Ischemic Optic Neuropathy

GENERAL INFORMATION PRIMARILY FOR PATIENTS AND LAY PEOPLE

This web page is intended to give basic information about ischemic optic neuropathy, or "stroke of the optic nerve". Ischemic optic neuropathy is one of the most common causes of loss of vision in persons past middle age, although younger people can get it as well. Knowledge about this disease will enable patients and their doctors to work together to understand the disease. Early diagnosis, recognition of various risk factors, and carrying out the treatment and follow-up visits, as recommended, are the most important aspects of care for persons with ischemic optic neuropathy. The following description of ischemic optic neuropathy is based on our basic, experimental and clinical studies. ^2-58,62

The Eye

The eye is often compared to a camera. Light comes in through the cornea, pupil, and lens at the front of the eye just as the lens of the camera lets in light to the film. This light is then focused on the inside wall of the eye called the retina (as on the film in a camera). This picture is then sent to the brain along the optic nerve which connects the eye to the brain. We see properly when all of these parts of the eye and brain are working together.

The optic nerve is unique because it is the only nerve in the body that a physician is able to see directly (without surgery) as it begins at the back of eye. The optic nerve is made up of a million tiny, delicate nerve fibers which are like wires. Many blood vessels nourish the optic nerve with blood rich in oxygen and nutrition. Vision actually takes place in the brain when the messages from the eye travel to the brain along the optic nerve, but the nerve has to be healthy to transmit these messages. The whole situation may be compared to a video camera (i.e. the eye) taking the picture and transmitting along the cable (the optic nerve) to the television (the brain); if the cable is damaged for any reason, although the video camera and the television may be perfectly normal, a distorted picture or no picture is seen on the television.

While explaining this disease, a doctor may say that there has been a "stroke at the back of the eye", "blocked blood vessel", or "broken blood vessel at the back of the eye". A "stroke" is an interruption of the blood supply to the brain or a nerve in the body. When a person has a major "stroke" in the brain, the blood supply to a part of the brain which controls speech or movement of the arms and legs is often affected. With a "stroke at the back of the eye" a loss of vision develops because the retina or the optic nerve may have its circulation interrupted. How much vision is lost depends on how much the retina or the optic nerve is affected. In this website we are discussing only the stroke of the optic nerve and NOT that of the retina.

ISCHEMIC OPTIC NEUROPATHY

Ischemia of the optic nerve results in ischemic optic neuropathy.^{6,9,15,19,30,36,41} Ischemia is a decrease in the blood supply to a tissue in the body which in turn decreases oxygen and nutrition. Without sufficient oxygen and nutrition, nerves cannot function properly and will eventually die. As an example, placing a tight rubber band around the wrist causes the fingers to begin to tingle and then lose the sensation of touch because the rubber band cuts off the blood supply, starving the nerves of oxygen and nutrients. If the blood supply to the optic nerve is interrupted, it produces ischemia of the optic nerve (technical name, "ischemic optic neuropathy"), and a loss of vision develops. The blood supply of the anterior (front part - left part in Fig. 1-B) of the optic nerve (also called the optic nerve head) is mainly by the posterior ciliary arteries (Fig. 1-B), while the blood supply to the posterior part (back part - right part in Fig. 1-A) is from several quite different sources but not the posterior ciliary arteries.^{5-8,14,20,25,27,37,41}

Types of Ischemic Optic Neuropathy

Ischemic optic neuropathy is of two types¹⁵, depending upon the part of the optic nerve involved:

1. Anterior ischemic optic neuropathy (commonly abbreviated to “AION”): This is due to acute ischemia of the front (anterior) part of the optic nerve (also called optic nerve head), which is supplied mainly by the posterior ciliary arteries. This web site deals only with the AION.
2. Posterior ischemic optic neuropathy (commonly abbreviated to “PION”): This is a much less commonly type.^19,41 It is due to acute ischemia of the back (posterior) part of the optic nerve, located some distance behind the eyeball; this part of the optic nerve is NOT supplied by the posterior ciliary arteries. This was first reported by me in 1981.¹⁹ A detailed current account of PION and its management is available in a recent publication based on my research.⁴¹