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( Retina)
The vertebrate retina is a light sensitive part inside the inner layer of the eye. Two of its three types of photoreceptor cells, rods and cones, receive light and transform it into image-forming signals which are transmitted through the optic nerve to the brain. In this respect, the retina is comparable to the film in a camera. The third and more recently discovered category of photosensitive cells is probably not involved in image-forming vision. These are a small proportion, about 2% in humans, of the retina's ganglion cells, themselves photosensitive through the photopigment melanopsin, which transmit information about light through the RHT (retinohypothalamic tract) directly to the SCN (suprachiasmatic nucleus) and other brain structures. Signals from these ganglion cells are used to adjust the size of the pupil, entrain the body's circadian rhythms and acutely suppress the pineal hormone melatonin, processes which in fact function in many blind people who do not have functioning rods and cones. The retina, indeed an extension of the brain, takes light and turns it into chemical energy in turn into nerve impulses sent to the higher regions of the brain via the optic nerve. In reality, the optic nerve is less a nerve than a central tract connecting the retina to the brain.[1] While rods and cones respond maximally to wavelengths around 555 nanometers (green), the light sensitive ganglion cells respond maximally to about 480nm (blue-violet). There are several different photopigments involved.
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Retina Subcategories
Retina Articles
New Hope in the Treatment of Wet Macular Degeneration by PAUL SCHECHTER
TREATMENT OF WET MACULAR DEGENERATION WITH ANTI-VEGF MEDICATIONS
The compounds known as Vascular Endothelial Growth Factors, or VEGF’s, are found in high concentration inside the eyes of patients with wet macular degeneration, and have be...
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