Click on a term to the left to look up the definition.
- 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.
- Aspheric Contact Lens
- Contact lenses for borderline astigmatic patients and for those who are just beginning to develop presbyopia.
- 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
- Visibility tint
- Contact Lens Solution
- Cleaning solution
- Rinsing solution
- Disinfecting solution
- Multipurpose solution
- Rewetting solution
- Conventional
- Usually a lens with a wear time of 6 to 12 months.
- 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.
- DK/t
- A term used to describe the amount of oxygen that will pass through a contact lens.
- Daily Wear (DW)
- This is a lens that a patient wears only during the day and takes out and cleans every night. It may be either disposable or non-disposable.
- 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.
- 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.”
- Farsighted
- Called hyperopia, this condition means that people can see distant objects very well, but have difficulty focusing on objects that are up close.
- Flat
- A base curve measurement. In some cases, a prescription or contact lens box may list a term like flat, median, or steep rather than a numeric value for the base curve. While the term refers to a specific value, it varies according to brand.
- 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.
- Hard Contact
- These were the earliest type of contact lens. They are made of a material called PMMA, which is actually Plexiglas. They do not let any oxygen through the contact to the cornea, except for the small amount dissolved in the person's tears. Because of this problem, they can't be worn for as many hours as RGP's. Very few people still wear this type of contact.
- High
- An add power measurement for bifocal lenses.
- Low
- An add power measurement for bifocal lenses.
- Median
- A base curve measurement. In some cases, a prescription or contact lens box may list a term like flat, median, or steep rather than a numeric value for the base curve. While the term refers to a specific value, it varies according to brand.
- 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.
- Multifocal Lens
- See Bifocal Lens
- Nearsighted
- Called myopia, people with this condition see near objects clearly but objects far away are blurry or out of focus.
- 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
- Actual medical doctors who have completed medical school, residency, etc. They can perform eye surgery as well as prescribe contacts and eyeglasses.
- Optician
- Eye care professionals similar to pharmacists in that they can dispense contact lenses but cannot prescribe them. Opticians are not doctors.
- Optometrist (OD)
- Eye care professionals, who are not medical doctors, but have several years of technical training so they can perform various medical tests and write prescriptions for contacts and eyeglasses. Despite the fact that they have never been to medical school, they are licensed by their state as "doctors of optometry."
- 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 health condition in which the eye exhibits a progressively diminished ability to focus on near objects with age.
- Progressive bifocal
- A progressive bifocal has a range of several different add powers built into it, so the same contact can be used by people who need varying levels of correction.
- Replacement Schedule
- See Wear Time
- Rigid Gas Permeable (RGP) Contact
- "RGP" stands for "Rigid Gas Permeable." This type of contact is made of a stiff plastic that lets more oxygen through the lens to the cornea than soft contacts do. They are also referred to as "gas perms."
- Rx
- This is an abbreviation used for "prescription” (It is actually an abbreviation of the Latin word for "recipe”).
- Sphere (SPH)
- See Power
- Spherical Prescription
- A prescription for someone who is simply nearsighted or farsighted. Most contact lens prescriptions are for spherical lenses.
- Steep
- A base curve measurement. In some cases, a prescription or contact lens box may list a term like flat, median, or steep rather than a numeric value for the base curve. While the term refers to a specific value, it varies according to brand.
- Strength (STR)
- See Power
- 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
- XW
- See Extended Wear
