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3 Eye Diseases Related to the Cones and Rods — Retinal Impairments

© Donald Reinhardt,2011

Color-blindness, retinitis pigmentosa, age-related macular degeneration (ARMD or AMD) are 3 different and important retinal eye diseases described here.

Retina, Normal and Abnormal, Retinitis Pigmentosa (Credit, Rizzo)
The human eye is a complex, highly-organized organ for vision. Human vision can vary from the most perfect vision known to total blindness and there are many variations between these two ends of the spectrum. Click here Eye Anatomy 14 Important Facts to know and further eye insights are provided Human Eye Anatomy and Disease.
1. Color-Blindness is Related to Deficiencies of Certain Chemicals in the Cones

The biochemical deficiencies cause color blindness of red, blue or green, or combinations of these colors. Color blindness is a non-correctable, inherited disease. Color-blindness is related to a genetic defect carried on the X chromosome. There are 2 X chromosomes in females, and only 1 X in males of the total of 46 chromosomes that humans have in each cell of their body. Colorblindness is more common in males than females. Since males have only 1 X chromosome if there is a defect on that X it will show up. Females with 2 X chromosomes, could have an error in 1 X compensated for by a good gene for normal vision on the other X chromosome. A colorblind female would have both X chromosomes with a defective gene for colorblindness.

2. Retinitis pigmentosa  is a Disease Characterized by Rod and Cone Degeneration as shown in the microscopic photo above. There is progressive loss of vision with total blindness as rods and cones degenerate. Compare the right and left sides of the photo to see the normal integrity of the retina and the diseased retina.

3. In Age-Related Macular Degeneration (AMD), the Macula (Fovea), which contains the highest concentration of cones and has the greatest visual acuity, shows cell degeneration and progressive loss of central vision over a period of several years.

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Donald Reinhardt is a Consultant in Medical and Industrial Microbiology and a Freelance Science writer. He is available for specific assignments for those who are interested – by contacting Other questions related to this teaching site should be directed to