Ophthalmic Optics and Principles 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 Optics and Principles flashcards as text
Using Prentice's Rule, what is the prismatic effect at a point 8 mm from the optical center of a +5.00 D lens?
Answer: 4Δ
Prentice's Rule: Prism (Δ) = d(cm) × F = 0.8 × 5.00 = 4.00Δ.
What is the purpose of the 'crossed cylinder' test in refraction?
Answer: To refine cylinder axis and power
The Jackson crossed cylinder (JCC) is used to precisely refine both the axis and power of the correcting cylinder during subjective refraction.
What is 'vergence' in the context of ophthalmic optics?
Answer: The curvature of wavefronts of light
Vergence describes the degree of convergence or divergence of a wavefront of light, measured in diopters.
A lens with a refractive index of 1.74 compared to 1.50 will be:
Answer: Thinner and lighter
Higher index materials bend light more strongly, allowing thinner lens profiles; modern high-index materials are also less dense, making lenses lighter.
What is the effect of increasing pantoscopic tilt on the effective power of a lens?
Answer: It induces plus sphere and minus cylinder
Increasing pantoscopic tilt introduces oblique astigmatism, effectively adding plus sphere power and a minus cylinder component to the lens's effective prescription.
Which formula correctly expresses the lensmaker's equation relationship for a thin lens?
Answer: P = (n-1)(1/R1 - 1/R2)
The lensmaker's equation is P = (n-1)(1/R1 - 1/R2), where n is the refractive index and R1, R2 are the radii of curvature of the two surfaces.
What is the spherical equivalent of -2.00 -1.00 × 180?
Answer: -2.50 D
Spherical equivalent = sphere + (cylinder/2) = -2.00 + (-1.00/2) = -2.00 + (-0.50) = -2.50 D.