Excitable cells 18: (McLean) PAthologic Nystagmus

Question 1

What is pathological nystagmus?

Answer 1

Involuntary constant to and fro movement of the eyes that is constant

Question 2

Main difference between infantile and acquired nystagmus?

Answer 2

Acquired sufferers experience oscillopsia -> the world moving around

Question 3

What happens in Electroculography

- adv. + dis.

Answer 3

2D

Cornea-retinal potential - difference in charge between cornea and retina - electrodes detect this

Movement of the eye relative to the electrode produces an electrical signal that corresponds to eye position

easy to set up

Question 4

Describe process of limbus tracking

- adv. + dis.

Answer 4

2D

Measures infrared light shone onto limbus (border of dark iris and light sclera)

As eye moves, light reflected changes based on eye position

High temporal resolution + non-invasive but needs to be precise

Question 5

Describe process of Video-oculography

- adv. + dis.

Answer 5

2D

Infrared tracking of pupil for eye movement and screen markers for head

High temporal and spacial resolution but does not record during blinks - can record gaze (head + eye position)

Question 6

Describe use of sclera search coil

- adv + dis.

Answer 6

3D

Magnetic contact lens inserted into eye

Gold standard - high resolution spatially and temporally
but invasive and uncomfortable

Question 7

Describe use of 3D video-oculography

Answer 7

3D

tracks pupil for verticle movements and iris to follow torsional

Lower res than sclera search coil but less invasive

Question 8

What characteristics should be considered in a nystagmus trace?

Answer 8

1) Intensity
- amplitude of oscillations

2) Plane
- 3D direction of eye movement

3) Wave form
- jerking, pendular, complex etc.
- any difference between individual eyes (conjugate, disconjugate)

4) Time
- frequency of oscillations

5) Occlusion
- patching ‘fixing’ eye sees nystagmus worsen

6) COnvergence
- changes in oscillation pattern at difference focus distances

7) Eccentricity
- head position has ‘null zone’ - where nystagmus is quietest

Question 9

Vision / eye defects in albinism?

Answer 9

Hypopigmentation -> light usually blocked by iris, but can shine through in albino individual

Poorly developed foveal pit

Nystagmus

Chiasmal abnormalities