<ul>
 <li>Anterior chamber volume: 250&mu;L (average depth is 3.1mm)</li>
 <li>Posterior chamber volume: 60&mu;L</li>
 <li>Normal intraocular pressure is generally 10-20mmHg (with a positive skew)</li>
 <li>Aqueous is the main nutrient source for the avascular lens and cornea</li>
 <ul>
 <li>Lower glucose than plasma</li>
 <li>Low protein</li>
 <li>High ascorbate</li>
 </ul>
 <li>
 Aqueous is secreted by the non-pigmented (inner) ciliary body epithelium into the posterior
 chamber, utilising the active transport of sodium via the Na/K ATPase pump
 </li>
 <ul>
 <li>Produced via (see above)</li>
 <ul>
 <li>Active secretion (70%)</li>
 <li>Ultrafiltration (20%)</li>
 <li>Osmosis (10%)</li>
 </ul>
 </ul>
 <li>Factors affected IOP:</li>
 <ul>
 <li>Circadian rhythm</li>
 <li>Episcleral venous pressure</li>
 <li>Rate of secretion</li>
 <li>Rate of flow</li>
 <li>Neural and hormonal influences</li>
 </ul>
</ul>
## Neural control
<ul>
 <li>Adrenergic and cholinergic receptors are present in the iris and CB</li>
 <ul>
 <li>Alpha2 receptors are the most abundant in the ciliary body</li>
 </ul>
 <li>
 Adrenergic receptors (and muscarinic receptors) are present in the ciliary epithelium. Note:
 adrenergic receptors regulate IOP via adenylate cyclase (a G-protein driven process)
 </li>
 <ul>
 <li>Beta-adrenergic ANTAGONISTS suppress flow (eg. timolol)</li>
 <ul>
 <li>
 Beta-adrenergic stimulation increases aqueous secretion by activating adenylate cyclase
 </li>
 </ul>
 <li>Alpha2-selective adrenergic agonists suppress flow (eg. clonidine)</li>
 <ul>
 <li>Inhibition of adenylate cyclase</li>
 </ul>
 </ul>
 <li>
 Cholinergic mechanisms are not involved in IOP control (despite the effect of pilocarpine in
 reducing IOP&hellip;)
 </li>
</ul>
## Circadian regulation
<ul>
 <li>
 Melatonin has IOP-lowering effects and may therefore produce the diurnal variation in IOP.
 </li>
 <ul>
 <li>IOP highest in the morning</li>
 <li>Secretion falls to 1ml/minute at night (from 2.6ml/min during the day)</li>
 </ul>
</ul>
<ClinicalCorrelate>
 Patients with glaucoma show greater diurnal fluctuation
</ClinicalCorrelate>
## Outflow
<ul>
 <li>Conventional: trabecular meshwork</li>
 <ul>
 <li>
 Pressure dependent
 </li>
 <li>
 Resistance to outflow here occurs at the level of the TM endothelium and within the matrix of
 the meshwork
 </li>
 <ul>
 <li>
 The juxtacanalicular cribiform meshwork accounts for the greatest
 resistance into Schlemm&rsquo;s canal
 </li>
 </ul>
 <li>
 These endothelial cells have mechanosensor/stretch receptors to regulate the formation of
 transcellular pores
 </li>
 <li>
 Aqueous is transported via transcytosis: water-containing vesicles move through micron-sized
 pores across the meshwork to Schlemm&rsquo;s canal (giant vacuoles)
 </li>
 <li>
 The endothelial cells have active phagocytic properties and are specialised for endocytic
 transport and contractility.&nbsp;
 </li>
 <ul>
 <li>Also produce the TM matrix components</li>
 </ul>
 <li>TM cells have adrenergic receptors and glucocorticoid receptors</li>
 <ul>
 <li>
 Glucocorticoids induce the expression of trabecular meshwork inducible glucocorticoid
 response protein (TIGR).
 </li>
 <li>Mutations in TIGR gene (myocillin gene) are found in glaucoma</li>
 </ul>
 </ul>
</ul>
<ul>
 <li>Uveoscleral: 10-40% of aqueous drainage</li>
 <ul>
 <li>
 Pressure independent
 </li>
 <li>
 Direct drainage into the anterior uvea at the CB (through gaps in the endothelial lining here)
 and then into the suprachoroidal space
 </li>
 <li>MMP-1 may contribute to uveoscleral drainage</li>
 <li>Pressure in the suprachoroid is 2-4mmHg lower than in the AC&nbsp;</li>
 </ul>
</ul>
<ClinicalCorrelate>
 
 This pressure differential can be reversed after trabeculectomy, leading to choroidal effusions,
 especially in the elderly.
 
</ClinicalCorrelate>
<ul>
 <li>Prostaglandins predominantly increase uveoscleral outflow to lower IOP</li>
 <li>Estimated at 0.3&mu;L/minute</li>
</ul>
<ul>
 <li>Episcleral drainage</li>
 <ul>
 <li>
 Schlemm&rsquo;s canal has direct vascular communication with a network of intrascleral
 collector channels
 </li>
 <li>These drain into scleral veins</li>
 <li>Normal episcleral venous pressure is 8-10mmHg</li>
 </ul>
</ul>

AC to Lens

Aqueous Humour Dynamics

Intro

FRCOphth Part 1 Study Notes

Orbit and ocular adnexae

Orbit

Extraocular Muscles

Orbital Blood Vessels

Paranasal Sinuses

Lacrimal Glands

Tear Film

Eyelids

Blinking

Anterior segment - ocular surface

Conjunctiva

Conjunctivitis

Sclera

Cornea

Corneal Structure And Development

Corneal Physiology

Angle

Ciliary Body

Iris

Pupil

Lens

Posterior segment

Choroid

Vitreous

Retinal Macrostructure

Neurosensory Retina

Retinal Pigment Epithelium

Neuroanatomy

Venous Sinuses

Cerebral Ventricles

Cerebral Blood Supply

Supranuclear Gaze Pathways

Head And Neck Autonomic Nervous Supply

Head And Neck Glands

Osteology

Nerves

Muscles And Pharyngeal Arches

Extraocular Nerves

Sensory Nerves

Physiology

Physics Of Blood Flow

Neuronal Control Of Blood Vessels

Oxygen-Haemoglobin Dissociation Curve

Cytochrome p450

Pituitary Gland

Thyroid Hormone Production

Insulin

Glucagon

Parathyroid Hormone

Corticosteroids

Catecholamines

Cardiac Cycle

Renal Physiology

Fluid Balance

Acid-Base Balance

Muscle Physiology

Sensory Fibres

Cutaneous Receptors

Endocytosis

Glycosaminoglycans

Condensed Ocular Biochemistry

Eye Movements

Accomodation

Vision

Visual Cycle And Phototransuction

Visual Pathway

Visual Acuity

Colour Vision

Binocular Vision

Pathology

Collagen

Tissue Damage

Inflammation

Disease Entities

Wound Healing

Thrombosis / Atherosclerosis

Cell Growth

Neoplasia

Histopathology

Nystagmus

Free Radicals And Antioxidants

Immunology

Ocular Immunology

Microbiology

Viral Infections

Bacterial Infections

Fungal Infections

Protozoa

Nematodes

Antimicrobials

Genetics

Chromosomes

Mitosis

Meiosis

Genes

Polypeptide Synthesis

Histones

MicroRNA

Hardy-Weinberg Equilibrium

Mutations

Chromosome Defects

Autosomal Inheritance

X-Linked Inheritance

Mitochondrial Inheritance

Multifactorial Inheritance