NCLE Advanced flashcards
NCLE Advanced · 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.
- Sagittal depth
- The height of a lens's curved surface measured from the chord plane to the apex; it increases with diameter and with steepness, and governs how a lens vaults the cornea.
- Dk/t
- Oxygen transmissibility: permeability (Dk, in barrer) divided by lens center thickness in centimeters. Halving thickness doubles Dk/t, so thinner lenses deliver more oxygen at a given permeability.
- Holden-Mertz criteria
- Minimum oxygen transmissibility needed to limit corneal edema to about 4%: roughly 24 barrer/cm for daily wear with the eye open and 87 barrer/cm for overnight wear.
- Prism ballast
- A soft toric stabilization method in which extra lens thickness at the bottom gives a gravity-induced weight that keeps the lens axis oriented and prevents rotation.
- LARS rule
- Axis adjustment for a rotating toric lens: if the lens rotates to the patient's Left, Add to the axis; if it rotates to the Right, Subtract. Correct the prescribed axis accordingly.
- Modulus
- A measure of lens material stiffness. Higher-modulus silicone hydrogels resist deformation but increase mechanical interaction with the ocular surface and are associated with arcuate epithelial lesions.
- Reverse geometry design
- An orthokeratology lens design with a flat central base curve surrounded by a steeper reverse curve and then an alignment curve, used to redistribute corneal epithelium and reduce myopia.
- Alignment fitting philosophy
- A rigid lens approach in which the base curve is fitted 0.05 to 0.10 mm steeper than the flattest keratometry reading so the lens parallels the cornea with minimal tear lens power.
- Tear lens power
- The optical effect of the tear layer between a rigid lens and the cornea, approximately equal to the dioptric difference between the base curve and the flattest K.
- Over-refraction
- Retinoscopy or subjective refraction performed while the contact lens is on the eye; it measures residual refractive error, which is added to the lens power for the final prescription.
- Horizontal visible iris diameter
- The visible horizontal diameter of the iris, typically 11.5 to 12.5 mm in adults; soft lens total diameter is usually chosen 2 to 4 mm larger for full limbal coverage.
- Push-up test
- A soft lens fit assessment in which the lens is nudged upward with the lower lid; easy displacement off the cornea suggests a loose fit, while resistance suggests a tight fit.
- Three- and nine-o'clock staining
- Corneal desiccation near the horizontal limbus seen with rigid lenses, caused by inadequate edge lift, poor wetting, or incomplete blinking; managed by increasing edge clearance.
- Wratten 12 filter
- A yellow barrier filter used with cobalt blue illumination during fluorescein evaluation; it enhances contrast between the green fluorescein pattern and the blue background.
- Corneal neovascularization
- Growth of limbal vessels into the normally avascular cornea, driven by chronic hypoxia or inflammation; vessels extending more than about 1.5 mm from the limbus require refitting.
- Epithelial microcysts
- Small refractile cysts in the corneal epithelium seen on retroillumination, an early marker of chronic hypoxic stress or solution toxicity that usually resolves after lens wear is reduced.
- Giant papillary conjunctivitis
- An immune-mediated reaction producing large papillae on the everted upper lid, driven by lens deposits and mechanical irritation; managed by discontinuing lenses and refitting with frequent replacement.
- Acanthamoeba keratitis
- A severe corneal infection associated with tap water, swimming, and homemade saline; it causes severe pain, radial keratoneuritis, and ring infiltrates and is difficult to treat.
- Superior epithelial arcuate lesion
- A curved epithelial defect located just inside the superior limbus, associated with high-modulus silicone hydrogel lenses and a tight upper lid; managed by refitting into lower-modulus material.
- Efron grading scale
- A standardized zero-to-four photographic scale for grading conjunctival redness, corneal staining, edema, and other slit-lamp findings so results can be compared reliably between visits.
- Rub and rinse
- A cleaning step in which the lens is rubbed with multipurpose solution and rinsed before storage; it removes biofilm and deposits far more effectively than soaking alone.
- Hydrogen peroxide system
- A preservative-free disinfection method requiring the lens to sit in peroxide with a neutralizing disc or tablet for about six hours; inserting before neutralization causes severe stinging.
- Lens case hygiene
- Empty and rinse the case with fresh solution, air-dry it open, and replace it about every three months; cases are a major biofilm reservoir linked to microbial keratitis.
- FDA soft lens groups
- Group I is low water nonionic, II high water nonionic, III low water ionic, and IV high water ionic; ionic high-water Group IV materials attract the most protein deposition.
- Tap water and lenses
- Contact lenses, cases, and hands should never be rinsed with tap water because it carries Acanthamoeba, Pseudomonas, and other organisms capable of causing severe keratitis.
- Replacement schedule
- The manufacturer-specified interval, such as daily, biweekly, or monthly, at which lenses are discarded; extending it increases deposit buildup, biofilm formation, and complication risk.
- FTC Contact Lens Rule
- A United States rule requiring eyecare prescribers to give patients their contact lens prescription automatically at no charge after a fitting and to verify prescriptions for sellers.
- Contact lens prescription elements
- A valid prescription includes patient name, examination date, issue date, expiration, power, base curve, diameter, brand, material, and prescriber identification.
- Class II device
- The FDA category covering most corrective soft and rigid contact lenses; it requires 510(k) premarket notification demonstrating substantial equivalence before the lens can be marketed.
- ANSI Z80.20
- The United States standard specifying tolerances, measurement methods, and labeling for contact lenses, including how base curve, diameter, and power are stated.
- MedWatch reporting
- The FDA program through which clinicians voluntarily report serious adverse events and device malfunctions, including contact lens-related infections and manufacturing defects.
- CPT 92310
- The procedure code for prescribing and fitting corneal contact lenses with medical supervision of adaptation, excluding aphakia; reporting frequency per eye is set by payer rules.