Just as a camera must focus an image precisely on its film, the eye must focus an image on the retina. An image focused in front of or behind the retina is blurred. Myopia occurs when the eye is too long causing the image to focus in front of the retina. The myopic eye elongates over many years causing the gradual worsening of near sightedness familiar to most myopic patients. This process must stabilize before laser vision correction can be performed. Ophthalmologists cannot control the length of the eye but can compensate for it by flattening the cornea, which moves the image back to the retina.

normal eye	Perfectly focused (emmetropic) eyes: Light enters eyes and is focused or "refracted" mostly by the cornea and partly by the lens. In eyes that focus properly, light rays falls sharply on the retina. These eyes require no corrective lenses.
myopic eye	Nearsighted (Myopic) eyes: Light is refracted too much and is not sharply focused on the retina. Spectacles and contacts lenses may be placed in front of the eyes to properly focus the light.

Hyperopia or farsightedness occurs when the eye is too short or the cornea is too flat. There is not enough focusing power in the eye to bring light rays to focus on the retina - the actual focal point would be behind the retina (Fig. 2). The image formed on the retina is blurred, and additional focusing power is needed. This may be added as spectacles or contact lenses. When a person is young, that additional power may be supplied naturally through the mechanism of accommodation, in which the lens of the eye changes shapes. Accommodation is normally used to permit the eye to refocus from far to near. Hyperopes may do this all the time to provide clearer distance vision. This has led to the common term of farsightedness, which implies that distance or far vision is better than near vision. As hyperopes age however, this ability to refocus to clear the distance vision declines, as the lens becomes less flexible and the ability to accommodate decreases. In a normal eye, this loss of accommodation is felt only as a difficulty in viewing close objects after the age of 40. Hyperopes will notice the effect for both distance and near. Younger individuals with low amounts of hyperopia may see well for distance and less well up close, while older individuals and those with higher hyperopia will need correction for both distance and reading.

normal eye	Perfectly focused (emmetropic) eyes: Light enters eyes and is focused or "refracted" mostly by the cornea and partly by the lens. In eyes that focus properly, light rays falls sharply on the retina. These eyes require no corrective lenses.
Hyperopic eye	Farsighted (Hyperopic) eyes: Light rays are not refracted enough and have not yet come to focus when they reach the retina.

Please note that the term "farsightedness" is correctly applied only to hyperopia as described above. People with normal distance vision who have trouble reading after age 40 are "presbyopic" (literally meaning "old sighted"). Presbyopia is a result of the natural decrease in the eye's lens to accommodate as we age. Thus, the loss of the ability to read with increasing age is presbyopia - not hyperopia or farsightedness.

Presbyopia is the medical term describing the loss of ability to see clearly close up. It normally begins after the age of 40 and is first noticed as trouble in reading fine print or in dim light. As the condition progresses to its maximum, usually over 10-15 years, difficulty with fine print increases and viewing objects at intermediate distance such as computer screens also becomes hard. The condition occurs because as the lens of the eye ages it continues to grow and becomes less flexible, thus losing its ability to change shape as required to shift focus from distance to near. Presbyopia happens to everyone even if they have perfect distance vision (emmetropia), or are nearsighted, farsighted or have astigmatism. Presbyopia may be corrected by spectacles including reading glasses, bifocals, or trifocals. For contact lens users it may be corrected by monovision, in which one eye is corrected for distance and the other for near; or by bifocal contacts.

The surgical correction of presbyopia at this time is limited to the monovision approach with one eye adjusted for distance and the other for close. This works best with individuals who have successfully used monovision with contact lenses. Surgery that is designed to reverse the true cause of presbyopia (i.e. the loss of the ability of the lens to accommodate) is currently being investigated. Initial results have been encouraging but in many cases the improvement faded over time. While there are several different surgical approaches under investigation, refinements and techniques continue but none have been approved by the US FDA.