Two Point Discrimination
Two point discrimination is the ability to distinguish that two objects touching the skin are two distinct points and not one. Two point discrimination is often tested with two sharp points during a neurological examination and is used to identify how finely innervated an area of skin is. In clinical settings, two point discrimination is a widely used technique for determining tactile agnosia. It should be completed with the patient’s eyes closed and it relies on the ability and/or willingness of the patient to subjectively report what she/he is feeling . The physician may use a simply a reshaped paperclip to do this test. The physician may alternate randomly between touching the patient with one point or with two points on the area being tested (e.g. finger, arm, leg, toe). The patient is then asked to report whether one or two points was felt. The smallest distance between two points that still results in the perception of two distinct stimuli is recorded as the patient’s two-point threshold. Performance on the two extremities can be compared for inconsistencies.
Explain the procedure to the patient with his/her eyes open. For example, “I am going to touch various parts of your arms (or other body part) with this instrument. I will touch you with either one or two points, and tell me if you feel one or two points when you feel the touch.”
- Demonstrate the procedure with the patient’s eyes open until the patient understands the procedure.
- The patient closes his/her eyes, or vision is otherwise occluded.
- Begin the test with the points of the anesthesiometer opened greater than the mean value for the body part being tested.
- Provide the stimulus by applying light and equal pressure across the two points.
- Have the patient identify if they feel one or two points.
- Move the two points closer together across consecutive trials until the patient cannot distinguish the two points as separate.
- Measure the distance between the two points using the aesthesiometer ruler.
- Repeat throughout suspected areas and document findings.
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