NBEO Ocular Anatomy & Physiology — Questions and Answers
Question 1: What is the function of the crystalline lens in the eye?
- To change shape (accommodate) to focus light from objects at varying distances onto the retina (Correct answer)
- To produce aqueous humor
- To detect color
- To protect the eye from UV light
Correct answer: To change shape (accommodate) to focus light from objects at varying distances onto the retina
The crystalline lens changes shape through ciliary muscle contraction, increasing its curvature for near focus and flattening for distance focus, a process called accommodation.
Question 2: What are the three layers of the eye?
- Fibrous (sclera/cornea), vascular (uvea: iris/ciliary body/choroid), and neural (retina) (Correct answer)
- Cornea, lens, and retina
- Iris, pupil, and sclera
- Anterior chamber, vitreous, and retina
Correct answer: Fibrous (sclera/cornea), vascular (uvea: iris/ciliary body/choroid), and neural (retina)
The eye has three concentric layers: the outer fibrous tunic (sclera and cornea), the middle vascular tunic (uvea: iris, ciliary body, choroid), and the inner neural tunic (retina).
Question 3: What is the macula and why is it clinically significant?
- The central area of the retina responsible for high-acuity color vision; its degeneration is the leading cause of central vision loss in older adults (Correct answer)
- A type of eye infection
- The white part of the eye
- A structure in the eyelid
Correct answer: The central area of the retina responsible for high-acuity color vision; its degeneration is the leading cause of central vision loss in older adults
The macula contains the highest concentration of cone photoreceptors, especially at the fovea, providing central vision for reading and facial recognition. Age-related macular degeneration (AMD) damages this critical area.
Question 4: What is intraocular pressure (IOP) and what maintains it?
- The fluid pressure inside the eye, maintained by the balance between aqueous humor production by the ciliary body and drainage through the trabecular meshwork (Correct answer)
- Blood pressure in the retinal vessels
- The pressure of the vitreous gel
- The tension of the extraocular muscles
Correct answer: The fluid pressure inside the eye, maintained by the balance between aqueous humor production by the ciliary body and drainage through the trabecular meshwork
IOP (normal: 10-21 mmHg) is maintained by aqueous humor produced by the ciliary body flowing through the pupil and draining through the trabecular meshwork. Elevated IOP is a major risk factor for glaucoma.
Question 5: What is the optic nerve and what condition damages it?
- The nerve carrying visual information from the retina to the brain; glaucoma progressively damages it, causing irreversible vision loss (Correct answer)
- A muscle that moves the eye
- The blood supply to the retina
- A structure that produces tears
Correct answer: The nerve carrying visual information from the retina to the brain; glaucoma progressively damages it, causing irreversible vision loss
The optic nerve (cranial nerve II) contains approximately 1.2 million nerve fibers transmitting visual signals. Glaucoma damages these fibers, typically starting with peripheral vision loss that progresses centrally.
Question 6: What is the cornea and what are its functions?
- The transparent front surface of the eye that provides about two-thirds of the eye's refractive power and protects internal structures (Correct answer)
- The colored part of the eye
- The light-sensitive layer at the back of the eye
- The gel filling the center of the eye
Correct answer: The transparent front surface of the eye that provides about two-thirds of the eye's refractive power and protects internal structures
The cornea is the eye's primary refractive surface, bending light as it enters the eye. Its transparency is maintained by precise arrangement of collagen fibers and controlled hydration through the endothelial pump mechanism.
NBEO Ocular Anatomy & Physiology
What is the function of the crystalline lens in the eye?