GENERAL EYE DEFINITIONS
Cornea: the transparent front part of the eye that covers the iris (the colored part of the eye) and the pupil. Contact lenses are placed on the cornea.
Myopia: nearsightedness. The eye is too long or the cornea is too curved and the light rays focus in front of the retina, causing blur. It is corrected with minus powered lenses.
Hyperopia: farsightedness. The eye is too short or the cornea is not curved enough and the light rays focus behind the retina, causing blur. It is corrected with plus powered lenses or by accommodating (accommodating is the automatic process of changing the shape of the lens inside the eye to focus on near objects).
Astigmatism: can occur by itself or with myopia or hyperopia. It is usually caused by the cornea being shaped irregularly so that the light rays focus at several different points inside the eye and cause blur. It is not a disease and is quite common. It is corrected with lenses that contain extra power in one portion of the lens.
Presbyopia: a normal part of the aging process. It usually begins in the 40's and makes reading difficult. As we read the lens inside the eye accommodates, or changes it shape, in order to focus at something up close. As we age this lens becomes less and less flexible, making focusing up close more difficult. Reading glasses, bifocals or special contact lenses are needed to do the focusing that the lens used to do when reading.
CONTACT LENS DEFINITIONS:
Daily wear: contact lenses worn during the day and removed before bedtime.
Continuous wear: contact lenses approved by the FDA to be slept in overnight. The amount of nights the contact lenses may be worn depends on the type of contact lens and the health of each patient's eye while wearing the contact lenses. Extended wear has been shown to increase the number of infections and problems a contact lens wearer may have compared to daily wear.
Planned replacement: contact lenses that are replaced at regular intervals throughout the year. They can be replaced every 2 weeks, every month or every 3 months depending on the lenses.
Disposables: technically, this term refers to only those lenses that are worn once and then thrown away (the one-day or daily disposables). However, many people also use this term to mean 2 week planned replacement lenses.
Gas permeable: firm contact lenses made of special plastics that allow oxygen to flow through them. They can correct most kinds of prescriptions including astigmatism and presbyopia. They are also used for orthokeratology.
Soft contact lenses: soft lenses are made of hydrophilic or water-loving plastics. They are flexible and drape across the cornea. They can correct most kinds of prescriptions including astigmatism and presbyopia.
Silicon contact lenses: these contact lenses are made out of silicon instead of the plastic (the material of soft contact lenses) and have been approved for up to 30 days of extended wear for some patients. They are similar to soft contact lenses for comfort, care and handling.
Spherical contact lenses: contact lenses that correct for nearsightedness or farsightedness. They do not correct for astigmatism.
Toric contact lenses: these are contact lenses that correct astigmatism. Toric contact lenses may be both soft or firm gas permeable contact lenses.
Monovision: this is a special type of contact lens fitting that can be used for patients with presbyopia. One eye is corrected for distance and the other eye is corrected for near. The brain learns to pay attention to the eye that gives the best vision when looking at certain distances.
Bifocal or multifocal contact lenses: these can be either gas permeable or soft contact lenses. They correct for presbyopia, nearsightedness and farsightedness.