Unit 5 - Diabetes 5 Flashcards
What is glaucoma?
Damage to the optic nerve resulting in deterioration of visual field caused by intra-ocular pressure being too high for normal functioning of optic nerve head
What is the cause of glaucoma?
Disease often associated with a disturbance in circulation of aqueous humour in the eye
What are the symptoms of glaucoma?
Raised intraocular pressure (IOP)
How is aqueous humour formed?
Clear fluid formed from blood
Filtered in ciliary process arterioles
Rate of formation = 2-3 uL/min
Total volume of aqueous humour = 125 uL
Which two enzymes are involved in the formation of aqueous humour?
- ATPase
- carbonic anhydrase
How is aqueous humour made?
- Filtered in ciliary body
- 75% active secretin
- 25% ultrafiltration - Flows into posterior chamber
- then into anterior chamber between lens and iris
- passes through trabecular meshwork
- drains via canal of schlemm
- 60 - 90% - into ocular veins
- also uveoscleral outflow
- 10 - 40%
What is the normal intraocular pressure in the aqueous humour?
16 mmHg
What causes raised intraocular pressure?
Drainage and secretion not being balanced
What is the effect of raised intraocular pressure?
Restriction of blood supply to optic nerve
- back pressure
Optic nerve atrophy
Reduces field of vision
What is the field of vision in glaucoma?
Normal
Reduced field
Tunnel vision
Blindness
What does the type of glaucoma depend on?
Poor aqueous humour drainage
- degeneration and subsequent collapse of trabecular meshwork
- mechanical blockage of trabecular meshwork by peripheral role of iris
- flapping back
Increase in filtration pressure
- rare
What are the two types of primary glaucomas?
Open angle
Closed angle
What is secondary glaucoma?
Rise in intraocular pressure as a result of a known cause
- inflammation
- trauma
- mechanical flapping back of iris
Describe primary open angle glaucoma (POAG)
Most common - 0.5% of population Slow onset - commonly high intraocular pressure - pathological changes in trabecular meshwork may occur > 40 years Short sighted > -6.00 dioptres More common in Afro-caribbeans - x 8 incidence - 10-15 years earlier - genetic predisposition Possible association with diabetes mellitus
Describe primary closed angle glaucoma (PCAG)
Blockage of trabecular meshwork Can be ocular emergency Symptoms - dilated pupils - pain and inflamed eyes - blurred vision - reflex nausea and vomiting - loss of vision (24 hours) - blindness (2 - 3 days) Can be drug induced - atropine
Describe secondary open angle glaucoma
Occurs secondary to other conditions Inflammation - uveitis - increased secretion of proteins and inflammatory mediators Pigment dispersion syndrome - pigment granules shed from iris and ciliary epithelium - block and damage TM Pseudoexfoliative syndrome - flakes peel off iris - block trabecular meshwork Steroid-responsive glaucoma - blockage of trabecular meshwork by glycosaminoglycans - released in response to steroids Trauma - blunt - penetrating trauma - causes bleed from vessels in iris/ciliary body - bleeding blocks trabecular meshwork
Describe secondary closed angle glaucoma
Inflammation - uveitis - iris can be pushed forward and adhere to TM Iris bombe - increased posterior pressure - iris bulges forward Lens related - cataract lens may swell and form synechiae - adhesion between lens and iris
How is glaucoma diagnosed?
Examination of optic disc
Measurement of intraocular pressure
Gonioscopy
How does the optic disc appear in glaucoma?
Cupped - depressed White due to nerve fibre degeneration - increased pressure may restrict blood supply - anoxia causes degeneration
Give two ways that the intraocular pressure can be measured
Contact tonometry
Air jet tonometry
What is gonioscopy?
Viewing the irideocorneal angle via a mirror or prism
What is the major aim of glaucoma treatment?
To prevent sight loss
What drug groups can be used to treat glaucoma?
Prostaglandin analogues Sympathetic modifiers Carbonic anhydrase inhibitors Miotics Osmotic agents
What is the first line treatment of glaucoma?
Prostaglandin analogues
