General Practice 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 General Practice flashcards as text
You can change a lens' focal length by:
Answer: Changing the curvature of one surface
The focal length of a lens is directly related to its optical power, which is determined by the refractive index of the lens material and the curvature of its surfaces. By altering the curvature of one or both surfaces, the degree to which light rays are converged or diverged changes. This modification directly impacts the lens's focal length, allowing for precise optical correction.
Meniscus, equiconcave, and flat concave are varieties of
Answer: Minus lenses
Meniscus, equiconcave, and flat concave (or plano-concave) are all types of concave lenses. Concave lenses are thinner in the center and thicker at the edges, causing light rays to diverge. These lenses are used to correct myopia (nearsightedness) and are therefore classified as minus lenses, having negative dioptric power.
What sort of lens has a surface that is both convex and concave?
Answer: Meniscus
A meniscus lens is characterized by having one convex surface and one concave surface. This design allows for better optical performance, reduced peripheral aberrations, and a thinner, more aesthetically pleasing lens, especially for higher prescriptions. Most modern spectacle lenses are manufactured with a meniscus shape.
A lens's power is indicated by the word "axis."
Answer: False
The 'axis' in an eyeglass prescription refers to the orientation of the cylinder power, which corrects astigmatism. It indicates the meridian of the lens that has no cylinder power, or where the cylinder power is oriented. The lens's overall power (sphere and cylinder) is measured in diopters, not by the axis, which is an angular measurement.
What word best describes the direction change of light as it moves from one medium to another?
Answer: Refraction
Refraction is the phenomenon where light changes direction, or bends, as it passes from one transparent medium into another with a different optical density. This bending of light is fundamental to how lenses work, allowing them to focus or diverge light rays to form images on the retina. Reflection, in contrast, is when light bounces off a surface.
What controls the quantity of light that reaches the eye?
Answer: Iris
The iris is the colored part of the eye that functions like the diaphragm of a camera. It contains muscles that contract or relax to change the size of the pupil, thereby regulating the amount of light entering the eye. In bright light, the iris constricts the pupil, and in dim light, it dilates the pupil to optimize vision.
What's the term of the phenomenon where the eye tends to turn from its natural position?
Answer: Phoria
A phoria is a latent deviation of the eye that is only present when binocular vision is interrupted, such as when one eye is covered. The eye tends to drift from its natural position but is typically controlled by the brain's fusion mechanisms when both eyes are open. A tropia, on the other hand, is a manifest deviation that is present even when both eyes are open.