From which sources does the cornea receive oxygen?

From which sources does the cornea receive oxygen?

• A. Only from the aqueous humor
• B. From the eyelid surfaces only
• C. lens material, water, precorneal tear film, aqueous humor, limbal capillaries, palpebral conjunctival capillaries
• D. Only from tear film

Answer: (C)

Oxygen for the cornea comes from multiple nearby sources because the cornea is avascular and must rely on diffusion. The front surface relies on the precorneal tear film—the tear film gains its oxygen from the air, allowing diffusion into the epithelium. The back surface receives oxygen from the aqueous humor as it diffuses through the endothelium into deeper layers. The outer periphery can get oxygen from blood vessels in the limbus, and the palpebral conjunctival capillaries near the eyelids also contribute to oxygenation of the peripheral and adjacent areas. So a choice that includes precorneal tear film, aqueous humor, and the surrounding capillary networks best reflects the real sources delivering oxygen to the cornea. Lens material and extra items listed don’t serve as oxygen sources for the cornea.

Oxygen for the cornea comes from multiple nearby sources because the cornea is avascular and must rely on diffusion. The front surface relies on the precorneal tear film—the tear film gains its oxygen from the air, allowing diffusion into the epithelium. The back surface receives oxygen from the aqueous humor as it diffuses through the endothelium into deeper layers. The outer periphery can get oxygen from blood vessels in the limbus, and the palpebral conjunctival capillaries near the eyelids also contribute to oxygenation of the peripheral and adjacent areas. So a choice that includes precorneal tear film, aqueous humor, and the surrounding capillary networks best reflects the real sources delivering oxygen to the cornea. Lens material and extra items listed don’t serve as oxygen sources for the cornea.