The Optician’s Glossary of Terms

Unlike a spherical lens that has a uniform front surface, the aspheric lens has a complex front curvature, changing power gradually from the centre to the edge of the lens.   This surface profile can reduce or eliminate distortion associated with basic spherical lenses.

The principal meridian of a cylindrical lens used to correct astigmatism. In contact lenses, it is the flattest meridian of a toric contact lens.

Distance from the back surface of a lens to the front surface of the cornea. For a contact lens, the value would be zero.

The central posterior (inside surface) curve of a contact lens. The measurement of the base curve is that of the radius of curvature of the sphere from which the lens is made.

A type of spectacle or contact lens design that includes two focal areas: one for near, one for distance.

A source of UV light of an approximate wavelength of 400 NM. It is used to excite fluorescein for observation tests.

A thin plastic lens designed to fit over the cornea, usually for the correction of refractive error

A Dispensing Optician with a specialist qualification in contact lens fitting.

Swelling and fluid retention in the cornea, usually related to lack of sufficient oxygen in contact lens wearers.

A single-use lens. Defined by the U.S. Food and Drug Administration as a contact lens that is used once and discarded. Worn during waking hours and removed at the end of each day and disposed of. Any lens that is intended to be removed from the eye, cleaned, rinsed, disinfected, and reinserted does not qualify for inclusion in this category under the FDA definition.

Accumulation of substances, usually tear film components (protein), onto the contact lens surface and/or in the lens material. Types of deposits include protein, mucus & lipid

An agent that kills surface bacteria and microorganisms commonly found on contact lenses.

A dispensing optician is a professionally qualified person who advises on, fits and supplies the most appropriate spectacles after taking account of each patient’s visual, lifestyle and vocational needs. Dispensing opticians are legally able to supply under sixteens and partially sighted patients.

A condition generally known as “normal vision” where light rays from distant objects are focused on the retina so vision is sharp and clear

Contact lenses designed to be worn continuously for up to 29 nights / 30 days.

A fluorescent dye that is instilled in the eye to evaluate the fit of rigid lenses and to highlight corneal staining, abrasions, and other anterior eye pathology. Fluorescein is observed with a Burton lamp or through the cobalt blue filter of a slit-lamp.

The inner, back surface of the eye made up of the retina, macula, optic disc, fovea and blood vessels.

Lenses having a “handling tint” are slightly tinted to make them more visible for both care and insertion of the lens. The tint on these lenses does not affect eye colour.

Also known as PMMA lenses, these traditional contact lenses are made from polymethylmethacrylate

Type of plastic material which contains water, and is commonly used in the manufacture of soft contact lenses.

This type of solution can be used to clean, disinfect, rinse, and store contact lenses. It is a great alternative for people who are sensitive to the preservatives in multipurpose solutions.  Neutralisation of the solution is important to avoid a stinging or burning sensation to the eyes.

People with Hypermetropia can have difficulty seeing objects close up. Hypermetropia occurs when the eyeball is too short from front to back, or the eye’s focusing mechanism is too weak, causing light rays to be focused behind, rather than on the retina.

Insufficient oxygen reaching the cornea.

A plastic lens implanted in place of the crystalline lens (either behind the cornea or behind the iris) during cataract surgery.

An instrument used to measure the curvature of the two principal meridians of the central cornea.

The measurement of the flattest and steepest meridians of the patient’s cornea using a Keratometer.

A treatment technique that is often prescribed for people age 40 and older who are affected by presbyopia. Presbyopia occurs when, as part of the natural ageing process, the eye’s crystalline lens loses its ability to bring close objects into clear focus. Monovision means wearing a contact lens for near vision on one eye and, if needed, a lens for distance vision on the other eye.

These are contact lenses that contain two or more viewing zones, allowing multiple prescriptions in one lens. Used in the correction of presbyopia, the aim is to allow the viewer to see near and far objects.

This type of solution is the most popular for contact lenses. It can be used to rinse, disinfect, clean and store lenses. Typically, using a multipurpose solution eliminates the need for protein removal products

A visual defect where the light rays focus in front of the retina instead of on it due to steeper cornea or longer eyeball. People with this condition can see nearby objects clearly but distant objects appear blurred.

Power added to a distance vision prescription to create a near vision prescription to correct presbyopia.

Ophthalmoscopy, also called fundoscopy, is a test that allows a health professional to observe the fundus of the eye and other structures using an ophthalmoscope. It is done as part of an eye examination. It is crucial in determining the health of the retina, optic disc, and vitreous humor.

A medical doctor uniquely trained in all aspects of eye care—medical, surgical, and optical—to diagnose and treat all disorders of the eye.

Health care professional who diagnoses and treats eye health and vision problems. An Optometrist can prescribe glasses and contact lenses, engage in low vision rehabilitation and vision therapy.

The refraction performed over a patient’s contact lenses to determine what power is needed to provide optimum visual acuity.

The amount of oxygen diffusing through a given amount of contact lens material in a given amount of time under specified testing conditions.

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.

A technique to obtain an objective measurement of the refractive error of a patient’s eyes. The examiner uses a retinoscope to shine light into the patient’s eye and observes the reflection (reflex) off the patient’s retina. While moving the streak or spot of light across the pupil the examiner observes the relative movement of the reflex and places lenses over the eye (using a trial frame and trial lenses) to “neutralize” the reflex.

Rigid Contact lenses that are manufactured from silicon or fluoro-silicon acrylate base material. These lenses are used for irregular eye prescriptions.

A salt solution that is available preserved or preservative-free. It is used for rinsing contact lenses after cleaning and preparing them for insertion. Saline solutions do not disinfect contact lenses.  The salt content is similar to the natural concentration found in tears.

An instrument consisting of a high-intensity light source that can be focused to shine a thin beam of light into the eye. The lamp allows an examination of the anterior segment and the posterior segment of the human eye. The binocular slit-lamp examination provides a 3D, magnified view of the eye structures in detail, enabling anatomical diagnoses to be made for a variety of eye conditions.

A standardized test chart used to measure visual acuity. Visual acuity is expressed as a fraction (e.g., 6/6) The first number is the distance the chart is viewed from. The second is the distance at which the person being tested can see a letter clearly.

A contact lens made of soft water-absorbing plastic that adheres closely to the cornea and with minimal discomfort to the eye.

Contact lenses that correct nearsightedness (myopia) and farsightedness (hyperopia). They have the same power in all meridians.

Also known as a “bandage lens,” this contact lens is designed to protect and aid in the healing of a sick eye. This unique lens is frequently combined with precise medication delivery schedules to heal the eye. (Ref: Contact Lens Council). It’s usually a large lens which blankets the cornea, retains its moisture, and protects the surface of the cornea. Since the lens is well-tolerated, it provides an effective, pain-relieving cover for the eye.

An eye test that determines the fluid pressure inside the eye. Elevated pressure is a possible sign of glaucoma.

Contact lenses that are designed to correct astigmatism by bearing two different optical powers at right angles to each other.

Spectacle frame with variable adjustments to best fit the patients face.  The frame rim is fitted with a number of cells into which trial lenses can be placed when testing vision. Trial Lenses – a series of Sphere and Cylindrical lenses used in vision testing.

Expressed as a fraction, in which the numerator denotes the testing distance and the denominator indicates the distance at which a person with normal eyesight can read the letters on the chart.