FREE ABO Optics and Refraction Questions and Answers

Question 1

A patient's refraction is -4.50 +1.00 x 090. To correct this refractive error, what type of lens is required?

Accepted Answer

A sphero-cylindrical concave lens

Answer

The spherical component of the refraction is -4.50 diopters, which indicates myopia. Myopia is corrected with a concave (minus power) lens. The "+1.00 x 090" component indicates astigmatism, requiring a cylindrical correction, making the overall lens a sphero-cylindrical concave lens.

Question 2

A patient has a steep vertical corneal meridian and a flat horizontal meridian. This type of astigmatism is known as:

Accepted Answer

With-the-rule astigmatism

Answer

With-the-rule (WTR) astigmatism is the most common type, where the vertical corneal meridian is steeper (has more power) than the horizontal meridian. This is typically corrected with a minus cylinder lens at or near the 180-degree axis.

Question 3

Snell's Law (n1 * sin(θ1) = n2 * sin(θ2)) is a fundamental principle in optics that describes:

Accepted Answer

The refraction of light as it passes between two different media.

Answer

Snell's Law describes the relationship between the angles of incidence (θ1) and refraction (θ2) and the refractive indices (n1, n2) of two different isotropic media. It governs how much a light ray bends when it crosses the boundary from one medium to another, which is the fundamental basis for how lenses work.

Question 4

What is the primary physiological cause of presbyopia?

Accepted Answer

Decreased elasticity and hardening of the crystalline lens.

Answer

Presbyopia is the age-related loss of accommodation. The primary cause is the progressive hardening (sclerosis) and loss of elasticity of the crystalline lens, which prevents it from changing shape sufficiently to focus on near objects, even with normal ciliary muscle contraction.

Question 5

During retinoscopy on an uncorrected myopic eye, the examiner working at a standard distance will observe:

Accepted Answer

"Against" motion when working outside the far point.

Answer

The far point of a myopic eye is a real point in space in front of the eye. When the retinoscope is positioned outside this far point (as is typical at a standard working distance), the light reflex will move in the opposite direction to the streak, which is termed "against" motion.

ABO - American Board of Ophthalmology Practice Test

ABO - American Board of Ophthalmology Practice Test

FREE ABO Optics and Refraction Questions and Answers