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Individual differences |
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The optokinetic reflex is a combination of a saccade and smooth pursuit eye movements. It is seen when an individual follows a moving object with their eyes, which then moves out of the field of vision at which point their eye moves back to the position it was in when it first saw the object. The reflex develops at about 6 months of age.
Optokinetic nystagmus (OKN) is nystagmus that occurs in response to a rotation movement. It is present normally. The optokinetic reflex allows the eye to follow objects in motion when the head remains stationary (e.g., observing individual telephone poles on the side of the road as one travels by them in a car).
Eliciting optokinetic nystagmus (OKN)Edit
If an optokinetic drum is available, rotate the drum in front of the patient. Ask the patient to look at the drum as you rotate it slowly. If an optokinetic drum is not available, move a strip of paper with alternating 2-inch black and white strips across the patient's visual field. Pass it in front of the patient's eye at reading distance while instructing the patient to look at it as it rapidly moves by. With normal vision, a nystagmus develops in both adults and infants. The nystagmus consists of initial slow phases in the direction of the stimulus (smooth pursuits), followed by fast, corrective phases (saccade). Presence of nystagmus indicates an intact visual pathway. Another effective method is to hold a mirror in front of the patient and slowly rotate the mirror to either side of the patient. The patient with an intact visual pathway will maintain eye contact with herself or himself. This compelling optokinetic stimulus forces reflex slow eye movements.
OKN can be used as a crude assessment of the visual system, particularly in infants. When factitious blindness or malingering is suspected, check for optokinetic nystagmus to determine whether there is an intact visual pathway.
- ↑ Atkinson J (1984). Human visual development over the first 6 months of life. A review and a hypothesis. Hum Neurobiol 3 (2): 61–74.
- Marx: Rosen's Emergency Medicine, 7th edition.
- Goldman: Goldman's Cecil Medicine, 24th edition.
- Yanoff & Duker: Ophthalmology, 3th edition.
Nervous system physiology: neurophysiology - reflex