Refractive Errors and Their Optical Correction 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 Refractive Errors and Their Optical Correction flashcards as text
Which refractive condition results from the axial length of the eye being too long, causing parallel light to focus anterior to the retina?
Answer: Myopia
In myopia (nearsightedness) the eyeball is axially too long, so the focal point of parallel rays falls in front of the retina. Concave (minus) lenses are prescribed to diverge light and shift the focus back onto the retinal plane.
A patient's prescription reads +3.25 DS. Which refractive error does this correct?
Answer: Hyperopia
Plus (convex) lenses converge light and correct hyperopia, where the eye is too short and incoming light would focus behind the retina without correction. The +3.25 DS brings the focal point forward to land on the retina.
In the prescription -2.00 -1.50 x 090, what does the cylindrical component (-1.50 x 090) correct?
Answer: Astigmatism
The cylinder power and its axis correct astigmatism — a refractive error caused by an unequally curved cornea or lens that produces two separate focal lines instead of a single focal point. The axis 090 indicates the meridian of no cylinder power (the sphere-only meridian).
At approximately what age does presbyopia typically become clinically symptomatic, requiring a reading addition?
Answer: 40–45 years
Presbyopia results from progressive hardening of the crystalline lens, which reduces accommodative amplitude. Symptoms typically become noticeable around age 40–45, and the required add power continues to increase until approximately the mid-60s.
What is the spherical equivalent of the prescription -3.00 -2.00 x 180?
Answer: -4.00 D
Spherical equivalent (SE) = sphere + (cylinder ÷ 2) = -3.00 + (-2.00 ÷ 2) = -3.00 + (-1.00) = -4.00 D. The spherical equivalent represents the single sphere power that most closely approximates the mean refractive effect of a sphero-cylindrical lens.
A low-to-moderate hyperope who does NOT wear correction will typically experience which of the following?
Answer: Potentially clear vision at distance and near by using accommodation, but with eye strain
Low-to-moderate hyperopes can use their accommodative reserve to compensate, achieving acceptable vision at both distance and near — but at the cost of chronic accommodative effort that leads to asthenopia (headaches, eye strain). High hyperopes eventually cannot fully compensate and experience blur at all distances.