How to Perform the Glabellar Tap on the Simpson-Angus Scale
The glabellar tap is performed by repeatedly tapping the patient's glabella (the area between the eyebrows above the nose) with your finger while standing behind or to the side of the patient, and you count the number of blinks in response to the tapping. 1, 2
Specific Technique
Position yourself behind or to the side of the patient so they cannot see your hand approaching, which prevents anticipatory blinking 2
Tap the glabella (the smooth area of the forehead between and slightly above the eyebrows) with your index or middle finger 1, 2
Use a consistent tapping rhythm - typically tap at a rate of approximately one tap per second 2
Continue tapping for at least 10 taps or until the patient stops blinking 1, 2
Count the number of blinks that occur in response to the tapping 1, 3
Scoring on the Simpson-Angus Scale
The glabellar tap is scored from 0 to 4 on the Simpson-Angus Scale 1:
- 0 = Normal: The patient habituates (stops blinking) after 3-5 taps 1, 2
- 1 = Mild: 6-10 blinks before habituation 2
- 2 = Moderate: 11-15 blinks before habituation 2
- 3 = Marked: 16-20 blinks before habituation 2
- 4 = Severe: More than 20 blinks or no habituation (patient continues blinking with each tap) 1, 2
Clinical Context and Limitations
The glabellar reflex is actually a poor measure of Parkinson's disease severity and should not be relied upon as a primary indicator of motor impairment. 4 While it is included in the Simpson-Angus Scale for assessing drug-induced parkinsonism, research shows only a weak correlation between blink number and actual motor severity or hypomimia 4. Patients with Parkinson's disease characteristically fail to habituate to the glabellar tap (they keep blinking), but this finding has limited clinical utility for measuring disease progression 4, 3.
The Simpson-Angus Scale remains one of the most reliable and valid instruments for assessing drug-induced extrapyramidal symptoms in psychiatric practice, with high inter-rater reliability when properly administered 5, 1. The total score is calculated by adding all 10 items and dividing by 10, with scores up to 0.3 considered within normal range 1.