2nd Cranial nerve – Optic nerve lesions

Definition:

A pathological process involving the optic nerve.

Causes:

Pathological processes affecting the visual field. Depending on the site of the lesion, a pathological process affecting the second cranial nerve can have various presentations:

Monocular blindness: Lesions of one eye or optic nerve such as in multiple sclerosis or giant cell arteritis.

Bilateral blindness: Methyl alcohol, tobacco amblyopia, and neurosyphilis.

Bitemporal hemianopia: Optic chiasm compression eg: internal carotid artery aneurysm, pituitary adenoma or craniopharyngioma.

Homonymous hemianopia: Affects half the visual field contralateral to the lesion in each eye. Lesions lie beyond the optic chiasm in the tracts, radiation or occipital cortex eg stroke, abscess, tumour.

Other lesions of the optic nerve include: optic neuritis, optic atrophy, syphilis, glaucoma; Leber’s optic atrophy; optic nerve compression and various metastatic and benign processes.

Examination:

Firstly one should determine the exact symptoms. A careful case history is invaluable in incriminating factors such as diabetes and cardiovascular pathologies.

The examination itself is aimed at assessing the patients visual acuity, and visual fields. Any visual corrective apparatus should be worn by the patient during the examination.

Usually visual acuity is assessed using a Schnellen chart and interpreting the results accordingly. Visual fields are assessed in the following manner. Ensure the patient can see out of both eyes. Position yourself at the height of the patient, and cover your own eye opposite to the patient’s covered eye. Instruct the patient to fix their gaze between your eyes, and using a pin head cover the vertical, horizontal and oblique axes, starting from the periphery and moving centrally, looking for any areas of blindness. Repeat with the other eye. Map out any areas of reduced vision.