glaucoma L1 Flashcards
acquired open angle glaucoma
Acquired close angle glaucoma
What are the 2 types of glaucoma?
acquired and congenital
What is open angle glaucoma?
Anterior chamber angle is open, aqueous humour can drain through the trabecular meshwork… BUT there is
Blockage occurs at/within the trabecular meshwork
What is closed angle glaucoma?
Anterior chamber angle is closed, aqueous humour is prevented from reaching the trabecular meshwork
What does primary mean?
No association with any other disease
What does secondary mean?
Occurs secondary to the presence of another ocular or systemic disease, abnormality or injury
What is the function of aqueous humour?
» maintains structural integrity of the globe
» maintains the position of the refractive surfaces relative to each other
* Nutrition of the avascular lens and cornea
* Removal of waste products from lens and cornea
What produces aqueous humor?
-ciliary body
What is the pathway of aqueous humour?
Ciliary body → Posterior chamber → Pupil → Anterior chamber ↓
Drainage apparatus ( out trab meshwork and schlemms canal)
What are th2 2 drainage routes of aqueous humour?
trabecular route
uveoscleral route
Describe the trabecular drainage route?
90% of outflow
* Aqueous flows through trabecular meshwork, into the canal of sclemm and away via the episcleral veins
* Pressure sensitive route
Describe the uveoscleral route?
10% of aqueous outflow
* Aqueous passes across the face of ciliary body into the suprachoroidal space and away via venous circulation of ciliary body, choroid and sclera
What is POAG?
slowly progressive optic neuropathy characterised by a distinctive excavation of the optic nerve head and progressive visual field loss
-most common type
-chronic
-2nd leading cause of blindnesss in the world
What are the sub divisions of POAG?
1.Normal tension glaucoma (NTG)
- Ocular hypertension (OHT)
summarise POAG
- IOP > 24mmHg at some point
- Glaucomatous optic nerve damage
- An open anterior chamber angle
- Characteristic visual field loss
- No secondary causes
Summarise NTG
- IOP consistently ≤ 24mmHg
- Glaucomatous optic nerve damage * An open anterior chamber angle
- Characteristic visual field loss * No secondary causes
Summarise OHT
IOP > 24mmHg
* No glaucomatous optic nerve damage
* No visual field loss
What is the difference between NTG and POAG?
-Considerable overlap between the 2
-NTG tends to have a more classic clinical profile and more vascular associations (but not always)
Less pronounced or even non-progressive
Inferotemporal NRR thinning predominantly
- Disc haemorrhages
NTG accounts for approx 15-25% POAG cases
What is the pathogenesis of POAG?
caused by progressive retinal ganglion cell death caused by mechanical or vascular damage
What is the mechanical theory?
increases/raised IOP puts pressure on the lamina cribosa and the optic nerve head.
-this damages the lamina cribs and the axons of the ONH
1.compression of the nerve fibre bundles= nerve fibre damage/loss
- disturbance of the axonal transport
- deformation of lamina cribs plates
What is the mechanical theory?
increases/raised IOP puts pressure on the lamina cribosa and the optic nerve head.
-this damages the lamina cribs and the axons of the ONH
1.compression of the nerve fibre bundles= nerve fibre damage/loss
- disturbance of the axonal transport
- deformation of lamina cribs plates
What is the vascular theory?
. Ocular blood flow may be reduced/innsufficient due to elevated IOP.
which causes compression of the capillaries supplying the ONH.
Damage induced by failure of the microvasculature to nourish ONH nerve fibres – cell death
What are the potential causes of the vascular theory?
- Faulty autoregulation
- Hypotension
- Vasospasm
- Cardiovascular disease
What are the risk factors of POAG?
what are the symptoms of POAG?
Asymptomatic
* Anterior eye is white and quiet
➢ Initial field loss is usually nasal and covered by other eye
➢ Symptoms may arise once visual field loss becomes significant
What are the key 4 signs of POAG?
- Optic Nerve Head
- Visual Field
- Intraocular pressure
- OCT
➢ Usually bilateral but asymmetric
What does the NRR look like in POAG?
NRR:
– Loss of ISNT rule
– Diffuse (generalised) thinning
– Focal thinning (notching)
What does the cup look like in POAG?
