Rods and Cones

Rods and cones are specialized cells, called photoreceptor cells, that are found in the retina and are responsible for our vision.

Photoreceptor Cells

However, these retinal cells perform different functions making it possible for us to see and to have clear vision during the day and at night.  Let me first explain the function these photorecptor cells perform. 

photoreceptor cells

√ They convert light into electrical messages. 

These messages are sent to the optic nerve which then send the message to the brain.  

√ Named for their shape 

√ Both are found in the retina

Dr. J. D. Solomon, ophthalmologist and author of Overcoming Macular Degeneration: A Guide to Seeing Beyond the Clouds states, "... the most important cells in the process of seeing are the rods and cones."

Rod Cells

There are many more rods than cone cells in the retina - especially outside the macula. The human eye contains about 130 million rods and about 7 million cones. Rods are:

√ Used for our peripheral vision and are concentrated in the outer edges of the retina.

√ Responsible for our night vision. Rods are needed for the perception of light and darkness and adapting to night time vision

√ Responsible for sensing motion

√ Cannot transmit sharp images or perceive fine detail. Cone cells give us our detailed vision

√ Not sensitive to and cannot perceive color. Cone cells allow us to see in color

√ Many more rod cells than cone cells are found in the retina - especially outside the macula; rod cells predominate our peripheral vision

Cone Cells

√ Are concentrated in the macula 

√ Are the only cells found in the fovea 

√ Responsible for straight ahead vision

√ Responsible for color perception

√ Responsible for sharp or detailed vision

√ Less sensitive to light than rod cells

Ophthalmologist, J.D. Solomon explains, "Each of the cones in the fovea connects with one ganglion cell going directly to the brain.  In other parts of the retina, each cone or rod connects to many ganglion cells, decreasing its effective output to the brain."

The cone cells are the photoreceptor cells that are most affected by macular degeneration. The breakdown of the surrounding layers of tissue prevents nutrients and oxygen from getting to these cells and from moving built up waste out of the area ...leading to the degeneration or dying of the cells.

Photoreceptors consume a surprising amount of fuel. "They have the highest concentration of mitochondria -- the "furnace" of the cell -- and use more energy than any other cell in the body," says senior investigator Lois Smith, MD, PhD, in Boston Children's Department of Ophthalmology.  "They have to be 'on call' all the time to signal light perception and have to recycle their components constantly."

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