Did You Know?

Sight Line

People with optic neuritis can lose some of their ability to perceive colour, especially red. As such, tests using colour plates with “hidden” numbers are used to support a diagnosis.

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The optic nerve delivers information from the retina to the brain via electrical impulses. Many people don’t realize this nerve is part of the central nervous system. It contains more than one million nerve fibres, protected by myelin sheaths that help speed impulses to the brain.

Injury to the optic nerve causes loss of vision, which can be lasting. Glaucoma is a group of diseases, and the most common condi­tion that affects this nerve. High intraocular pressure from fluid buildup is usually, although not always, the culprit. Early detection can minimize damage.

Optic neuritis is another, albeit rare, condition. It generally happens when the immune system erroneously attacks the myelin that covers the nerve, causing inflamma­tion and damaging myelin. Pain and loss of vision, sometimes permanent, result.

Neuro-ophthalmologists specialize in diagnosing and treating diseases of the optic nerve. There is no way to transplant an entire eyeball, because the optic nerve is too complex to reconstruct.

It Takes a Lot of Nerve

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The central nervous system contains two kinds of cells: glial cells and nerve cells, or neurons. Nerve cells conduct electrical and chemical impulses to communicate with each other, muscle cells and gland cells. Each neuron is connected to about 1,000 other neurons, which make up extensive communication networks responsible for everything we feel, think and do.

Visible only under a microscope, most neurons have a cell body, or soma; dendrites, which branch out from the soma; and an axon, which can be short or long. Dendrites receive and axons transmit information. Most axons in the central nervous system are swathed in myelin, which helps transmit signals smoothly; without it, one cannot function.