CPOA Basic Science 5 — Questions and Answers
Question 1: The choroid is mainly responsible for:
- Producing aqueous humor
- Providing blood supply to the outer retina (Correct answer)
- Regulating intraocular pressure
- Controlling pupil size
Correct answer: Providing blood supply to the outer retina
The highly vascular choroid supplies oxygen and nutrients to the outer third of the retina, including the photoreceptors.
Question 2: In the context of optics, the unit diopter (D) measures:
- Distance in millimeters
- The refracting power of a lens (Correct answer)
- The wavelength of light
- Visual acuity
Correct answer: The refracting power of a lens
A diopter is the unit of measurement for the refracting power (vergence power) of a lens, defined as 1 divided by the focal length in meters.
Question 3: Which extraocular muscle is responsible for abducting (moving laterally) the eye?
- Medial rectus
- Superior rectus
- Lateral rectus (Correct answer)
- Inferior oblique
Correct answer: Lateral rectus
The lateral rectus muscle, innervated by CN VI (abducens), is the primary abductor of the eye, moving it away from the nose.
Question 4: The optic chiasm is the structure where:
- Both optic nerves merge into one
- Nasal retinal fibers from each eye cross to the opposite side (Correct answer)
- All visual fibers terminate in the brain
- The optic nerve meets the globe
Correct answer: Nasal retinal fibers from each eye cross to the opposite side
At the optic chiasm, nerve fibers from the nasal half of each retina decussate (cross) to the contralateral optic tract, while temporal fibers remain ipsilateral.
Question 5: The lens of the eye grows throughout a person's lifetime, adding layers like an onion. This growth contributes to which age-related condition?
- Macular degeneration
- Presbyopia (Correct answer)
- Retinal detachment
- Diabetic retinopathy
Correct answer: Presbyopia
As the lens grows and becomes denser and less flexible with age, its ability to change shape for near focus (accommodation) decreases, resulting in presbyopia.
Question 6: Which type of astigmatism exists when the principal meridians are not at 90° to each other?
- Regular astigmatism
- Against-the-rule astigmatism
- Irregular astigmatism (Correct answer)
- With-the-rule astigmatism
Correct answer: Irregular astigmatism
Irregular astigmatism occurs when the two principal meridians are not perpendicular; it cannot be fully corrected with standard cylindrical spectacle lenses.
Question 7: The tear film's aqueous layer is primarily produced by which gland?
- Meibomian glands
- Goblet cells of the conjunctiva
- Lacrimal gland (Correct answer)
- Glands of Zeis
Correct answer: Lacrimal gland
The lacrimal gland, located in the superotemporal orbit, produces the aqueous component that makes up the bulk of the tear film.
CPOA Basic Science 5
The choroid is mainly responsible for: