Dr.r.subramaniyan, 09 3-17, Aqueous Humour Dynamics

1. AQUEOUS
HUMOUR
DYNAMICS

2. FUNCTIONS
• Aqueous humor is a clear, colourless, watery solution continuously
circulated from the posterior chamber throughout the anterior
chamber.
• Maintains the intraocular pressure.
• Maintains the shape and the internal structural arrangement of the
eye.
• Cornea takes glucose and oxygen from the aqueous.
• Lens uses glucose, oxygen and amino acids from the aqueous.

3. PHYSICOCHEMICAL PROPERTIES
• VOLUME 0.31 ml
• (o.25 ml in anterior chamber and 0.06 ml in posterior chamber)
• Refractive index 1.336
• Density greater than water
• Hyperosmotic ( compared to plasma) 3-5 mOsm/l
• pH: acidic
• Rate of formation: 2.3 µl/min.
• Protein content less.

4. FACTORS AFFECTING COMPOSITION OF
AQUEOUS HUMOUR
• BLOOD AQUEOUS BARRIER
• Protein and large molecular size substances are largely prevented
from entering the cavities. This maintains the clarity of the media of
the eye.
• Formed by the tight junctions between the cells of epithelium of the
ciliary body and endothelium of iris capillaries.

5. EFFECT OF BREAKDOWN OF BLOOD AQUEOUS
BARRIER ON AQUEOUS HUMOUR COMPOSITION
• Proteins and antibodies in aqueous equilibrate with those in plasma
to form plasmoid aqueous (secondary aqueous).
• Recognised clinically in slit lamp microscope as Tyndall Beam.
• Fibrinogen appears in aqueous, which may allow the aqueous actually
to clot.
• Ionic composition of the aqueous approches same as plasma.

6. Aqueous humor production
• Active secretion by double-
layered ciliary epithelium.
• Primarily derived from the
plasma within the capillary
network of the ciliary
processes.

7. Aqueous humor
• Secretion depends on:
• Integrity of blood aqueous barrier
• Blood flow to ciliary body
• Neurohormonal regulation of blood and ciliary body
• Adrenergic innervation

8. Aqueous humor outflow
• Trabecular out flow (90%)
• Uveoscleral out flow (10-20%)

9. Trabecular outflow channel
Posterior chamber
Anterior chamber
Angle of anterior chamber ( Trabecular meshwork)
Schlemm’s canal
Collector channels
Episcleral vein, aqueous vein

12. UVEA SCLERAL OUTFLOW
• Pressure independent outflow
• Responsible for 10-20 % of outflow
Ciliary body
Suprachoroidal space
Venous circulation in the ciliary body, choroid,
sclera

13. INTRAOCULAR PRESSURE
• Refers to the pressure exerted by the intraocular contents on the
coats of the eyeball.
• IOP is maintained by the a dynamic equilibrium between the aqueous
humour formation, aqueous humour outflow, and episcleral venous
pressure.
• Normal IOP is 10 – 21 mm Hg.

14. Factors affecting IOP
• Rate of aqueous production
• Resistance to aqueous outflow
Pretrabecular , trabecular and post trabecular
• Level of episcleral venous pressure.

15. Factors influencing IOP
HEREDITARY
• Age more than 40
• Time of the day: pressure highest in the morning, lowest in the evening
Diurnal variation of More than 8 mm is considered pathognomonic of glaucoma.
• Systemic venous pressure- external pressure of jugular veins, compression of superior vena cava by tumour,
cavernous sinus thrombosis.
• General anaesthesia decreases IOP (except nitrous oxide, ketamine)
• Topical drugs
• Blockage of the circulation of aqueous – angle of AC, pupillary block

16. MEASUREMENT OF IOP

17. VISUAL FIELD
• Portion of space in which objects are simultaneously visible to the
steadily fixating eye.

18. VISUAL FIELD EXAMINATION
Screening tests
• Confrontational visual field testing
• Amsler grid (assesses the central 10° the visual field ) .
Quantitative measurements using manual or automated perimetry

21. VISUAL FIELD DEFECTS
• Relative paracentral scotoma
• Roenne’s nasal step
• Seidel scotoma
• Arcuate scotoma
• Double arcuate / ring scotoma
• End stage / near total field defect

25. THANK YOU !!!