NOCE / ABO Basic flashcards
NOCE / ABO Basic · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Corneal refractive power
- The cornea contributes roughly two-thirds of the eye's total refractive power, about 43 diopters of an eye total near 60 diopters, because of the air–tear film interface.
- Accommodation mechanism
- Ciliary muscle contraction releases zonular tension, allowing the crystalline lens to become more convex and increase plus power for near vision.
- Myopia
- A refractive condition in which parallel light rays focus anterior to the retina at rest, corrected with minus concave lenses that diverge light before it enters the eye.
- Snell's law
- n1 sin θ1 equals n2 sin θ2; it describes how a light ray bends at the boundary between two media of different refractive indices.
- Prentice's rule
- Induced prism in prism diopters equals decentration in centimeters multiplied by lens power in diopters; used to calculate prism from off-center viewing.
- Index of refraction
- The ratio of light speed in vacuum to its speed in a medium; higher index materials bend light more and allow thinner lenses.
- Thin lens power sum
- Two thin lenses in contact add directly, total power equals F1 plus F2; when separated by distance d, subtract d times F1 times F2.
- Spherical equivalent
- Sphere power plus one-half of the cylinder power; used to estimate the overall refractive effect of a toric lens or prescription.
- Toric transposition
- To convert between plus and minus cylinder form, add cylinder to sphere, change the cylinder sign, and rotate the axis by 90 degrees.
- Vertex distance compensation
- When lens power exceeds about plus or minus 4 diopters, the compensated power equals F divided by (1 minus d times F), with d in meters.
- Polycarbonate properties
- Index 1.586, Abbe value about 30, very high impact resistance and inherent UV absorption; the low Abbe value causes more chromatic aberration than CR-39.
- CR-39 lens material
- A thermoset plastic with index 1.498, Abbe value about 58, and specific gravity 1.32, offering good optical clarity and moderate impact resistance.
- Anti-reflective coating
- Multilayer thin films reduce surface reflections, increase light transmission, and decrease glare, improving cosmetics and night vision clarity.
- Progressive addition lens
- A lens with continuous power change from distance to near, having a corridor, distance zone, near zone, and peripheral unwanted astigmatism.
- Boxing system A measurement
- The horizontal width of the lens shape measured at its widest point inside a rectangle drawn tangent to the frame's lens opening.
- Frame PD
- Geometric center distance equal to the A measurement plus the distance between lenses, the DBL; used to compute decentration for lens layout.
- Pantoscopic tilt
- Downward tilt of the frame front, typically 8 to 12 degrees, which aligns the optical axis with the line of sight in downgaze.
- Minimum blank size
- Effective diameter plus twice the decentration plus 2 mm; the smallest uncut lens that will produce the required optical center.
- Lensometry
- Use of a lensmeter to verify sphere, cylinder, axis, prism, and add power of the finished lens against the written prescription.
- Decentration formula
- Decentration per lens equals frame PD minus patient PD divided by two; it positions the optical center to avoid unwanted prism.
- Plastic frame adjustment
- Heat the frame with hot air or a bead warmer until pliable, bend slowly, and hold until cool; cold bending can craze or crack the material.
- Nose pad alignment
- Both pads should contact the nose evenly with equal pressure, sit on the nasal sides, and support the frame weight without slipping.
- Dispensing verification
- Confirm lens powers, PD, axis, and frame alignment with the patient wearing the glasses, then adjust the fit and explain care.
- ANSI Z87.1
- The standard for occupational eye and face protection; compliant frames and lenses carry the Z87 marking and must pass high-velocity impact tests.
- FTC Contact Lens Rule
- Requires that patients receive a copy of their contact lens prescription, including all parameters, so they may buy lenses from any seller.
- Drop ball test
- An impact test in which a steel ball is dropped onto a lens; dress lenses must pass it to be dispensed as impact resistant.
- Dk/t
- Oxygen transmissibility of a contact lens: the material's oxygen permeability Dk divided by lens center thickness t; higher values mean more oxygen.
- Silicone hydrogel lenses
- Soft contact lenses combining silicone for high oxygen permeability with hydrogel for wettability and comfort, often with lower water content.
- Contact lens base curve
- The radius of curvature of the lens back surface, chosen from corneal keratometry readings to align with the cornea and give a proper fit.
- Vision plan vs medical
- Vision plans cover routine eye exams and eyewear, while medical insurance covers diagnosis and treatment of eye disease, often with different billing codes.
- Remake and redispense
- A lens or frame returned to the laboratory for rework; tracking remake reasons helps control lab costs and identify measurement errors.
- Progressive seg height
- The vertical position of the fitting cross measured from the bottom of the lens, usually placed at or near the pupil center.