The number of times in a minute that the eyelids close spontaneously. In a healthy person, the blink rate ranges from 10 closures per minute during activities such as reading or watching television to 30 closures per minute during conversation. In a person with Parkinson’s disease, the blink rate can be as slow as zero to five closures in a minute regardless of activity. This is a manifestation of dopamine depletion in the striatum, the brain structure responsible for muscle movement and coordination, that results in rigidity of the muscles of the eyelids. This rigidity causes the lids to stay open. one function of blinking is to bathe the eye in tears to help flush away irritants and debris. When spontaneous blinking is reduced, the eye can become dry and painful. Usually the person with Parkinson’s can consciously blink; making the effort to do so on a regular basis during waking hours can help offset decreased spontaneous blinking. using artificial tear eye drops to keep the eye lubricated and clear of debris helps reduce irritation.
Sometimes rigidity can affect the lower eyelid to the extent that it pulls somewhat away from the surface of the eye. This allows tears to spill over the lid and run down the face, giving the impression that the person is crying. Blink rate returns to normal or near-normal when treatment, such as administration of dopamine agonist medications, early in the disease or Levodopa as Parkinson’s progresses, restores other muscle function. As treatment effectiveness declines in later stages of the disease, blink rate again slows as other symptoms also worsen.
