COST COST Ocular Anatomy and Physiology 2 — Questions and Answers
Question 1: What is the approximate axial length of a typical emmetropic adult human eye?
- 18 mm
- 24 mm (Correct answer)
- 30 mm
- 12 mm
Correct answer: 24 mm
The average emmetropic adult eye has an axial length of approximately 24 mm, which is a key biometric measurement used in IOL power calculations.
Question 2: The vitreous humor occupies approximately what percentage of the total volume of the eye?
- 20%
- 40%
- 60% (Correct answer)
- 80%
Correct answer: 60%
The vitreous humor fills the posterior segment and accounts for roughly 60% of the eye's total volume, providing structural support and a clear optical medium.
Question 3: Which cells of the retina are primarily responsible for phototransduction in low-light (scotopic) conditions?
- Cone cells
- Rod cells (Correct answer)
- Ganglion cells
- Bipolar cells
Correct answer: Rod cells
Rod photoreceptors contain rhodopsin and are exquisitely sensitive to dim light, making them the primary mediators of scotopic (night) vision.
Question 4: The lens of the eye is held in place by which fibrous structure?
- Hyaloid ligament
- Zonules of Zinn (zonular fibers) (Correct answer)
- Ciliary muscle tendons
- Posterior capsule
Correct answer: Zonules of Zinn (zonular fibers)
The zonules of Zinn (suspensory ligament of the lens) are fibrillin-rich fibers that connect the ciliary body to the lens equator, holding the lens in position.
Question 5: Which layer of the retina lies immediately adjacent to the retinal pigment epithelium (RPE)?
- Ganglion cell layer
- Inner nuclear layer
- Photoreceptor outer segments (Correct answer)
- Nerve fiber layer
Correct answer: Photoreceptor outer segments
The outer segments of photoreceptors (rods and cones) are in direct contact with the microvilli of the RPE, which phagocytoses shed outer segment discs.
Question 6: Which structure forms the blood-ocular barrier on the outer retina side?
- Trabecular meshwork
- Bruch's membrane and RPE tight junctions (Correct answer)
- Internal limiting membrane
- Hyaloid membrane
Correct answer: Bruch's membrane and RPE tight junctions
Tight junctions between RPE cells, along with Bruch's membrane, form the outer blood-retinal barrier, regulating transport between the choriocapillaris and the retina.
COST COST Ocular Anatomy and Physiology 2
What is the approximate axial length of a typical emmetropic adult human eye?