Where is light that enters the eye focuses

The retina is the light-sensitive tissue that lines the inside surface of the eye. The retina contains photoreceptor cells that convert or process incoming light into electrical impulses. There are two types of photoreceptors: rods and cones, which are the light-processing cells responsible for peripheral side and central straight-ahead vision.

You can get a closer look at different parts of eye with this interactive eye diagram from the National Eye Institute. You can learn more about the parts of the eye and refractive errors, including myopia nearsightedness , hyperopia farsightedness , and astigmatism both near and far blurriness at Refractive Error and Astigmatism and A Guide to Eye Conditions.

Jake Whalen: Living and Coping with Keratoconus Jake Whalen is a freelance copywriter who has struggled for most of his life with keratoconus. Learn more about the basics of effective eye care, including: The difference between normal eye and vision changes and symptoms of vision problems The different types of eye care professionals Questions to ask when you see an eye care specialist.

Check out our Getting Started Kit for more ideas to help you live well with low vision. Sign up with VisionAware to receive free weekly email alerts for more helpful information and tips for everyday living with vision loss.

Some Facts about the Retina The retina is the light-sensitive tissue that lines the inside surface of the eye. Rods The specialized, highly light-sensitive retinal processing cells that are able to function in low light levels. They are less sensitive to color perception.

A normal retina contains approximately million rods, primarily in the peripheral, or outer, retina. Rods provide scotopic vision which refers to eyesight in low light conditions. Cones The specialized retinal processing cells that function in bright light levels and provide central or straight-ahead vision, along with sharp visual acuity, detail, and color vision. They require bright light to function and are not sensitive to lower light levels. A normal retina contains approximately million cones, primarily in the macula , the small area in the center of the retina that provides clear central vision.

Cones are the most concentrated in the fovea , which is located in the center of the macula and provides the sharpest detail vision. Cones provide photopic vision , which refers to eyesight in daylight conditions. The cornea and the crystalline lens are both important for the eye to focus light.

The distance from the magnifying lens to the piece of paper is the focal length. This bending is possible because of the curve of the cornea as well as the change in refractive index as light moves from air into the cornea and then into the aqueous fluid between the cornea and the iris.

Air has a refractive index of 1. This becomes noticeable if you try to look at something when you are under water. Things appear out of focus because the cornea is designed to work with light passing into it from air rather than from water.

Wearing swimming goggles under water allows the layer of air to be present. Behind the aqueous fluid is the second lens system. It consists of a convex lens that is soft and pliable. The ciliary muscle is a circular ring of muscle that attaches all the way around the lens.

This ciliary muscle can change the shape of the crystalline lens by stretching it at the edges. It is attached to the lens by zonules ligament fibres that can be tight or loose. When you are looking at a near object, the lens needs to become more rounded at the central surface in order to focus the light rays. This ability to change focus for close-up objects is called accommodation.

The Schachar mechanism can be demonstrated using a Mylar balloon a shiny silver flat balloon that is often used with helium. And when there is low light, the iris opens up the pupil to let in more light. Lens Focuses light rays onto the retina. The lens is transparent, and can be replaced if necessary.

Our lens deteriorates as we age, resulting in the need for reading glasses. Intraocular lenses are used to replace lenses clouded by cataracts. Macula The area in the retina that contains special light-sensitive cells.

In the macula these light-sensitive cells allow us to see fine details clearly in the center of our visual field. The deterioration of the macula is a common condition as we get older age related macular degeneration or ARMD.

Optic Nerve A bundle of more than a million nerve fibers carrying visual messages from the retina to the brain. In order to see, we must have light and our eyes must be connected to the brain. Your brain actually controls what you see, since it combines images. The retina sees images upside down but the brain turns images right side up. This reversal of the images that we see is much like a mirror in a camera. Glaucoma is one of the most common eye conditions related to optic nerve damage.

Pupil The dark center opening in the middle of the iris.