Cup:
– Vertical cupping
– Large or enlarging c/d ratio
– Deep or deepening cupping
– Change in lamina cribrosa pores
– Asymmetry (>0.2)
– Progression over time
What are the vascular changes in POAG?
– Baring
– Bayonetting
– Overpassing
– Nasalisation
– Disc haemorrhages
What is diffuse loss of the NRR?
concentric enlargement of cup
Diffuse (generalised) thinning
What is a focal loss of the NRR?
Thinning or notching in a certain region
Inferior rim usually affected first, followed by superior rim
Early stages: loss of ISNT rule, inferior thinning of NRR, vertical enlargement of cup
Superior notching of NRR
inferior notching
reduced iop
reduced progression of glaucoma
Barring
circumlinear vessels no longer run coincident with the cup margin and are ‘bared’
Bayonetting
retinal vessels may disappear as they make a sharp turn into the cup
change of angle of blood vessel as it passes from NRR to optic cup (sharp bend)
If blood vessels bend or kink sharply when they pass over the edge of the cup= sign of erosion or loss of nor
Overpassing:
blood vessel isolated from disc margin and floor and is left ‘hanging’ in the volume of the cup (bridges the cup)
Nasalisation of vessels:
– Progressive loss of NRR tissue leads to loss of support for blood vessels
Disc haemorrhages:
– Splinter or flame shaped
– Transient (1-8 months)
– High risk of future damage
– Precede notching, NFL defects and/or visual field loss
– NTG?
Disc haemorrhages:
– Splinter or flame shaped
– Transient (1-8 months)
– High risk of future damage
– Precede notching, NFL defects and/or visual field loss
– NTG?
What are nerve fibre layer defects?
Subtle defects – more visible with red-free illumination
* Often precede development of visible ONH changes and visual field loss
* Two patterns:
– Localised wedge shaped defects
– Diffuse defects
What is Peripapillary atrophy (PPA)?
- Caused by chorioretinal thinning and disruption of RPE
- Present in up to 80% of normal eyes (ageing process)
Divide peripapillary region into two zones: alpha and beta zone
What is the alpha zone?
Alpha:
– outer crescent
– irregular hypo and hyper- pigmentation
– common in normal eyes
What is the beta zone?
– area adjacent to disc
– visible sclera, choroidal vessels and total loss of RPE
– more significant to glaucoma
Peripapillary atrophy (PPA)
What does PPA look ike when someone has glaucoma?
– Both zones significantly larger
– Beta zone more frequently present
– Sensitive indicator if present in a disc with small c/d ratio
– Location relates to damaged region
Differential diagnosis of PPA?
Choroidal crescent: seen if RPE stops short of ONH
* Scleral crescent: seen if both RPE and choroid stop short of ONH
* Pigment crescent: seen where RPE thickens or folds
End stage POAG
Suspect glaucoma
IOP > 24mmHg (actual value- contact tonometry + pachymetry)
Diurnal variation of >5mmHg (on phasing- testing IOP at phases during the day)
- Asymmetry between eyes of >5mmHg
sus readings
Suspicious readings should always be repeated
- Level of IOP that causes damage can vary between individuals
- Consider corneal thickness
- 15-25% of patients with glaucoma may have normal IOP (NTG)
What is the average corneal thickness
- Average corneal thickness = 550 microns
- 10 microns = 0.5mmHg (very approximate)
How does CCT affect IOP?
Thicker than average cornea: artificially high IOP reading
- Thinner than average cornea: artificially low IOP reading
What are the characteristic visual field defects in POAG?
– Paracentral scotoma
– Nasal step
– Arcuate scotoma
– Tunnel vision (Macula sparing)
Defect should be
Defect should be: * Reproducible
* Consistent with optic disc appearance
* Visual field plot should be reliable
(<20% fixation losses, <33% false +ves and false –ves)
What are the 3 visual field defects in POAG
- paracentral scotoma
2.nasal step - arcuate scotoma
paracentral scotoma
nasal step
arcuate scotoma
What is likely to cause false readings in OCT?
➢ Axial length*
➢ Optic disc size or tilt
➢ Angle between optic nerve head and fovea
