Myopia, or nearsightedness, occurs when the eye is too long for its refractive power. Light tends to land in front of the retina, causing blurred vision when viewing objects at a long distance. When objects are brought closer, light is refracted to land on the retina, allowing for clear vision. This is why myopia is commonly called nearsightedness - myopic individuals can see well up close, but have trouble seeing things far away. Although changes in cornea or lens shape can cause myopia, the most common culprit is the eye being too long. Myopia can be treated with glasses, contact lenses, refractive surgery such as LASIK, or a newer realm of eyecare known as myopia management. Myopia management focuses on preventing the eye from growing longer, essentially halting the progressive worsening of myopia.

Hyperopia, or farsightedness, occurs when the eye is too short for its refractive power. Light tends to land behind the retina, causing blurred vision. Our eyes have the ability to accommodate, or increase their refractive power, which often results in people with hyperopia being able to compensate for the blur at a distance. There is a limit to accommodation, and thus people with hyperopia often have trouble focusing on objects that are near to them - hence it is commonly referred to as farsightedness. Those with hyperopia often experience presbyopia (the loss of the ability to accommodate resulting in the inability to view objects up close- this happens to everyone usually beginning around age 40) earlier than individuals with myopia or without refractive error. Like myopia, hyperopia is mostly caused by the eye being too short, but may also be due to irregularities in the cornea or lens shape. Hyperopia is frequently treated with glasses, contact lenses, or refractive surgery such as LASIK.

Astigmatism occurs when the cornea or lens is not perfectly round and takes on a shape similar to that of the back of a spoon or a football. This causes light to land in more than one spot in the back of the eye, resulting in blurry vision both up close and at a distance. Often people with astigmatism will complain that light tends to shine in multiple directions, particularly headlights or traffic lights when driving at night. Astigmatism is typically treated with glasses, contact lenses, or refractive surgery.