The eye can be affected by many diseases, and any part of the eye can be affected by disease. Most diseases are fairly common and have treatments that can help decrease vision loss, but some diseases are extremely rare and have unusual presentations. Vision is often severely affected in unusual eye diseases. Achromatopsia, Charles Bonnet syndrome and sympathetic ophthalmia are three such diseases.
Achromatopsia
Congenital Achromatopsia is colorblindness caused by lack of normal cone vision. Achromatopsia is a recessive genetic disease, meaning both parents must carry the gene for a child to have the condition. Rods and cones are responsible for vision, but rods supply only monochromatic night vision and cones supply color and visual acuity. People with this congenital familial disease must rely on vision supplied only by rods--which don't allow for good vision detail or for any color vision--in the most severe forms.
Vision loss is common along with nystagmus, an involuntary movement of the eyeballs. Achromatopsia causes severe light sensitivity because people with the disease don't have photoreceptors that adapt to bright light, say Richard and Laura Windsor, O.D.s, in an article published in Vision Enhancement Journal called "Understanding Achromatopsia." People with the disease benefit from wearing very dark tinted lenses with dark red filters and red central contact lenses to allow them to see in bright light.
Charles Bonnet Syndrome
People with Charles Bonnet syndrome generally have severe vision loss that occurred in adulthood, from macular degeneration or another disease process. Charles Bonnet causes hallucinations that may last only a year or so after the vision loss, according to the Royal National Institute of Blind People. People may see beautiful landscapes or strange people; their hallucinations may move or not move, and may be seen in color or in black and white. Charles Bonnet hallucinations affect vision only; there are no auditory accompaniments to the disorder. Visions may appear suddenly and last just a few minutes before disappearing.
Charles Bonnet syndrome can make it difficult to get around, especially if lines or intricate patterns are part of the hallucination. Knowing that they're a manifestation of vision loss and not a sign of mental illness help people handle the images.
Sympathetic Ophthalmia
Sympathetic ophthalmia occurs when one eye has been severely traumatized, usually by a penetrating object; the disease has occasionally occurred after normal cataract or glaucoma surgery. The disease usually occurs within 2 to 12 weeks after injury but can occur as long as 30 years after injury. If the damaged eye develops uveitis, an inflammation of the middle portion of the eye, the undamaged eye also develops the same problem even though it hasn't been injured in any way. Symptoms can include redness, pain, floaters and light sensitivity.
If the damaged eye has no vision potential, removing it within two weeks of the original injury prevents sympathetic ophthalmia, according to the Merck Manual. This prevents complete loss of sight in both eyes.
