Glaucoma introduction & POAG Flashcards
What is glaucoma?
A group of eye diseases that damage the optic nerve
Which cells are affected in glaucoma?
Retinal ganglion cells (RGCs)
What do RGCs do?
When light enters the eye, RGCs will transmit the info to the brain via their axons which are long fibres that make up the optic nerve. They allow you to see as they send the image to your brain
Why is glaucoma damage irreversible?
RGCs are part of the body’s central nervous system, which does not regenerate once damaged.
What are the types of glaucoma?
Primary:
- POAG
- PACG
- Congenital
Secondary:
1.
What is the most common type of glaucoma?
Primary Open Angle Glaucoma (POAG)
What is Primary glaucoma?
Occurs without any preceding ocular or systemic disease
What is in the ‘open angle describing POAG and how is it measured?
The angle between the cornea and iris measured using van Herrick
What happens is open angle glaucoma?
The aqueous drainage is normal from the posterior chamber, to the pupil into the anterior chamber but the problem is with the trabecular meshwork itself.
What are the demographic risk factors of POAG?
Over 40, afro-caribbean, family history (they have thinner corneas and more vasculopathy)
What are the ocular risk factors of POAG?
High IOP, myopia, thin cornea
What are the sytemic risk factors of POAG?
Diabetes, migraine, raynaud’s
How does the cornea cause a risk for glaucoma?
Thin cornea is linked to thin lamina cribrosa which is more susceptible to damage hence increasing risk of glaucoma
How do the migraines cause a risk for glaucoma?
A link between vasculopathy (disease affecting blood vessels) so those with migraines, raynaud’s and low blood pressure at increased risk. Lack of ocular perfusion around the optic nerve so the blood supply is weaker putting it at risk of damage
What are symptoms of POAG?
Asymptomatic until end stages where they get peripheral field loss
What tests are important to detect glaucoma?
DAFT discs,angle,fields,tonometry
How do you measure IOP?
NCT or GAT
Why is CCT (Central corneal thickness CCT) important?
A thin CCT will result in an underestimation of IOP, whilst a thick CCT will cause an overestimation of IOP
What is normal CCT?
520 Microns
What is normal IOP?
8-23mmHg Does high IOP mean glaucoma? No
What is IOP affected by?
-CCT -Diurnal variation
What is dinural variation?
IOP higher in the morning
When do you refer for suspect POAG based on high IOP?
If 24mm Hg or more then refer only if: you have measured IOP using GAT and done on a different occasion
What are the signs of a glaucomatous optic nerve?
Large CD ratio >0.6 CD asymmetry >0.2 NRR thinning (Superior and inferior, ISNT not obeyed) Lamina cribrosa pores visible Notching of NRR Pallor Baring of blood vessels Fly over vessels Bayonetting and nasalization of vessels Peripapillary atrophy (PPA) Optic disc hemorrhages RNFL changes
Why race has larger optic discs?
Afro-Caribbean population
If the disc is larger then what else is larger?
Larger disc= larger cup
How many nerve fibres pass through the optic nerve?
1.2 million
What is asymmetry a sign of glaucoma?
Glaucoma is typically an asymmetric disease Early optic nerve head changes may produce a right-left eye asymmetry.
What is the Neuroretinal rim?
Layer of neural tissue between edge of disc and edge of cup.
How does the NRR appear in a healthy eye?
ISNT obeyed, thickest to thinnest
What thins first in glaucoma?
inferior or superior NRR thinning
What is the lamina cribrosa?
A connective tissue meshwork located deep in the optic nerve head, contains pores through which all retinal ganglion cell axons pass on their way to the brain
Why is LC pores being visible a sign of glaucoma?
Increased visibility associated with larger CD ratio
What is notching?
Notching of the NRR represents a focal loss of the nerve fibres and is especially of concern if the notch is located infra-temporal or supratemporal.
What type of NRR is more common in open angle glaucoma?
Diffuse loss more common that localised loss so notching is less common)
What does pallor mean?
As nerve fibres die so the disc becomes paler
What is baring of blood vessels?
Baring of the circumlinear vessel occurs when areas of pallor develop between these small branches of the central retinal vessels and the cup margin
What is bayoneting?
In areas where the rim has been lost, retinal vessels can sharply change direction as they pass under the overhanging edge of the cup. This is known as bayonetting
What is nasalisation?
As glaucomatous cupping occurs, the blood vessels appear to shift nasally due to loss of the neuroretinal rim.
What are fly over vessels?
Fly-over vessels are seen when rim tissue underlying the retinal vessels that cross the disc margin is lost, which can give the appearance of vessels floating above areas of deeper cupping.
What is PPA?
Atrophy surrounding the disc. A and b zone
What is a zone and b zone PPA?
The a-zone atrophy is more common in normal eyes and is located on the outer surface of zone beta if present. The inner ß-zone beta represents loss of retinal pigment epithelium and is uncommon in non-glaucomatous eyes
What are Optic disc hemorrhages shape and location?
Splinter- or flame-shaped and located in the pre-laminar area of the optic disc in the superficial retinal nerve fibre layer. They can also be found in deeper parts of the disc margin and in the disc cup. Haemorrhages associated with glaucoma are often observed in the inferotemporal sector of the optic disc
Image shows splinter
What are other conditions can cause a disc haemorrhage?
Posterior vitreous detachment, optic disc drusen, non-glaucomatous optic neuropathies, and vascular occlusive diseases of the retina. Systemic disorders: diabetes, systemic hypertension, systemic lupus erythomatosis and leukaemia. They can also be associated with use of anti-coagulants.
What is the RNFL?
The retinal nerve fibre layer (RNFL) describes the radial expansion of the optic nerve fibres from their point of entrance at the optic disc. These opaque striations form arcuate bundles of nerve fibres where changes can occur in glaucoma.
How can you examine RNFL defects?
OCT= Red-free (green) light to enhance contrast, examining the peripapillary region for slit shaped, wedge shaped or diffuse defects.
What VF defect do you see in glaucoma?
Nerve fibre bundle defects (paracentral, arcuate, nasal step) and overall depressions, baring of the blind spot and enlargement of the blind spot.
Defects tend to follow the distribution of nerve fibres, be asymmetric between eyes and hemispheres and can be variable and intermittent.
What do VF defect do you see in end stage glaucoma?
Tunnel vision
What is the GHT?
The glaucoma hemifield test compares the number and severity of the pattern deviation probability symbols between the top and bottom halves of the field and has been shown to be sensitive to early glaucoma visual field loss.
The mean deviation, pattern standard deviation and visual field index provide summary measures that may be useful metrics in the assessment of progression.
