Which process contributes the majority of aqueous production?

Which process contributes the majority of aqueous production?

• A. Active secretion by ciliary body epithelium accounts for about 80% (carbonic anhydrase); diffusion and ultrafiltration of plasma also occur
• B. Diffusion through the cornea
• C. Vitreous humor secretion
• D. Lacrimal gland secretion into the anterior chamber

Answer: (A)

Aqueous humor is produced mainly by active secretion from the ciliary body epithelium. The nonpigmented ciliary epithelium uses ion transport, with carbonic anhydrase playing a key role in generating bicarbonate. This creates an osmotic gradient that drives water into the posterior chamber, so most of the aqueous fluid comes from this active process—roughly about 80%. The rest comes from diffusion and ultrafiltration of plasma across the ciliary capillaries. Other routes don’t contribute significantly to aqueous production. The cornea doesn’t secrete aqueous; diffusion through the cornea relates to nutrient exchange for the cornea itself. The vitreous humor isn’t actively secreted in amounts that affect aqueous production. The lacrimal gland delivers tears to the ocular surface, not into the anterior chamber. Clinically, inhibiting carbonic anhydrase reduces aqueous formation, helping lower intraocular pressure.

Aqueous humor is produced mainly by active secretion from the ciliary body epithelium. The nonpigmented ciliary epithelium uses ion transport, with carbonic anhydrase playing a key role in generating bicarbonate. This creates an osmotic gradient that drives water into the posterior chamber, so most of the aqueous fluid comes from this active process—roughly about 80%. The rest comes from diffusion and ultrafiltration of plasma across the ciliary capillaries.

Other routes don’t contribute significantly to aqueous production. The cornea doesn’t secrete aqueous; diffusion through the cornea relates to nutrient exchange for the cornea itself. The vitreous humor isn’t actively secreted in amounts that affect aqueous production. The lacrimal gland delivers tears to the ocular surface, not into the anterior chamber.

Clinically, inhibiting carbonic anhydrase reduces aqueous formation, helping lower intraocular pressure.