Blink Rate May Help Predict Blood Levodopa Levels in Parkinson’s Patients, Study Suggests

Measuring how often a person spontaneously blinks could help predict motor changes in people with Parkinson’s disease being treated with levodopa, a study suggests.

The study, “Using Spontaneous Eye-blink Rates to Predict the Motor Status of Patients with Parkinson’s Disease,” was published in the journal Internal Medicine.

Levodopa is used as standard therapy for Parkinson’s disease, which is characterized by loss of dopamine-producing brain cells. The therapeutic formulation can cross the blood-brain barrier and enter the brain, where it is converted into dopamine. This dopamine then activates dopamine receptors and improves the function of movement control centers in the brain.

Especially in advanced disease, during which the body is making less of its own dopamine, maintaining just the right levels of levodopa in the blood is critical. The level of levodopa needs to be high enough to sustain a therapeutic effect, but if it gets too high, the patient may experience undesirable dyskinesia (uncontrolled body movements).

However, getting the level just right can be a fickle process. Levodopa is processed quite rapidly in the body, remaining actively stable inside the body for less than two hours, and its precise absorption pattern is governed by a complex set of interacting factors.

Thus, the level of levodopa has to be measured at multiple times in a patient to ensure that it is kept within more efficient levels. But this monitoring process requires taking multiple blood samples, which can be impractical and invasive. Therefore, researchers are investigating other strategies to assess levodopa levels without requiring blood samples. Previous research has demonstrated a connection between levels of dopamine in the brain and the rate at which a person spontaneously blinks.

Supported by these findings, Japanese researchers hypothesized that blinking rate could be correlated with levels of levodopa in the blood, and as such, blinking rates might be able to act as a more feasibly measurable proxy to assess levodopa levels.

To test this, the team gave a device that measures blinking to three people with Parkinson’s disease. The Jins Meme device is shaped like ordinary eyeglasses and is wirelessly connected to a computer, which processes the wearer’s data to calculate a “Blink Index.”

The researchers also collected blood samples every 15 minutes for the hour before the patients took levodopa, and then every half hour to one hour thereafter.

The blinking rate of the three patients varied widely over time. The researchers noted that blinking rates at the beginning of the study were quite high, which they believed could be due to the patients adjusting to the device. Despite this, blink rates did correlate with levodopa levels in the blood.

All the patients tended to have higher blinking rates when their levodopa levels were high, and vice versa. “This finding suggests that [blink rate] can be used as a substitute for plasma levodopa levels,” the researchers wrote. Therefore, “the continuous monitoring of [blink rate] may be useful for predicting the motor status in patients” with Parkinson’s.

Larger studies are needed to further validate and test the diagnostic potential of blink rates, the researchers said. Still, this study does serve as a proof-of-concept for using blinking rate as a proxy for levodopa levels in the blood of people with Parkinson’s.