Ophthalmic Lenses and Materials Flashcards
7 cards from real ABO NOCE Basic Opticianry practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Ophthalmic Lenses and Materials flashcards as text
When dispensing lenses with anti-reflective (AR) coating, why must a hard coat be applied beneath the AR coating?
Answer: To provide a smooth, durable surface for the AR layers to adhere to
Hard coat creates a smooth, durable surface that allows the thin vacuum-deposited AR layers to adhere properly and reduces microabrasions that would compromise coating performance.
A photochromic lens darkens when exposed to UV radiation because of which mechanism?
Answer: UV radiation activates silver halide or organic molecules embedded in the lens, causing a color change
Photochromic lenses contain silver halide crystals or organic photochromic molecules that undergo a reversible chemical reaction when exposed to UV radiation, causing the lens to darken.
What is the main advantage of Trivex over polycarbonate as an impact-resistant lens material?
Answer: Trivex has a higher Abbe value providing better optical clarity
Trivex has an Abbe value of approximately 45 compared to polycarbonate's 30, giving Trivex significantly better optical clarity and less chromatic aberration while maintaining excellent impact resistance.
In a progressive addition lens, where is the distance optical power measured?
Answer: In the fitting cross or distance reference point (DRP)
The distance power of a PAL is measured at the distance reference point (DRP) or fitting cross, which is positioned in front of the patient's pupil for distance viewing.
Which type of lens segment shape in a bifocal provides the widest near field of view?
Answer: Executive (E-style) full-width segment
The Executive (E-style or Franklin-style) bifocal extends the near segment across the full width of the lens, providing the widest possible near field of view.
What is 'base curve' in ophthalmic lens terminology?
Answer: The front surface curve of the lens, which determines the lens form
Base curve refers to the front (convex) surface curvature of an ophthalmic lens; it determines the lens form (flat, steep, or best form) and affects peripheral optics.
A patient's lens prescription is +5.00 DS. Where is the thickest point of this finished lens?
Answer: At the optical center
Positive (plus) lenses are thickest at the optical center and taper toward the edges — opposite of minus lenses which are thinnest at the center.