Cataracts: This is a clouding of the lens.Astigmatism: The cornea or lens is incorrectly curved, so light does not focus properly on the retina.It can be harmless, but it may indicate a more serious medical problem, such as a stroke. Anisocoria: This occurs when the pupils are an unequal size.Amblyopia: This begins in childhood and is often called “lazy eye.” One eye does not develop fully because the other, stronger eye dominates.Age-related macular degeneration: This causes blurry vision in the center of the visual field.A person has difficulty distinguishing between certain colors. Achromatopsia: Also known as color blindness, this genetic condition affects the cone cells.The visual cortex brings together impulses from both eyes to create images.Ī wide range of health issues can affect the eyes. The signals generated by the retina end up in the visual cortex, a part of the brain that processes visual information. The brain gives depth perception by coordinating the signals from both eyes. Together, they carry all the necessary information from our visual field. For instance, some are sensitive to contrast and movement, others to shape and detail. Because there are no rods or cones here, it is also called the “blind spot.”ĭifferent kinds of ganglion cells register different types of visual information. The ganglion cells leave the eye at a point called the optic disc. Thin retinal fibers called ganglion cells carry light information from the retina to the brain. The optic nerve is a thick bundle of nerve fibers that transmits signals from the retina to the brain. Each eye contains around 125 million rods. They can detect the lowest amounts of light and allow people to see at night. They are responsible for black and white vision. Rods generally exist around the edges of the retina. Red and green cones mostly occur in the center of the fovea, while the blue ones are mostly around the outside. There are different types, depending on the color that they are sensitive to. The fovea, a small pit at the center of the macula, has a high density of cone cells and no rods.Ĭones help people see in typical light conditions and distinguish colors. The retina contains around 6 million cone cells. The two primary photoreceptor cells are called “rods” and “cones.” When these sense light, they send electrical signals to the brain.Ĭones are present in the macula, the central part of the retina. Photoreceptor cells in the retina contain protein molecules called opsins that are sensitive to light. These signals are sent to the brain for processing. It contains millions of light-sensitive photoreceptor cells that detect light and convert it into electrical signals. The retina is the innermost layer of the eye. These include the retina and the optic nerve. It makes up most of the eye’s mass.Īqueous fluid is more watery, and it circulates through the front of the eye. Vitreous fluid is thick and gel-like and is present in the back of the eye. Two fluids circulate throughout the eyes to provide structure and nutrients. Because the cornea must remain clear to refract light, it has no blood vessels. It is the eye’s first defense against foreign objects and injury. The cornea is densely populated with nerve endings and is highly sensitive. It also helps the eye focus by directing light into the eye.
The cornea, like the lashes, eyelids, and tear fluid, protects the eye from injury and foreign objects, such as dust. This chamber is a fluid-filled area between the cornea and iris. The cornea is a clear, dome-like layer that covers the pupil, iris, and anterior chamber. As it contracts or relaxes, it changes the shape of the lens. This is a muscular ring attached to the lens. With age, the lens becomes stiffer and less flexible, making focusing more difficult. The lens can change shape, helping the eye focus light accurately onto the retina. In this way, it is similar to the aperture on a camera.Īfter it travels through the pupil, light reaches the lens. It has muscles that control the size of the pupil and the amount of light that reaches the retina. This allows the eye to take in as much light as possible. In bright light, the pupil constricts to protect the sensitive retina from damage. The pupil expands and shrinks in response to light. This is the dark spot in the center of the colored part of the eye. If tissues are the wrong shape, misaligned, or damaged, vision can be blurry. Refracting tissues focus incoming light onto light-sensitive tissues to give a clear, sharp image. There are three main types of tissue in the eye:īelow, we look at each of these types. Muscles connected to the eyeball allow the eye to move according to the direction of the person’s gaze. The rest is inside the eye socket, or orbit. The only part of the eye that people can see is the front.
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