The Front of the Eye Light is focused into the eye through the clear, dome-shaped front portion of the eye called the cornea. Behind the cornea is a fluid-filled space called the anterior chamber. The fluid is called aqueous humor. The eye is always producing aqueous humor. To maintain a constant eye pressure, aqueous humor also drains from the eye in an area called the drainage angle.
Parts of the Eye Outside the Eyeball The eye sits in a protective bony socket called the orbit. Six extraocular muscles in the orbit are attached to the eye. These muscles move the eye up and down, side to side, and rotate the eye. The extraocular muscles are attached to the white part of the eye called the sclera. This is a strong layer of tissue that covers nearly the entire surface of the eyeball.
The layers of the tear film keep the front of the eye lubricated. Tears lubricate the eye and are made up of three layers. These three layers together are called the tear film. The mucous layer is made by the conjunctiva. The watery part of the tears is made by the lacrimal gland. The eye’s lacrimal gland sits under the outside edge of the eyebrow (away from the nose) in the orbit. The meibomian gland makes the oil that becomes another part of the tear film. Tears drain from the eye through the tear duct.
Behind the anterior chamber is the eye’s iris (the colored part of the eye) and the dark hole in the middle called the pupil. Muscles in the iris dilate (widen) or constrict (narrow) the pupil to control the amount of light reaching the back of the eye. Directly behind the pupil sits the lens. The lens focuses light toward the back of the eye. The lens changes shape to help the eye focus on objects up close. Small fibers called zonules are attached to the capsule holding the lens, suspending it from the eye wall. The lens is surrounded by the lens capsule, which is left in place when the lens is removed during cataract surgery. Some types of replacement intraocular lenses go inside the capsule, where the natural lens was. By helping to focus light as it enters the eye, the cornea and the lens both play important roles in giving us clear vision. In fact, 70% of the eye’s focusing power comes from the cornea and 30% from the lens.
The Back of the Eye The vitreous cavity lies between the lens and the back of the eye. A jellylike substance called vitreous humor fills the cavity. Light that is focused into the eye by the cornea and lens passes through the vitreous onto the retina — the light-sensitive tissue lining the back of the eye. A tiny but very specialized area of the retina called the macula is responsible for giving us our detailed, central vision. The other part of the retina, the peripheral retina, provides us with our peripheral (side) vision.
The retina has special cells called photoreceptors. These cells change light into energy that is transmitted to the brain. There are two types of photoreceptors: rods and cones. Rods perceive black and white, and enable night vision. Cones perceive color, and provide central (detail) vision. The retina sends light as electrical impulses through the optic nerve to the brain. The optic nerve is made up of millions of nerve fibers that transmit these impulses to the visual cortex — the part of the brain responsible for our sight.
Common eye conditions range from refractive errors (myopia, astigmatism) to age-related diseases like cataracts, glaucoma, and macular degeneration, often causing blurred vision, pain, or vision loss. Common causes include genetics, aging, diabetes, and infections. Diagnosis involves comprehensive, dilated eye exams, with treatments ranging from glasses and eye drops to surgery, depending on the condition. National Eye Institute (.gov) National Eye Institute (.gov) Common Eye Conditions and Disorders Refractive Errors: Nearsightedness (myopia), farsightedness (hyperopia), astigmatism, and presbyopia (age-related close-up vision loss). Age-Related Conditions: Cataracts (cloudy lens), Age-Related Macular Degeneration (AMD), and dry eye. Chronic/Serious Conditions: Glaucoma (optic nerve damage), Diabetic Retinopathy (leading cause of blindness in working-age adults), and retinal detachment. Infections/Inflammation: Conjunctivitis (pink eye), Blepharitis (inflamed eyelids), and corneal diseases. Functional Issues: Amblyopia (lazy eye) and Strabismus (crossed eyes). National Eye Institute (.gov) National Eye Institute (.gov) +1 Common Symptoms Vision Changes: Blurry, double, or dimmed vision, and loss of central vision. Physical Changes: Redness, inflammation, itching, or swelling of the eyelid. Sensory Changes: Eye pain, light sensitivity, flashes of light, and floaters. National Eye Institute (.gov) National Eye Institute (.gov) +2 Diagnosis and Treatment Diagnosis: Primarily through comprehensive, dilated eye exams to detect disease early. Treatment: Refractive Errors: Corrective lenses (eyeglasses, contacts) or refractive surgery. Cataracts/Retinal Issues: Surgical interventions, such as cataract removal. Glaucoma/Dry Eye: Prescription eye drops, lasers, or, in severe cases, surgery to manage pressure or inflammation.
