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Understanding Aqueous Humor: Nature, Formation, Drainage, and Functions

Discover the crucial role of aqueous humor in eye health, from its composition and formation to circulation and drainage mechanisms. Learn about factors affecting aqueous humor and its significance in maintaining intraocular pressure and eye function.

jenniferpittman
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Understanding Aqueous Humor: Nature, Formation, Drainage, and Functions

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  1. Aqueous humor

  2. Introduction • Aqueous humor is an important intra-ocular fluid • Occupies the anterior segment space including the anterior and posterior chambers • Has optical and nutritive functions

  3. Nature of aqueous • Optically transparent • Free of blood and cells • Free from high molecular weight solutes like proteins • Formed by a complex mechanism • Drains through a complex pathway • Rate of formation = rate of drainage

  4. Water Main component Electrolytes Bicarbonate Chloride Phosphate Calcium Hydrogen ion Oxygen Potassium Sodium Organic substances Ascorbate Citrate Creatinine Glucose Lactate Protein Urea Others Hyaluronic acid Vitamin B12 Composition of aqueous

  5. Formation of aqueous • Formed by the non-pigmented epithelium of the ciliary processes of the ciliary body • Formed from the plasma of the blood • Mechanism of formation – • Simple filtration • Ultrafiltration • Secretion

  6. Simple filtration • A function of permeability of the capillary walls • Diffusion across the cell membranes of the uveal capillaries • Against a concentration gradient • Passive process • Lipid soluble substances diffuse easily • Two-way process

  7. Active secretion • 70% of aqueous formation • Energy dependent active process • Enzyme contributing- • Na/K ATPase • Carbonic anhydrase • Transport of solutes against concentration gradient

  8. Ultrafiltration • Bulk flow of water soluble substances across the epithelium • Passive mechanism • Depends on the balance in hydrostatic forces • Pressure favouring aqueous formation • Intra-capillary pressure • Intra-ocular pressure • Pressure opposing aqueous formation • Tissue oncotic pressure

  9. Circulation of aqueous Ciliary processes Posterior chamber Pupil Anterior chamber Angle of anterior chamber

  10. Drainage of aqueous • Conventional pressure dependent outflow (IOP and Episcleral venous pressure) • Trabecular meshwork • Schlemm’s canal • Aqueous veins • Episcleral veins • Systemic circulation

  11. Drainage of aqueous • Uveoscleral pressure independent outflow • Constant rate pump • Supraciliary space • Sclera • Periocular orbital space • Blood vessels

  12. Aqueous humor summary • Rate of Aqueous Humor Formation: 2.0 - 3.0 L/min. • Volume of Anterior Chamber 250L • Volume of Posterior Chamber 60L • Turnover of aqueous: 1.5 - 2 hours

  13. Functions of aqueous • Maintains IOP • Optical functions • Nutrition to the avascular tissues of the eye • Drains waste from the avascular tissues of the eye

  14. Abnormal aqueous • Uveitis- plasmoid aqueous • Intra-ocular malignancy • Glaucoma • Retinal detachment

  15. Factors affecting • Factors increasing aqueous formation • Physiologic- morning or afternoon • Factors decreasing aqueous formation • Sleep, age, uveitis, raised IOP • Factors increasing aqueous drainage • Drugs, ciliary muscle contraction • Factors decreasing aqueous drainage • Increased episcleral venous pressure, trabecular damage, mechanical obstructions

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