MOC PQA - Optician flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Diopter definition

Unit of refractive power equal to the reciprocal of focal length in meters; a 2.00 D lens has a focal length of 0.50 m.

Prentice's rule

Prism in diopters equals decentration in centimeters multiplied by lens power in diopters; direction follows the base toward the decentration side for plus lenses.

Vertex distance formula

Effective power change is calculated as F_new = F/(1 − d·F), where d is the change in vertex distance in meters; clinically significant above about four diopters.

Abbe value meaning

A measure of dispersion; higher Abbe values indicate less chromatic aberration, while lower values produce more color fringing, especially off-axis.

Boxing system dimensions

Frame size is written as lens width, bridge width, and temple length; effective diameter is the largest box dimension used to calculate minimum blank size.

Pantoscopic tilt

Downward tilt of the lens plane relative to the vertical, typically 8 to 12 degrees; it affects effective power and cylinder in high prescriptions.

Face-form angle

Horizontal wrap of the frame front, usually 5 to 8 degrees; excessive wrap induces prism and requires compensated lens design.

Minimum blank size

Calculated as effective diameter plus twice the decentration plus about 2 mm edge allowance; inadequate blank size forces unwanted decentration.

Progressive corridor

The zone of increasing plus power between distance and near; shorter corridors suit small lens heights but increase peripheral distortion.

Polycarbonate properties

Refractive index about 1.586, Abbe value about 30, and high impact resistance; commonly required for children's and safety eyewear.

Anti-reflective coating

Multilayer surface treatment that reduces reflections and increases light transmission; typically includes a hard coat and hydrophobic top layer.

Photochromic limitation

Lenses darken with ultraviolet exposure; windshields block UV, so they may not darken adequately while driving.

Transposition rule

Add cylinder power to sphere, reverse the cylinder sign, and change the axis by 90 degrees; the prescription remains optically equivalent.

Spherical equivalent

Sphere power plus half the cylinder power; used for contact lens conversion when cylinder is small or clinically insignificant.

Monocular PD

Distance from the bridge of the nose to each pupil, measured separately; the sum gives binocular PD and reduces error from head turn.

Prism resolution

Horizontal and vertical prism components combine as vectors; resultant prism equals the square root of the sum of squares.

Dk and Dk/t

Dk is oxygen permeability of a contact lens material; Dk/t is transmissibility through a given lens thickness and predicts corneal oxygen supply.

RGP fit assessment

Fluorescein pattern shows apical clearance, mid-peripheral bearing, and edge lift; central bearing indicates a flat fit and central pooling a steep fit.

Peroxide care system

Hydrogen peroxide disinfection requires a neutralizing case and full soak time; incomplete neutralization causes burning and corneal irritation.

Acanthamoeba risk

Exposure to non-sterile water, including tap water, swimming, and showering while wearing lenses, increases risk of this serious corneal infection.

Corneal refractive power

The cornea provides about two-thirds of the eye's refractive power, roughly 43 diopters; the crystalline lens contributes about 15 to 20 diopters.

Axial length and myopia

Each 1 mm increase in axial length corresponds to roughly 3 diopters of myopia and is associated with increased retinal detachment risk.

Presbyopia onset

Age-related loss of accommodative amplitude, typically noticed in the early to mid-40s; add power usually starts near +1.00 diopter.

Anisometropia effect

A difference in refractive error between eyes greater than about 2 diopters may cause aniseikonia and adaptation problems with spectacles.

Lensmeter function

Instrument that measures sphere, cylinder, axis, prism, and optical center of a lens; calibration should be verified with a known lens.

Lens clock use

Device that reads surface curvature in diopters; used to verify base curve and surface power by converting sagitta to power.

Frame heater caution

Softens acetate for adjustment; overheating causes blistering and loss of shape, so heat should be applied gradually and evenly.

Hinge screw matching

Replacement screws must match thread size and length; mismatched screws damage hinge threads and require tapping or hinge replacement.

Prescription as record

A medical document containing prescriber information, date, and expiration; release and retention must follow privacy and record-keeping rules.

Scope of practice

Defines which tests and fittings an optician may perform; exceeding scope is a licensing violation and may create liability.

Informed consent

Clear communication of risks, alternatives, and costs before a procedure or fitting; documented consent supports patient autonomy and ethical practice.

Conflict of interest

Ownership interests, referral arrangements, or incentives that may influence recommendations; must be disclosed and comply with anti-kickback laws.