ABO Ocular Anatomy & Physiology — Questions and Answers
Question 1: Which structure of the eye is primarily responsible for focusing light at different distances?
- Crystalline lens (Correct answer)
- Cornea
- Iris
- Vitreous humor
Correct answer: Crystalline lens
The crystalline lens changes shape through accommodation to focus light from objects at varying distances onto the retina.
Question 2: What is the function of the ciliary body?
- To produce aqueous humor and control lens accommodation (Correct answer)
- To produce vitreous humor
- To drain aqueous humor from the eye
- To protect the optic nerve
Correct answer: To produce aqueous humor and control lens accommodation
The ciliary body has two main functions: it produces aqueous humor and contains the ciliary muscle that controls accommodation by changing the shape of the lens.
Question 3: Which layer of the cornea is primarily responsible for maintaining corneal transparency through its pump function?
- Endothelium (Correct answer)
- Epithelium
- Stroma
- Bowman's layer
Correct answer: Endothelium
The corneal endothelium maintains transparency by actively pumping water out of the stroma, preventing corneal edema and clouding.
Question 4: Where are the cone photoreceptors most densely concentrated?
- Fovea (Correct answer)
- Peripheral retina
- Optic disc
- Ora serrata
Correct answer: Fovea
The fovea contains the highest concentration of cone photoreceptors and is responsible for sharp central vision and color perception.
Question 5: What is the approximate refractive power of the human cornea?
- 43 diopters (Correct answer)
- 20 diopters
- 60 diopters
- 10 diopters
Correct answer: 43 diopters
The cornea contributes approximately 43 diopters (about two-thirds) of the eye's total refractive power of approximately 60 diopters.
Question 6: Which cranial nerve innervates the lateral rectus muscle?
- Abducens nerve (CN VI) (Correct answer)
- Oculomotor nerve (CN III)
- Trochlear nerve (CN IV)
- Optic nerve (CN II)
Correct answer: Abducens nerve (CN VI)
The abducens nerve (cranial nerve VI) innervates the lateral rectus muscle, which is responsible for abducting (turning outward) the eye.
ABO Ocular Anatomy & Physiology
Which structure of the eye is primarily responsible for focusing light at different distances?