The tests performed to localize the site of pathology in acute facial nerve palsy are known as topodiagnostic tests. It refers to the functional testing of an individual facial nerve branch in an attempt to locate the level of dysfunction of injury. These tests are of limited value as they provide limited correlation with the site of nerve damage and have no prognostic value.
TOPODIAGNOSTIC TESTS ARE AS FOLLOWS:
1. Schirmer test
-Test for greater superficial petrosal nerve
-Compares the lacrimation of two sides
-A strip of filter paper is hooked in the lower fornix of each eye and the amount of wet strip is measured.
(>10 mm wet ~ adequate function)
2. Stapedial reflex test
– Tested by Impedence audiometry
-It is a test for nerve to stapedius
3. Taste test
-Also known as Electrogustometry
-Tests for Chorda Tympani branch of facial nerve
4. Submandibular salivary flow test
-Measure the function of Chorda Tympani
-Polythene tubes are passed into both warton ducts and drops of saliva counted during one minute.