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9. Optic Nerve
Simulations of Vision Loss
What is it like to be blind or visually impaired? Although no simulation can mimic exactly a vision loss, the following pictures are meant to give the viewer some idea of what certain eye diseases are like.
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Normal View (start here)
This is a normal view of a teenager. In this and all subsequent pictures, fixate on the nose to simulate the vision loss.
In diabetic retinopathy, the blood vessels in the back of the eye (retina) may rupture and leak. This causes parts of the retina to die and results in a loss of vision where the leaking occurred.
In age-related macular degeneration, the center part of the eye and retina known as the macula dies-off, leaving a black hole or "scotoma" right where you're looking - in this case the teenager's nose. Because people with age-related macular degeneration have to rely on side vision to read, visual acuity is greatly reduced and if both eyes are affected the person would have to give-up driving a car.
A cataract is a clouding of the lens of the eye and light that passes through the lens to the retina is scattered. The scattered light causes images to be blurred and visual acuity is reduced.
Although very different diseases, both glaucoma and retinitis pigmentosa (RP) cause a loss of side vision, leading to "tunnel vision". Often a patient with glaucoma or RP will become legally blind because of the severe loss of side vision - defined as a visual field of 20 degrees of visual angle or less in the better eye. Twenty degrees of visual angle is about the size of an one foot ruler held at arms length. At the end stage of glaucoma and RP central vision often fades away.
A ring or donut shaped scotoma is an area of reduced vision that forms a shape similar to a ring or donut - the patient can see fine in the center and off-center a little bit but then there is an area of reduced vision followed by another area or normal vision as depicted in the above photograph. Sometimes the ring or donut will not be totally round or complete but may appear like two crescent moons facing each other. A ring scotoma is often an early sign of a serious retinal disease/degeneration such as retinitis pigmentosa or other type of rod-cone degeneration.
A left (or right) homonymous hemianopia (also called hemianopsia) means that the patient cannot see anything in the entire left or right visual field in both eyes. Because both eyes are affected more or less equally, the location of the problem must be at the optic chiasm or further back along the visual pathways. Some patients may state, truthfully, that they cannot see anything in the affected visual field. But sometimes the patient may be able to fixate or look directly at or point to a visual object located in the affected visual field, even though they do not consciously "see" the object. This condition is referred to as "Blind Sight".
Sometimes a left homonymous hemianopia (hemianopsia) will not include the very central part of the visual field, called the macula. As a consequence, "...with macular sparing."
As we age, the lens of the eye yellows and becomes fixed and unable to focus, the pupil does not dilate very well to changes in illumination, and the retina and cortex become less able to process visual information. Contrast sensitivity decreases, visual acuity drops somewhat, and vision in low light levels suffers. As a consequence, the elderly often complain that images do not look as sharp, they need more light to see clearly and low contrast objects may not be seen at all.
Floaters are condensations of cells in the vitreous or gel part of the eye. Floaters can look like a number of things including dots, spots, dots with arms, spiders, clumps of dots or strings. Floaters are most easily seen when looking at the clear blue sky and moving ones eyes back and forth. Floaters are very common and are the main problem or concern of web site visitors. Floaters are common in the elderly, patients with nearsightedness (myopia) , diabetes and high blood pressure. One or a few floaters is common. The sudden appearance of a large number of floaters warrants a trip to the eye doctor's office. In general once a patient has a floater(s) they'll always have floaters, although they appear to come and go. Web site visitors have raised the possibility that vitamin A supplements may cause floaters, although a direct link has not been established.
Sometimes in a migraine, the patient will experience visual symptoms similar to that shown in the above picture. The center of the visual effect may be in the patients central vision or it may appear off to one side. First, the very central part of vision is affected with decreased vision and the shimmering appearance of lines as illustrated. As time goes by, the area of vision affected grows and when central vision may appear somewhat blurred, the shimmering lines expand outward and may engulf most of the visual field. The visual effect affects both eyes similarly. Once the visual effect diminishes, vision returns to normal and the patient may experience other symptoms of the migraine including headache, nausea, loss of balance, ringing in the ears and other body sensations.
Left eye view
Right Eye View
Pituitary tumors (lesions, classic pituitary adenomas) can sometimes cause very different losses of vision in the left and right eyes. For example, as simulated above, with the left eye the patient may see clearly only on the right side while with the right eye the patient may see clearly only on the left side. If the scotomas (i.e., blind spots in vision) are large, the patient may experience unstable vision characterized by bouts of double vision (diplopia) and confusion with object localization in 3D space. Visual acuity may also be affected in one or both eyes, again sometimes very differently: visual acuity can be 20/20 in one eye and the patient may only be able to count fingers with the other eye. Any field loss of vision warrants an immediate trip to the eye doctor; ASAP. Other types of pathology can also cause visual field losses, so just because you have a field loss does not mean that you have a pituitary tumor.
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The large white mass is a retinoblastoma. Slightly right of the tumor is the optic nerve head and exiting blood vessels. Retinoblastoma is a malignant tumor leading to death in about 15 - 20% of patients. The usual treatment is removal of the eye(s) to prevent the spread of the tumor along the optic nerve to the brain. In select cases, other treatments may be tried to destroy the tumor and to maintain some sight in the affected eye(s). For a view of a normal retina, see the Past Featured Article on optic nerve hypoplasia. (May need high resolution monitor to see this image clearly)
When a young baby is shaken vigorously, the blood vessels of the eye as well as of the brain hemorrhage, leading to loss of sight and sometimes life. In this case, hemorrhages can be seen throughout the retina as darker spots against the lighter background of the retina. For a view of a normal retina, see the Past Featured Article on optic nerve hypoplasia. (May need high resolution monitor to see this image clearly)
In the center of this retinal photograph is the optic nerve head. The small white area is the optic nerve, which is a lot smaller than normal. Optic nerve hypoplasia is the medical term for a small optic nerve. Note the ring of darker pigmentation surrounding the optic nerve. Blood vessels can be seen exiting the optic nerve to provide the retina with blood. See the past featured article on optic nerve hypoplasia. For a view of a normal retina, see the Past Featured Article on optic nerve hypoplasia. (May need high resolution monitor to see this image clearly)
2008 OLERF Annual Report (PDF file)