Quick and precise eye movements are critical to fixate and stabilize an image on the retina. The retina is the spot on the inner lining of the back wall of the eye that captures light and images. It is necessary to maintain a fixed image on the retina to stabilize vision during body movement. The neck and the eyes work together to stabilize and localize an image by vestibular and optokinetic reflexes. The reflexes present a platform for the execution of voluntary eye movements.
Optokinetic eye movements occur when the visual field is in motion, such as when a person is looking out through the window of a moving vehicle. The optokinetic reflex or optokinetic nystagmus (OKN) is the primary system that stabilizes an image on the retina in a mobile environment or during head movements. It induces eye movement in reaction to the objects in motion in the margins while a person's head is stationary. OKN is marked by a slow, steady eye movement in line with the mobile scene to stabilize the image on the retina.
The optokinetic system works with the vestibular system to retain the focus of the picture on the retina in head movements. The vestibulo-ocular reflex causes eye movement in the side opposite to the head movement. When a person looks at a moving scene, their eye movements consist of slow movements in the direction of the object and rapid shift in the opposite direction. There is a combined stimulation of the optokinetic and vestibular systems. The optokinetic reflex can compensate for slow or sustained head movements, which are poorly distinguished through the vestibular system. It works to stabilize retinal images.
The optokinetic system is evident in infants at about six months of age and continues throughout life. It is essential in daily experiences such as driving, sports, leisure travel, etc.
Also Known As
- Optokinetic reflex
- Optokinetic nystagmus
Problems & Disorders
Optokinetic system abnormalities include:
- Neurodevelopmental disorders, such as amblyopia
- A child who can't do the Random E test by five years of age
- Lower facial weakness where the middle cerebral artery is affected
- Ocular motor abnormalities – the ocular motor is not functioning properly
- Acquired alexia – for example, where a patient pretends they need glasses
There is a wide range of factors that can cause abnormal OKN responses, including:
- Parietal injury
- Aberrant regeneration of the third nerve
- Poor visual acuity in infants and young children
- Parinaud's syndrome - an inability to move the eyes up and down
- Subclinical internuclear ophthalmoplegia - This is an anomaly of conjugate sideways stare in which the affected eye displays impairment of adduction
The optokinetic response is used to evaluate the condition of the visual system. The OKN test may include:
- Optokinetic drum
- Optokinetic tape or flag
- Computer-aided measurement
The optokinetic drum is the most frequently used technique. The patient will sit next to a table. The doctor will set up a drum on the table such that it rotates around a vertical line at the patient's eye level. The test will begin with the patient looking at the drum at a range of approximately 40 centimeters. The doctor will start the motor and select a rotating speed for the drum and instruct the patient to focus on the spinning drum. Then he/she will gradually move the patient away from the drum and note the distance at which the optokinetic response is no longer evident.
The doctor may also use a mirror instead of a drum. He/she will hold a mirror before the patient and gradually turn it around to either side of the patient. It is an effective optokinetic stimulus that forces reflex slow eye movements. A patient with a sound, visual pathway will keep eye contact with themselves.
It is essential to detect vision disorders in early childhood to prevent neurodevelopmental conditions. However, reliable clinical measurement of visual function in younger children is a challenge. Computer-aided measurement and analysis are particularly useful in young patients. It is quick, non-invasive, and allows unrestrained head movement. The method can facilitate rapid, accurate and controlled clinical measurement of visual function in children, including the uncooperative nonverbal patients.
The doctor may also use the OKN test to expose deceit or malingering.
Many forms of optokinetic-vestibular conditions can be treated with physical therapy, drug therapy, or psychotherapeutic measures. In rare cases, the doctor may suggest surgery.
Optokinetic stimulation is efficient in stimulating the brain and is an invaluable therapeutic technique. Optokinetic or eye movement exercises are effective in increasing the activation of brain areas that could be functioning below their average capacity.
The doctor may prescribe drugs to treat ocular motor, central vestibular and cerebellar disorders, such as episodic ataxia type 2, vestibular migraine and upbeat, downbeat and other types of nystagmus.
The doctor may prescribe contact lenses or eyeglasses in some cases, such as nystagmus, to help the patient see well.
However, many other optokinetic-vestibular disorders, like ocular flutter opsoclonus, see-saw nystagmus, or central positioning, are still challenging to treat.