Optics and Refraction Flashcards
7 cards from real Board Certified Ophthalmologist practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Optics and Refraction flashcards as text
What is the spherical equivalent of +2.00 -3.00 x 090?
Answer: +0.50 D
Spherical equivalent is the sphere plus half the cylinder: +2.00 + (-1.50) = +0.50 D.
What is the correct transposition of -1.00 +2.00 x 180?
Answer: +1.00 -2.00 x 090
To transpose, add the cylinder to the sphere, reverse the cylinder's sign, and rotate the axis 90 degrees.
At a 67 cm working distance, a retinoscopist neutralizes the reflex with +3.00 D. What is the patient's net refractive error?
Answer: +1.50 D
A 67 cm working distance adds about 1.50 D, which is subtracted from the gross finding: +3.00 - 1.50 = +1.50 D.
During retinoscopy, the examiner sees 'against' motion. What does this mean?
Answer: The patient's far point is between the examiner and the patient; add minus
Against motion means the far point lies in front of the peephole, so minus lens power is needed to reach neutrality.
About what pinhole diameter gives the best acuity when screening for uncorrected refractive error?
Answer: About 1.2 mm
A pinhole of about 1.2 mm balances a smaller blur circle against increasing diffraction and reduced light.
What happens when a high-plus spectacle lens is moved farther from the eye?
Answer: Its effective power at the cornea increases
Moving a plus lens away from the eye increases its effective power, which is why aphakic patients slide glasses down their nose to read.
What is the conventional magnification of a +20.00 D simple hand magnifier?
Answer: 5x
Conventional magnification of a simple magnifier is D/4, so 20/4 = 5x.