ABO Ocular Anatomy & Physiology 5 — Questions and Answers
Question 1: The lacrimal gland produces the aqueous component of the tear film. Its secretory activity is stimulated primarily by:
- Sympathetic fibers from the superior cervical ganglion
- Parasympathetic fibers from the facial nerve (CN VII) (Correct answer)
- Sensory fibers from the trigeminal nerve (CN V1)
- Somatic motor fibers from CN III
Correct answer: Parasympathetic fibers from the facial nerve (CN VII)
Parasympathetic fibers traveling with the facial nerve (CN VII) via the pterygopalatine ganglion stimulate lacrimal gland secretion.
Question 2: The retinal blood supply from the central retinal artery nourishes which retinal layers?
- Only the outer retina including photoreceptors
- The inner two-thirds of the retina (inner nuclear layer and inward) (Correct answer)
- The entire retina including the RPE
- Only the ganglion cell layer
Correct answer: The inner two-thirds of the retina (inner nuclear layer and inward)
The central retinal artery supplies the inner two-thirds of the retina (from the nerve fiber layer to the inner nuclear layer), while the outer retina is supplied by the choroid.
Question 3: Which muscle is the sole abductor of the eye, innervated exclusively by CN VI?
- Medial rectus
- Lateral rectus (Correct answer)
- Superior rectus
- Inferior oblique
Correct answer: Lateral rectus
The lateral rectus is the only extraocular muscle innervated by the abducens nerve (CN VI) and is the primary abductor of the eye.
Question 4: What is the approximate normal central corneal thickness in adults?
- 250-350 microns
- 400-450 microns
- 520-560 microns (Correct answer)
- 650-700 microns
Correct answer: 520-560 microns
Normal central corneal thickness averages approximately 520-560 microns (about 0.5 mm), which is clinically important for IOP measurement correction.
Question 5: The scleral spur is a ridge of dense connective tissue that serves as the attachment point for which structure?
- The corneal stroma anteriorly
- The ciliary muscle and the posterior portion of the trabecular meshwork (Correct answer)
- The zonular fibers
- The extraocular rectus muscles
Correct answer: The ciliary muscle and the posterior portion of the trabecular meshwork
The scleral spur anchors the ciliary muscle and the posterior trabecular meshwork, and its position is a key gonioscopic landmark.
Question 6: Which retinal cell type is primarily responsible for initiating the phototransduction cascade in dim light (scotopic vision)?
- S-cones (short-wavelength cones)
- M-cones (medium-wavelength cones)
- Rod photoreceptors (Correct answer)
- Intrinsically photosensitive retinal ganglion cells (ipRGCs)
Correct answer: Rod photoreceptors
Rod photoreceptors contain rhodopsin and are exquisitely sensitive to low light levels, mediating scotopic (dim light) vision.
Question 7: The Müller cells of the retina perform all of the following functions EXCEPT:
- Potassium buffering in the retina
- Glutamate recycling at synapses
- Phagocytosis of shed photoreceptor outer segments (Correct answer)
- Providing structural support to the retinal architecture
Correct answer: Phagocytosis of shed photoreceptor outer segments
Phagocytosis of shed photoreceptor outer segment discs is performed by the RPE, not Müller cells; Müller cells buffer K+, recycle glutamate, and provide structural support.
ABO Ocular Anatomy & Physiology 5
The lacrimal gland produces the aqueous component of the tear film.
Its secretory activity is stimulated primarily by: