How many receptors in the human eye

Just like a lens in a camera sends a message to produce a film, the lens in the eye 'refracts' bends incoming light onto the retina. The retina is made up by millions of specialised cells known as rods and cones, which work together to transform the image into electrical energy, which is sent to the optic disk on the retina and transferred via electrical impulses along the optic nerve to be processed by the brain. Donate now Modern slavery and human trafficking statement Contact Cookies High contrast.

Light passes right through the cornea and into a transparent, flexible tissue called the lens. This lens focuses the light, sending it through the liquid-filled globe of the eyeball to the back interior wall of the eye.

The tissue there, known as the retina, contains millions of light-sensitive cells. They are especially concentrated in an area called the fovea FOH-vee-ah. This densely packed set of cells gives us the clearest picture of our world. When the eye focuses on an object, it directs the light bouncing off the object directly onto the fovea to get the best image.

The light-sensing cells on the retina are known as photoreceptors. Two important types are rods and cones. Each human retina and you have two, one in each eye contains million rods and about 6 million cones. This is 70 percent of all the sensory receptors in your entire body — for touch, taste smell, hearing and sight all put together.

Each rod or cone cell at the back of the eye has a stack of discs inside, The discs contain a pigment molecule. Rods and cones each have a different opsin. Cones have a pigment-protein pair called photopsin Foh-TOP-sin. It comes in three different types, and each cone has just one type. They come in red, green or blue — the colors that each cone type is best at absorbing.

Cones respond to light that has passed through the lens and onto the fovea. As each cone absorbs its color of light, it produces an electrical signal. These signals travel to the brain, filling our worlds with color. In September , a vision researcher at the University of Washington in Seattle discovered some cones also sense white light. There are about million rods in the human retina. The cones are not as sensitive to light as the rods.

However, cones are most sensitive to one of three different colors green, red or blue. Signals from the cones are sent to the brain which then translates these messages into the perception of color. Cones, however, work only in bright light. That's why you cannot see color very well in dark places.

So, the cones are used for color vision and are better suited for detecting fine details. There are about 6 million cones in the human retina. Some people cannot tell some colors from others - these people are "color blind. The fovea , shown here on the left, is the central region of the retina that provides for the most clear vision.

In the fovea, there are NO rods The cones are also packed closer together here in the fovea than in the rest of the retina. This is a reasonable number considering that recent studies have shown wide ranges of cone ratios in people with normal color vision.

In the central fovea an area of approximately 0. The S-cones are semi-regularly distributed and the M- and L-cones are randomly distributed. Throughout the whole retina the ratio of L- and M- cones to S-cones is about Spatial Acuity Estimate From Mosaic. From the cone mosaic we can estimate spatial acuity or the ability to see fine detail. The distance between cone centers in the hexagonal packing of the cones is about 0. To convert this to degrees of visual angle you need to know that there are 0.

The Nyquist frequency, f , is the frequency at which aliasing begins. In actuality, the foveal Nyquist limit is more like 60 cycles per degree. This may be a result of the hexagonal rather than the rectangular packing of the cone mosaic. The optics of the eye blur the retinal image so that this aliasing is not produced. Using laser interferometry, the optics of the eye can be bypassed so we can reveal this aliasing. We will discuss this in more detail in the chapter on visual acuity.

The mosaic of the retina in addition to the processing in the visual system produces another ability to see fine resolution and ascertain alignment of object called hyperacuity. This corresponds to seeing the misalignment in headlights 39 miles away.

Maybe you can try working this out to see if I am exaggerating. Continue on to Transduction.