Intraocular Fluid

• Fluid present in eyeball.
• Responsible to maintain eyeball shape.
• Two types: a) Aqueous humor and b) Vitreous humor

Aqueous Humor

• Fluid thin in nature present in front of retina.
• Space is present in between lens and cornea.
• Aqueous humor fills that space.
• The space also divides into anterior and posterior chamber.
• Iris divides the space into two chambers.
• Pupil helps to communicate both these chambers.

Image source: aao

Properties of Aqueous humor

• Volume of this fluid is 0.13 ml.
• It is alkaline in nature with pH 7.5.
• It has viscosity of 1.029.
• This fluid has refractive index of 1.34.

Composition of Aqueous humor

• It is composed of water and solids.
• Water makes 98.7% and solids make 1.3%.
• Solids contain different organic and inorganic substances.
• Albumin, globulin, glucose, lactate, pyruvate, urea present as organic substances.
• Calcium, sodium, magnesium, chlorides, potassium, bicarbonates, phosphates make inorganic part.

Image source: brainkart

Aqueous humor formation

• Ciliary processes forms this fluid.
• Plasma within capillary network of ciliary processes forms it.
• Diffusion, ultrafiltration and active transport are the involved process.
• Transport occurs through epithelial cells that lines ciliary processes.
• This fluid then passes through suspensory ligaments.
• From there, it reaches the posterior chamber.
• Fluid finally comes to anterior chamber via pupil.
• It is a continuous process i.e., formation of this fluid.
• In one minute, 2-3 µL of fluid is formed.
• In anterior chamber, this fluid is about 230-250 µL.
• 50-60 µL is the amount present in posterior chamber.

Drainage of aqueous humor

Anterior chamber → limbus (angle between cornea and iris) →  meshwork of trabeculae → canal of schlemn →

→ anterior ciliary vein → venous system.

( meshwork of trabeculae –  situated near the junction of iris and cornea)

                                                   Fig: flowchart of drainage of aqueous humor

Image source: mdpi

Functions of Aqueous humor

• Shape of eyeball maintained.
• Intraocular pressure maintained.
• Lens and cornea gets nutrients, oxygen and electrolytes.

(Lens and cornea are avascular structures)

• Lens and cornea contains metabolic end products.
• They are removed by this fluid.

Vitreous humor

• Fluid present in the space between lens and retina.
• Comprises 2/3^rd of the eye volume.
• Hydrophilic, transparent, inert, colorless and gel structure.
• 99% of this fluid is water and 1 % is protein, sugars, salts, collagen, etc.
• Highly viscous and gelatinous, also called vitreous body.
• Fine fibrillar network of proteoglycan molecules forms this fluid.
• Albumin and hyaluronic acid are the major components.
• These substances enter the vitreous body from blood.
• Diffusion helps to transfer these substances.

Functions of vitreous humor

• Maintain the round shape of eyeball.
• Center of eyes remain clear so light can get to the retina and vision begins.
• Help in absorbing unexpected disturbances to the eye.
• Help to prevent eye damage.
• Pressure exerted by vitreous humor keeps the retina stable and in place.

References: 

i) https://www.brightfocus.org/glaucoma/infographic/aqueous-humor-flow-and-function

ii) https://www.brainkart.com/article/Fluid-System-of-the-Eye–Intraocular-Fluid_19674/

iii) https://healthjade.net/intraocular-pressure/

Intraocular Fluid