CHAPTER 5

THE OPTIC DISC 

Examination of the Optic Disc

The examination of the optic disc is an essential part of neurological assessment. The patient is asked to sit on the examination table, the lights are turned off and the patient is asked to fix their gaze at a distant point in the primary position. Using the direct ophthalmoscope, the examiner approaches the side of the patient at a 20 degree angle and if a blood vessel is seen, following that blood vessel leads to the optic disc.                                 

    Figure 5.1 Normal Fundus(included int orginal book)

Optic atrophy is the pallor of the optic disc with shrinkage of the head of the optic nerve as well as the retinal vessels and nerve fiber layer adjacent to the optic disc. This may result in decreased visual acuity, decreased color vision and abnormal visual evoked potentials.

In bow tie optic atrophy there is atrophy of the nasal and temporal sides of the optic disc with sparing of superior and inferior fibers because they arise from ganglion cells of both temporal and nasal sides of the retina. This is seen in optic tract lesions dorsal to the optic chiasm but anterior to the lateral geniculate body. The healed optic neuritis may cause optic atrophy. In addition, medications such as digitalis, streptomycin, lead and arsenic poisoning may cause optic neuropathy. Vitamin B1, B6, B12 and niacin deficiencies may also result in optic neuropathy leading to optic atrophy. These patients may present with decreased visual acuity and a central scotoma.

Abnormalities of Fundus

A. PAPILLEDEMA

Papilledema is defined as the swelling of the optic discs bilaterally due to increased intracranial pressure which is transmitted by the cerebrospinal fluid in the subarachnoid space to the heads of the optic nerves. Papilledema due to increased intracranial pressure is usually bilateral, however in rare cases, it may be unilateral. There is congestion of the optic discs with absence of the venous pulsations. If the venous pulsations are seen then the CSF pressure is usually less than 20 cm of water, however, 15-20% of the normal population has absence of venous pulsations. Therefore, the presence of venous pulsations is only helpful to rule out papilledema. The retinal blood vessels around the disc margins may become obscured by the swelling, the central cup may become obliterated, and there may be retinal hemorrhages. Since papilledema is a medical emergency, a CT scan of the head is done to rule out an intracranial focal mass lesion on an urgent basis. If the CT scan of the head is normal then CSF analysis for infectious, neoplastic or inflammatory causes is done and the opening pressure is also measured. Papilledema typically causes enlargement of the blind spots on visual field testing. Transient visual obscurations lasting a few seconds with sudden changes in position may occur many times a day. The visual field loss tends to be greater and earlier than loss of central vision in papilledema.

Pseudotumor cerebri is a condition usually seen in young obese females and presents with generalized headaches. CT scan of the head and CSF (CONTINUES IN THE ORIGNAL BOOK..)