The trigeminal nerve, fifth cranial nerve, can be tested clinically to assess its integrity and adequate functioning. Its primary role is to supply the face and cornea with sensory perception, as well as motor function to the muscles of mastication.
The trigeminal nerve can be subdivided into three branches: Vi) ophthalmic, Vii) mandibular and Viii) maxillary. Light touch is assessed for each of the divisions. This can be done by having the patient close their eyes and the practitioner compare left and right sensation of each division of the trigeminal nerve using the patient’s feedback.
The corneal reflex is assessed by instructing the patient to look straight ahead and having the practitioner lightly touch the patient’s cornea with a bit of cotton wool. A normal reaction is for the patient to close their eyes. The afferent limb of this reflex is supplied by the trigeminal nerve and efferent limb supplied by the facial nerve.
The muscles of mastication (masseter, temporalis, and pterygoids), may be assessed by having the patient clench their teeth and the examiner palpating the tone of the muscles.
The jaw jerk reflex may be assessed by gently taping the patient’s relaxed jaw with a reflex hammer. A normal reaction is for there to be minimal movement.
Test findings (inc Positive & Negative results):
Some degree of inaccuracy relating to the feedback of light touch along the distributions of the trigeminal nerve is acceptable. However, recurrent, prolonged and generalised (be it over one or more divisions) inaccuracies and confusions are a cause for concern and may be indicative of a lesion of the trigeminal nerve or higher centres.
The two limbs forming the corneal reflex are distinct nerves therefor an absent or weakened reflex may be indicative of a lesion or lesions either at the trigeminal nerve, facial nerve, higher centres or a combination of the aforementioned.
When testing the mandibular division of the trigeminal nerve the practitioner should bear in mind that testing this nerve too laterally will test the great auricular nerve (C2-C3).
The most common condition to affect the trigeminal nerve is trigeminal neuralgia.