Ophthalmic Optics and Principles Flashcards
6 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 6 Ophthalmic Optics and Principles flashcards as text
A patient's prescription is -5.00 DS, and their monocular PD is 32mm OU. The finished eyewear is fabricated with the geometric centers placed at a total distance of 70mm. How much total prism is induced by the error?
Answer: 3.0Δ Base Out
The total specified PD is 32mm + 32mm = 64mm. The lenses were made with optical centers at 70mm. The total decentration is 70mm - 64mm = 6mm, or 3mm per eye outward (temporally). Prentice's Rule states Prism (Δ) = Power (D) x Decentration (cm). For one eye: 5.00 D x 0.3 cm = 1.5Δ. For a minus lens, decentering outward induces Base Out prism. Since this occurs in both eyes, the total prismatic effect is 1.5Δ + 1.5Δ = 3.0Δ Base Out.
What is the focal length of a +4.00 D lens?
Answer: 25 cm
The formula to find the focal length (f) in meters from the dioptric power (D) is f = 1/D. In this case, f = 1 / 4.00 = 0.25 meters. To convert meters to centimeters, multiply by 100. So, 0.25 m * 100 = 25 cm.
Which of the following is an optical aberration that occurs because a lens material refracts different wavelengths of light at slightly different angles, causing color fringes?
Answer: Chromatic Aberration
Chromatic aberration is caused by the dispersion of light as it passes through a lens. Because the refractive index of a material is slightly different for each wavelength (color) of light, white light is split into its spectral components, which can be perceived by the wearer as color fringes around objects.
What is the correct minus cylinder transposition of the prescription +1.75 +2.25 x 045?
Answer: +4.00 -2.25 x 135
To transpose from plus to minus cylinder form: 1) Add the sphere and cylinder powers to get the new sphere (+1.75 + 2.25 = +4.00). 2) Change the sign of the cylinder (+2.25 becomes -2.25). 3) Change the axis by 90 degrees (45 + 90 = 135). The transposed prescription is +4.00 -2.25 x 135.
A patient is refracted with a prescription of -12.00 D at a vertex distance of 10mm. If their new glasses are fit with a vertex distance of 14mm, what compensated power should be ordered to provide the same effective power?
Answer: -12.50 D
When a high-power minus lens is moved further away from the eye (an increase of 4mm in this case), it becomes effectively weaker. To compensate for this, a stronger (more minus) power must be ordered. Using the compensation formula, the new power is approximately -12.52 D. The closest standard power is -12.50 D.
Which of the following lens materials generally has the highest index of refraction?
Answer: High-Index 1.74
The index of refraction measures how efficiently a material bends light. A higher index allows for a thinner lens profile for a given power. Among the choices, High-Index 1.74 has the highest refractive index (around 1.74), compared to Polycarbonate (~1.59), Trivex (~1.53), and CR-39 (~1.50).