OPTIC NERVE DISEASE (OPTIC NEUROPATHY)

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Optic nerve disease (optic neuropathy)

The optic nerve extending from the posterior aspect of the eye to the optic chiasm is really not a nerve at all. It is an extension of the brain proper. Surrounded by meninges and composed of approximately 1.2 million axons from ganglion cells of the retina its blood supply is derived from the ophthalmic artery.

Again any inflammation, compromise of the blood supply, cell nutrition or acute compression of the optic nerve will reduce vision on the affected side. Remember: The decussation of the optic nerve occurs in the chiasm and any reduction in function from this area to the occipital lobe will not cause a loss of central vision but rather a limitation in the visual field in both eyes.

The most common causes of an acute loss of vision arises from the optic nerve is vascular or inflammatory.

Optic Neuritis is such an inflammatory condition. It results from demyelination secondary to possible viral or autoimmune etiology. This demyelination causes a slowing of nerve transmission and can reduce vision to as low as counting fingers. Patients are more likely to be younger (18-50 yrs) and symptoms may vary. At times there is an associated pain on eye movement, worsening of vision with increased body temperature (Uthoff`s sign), flashing lights, and loss of colour perception. The vision becomes progressively worse over 1-2wks with gradual improvement in 90% of patients over the 4 to 12 weeks. Close to 90% of patients will regain 20/40 vision or better.

16. Slide 16 There is a definite association with Multiple Sclerosis which is believed to be more likely if the patient is female, ages between 21-40, and a winter onset. A careful history-taking looking for previous or current episodes of other neurological deficit is in order.
Physical exam should reveal a loss of central vision, which is rarely spared by this entity. The eye and optic nerve head may appear entirely normal (Retrobulbar Neuritis). However a Relative Afferent Pupillary Defect can usually be demonstrated. This is a very powerful test to determine any optic nerve disease. Simply put the pupillary fibers follow the retinal ganglion cell fibers out of the eye. They split off the optic tract prior to the lateral geniculate ganglion and combine in the midbrain. Here a rather sophisticated arrangement takes place where the light stimulus from both eyes is balanced and pupillary sphincter muscle stimulation is sent back to the iris via the third nerve fibers. This is why an eye may be stone blind and still have a similar pupil size to the opposite seeing eye.

17. Slide 17 The swinging flashlight test is employed to check for such a discrepancy. Here the pupillary reaction of one eye is compared to that of the other eye. Normal seeing eyes (suggesting normal optic nerve function) will show equal reaction amount and speed. An eye with an optic nerve lesion however will demonstrate a poor relative reaction to the opposite eye since the pupillary fibers and the vision fibers have been affected. This is also known as a Marcus Gunn pupil and will generally not occur in lesions other than those affecting the optic nerve.
Lab work is directed to ruling out any vasculitic cause and if this is a repeat episode or is associated with other neurological deficits an MRI is performed to rule out any other plaques.
Treatment for an optic neuritis is limited. A recent multicentre study showed there was no benefit to the administration of oral prednisone and it actually appeared to precipitate further attacks. However high dose IV methylprednisolone for three days followed by oral prednisone was shown to improve vision faster. By three to six months this advantage was lost.
Temporal Arteritis, also known as Giant Cell Arteritis is a generalized vasculitic process affecting people over the age of 55 and inflaming the walls of large and medium sized vessels throughout the body. The ocular involvement is due to loss of blood supply to the optic nerve. Other vessels supplying the heart, brain kidney and liver may be compromised. The patient may complain of a history of malaise, weight loss, muscle weakness or tenderness (polymyalgia rheumatica), and jaw claudication.

18-19. Slides 18 and 19 Visual loss may initially be unilateral and is permanent. If left untreated bilateral blindness may develop. Death is typically due to cardiac or brain involvement.
Once one is suspicious of the diagnosis treatment with high dose oral steroids must be initiated immediately. Usually 60 to 100mg of prednisone.

20. An ESR is performed which will be elevated though exceptions do occur. The diagnosis is ultimately made with a temporal artery biopsy demonstrating giant cells in the substantia media.

Painless loss of vision: Contents | < Previous | Next >

16.	Slide 16 There is a definite association with Multiple Sclerosis which is believed to be more likely if the patient is female, ages between 21-40, and a winter onset. A careful history-taking looking for previous or current episodes of other neurological deficit is in order. Physical exam should reveal a loss of central vision, which is rarely spared by this entity. The eye and optic nerve head may appear entirely normal (Retrobulbar Neuritis). However a Relative Afferent Pupillary Defect can usually be demonstrated. This is a very powerful test to determine any optic nerve disease. Simply put the pupillary fibers follow the retinal ganglion cell fibers out of the eye. They split off the optic tract prior to the lateral geniculate ganglion and combine in the midbrain. Here a rather sophisticated arrangement takes place where the light stimulus from both eyes is balanced and pupillary sphincter muscle stimulation is sent back to the iris via the third nerve fibers. This is why an eye may be stone blind and still have a similar pupil size to the opposite seeing eye.
17.	Slide 17 The swinging flashlight test is employed to check for such a discrepancy. Here the pupillary reaction of one eye is compared to that of the other eye. Normal seeing eyes (suggesting normal optic nerve function) will show equal reaction amount and speed. An eye with an optic nerve lesion however will demonstrate a poor relative reaction to the opposite eye since the pupillary fibers and the vision fibers have been affected. This is also known as a Marcus Gunn pupil and will generally not occur in lesions other than those affecting the optic nerve. Lab work is directed to ruling out any vasculitic cause and if this is a repeat episode or is associated with other neurological deficits an MRI is performed to rule out any other plaques. Treatment for an optic neuritis is limited. A recent multicentre study showed there was no benefit to the administration of oral prednisone and it actually appeared to precipitate further attacks. However high dose IV methylprednisolone for three days followed by oral prednisone was shown to improve vision faster. By three to six months this advantage was lost. Temporal Arteritis, also known as Giant Cell Arteritis is a generalized vasculitic process affecting people over the age of 55 and inflaming the walls of large and medium sized vessels throughout the body. The ocular involvement is due to loss of blood supply to the optic nerve. Other vessels supplying the heart, brain kidney and liver may be compromised. The patient may complain of a history of malaise, weight loss, muscle weakness or tenderness (polymyalgia rheumatica), and jaw claudication.
18-19.	Slides 18 and 19 Visual loss may initially be unilateral and is permanent. If left untreated bilateral blindness may develop. Death is typically due to cardiac or brain involvement. Once one is suspicious of the diagnosis treatment with high dose oral steroids must be initiated immediately. Usually 60 to 100mg of prednisone.
20.	An ESR is performed which will be elevated though exceptions do occur. The diagnosis is ultimately made with a temporal artery biopsy demonstrating giant cells in the substantia media.