Topics to be understood: Cone and Rod Cells (eye), School-grade Genetics
Q. What is Achromatopsia?
A. While it could mean several other disorders, Achromatopsia generally refers to the inability to perceive colours and achieve satisfactory visual acuity in exterior daylight. (AKA bad eyesight under the sun) It could be a genetic disorder or acquired.
Q. How is it acquired?
A. By head injuries. Usually it's because of damage to the cerebral cortex (new brain) or the thalamus (in the mid brain). Damage to cerebral cortex could be because of physical trauma, hemorrhage, or tumor growth. As the thalamus is generally well-protected, it is usually damaged by tumor growth.
Q. What about inherited achromatopsia?
A. There are 2 types of genetic-related achromatopsia: rod monochromacy and blue cone monochromacy.
- Rod monochromacy: To acquire this, one must have genes from both parents (autosomal recessive inheritance). This affects male and female equally. If both parents are only carriers, there is 1 : 4 odds their offspring will get it. So far, the incidence of rod monochromacy affected 1 to 33,000 births in the U.S. and the rest of the world.
- Blue cone monochromacy: While the cones grew normally, the retina is unable to fill them with red and green pigment. Some patients show progressive deterioration of the part populated with cones (the macula). As it is an X-chromosome related disorder, this happens to almost always males. The chromosome that produces the red and green pigment is the X one.
Useful Downloads:
http://www.achromat.org/uc.pdf
Links:
http://www.achromat.org
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