadic in occurrence and are present in light and dark conditions as “back-to-back” oscillations with a 200 msec latency. They have a range of amplitude of (0.5-3 deg) |
|
|
Term
| Clinical Significance in Square Wave Jerks |
|
Definition
| 1. They are observed in normals 25-60%, but can be transiently suppressed in normals by the HOLD and FIXATE command. 2. When the saccades are consistently present with increasing frequency (>>30 per min), they may be diagnostic of: a. cerebellar disease b. early manifestation of a congenital nystagmus. |
|
|
Term
| Possible etiology for Square wave jerks of the abnormally large square wave jerks includes: |
|
Definition
| disorder of the Pause cells, cerebellar-related saccadic gain control (dysmetria) |
|
|
Term
| In the absence of an underlying disease condition, square wave jerks can be |
|
Definition
|
|
Term
|
Definition
| These are very larger [5-15 deg] saccades, They occur more frequently (at 2-3 Hz), Latency of 50-150 msec and remove the eye from the target for only about 100 ms. |
|
|
Term
| Macro Square-wave Jerks are primarily found in |
|
Definition
| cerebellar disease such as multiple sclerosis. |
|
|
Term
| Macro-saccadic Oscillations are different from macro square-wave jerks because: |
|
Definition
| 1. They produce a sequence of increasing and decreasing amplitude saccades on either sides of the fixation point. 2. They have inter-saccadic intervals of 200 msec. |
|
|
Term
| Macro-saccadic Oscillations represents the |
|
Definition
| classic case of an unstable high gain system oscillation. |
|
|
Term
|
Definition
| These are rhythmic involuntary oscillations of the eye. |
|
|
Term
|
Definition
| 50 % of patients with strabismus have nystagmus but only 15% of patients with congenital nystagmus have strabismus. It exists in either a pendulum or a jerk form. In the pendulum type foveation occurs at the peak of the waveform during which velocity is slowest. In the jerk type foveation occurs immediately after the rapid corrective saccade for ~100 msec |
|
|
Term
| Nystagmus characteristics |
|
Definition
| 1. Null Position of a nystagmus , This identifies the direction of gaze for which the intensity of the nystagmus is least with head in the straight-ahead position. 2. V.A. is optimal. 3. Patients with nystagmus tilt their heads in direction opposite to the null position. |
|
|
Term
|
Definition
| This is due to a high-gain instability in the slow control system and may be diagnostic of: 1. congenital (albinism) or acquired (demyelinating diseases; brainstem lesions and amblyopia).A congenital form is typically purely horizontal |
|
|
Term
| Pendular Nystagmus acquired form (components, amplitude, frequency, peak velocity |
|
Definition
| usually has vertical and torsional components and exhibit more inter-ocular waveforms variability. amplitude: 0.5-10 deg; typically 2-8 deg. frequency: 2-8 Hz peak velocity: ~100 deg/sec |
|
|
Term
| Pendular Nystagmus Treatment: |
|
Definition
| auditory biofeedback therapy |
|
|
Term
|
Definition
| Congenital jerk form: 1. seen during the first year of life 2. amplitude: 0.25-5 deg 3. frequency: 1-2 Hz 4. has an exponentially increasing slow phase velocities as high as 100 deg/sec 5. the slow phase moves the eye away from the object. |
|
|
Term
|
Definition
| It is horizontal and conjugate, corrective saccades return the eye to target for an extended foveation period of (50-100 msec) or more. Nystagmus intensity decreases in binocular near viewing. The direction of nystagmus is defined by the direction of the saccadic (fast) component |
|
|
Term
| Acquired Jerk Nystagmus (Gaze Evoked Nystagmus) Characteristics: |
|
Definition
| Similar in character to the congenital form. Has a slow phase velocity waveform that decreases exponentially. The slow phase moves the eye away from the eccentric position of gaze towards the midline. |
|
|
Term
| Acquired Jerk Nystagmus (Gaze Evoked Nystagmus) The physiological form (amplitude, frequency, and occurs when gaze angle is? |
|
Definition
| an amplitude of 1-2 deg., frequency of 1-3 Hz, occurs when gaze angle is 25-65 deg |
|
|
Term
| In manifest latent nystagmus, the direction is towards the |
|
Definition
| viewing eye. This condition reflects a leaky neural integrator with an exponential decay function. |
|
|
Term
| Nystagmus (Foveation Strategy) |
|
Definition
| Foveation of target occurs at positions 0 & 2 (Fig. 10) where eye velocity is slowest. In the pendulum form it corresponds to the peak of waveform. In the jerk form it is immediately after the saccade. |
|
|
Term
| Nystagmus types Congenital |
|
Definition
| Latent or Manifest Latent, Binocular, Horizontal, Jerk or pendulum, Diminished by convergence, Increased by attempted fixation, Inverted OKN, Torticollis , Abolished in sleep |
|
|
Term
|
Definition
| Opsoclonus or Ocular flutter, Oscillopsia |
|
|
Term
| The direction of nystagmus is defined |
|
Definition
| by the direction of the saccadic (fast) component |
|
|
Term
|
Definition
| decreases in binocular near viewing |
|
|
