With normal vision, an image is sharply focused onto the retina. In nearsightedness (known as myopia), the point of focus falls in front of the retina – making distant objects appear blurry.
Nearsightedness (myopia) is a common vision condition in which you can clearly see objects that are close to you, but objects farther away are blurry.
People who are farsighted see objects that are at a distance better than objects close to them. If you are farsighted, close objects may be so blurry so that you cannot perform tasks such as reading or sewing. A farsighted eye sees things differently than an eye that is not farsighted.
Astigmatism is an imperfection in the curvature of your cornea — the clear, round dome covering the eye’s iris and pupil — or in the shape of the eye’s lens. Usually, the cornea and lens are smooth and curved equally in all directions, helping to focus light rays sharply onto the retina at the back of your eye. However, if your cornea or lens isn’t smooth and evenly curved, light rays aren’t refracted properly. This is called a refractive error.
Presbyopia (which literally means “aging eye”) is an age-related eye condition that makes it more difficult to see very close.
When you are young, the lens in your eye is soft and flexible. The lens of the eye changes its shape easily, allowing you to focus on objects both close and far away.
After the age of 40, the lens becomes more rigid. Because the lens can’t change shape as easily as it once did, it is more difficult to read at close range. This normal condition is called presbyopia.
Since nearly everyone develops presbyopia, if a person also has myopia (nearsightedness), hyperopia (farsightedness) or astigmatism, the conditions will combine. People with myopia may have fewer problems with presbyopia.
Dry eye syndrome is a chronic lack of sufficient lubrication and moisture on the surface of the eye. Its consequences range from subtle but constant irritation to ocular inflammation of the anterior (front) tissues of the eye.
Dry eyes also are described by the medical term, keratitis sicca, which generally means decreased quality or quantity of tears. Keratoconjunctivitis sicca refers to eye dryness affecting the cornea and conjunctiva.
Eye allergies, called allergic conjunctivitis, are a common condition that occurs when the eyes react to something that irritates them (called an allergen). The eyes produce a substance called histamine to fight off the allergen. As a result, the eyelids and the conjunctiva — the thin, filmy membrane that covers the inside of your eyelids and the white part of your eye (sclera) — become red, swollen and itchy, with tearing and burning. Unlike bacterial or viral conjunctivitis, allergic conjunctivitis is not spread from person to person.
Blepharitis is a common and ongoing condition where the eyelids become inflamed (swollen) with oily particles and bacteria coating the eyelid margin near the base of the eyelashes. This annoying condition causes irritation, itchiness, redness, and stinging or burning of the eyes. While the underlying causes of blepharitis aren’t completely understood, it can be associated with a bacterial eye infection, symptoms of dry eyes, or certain skin conditions such as acne rosacea.
Conjunctivitis is the term used to describe swelling (inflammation) of the conjunctiva — the thin, filmy membrane that covers the inside of your eyelids and the white part of your eye (known as the sclera). This condition is often called “pink eye". The conjunctiva, which contains tiny blood vessels, produces mucus to keep the surface of your eye moist and protected. When the conjunctiva becomes irritated or swollen, the blood vessels become larger and more prominent, making your eye appear red. Signs of pink eye may occur in one or both eyes. There are three types of conjunctivitis: