NCLE Advanced key terms

The radius of curvature of the central posterior surface of a contact lens, given in millimeters. A shorter radius makes a steeper lens that fits more tightly against the cornea.

The overall width of a contact lens measured across its widest point in millimeters. Diameter affects corneal coverage, centration, and how the lens interacts with the eyelids.

The height of a lens's posterior surface measured from the plane of its edge to the center. It describes how deeply the lens vaults over the cornea and drives fit relationships.

The central portion of a contact lens that carries the corrective power and sits over the pupil. Its width affects visual quality and how the lens behaves on the eye.

A flattening curve near the edge of a rigid lens, outside the optical zone. It controls edge clearance and tear exchange and influences comfort.

The gap between the posterior edge of a rigid lens and the cornea. Enough lift lets tears flow beneath the lens; too much causes discomfort and lens instability.

A rigid lens made of a material that transmits oxygen. It keeps its own shape on the eye and can correct irregular astigmatism by creating a tear layer over the cornea.

A soft lens with toric surfaces, plus a design feature that keeps the cylinder axis from rotating. It corrects astigmatism while retaining the comfort of a hydrogel material.

A stabilization method that adds thickness or prism to the lower part of a toric soft lens. Gravity and lid forces then hold the lens axis in the correct orientation.

A lens whose surface curvature changes steadily from center to edge instead of having a single radius. It is used to reduce spherical aberration and shape the fit.

A rigid lens whose second curve is steeper than its central base curve. It is used in orthokeratology to reshape the corneal epithelium and temporarily reduce myopia.

A large-diameter rigid lens that lands on the sclera and vaults over the cornea, trapping a pool of tears. It is used for irregular corneas, dry eye, and high refractive errors.

The oxygen transmissibility of a lens, found by dividing the material's oxygen permeability (Dk) by its thickness. Higher values mean more oxygen reaches the cornea.

Measurement of the curvature of the central anterior cornea, reported in diopters across two principal meridians. It guides initial lens selection and reveals corneal astigmatism.

A computer-generated map of corneal curvature and elevation over a broad area. It helps detect irregular astigmatism, choose specialty designs, and monitor change over time.

The pattern of dye-stained tears seen beneath a rigid lens under blue light with a yellow filter. It shows areas of bearing, pooled clearance, and edge lift.

A refraction done with the contact lens still on the eye. It measures leftover refractive error and tells the fitter how to adjust the lens power.

An off-center resting position of a contact lens. It can reduce comfort or vision and often points to a fit that is too steep, too flat, or poorly stabilized.

A painful, red eye with an immobile lens, corneal edema, and diminished tears. It follows a lens that fits too tightly, particularly after overnight wear.

Growth of new blood vessels into the clear cornea, which is normally vessel-free. It usually results from chronic low oxygen or mechanical rubbing from lens wear.

Fluid buildup that swells the cornea, commonly from reduced oxygen or poor tear exchange under a lens. It causes haze, halos, and blurred vision.

An inflammatory reaction of the upper inner eyelid with enlarged papillae. It is linked to lens deposits, rough edges, and mechanical irritation, and causes itching and lens intolerance.

A corneal infection that can threaten sight. It is associated with extended wear and poor hygiene and shows up as pain, redness, discharge, and a corneal infiltrate.

Uptake of fluorescein dye by damaged corneal surface cells from lens wear. Grading its size, depth, and pattern helps separate mechanical, hypoxic, and solution-related causes.

A reversible change in corneal shape caused by long-term rigid lens wear. It produces spectacle blur and distorted keratometry and topography readings.

A shortfall in the oxygen reaching the cornea. With lenses it comes from low oxygen transmissibility or thick designs and can lead to edema and new blood vessels.

A layer of tear-derived protein clinging to a lens surface. Left in place, it causes discomfort, blurred vision, and inflammatory reactions.

A tablet or solution that breaks down protein that routine daily cleaners leave behind. It is used at set intervals, such as weekly, on soft lenses as directed.

One product that cleans, rinses, disinfects, and stores soft lenses. It depends on surfactants and preservatives and works best when lenses are rubbed and rinsed first.

A care system that uses hydrogen peroxide to disinfect lenses. The peroxide must be completely neutralized, usually by a coated disc or tablet, before the lens goes on the eye.

The manual cleaning step in which solution and friction are applied to a lens before storage. It lifts deposits and organisms that soaking alone leaves behind.

The recommended interval for throwing away and replacing lenses, such as daily, every two weeks, or monthly. Following it limits deposit buildup and reduces complications.

The prescribed pattern of lens use, including daily wear time and whether lenses stay in overnight. It shapes oxygen exposure and the risk of complications.

Explaining the risks, benefits, and alternatives of contact lens wear and confirming the patient agrees before fitting begins. The discussion is documented in the record.

The rule that a patient must receive their contact lens prescription after a fitting so they can buy lenses from any source. It supports patient choice.

The length of time patient records, including lens parameters and follow-up findings, must be kept. It is set by state law and professional guidelines.

OSHA rules for infection control in health care settings, covering gloves, hand hygiene, and safe disposal of contaminated items. It protects staff and patients from bloodborne disease.

Confirming a delivered lens matches the ordered power, base curve, diameter, and material before it is dispensed. It prevents dispensing errors and remakes.