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Lens4Vision

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Glossary Terms

  • Glossary Terms

    Add Power: As people become older the lens in their eye becomes harder, thus making it more and more difficult to focus on things close to them, such as reading material. Bifocal contacts have both a power and an additional measurement called an "add power" that assists in bringing near vision into focus. The "add power" will always be a + (plus) number. Some lenses will list the add power as high, medium, or low rather than as a number. The corresponding numeric value for these terms varies by brand.

    Annual Replacement Lenses: Conventional contact lenses that are replaced yearly.

    Astigmatism: This is a condition where the shape of the front of the eye bulges forward slightly instead of being perfectly round. It creates a long, oval shaped band across the middle of the person's vision which requires more correction than the rest of the eye. This condition can be corrected by the use of a toric lens.

    Axis: This measurement indicates the placement of the extra power of a toric lens. The oval band in the person's vision that needs the extra power could run up and down, right to left, or at any angle in between. The axis will usually be a number between 0 and 180 degrees.

    Base Curve (BC): This measurement is the shape of the back surface of the lens. It determines how the lens fits. Most brands come in more than one, and it is usually an 8.x or 9.x number. A few brands use non-numeric base curves such as flat, median, or steep.

    Bifocal Lens: Bifocal (or "multi-focal") lenses are used for correcting two different vision problems at the same time; blurred distance vision and blurred near vision.

    Brand: The name of the contact lens, such as “Acuvue Oasys”, is actually the brand. Different brands tend to have unique parameters and are made of different materials, so it is not possible to substitute a brand that is different from what is prescribed. There are no "generic" brands of contacts.

    Colored Contacts: Enhancing; Opaque and visibility tint.

    Cylinder (CYL): This measurement refers to the amount of extra power needed to correct the astigmatism. It will always be a - (minus) number in contact lens prescriptions.

    Conventional Wear Contact Lens: A contact lens prescribed to be replaced after 12 months or as directed by the eye care practitioner.

    Custom Toric Contact Lens: Corrects mid to high levels of astigmatism and is generally manufactured on an Rx basis specifically for a particular individual.

    Daily Wear Contact Lens: These lenses are intended to be worn during waking hours (less than 24 hours) and cleaned and disinfected each time they are removed from the eye.

    Diameter (DIA): This measurement refers to the width across the lens in millimeters. Most brands come in one or two sizes. It is usually a 14.x number, but can range from 13.x to 15.x.

    Disposable Contact: Any contact lens with a daily, weekly, or monthly replacement schedule is considered disposable.

    Disposable: Usually a lens with a wear time of less than 6 months.

    DK/t value: A term used to describe the amount of oxygen that will pass through a contact lens.

    ECP: Eye Care Provider, a generic term for an Optician, Optometrist, or Ophthalmologist.

    Extended Range (XR): Extended range lenses offer additional powers beyond those normally featured on the lens in question.

    Extended Wear (EW): This means wearers can sleep in the lens if the doctor has directed them to do so. An extended wear lens may also be worn like a daily wear lens if the doctor thinks it would be better to take it out every night. This type may also be either disposable or non-disposable. On some lenses this may be labeled “XW.”

    Extended Wear Contact Lens: Contact lens designed to be worn round-the-clock for intervals of one to seven days.

    Flex Wear (FW): This means the same thing as extended wear. You can sleep with the lenses in if the doctor approves, or it may be worn only during the day.

    Lazy Eye: A condition in which there is loss of vision for no apparent reason; the eye appears healthy, but vision is poor. This is also known as amblyopia. The decreased vision is not correctable with optical devices.

    LASIK:abbreviation for Laser-Assisted In Situ Keratomileusis. A kind of laser surgery designed to improve focus by altering the shape of the cornea.

    Monovision: This is a bifocal solution in which one eye is corrected to see up close and the other is corrected to see far away (rather than having both corrections in each contact lens). This means one eye is always out of focus. The brain learns to pay attention to only one eye at a time, depending on whether the patient is looking at something up close or at a distance. Monovision correction allows a person who would normally have to wear expensive bifocal lenses to wear regular contact lenses.

    OD: Right eye (abbreviation of "oculus dexter," which is "right eye" in Latin).

    OS: Left eye (abbreviation of "oculus sinister," which is "left eye" in Latin).

    OU: Both eyes are the same (abbreviation for "oculus uterque").

    Ophthalmologist: medical doctor (MD) uniquely trained in all aspects of eye care-medical, surgical, and optical-to diagnose and treat all disorders of the eye.

    Optometrist (OD): State-licensed health care professional who diagnoses and treats eye health and vision problems. An OD can prescribe glasses, contact lenses, engage in low vision rehabilitation and vision therapy, has the authority to prescribe ophthalmic medications and perform certain surgical procedures.

    Optician:A paramedical professional who manufacturers and dispenses eyeglasses and helps in the selection of frames. The optician may also dispense and/or fir contact lenses, depending on individual states’ licensing practices.

    Planned Replacement Contact Lens: These contact lenses are replaced on a planned schedule, usually every two weeks, monthly, or quarterly. They are available for most prescriptions and require minimal care because they are frequently replaced.

    Plano: This measurement means no power. Colored lenses for a person who does not need vision correction will be plano. Occasionally a toric lens will also have a plano power, which means that the person only needs contacts to correct their astigmatism.

    Power (PWR): This measurement is sometimes called sphere or strength. It is the strength or amount of correction needed. The power will always have a + (plus) or - (minus) in front of it. It is measured in diopters, and usually goes up in 0.25 steps. Plus powers are for farsighted people, while minus powers are for nearsighted people.

    Presbyopia: A condition that occurs as the eye’s lens grows older and begins to lose some of the elasticity needed to switch focus between viewing near and far objects. Most people begin to experience the effects in their mid-forties.

    Replacement Schedule: This is a general term used to refer to the schedule by which one should replace their contact lenses. In order to achieve comfortable, problem-free lens wear, please consult your eye care practitioner for a replacement schedule that is suitable for you.

    Rx: This is an abbreviation used for "prescription” (It is actually an abbreviation of the Latin word for "recipe”).

    Spherical Prescription: A prescription for someone who is simply nearsighted or farsighted. Most contact lens prescriptions are for spherical lenses.

    Toric: A toric lens has extra power that can correct the effects of astigmatism. Toric prescriptions have two extra measurements in addition to power, base curve, and diameter, cylinder and axis.

    Vial: Generally the same as a conventional lens, referring to the small vial in which the lens is packaged.

    Wear time: Each brand of contact is made to last a certain length of time. At the end of this time period, you should replace the pair you are wearing with a new pair. The manufacturer of each brand will recommend a specific wear time, but your doctor has the final say on how often you should replace your contacts.

    • Conventional

    • 1 Day Replacement

    • 1 to 2 Week Replacement. These lenses can be either DW or FW. FW lenses can be worn for up to 7 days before they have to be taken out and cleaned (although most people need to clean them more often.) They usually come in 6 packs (with 6 lenses of the same prescription in each box). Four boxes (which is 12 pair, or 24 lenses) will usually last for 6 months if the patient is wearing them 2 weeks at a time.

    • Monthly Replacement