EXAMINATION OF CRANIAL NERVES
EXAMINATION OF CRANIAL NERVES
AIM: To assess the functional status of the 12 cranial nerves.
REQUIREMENTS: Asafoetida and clove oil, Snellen’s chart, Torch, coloured subjects, piece of coton, tuning fork, watch, salt, sugar, hot and cold water.
PROCEDURE AND DISCUSSION
GENERAL EXAMINATION AND HIGHER FUNCTION: As previous experiment.
EXAMINATION OF CRANIAL NERVES:
I. Olfactory Nerve
Exclude any nasal congestion due to common cold or any other cause, or any nasal obstruction which can interfere wrth smell.
Ask the subject to close his eyes and one nostril with his finger. Bring asafoeitida near the open nostril and ask him whether he gets any smell. If so to identify the substance. Also test, with other substances familiar to him eg: Clove oil, cut onions, coffee powder etc. Test the other nostril after closing the first. Avoid irritant substances as they can stimulate trigeminal nerve.
Anosmia - absence of smell
Parosmia - perverted sense of smell. eg: Pleasant smell may be felt as offensive smell. Hallucinations of smell may constitute aura of epilepsy
II. Optic Nerve: is a purely sensory nerve. It is assessed based on 3 important aspects.
a. Acuity of Vision is tested using Snellen’s chart. It is a white board. on which eight rows of black letters are printed, in decreasing size from above downwards. The size of letters is based on the fact that two points that subtend an angle of 1 minute at nodal point of eye can be discretely seen. So the letters in the top row form an angle of 1 minute at the nodal point when placed at a distance of 60 meters. The letters in the lower rows form 1 minute angle at distances of 36, 24, 18, 12, 9, 6 and 5 meters in descending order.
The subject is seated at 6 meters from the chart, well illuminated by a lamp. Ask him to close one eye and read the letters in the chart from above downwards. Lowest row that can be read is noted.
Visual acuity is expressed as follows:
Visual acuity = Distance at which the subiect can read the row i.e. Distance from the chart Distance at which normal eye can read the row. No. of the row, can read
Normal visual acuity = 6/6 If only upto second row can be read the visual acuity is 6/36
If visual acuity is less than 6 I 60 he is brought closer to the chart, if he can read top row at a distance of 2 meters, visual acuity is 2 I 60. The other eye is also similarly tested. If VA is less than 1/60, counting fingers, hand movement and perception of light are to be tested. If perception of light is also negative it is complete blindness.
b. Field of vision: of an eye is the part of the outside world that is visible to the eye, when the gaze is fixed at an object, with the other eye closed. An approximate idea of the visual field can be obtained by:
The subject and the examiner sit facing each other at a distance of about 1 meter. To examine the right eye, ask the subject to close his left eye with his left hand and to look into the examiner’s left eye while the examiner keeps his right eye closed with his right hand. Ask him not to move his eye. The examiner fixes his gaze into the right eye of the subject, and extends his left arm fully to the left and holds his hand midway between himself and the subject. Keep on moving the index finger and bring it nearer until the examiner can seen it. Ask the subject whether he can see the moving finger, if not, bring it closer and find out at which point he can see it. Here examiner’s field of vision is taken to be normal and the subject’s field of vision is compared with it. This is repeated in different directions ie. from above, below, right, left, etc. Similarly field of vision of left eye is also tested. For accurate assessment for field of vision and for obtaining a permanent chart of visual field map, Perimetry is done.