Aqueous Flashcards
What is the ciliary epithelium derived from?
Neuroectoderm
What is the ciliary epithelium a continuation of?
Neural layer of retina
What is the outer pigmented layer a continuation of?
RPE
What is the AC volume?
What is the rate of aqueous formation?
200-250uL
2-3uL/min
What form the blood aqueous barrier?
Tight junction between inner non-pigmented epithelial cells precent exudate from the fenestrated ciliary capillaries reaching the aqueous
Non-fenestrated iris vessels
How is aqueous humour formed?
70% active secretion
20% ultrafiltration
10% osmosis
What cells secrete aqueous
Mitochondiria rich non-pigmented epithelium
Pigmented epithelium also plays a part
What is the rate of aqueous flow?
2.75uL/min
What are the functions of the aqueous
Supply nutrition to the lens, corneal endothelium and stroma
Maintain IOP
Remain transparent
What is the composition of aqueous?
LOW PROTEIN
HIGHT ASCORBATE -reduce oxidtive damage from UV
Similar to plasma
Na 140mmol/l
K 4mmol/l
Glucose 80% of plasma
Lactate 2x plasma level
Ascorbic acid 50x that of plasma
Protein 1/500 of plasma as blood aqueous barrier
IgG and IgM
Plasminogen
Growth factors
What are the outflow pathways of aqueous
Mostly through trabecular meshwork and canal of Schlemm
Into the episcleral veins
Uveoscleral outflow 0.3uL.min
What cells line Schlemms canal? How does aqueous transport occur?
Non fenestrated single layer of endothelium with tight junctions
Micropinocytic vesicles and giant vacuoles within endothelial cells allow aqueous transport
How does IOP change through the day
diurnal rhythm
Peaks in late morning and trough in early afternoon
What is mean IOP
15-16mmHg
What effect does sleep/GA have on IOP
Decrease due to reduction in extraocular muscle tone
What effect does suxamethonium have on IOP
Transient marked rise
What does an increase in central venous pressure do to IOP
Raise in episcleral venous pressure and hence IOP
What is the path of the aqueous humour?
WSecreted by the non-pigmented ciliary epithelium in ciliary processes of anteiror pars plicata
Ciruclates into posteiror chamber
Through pupil
Towards anteiror chamber angle (area where cornea and iris join)
Drains through outflow apparatus (trabecular meshwork via canal of schlemm into episcleral veins)
10% drains through uveoscleral route
What factors affect aqueous production and drainage hence IOP
Episcleral venous pressure
Rate of flow of aqueous
Circadian rhythm
Neural and hormonal influences
What is the process of aqueous production?
Diffusion and ultrafiltration of plasma - reservoir int he stroma - active secretion across ciliary epithelium to form posterior chamber aqueous humour
What enzymes are involved in active secretion
Na/K/ATPase
Carbonic anhydrase - CO2+H2O - HCO3- +H+ - inhibtion of HCO3 leads to inhibition of active transport of Na into the NPE, reducing aqueous formation
What is the function of the ciliary body?
Provides neovascular supply to the anteiror segment,
constitutes part of blood aqueous barrier
Reponsible for accommodation
What is blood supply to cilairy body?
Long posteiror cilairy arteries
Major iris circle
What are the arrangement of muscle fibres in the ciliary muscle?
External longitudinal attached to scleral spur
Middle radial
Internal circular
