Overview & Introduction

Nystagmus- Is involuntary rapid movements of the eyeballs consisting of fast and slow phases; named according to direction of fast phased. Nystagmus refers to involuntary rhythmic movement of the eyes that include two components: a slow drifting away from the target and a fast return to the target.

Some people are born with Nystagmus as it can be be inherited and show up in childhood development or in the adult life. Sometimes Nystagmus is due to some sort of illness or accident. The main thing that is understood about Nystagmus is that it is an underlying eye and medical problems.

There are many type of nystagmus conditions out there but this page will only focus on a few main conditions of nystagmus.

· Functional anatomical review (including structure(s), location…)

External eye anatomy
External eye anatomy

· Input & Output pathways (e.g., neuronal connections)

The input and output pathways are going to be the same with nystagmus as with any eye movement. The input comes comes from the first the photorecptors (rods and cones) The information gathered by millions of receptor cells is projected next onto millions of bipolar cells, which, in turn, send projects to retinal ganglion cells. These cells encode different aspects of the visual stimulus, and thus carry independent, parallel, streams of information about stimulus size, color, and movement to the visual thalamus.
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The voluntary saccades circuit. The frontal eye field generates the command signals that initiate eye movement in a contralateral direction (i.e., to the right in this figure). The signal is sent to the superior colliculus and caudate nucleus. The superior colliculus, in turn, sends control signals to the gaze centers in the midbrain and pons reticular formation. The posterior parietal cortex, part of the dorsal visual stream, determines whether the visual target has been achieved and sends corrective signals to the frontal eye field and superior colliculus when the visual target has not come into view. The basal ganglion structures, the caudate and substantia nigra, help regulate the action of the superior colliculus.

· Presentation of the topic or issue in detail

Nystagmus as previously stated, is a vision disorder where uncontrollable, and repetitive movements of the eyes can cause reduced vision. The motions that these eye can produce are horizontal, vertical and torsional (circular motion). Due to this issue, eyes are unable to hold steady to an object being viewed. People with this condition will often times try unusual head movements and position as a means of compensating for it all.

Forms of Nystagmus can include:
  1. Congenital - develops between 2-3 months of age. Eyes move in a horizontal swinging motion. This form of nystagmus is is commonly associated with other medical conditions such as albinism, congenital absence of the iris, congenital cataract and undeveloped optic nerves

  2. Spasmus nutans - develops b+etween 6 months and 3 years of age but will go away between 2-8 years of age. Children with this condition display head nodding and tilt. Their eyes can move in any direction. It doesn't require treatment.

  3. Acquired - Becomes present during later childhood or adulthood and maybe due to a central nervous system disorder.

  4. Pendurlar - eyes move in the same direction, at the same speed
  5. Jerk Nystagmus - eyes will move slowly in one direction and then jerk back quickly in the other direction
  6. Optokinetic Nystagmus - mix of smooth pursuit and saccades
  7. Pathological Nystagmus - eyes move slowly from fixed position or intended position and results from abnormality in neuro-regulatory gaze-holding system controlling eccentric gaze

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· Summary or concluding paragraph

Nystagmus is caused from an instability or malfunction of the structure responsible for controlling eye movements. In early childhood development nystagmus can be due to an issue with the visual pathway to the brain. When acquired nystagmus occurs it can be due to other conditions such as stroke or a blow to the head.

How is nystagmus diagnosed?
  1. Nystagmus can be diagnosed through a comprehensive eye exam. Testing for nystagmus, with special emphasis on how the eyes move, may include:
  2. Patient history to determine any symptoms the patient is experiencing and the presence of any general health problems, medications taken, or environmental factors that may be contributing to the symptoms.
  3. Visual acuity measurements to assess the extent to which vision may be affected.
  4. A refraction to determine the appropriate lens power needed to compensate for any refractive error (nearsightedness, farsightedness, or astigmatism).

Testing how the eyes focus, move and work together. In order to obtain a clear, single image of what is being viewed, the eyes must effectively change focus, move and work in unison. This testing will look for problems that affect the control of eye movements or make it difficult to use both eyes together.

Since nystagmus is often the result of other underlying health problems, your optometrist may refer you to your primary care physician or other medical specialist for further testing.

Nystagmus cannot be cured.

While eyeglasses and contact lenses do not correct nystagmus, they can help to correct other vision problems such as nearsightedness, farsightedness or astigmatism.

Some types of nystagmus improve throughout childhood. In addition, vision may be enhanced with prisms and special glasses. The use of large-print books, magnifying devices and increased lighting can also be helpful.

Rarely, surgery is performed to alter the position of the muscles, which move the eyes. While it does not cure nystagmus, it may reduce the amount of head turn needed for best vision.

Treatment for other underlying eye or medical problems may help to improve or reduce nystagmus.

· Glossary of terms

  • Superior oblique will aid in turning the eye downwards and outwards (due to cranial nerve IV)
  • Superior rectus turns the eye upwards and downwards (due to cranial nerve VI)
  • Lateral rectus rotates eye laterally/horizontally with antagonist relaxation of medial rectus (due to cranial nerve (VI)
  • Medial rectus rotates eye medially/horizontally with antagonist relaxation of lateral rectus (due to cranial nerve III)
  • Inferior rectus turns the eye inwards and downwards (due to cranial nerve III)
  • Inferior oblique turns eye upwards and outwards (due to cranial nerve VI)
  • Albinism - A melanin deficiency that leads to little or no color in eye
  • Congenital- present from birth
  • Occulomotor nerve- innervates the medial, superior and inferior recti & the inferior oblique (CN III)
  • Trochlear nerve - innervated the superior oblique (CN IV)
  • Abducens nerve - innervates the lateral rectus (CN VI)
  • Smooth pursuit - stable viewing of moving object
  • Saccades - Keeps target in field of view voluntary or reflex based
· Listing of relevant links or suggesting readings (include a brief description of content)

  1. Basic Clinical Neuroscience (2nd ed) - Clinical book approach to human neuronanatomy and physiology
  2. http://neuroscience.uth.tmc.edu/ - Neuroscience website
  3. http://www.aoa.org/patients-and-public/eye-and-vision-problems/glossary-of-eye-and-vision-conditions/nystagmus#1 - Optometry website
· Quiz questions & answers (5-10 Multiple Choice / T-F & 3-5 Short Answer / Essay)

  1. T or F - Nystagmus can be a congenital disorder ?
  2. What are the three type of eye movements during nystagmus ?
  3. Which cranial nerve innervates the superior rectus ?
  4. T or F - Pendular nystagmus causes the eyes to move in the same direction at different speeds?
  5. T or F - Congenital nystagmus is is acquired at age 2?
  6. Which muscle/s does the cranial nerve IV control ?
  7. Maintaining a stable view on a moving object is what kind of eye movement?
  8. T or F - The central eye fields generates commands that innitiate eye movement in the ipsilateral direction?
  9. T or F - Unusual head positions are done by people with nystagmus to compensate for keeping focus on object being viewed?
  10. Which eye muscle innervates the eye inwards and downwards?

- Answers
  1. T
  2. Horizontal, vertical, Torsional
  3. Cranial Nerve IV- Trochlear nerve
  4. F
  5. F
  6. Superior Oblique
  7. Smooth Pursuit
  8. F
  9. T
  10. Inferior rectus
· References