Protanopia (p. 150)- This occurs when a person perceives short-wavelength light as blue, and as the wavelength is increased, the blue becomes less and less saturated until the person perceives gray. The wavelength at which the protonope perceives gray (492 nm) is called the neutral point, and at wavelengths above this neutral point, the person perceives yellow. This affects 1 percent of males and 0.02 percent of females.
Deuteranopia (p. 150)- This occurs when a person perceives blue at short wavelengths, sees yellow at long wavelengths and has a neutral point (as described above) at 498 nm. This affects 1 percent of males and 0.01 percent of females.
Tritanopia- (p. 150)- This occurs when a person perceives blue at short wavelengths, sees red at long wavelengths, and has a neutral point at 570 nm. This is a very rare disorder, affecting only 0.002 percent of males and 0.001 percent of females.
Protanopia, deuteranopia and tritanopia are all types of dichromatism. Dichromatism is a form of color blindness in which a person needs only two wavelengths to match all other wavelengths in the spectrum. This means that the person experiences some colors, yet at different frequencies and wavelengths than would occur with normal vision. This can be seen in the picture below:
This diagram shows how a Protanope, Deuteranope and Tritanope perceive colors. The number under the dividing line between colors is the location of the neutral point, or the place at which the person would perceive gray.
These types of color vision are inherited through a gene on the X chromosome, and females are less likely to be color-deficient since only one normal color gene is required for them to see properly. This is a sex-linked type of color vision, since women can carry a gene for this, pass it on to their offspring, yet not be affected by it themselves.
For more information on Protanopia, Deuteranopia, and Tritanopia, see this web page:
http://lyco.lycoming.edu/~newman/courses/bio22298/disorderpapers/Colorblindness/preliminary.htm
To take a test to determine if you have protanopia or deuteranopia, go to this website:
http://www.umds.ac.uk/physiology/daveb/brainday/colourblindness/cblind.htm
Diabetic Retinopathy (p.525) - Damage to the retinal that is a side effect of diabetes. This condition causes neovascularization, or the formation of abnormal blood vessels that do not supply the retina with adequate oxygen and that bleed into the vitreous humor.
Most often, diabetic retinopathy has no recognizable symptoms. There is no pain, and a person may not notice a difference in vision until the disease becomes more severe. When vision does change, it is because the macula swells in size due to leaking fluid. The macula is the section of the retina that provides clear, central vision. When it expands, this is a condition called macular edema. If blood vessels grow on the retina's surface, they can bleed directly into the eye and obstruct vision.
Even in these advanced cases, the disease may become very serious without any noticeable symptoms. Because of this fact, it's imperative that people with diabetes see their eye doctor consistently--at least once a year. When visiting the doctor, people who suffer from diabetes should have their eyes dilated to enable the doctor to see a larger portion of the eye and check for possible signs of the disease.
Diabetic retinopathy can be treated by laser surgery, which causes abnormal blood vessels to shrink. By having this type of surgery, the risk of severe vision loss from this disease is reduced by 60 percent. Often, this surgery cannot restore lost vision, so it's important to diagnose this disease at its early stage.
There is no completely proven way to prevent diabetic retinopathy, but it is possible to reduce your risk of having this condition. This can be done by controlling your blood sugar level, attempting to keep it as close to normal as possible. In studies, this has been shown to delay the onset of this disease and lessen the occurrence of severe cases of diabetic retinopathy.
When a person suffers from diabetic retinopathy, print appears to be distorted. If the person also has cataracts, the print seems blurred in addition.