Nystagmus is an eye condition in which the eyes beat back and forth and appear to shake to another person watching the eyes. This can be a symptom of another underlying problem or can occur alone.
Basics of Eye Movements
To fully understand nystagmus, first the basics of normal or typical eye movements must be understood.
In normal movements, the eyes can move together in unison to one direction or can move in opposite directions such as when crossing the eyes to look at a near object.
These movements are voluntary and require conscious thought to begin and end the movement.
There are also tiny involuntary movements which assist the eye maintain a clear, focused image when looking at something for an extended period of time.
While these movements are involuntary and do not require thought to make them, the movements also are so small that they are unnoticed.
Basics of Nystagmus
While normal eye movements are begun voluntarily, nystagmus is completely involuntary both to begin and end.
In nystagmus, both eyes are moving slowly in the same direction and then quickly moving back to the center or starting position.
The eyes can beat side to side, up and down, or in a diagonal pattern.
Unless the brain has adapted to the nystagmus, the nystagmus will produce a blurry or off-balance vision and may cause symptoms of motion sickness.
Causes of Nystagmus
Nystagmus can be caused by an eye condition, an environmental or motion change, or can be without a known cause.
Nystagmus is normal in specific situations such as after spinning in a circle quickly, looking all the way to the right or left, or watching a stationary object while in a moving vehicle (like watching fence posts from a car while it is driving).
In some cases, the nystagmus is present from birth without any ocular condition which would explain the nystagmus. In these cases, an extensive brain and eye health check is done to rule out all other conditions.
Eye Conditions which Can Cause Nystagmus
Nystagmus is most often a symptom that is associated with another eye condition like albinism, an under-developed eye, trauma or an injury to the brain or eye, or as a side effect from a medication.
Albinism, both ocular albinism and oculocutaneous albinism, can cause congenital nystagmus. In these cases, the nystagmus is present from birth and the eyes have adapted to the shaking of the nystagmus so there is no feeling of movement.
If the eye is not fully developed, a part of the retina known as the fovea can fail to develop or form. This condition results in reduced vision and nystagmus from birth. Like albinism, these cases will not have issues with the motion.
If an injury or medication is the cause of the nystagmus, then the onset is after birth and the eyes are not adapted to the beating motion. Because the eyes are not used to the motion, it will likely cause blurry vision, a feeling of vertigo, and dizziness that can feel like motion sickness.
As there are few treatments for nystagmus, the main options are to identify the cause if the nystagmus is new onset – stopping a new medication or repairing the injury site – or to identify the point where the nystagmus is the least bothersome.
If there is a position of gaze which the nystagmus is reduced or removed, moving the fixation into that gaze will allow better vision and less symptoms of nystagmus.