Classifications, screening and genetics of the glaucomas (Dave Edgar) Flashcards Preview

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what is the definitions of the glaucomas

Glaucoma (or more correctly but less conveniently “the glaucomas”) is the name given to a group of ocular conditions that produce a characteristic optic neuropathy

glaucomas - a group of ocular conditions which give the same end point
optic neuropathy - pale optic disc with increased cup to disc ratio and loss of NRR


what 2 categories are the glaucomas classified into

- primary - the condition is not associated with any other ocular disorder

- secondary - an increase in IOP occurs
secondary to another ocular or non-ocular disorder e.g. steroid induced glaucoma


which type of glaucoma is usually recognised quite early on

secondary recognised earlier than primary


list the 3 types of primary glaucomas and how much each accounts for in primary glaucomas

- Primary angle closure glaucoma
About 15% of the primary glaucomas in UK

- Primary (or Chronic) open angle glaucoma (POAG or COAG)
About 85% of the primary glaucomas in UK

Congenital glaucoma


what is unknown about Primary (or Chronic) open angle glaucoma

Mechanism for the disease


what is the possible definition for Primary (or Chronic) open angle glaucoma and what is a very important risk factor

A form of chronic injury to axons of the retinal ganglion cells and other optic nerve tissues, mainly at the level of the optic disc and lamina cribrosa, frequently associated with characteristic, but not diagnostic, visual field defects

IOP, which is often raised above average levels, is a very important risk factor


what are the 2 main theories on the pathogenesis of glaucomatous optic neuropathy in open angle glaucoma and describe what happens in each one

- Mechanical (or IOP mediated)
Axon damage within the optic nerve head is caused by pressure-induced deformation of the lamina cribrosa

- Vasogenic (or vascular)
The quality of blood supply to the ONH is impaired which leads to hypoxia and reduced nutrition to ONH, and then to axon death


what happens to the lamina cribrosa in the mechanical theory on the pathogenesis of glaucomatous optic neuropathy in open angle glaucoma

the bending and bowing of the plates causing deformation of the lamina cribrosa


describe the appearance of a typical visual field defect defect in moderate open angle glaucoma and explain why it is characteristic but not diagnostic of glaucoma

- Classic arcuate shape with sharp cut off on horizontal nasal quadrant called nasal step
- can get the same in other defects e.g. multiple sclerosis or congenital nerve defect


in POAG, which area of the visual field is affected and which vf test is best to pick up on early signs

- central 24 degrees is affected
- central 24-2 is the vf test used because most diseases affects the optic nerve and central vf


list the 8 risk factors of POAG, starting from highest to lowest

POAG is multifactorial. Risk factors include:
Family history+
Corneal thickness


give 3 points as to how IOP and POAG are linked

- Prevalence of POAG increases as IOP increases
- Risk of subsequent field loss increases with increasing IOP
- Significant reductions in IOP reduce the risk of subsequent nerve damage


what is the aim of anti glaucoma drugs

to aim for a target IOP that will cause no further damage

when ophthalmologists decide to treat glaucoma, they look at the patient's pressures on diagnosis, which is based on individual factors relating to the px, the ophthalmologist will then decide on a target pressure, to stop progression of the disease or to minimise/slow down the progression of the disease


what is the prevalence of POAG as stated by Beaver Dam and Roscommon and what did both studies' results have in common about the patients

Beaver Dam 2.1%
Roscommon 1.87%

both in over 40's in rural caucasian populations


what is the prevalence of POAG in the black and white population by Baltimore

blacks 4.18%
whites 1.29%

from people in inner city populations


what does the NICE guidelines state about the prevalence of glaucoma in those over 40 and those over 75 years go age

- approximately 2% of those over 40
- approximately 10% of those over 75


what are the 2 classifications of POAG

- normal tension glaucoma (NTG)
still occasionally referred to as “low tension glaucoma”

- high-tension glaucoma


what 2 types of definition is there of normal tension glaucoma (NTG)

- qualitative definition:
would be “a glaucomatous optic neuropathy with IOP within the statistically normal range”

- quantitative definition:
a glaucomatous optic neuropathy, but the IOP never exceeds 21 mm Hg

a glaucomatous optic neuropathy with a mean IOP over a 24 hour period of less than 21 mm Hg and peak pressures of less than 24 mm Hg

a type of COAG where IOP has rarely been recorded above 21 mm Hg
This is the NICE definition

all quantitative definitions mention 21mmHg


where did the value of 21mmHg come from and what does research say about the distribution of IOP

- 21mmHg is the mean IOP (16mm Hg) + 2 Standard Deviations
SD = 2.5mmHg, 2SD = 5mmHg

IOP is NOT normally distributed

If IOP was normally distributed then about 2.5% of the population would have IOPs > 21mm Hg - but some say the actual figure is closer to 8% (based on normal IOP in the bedford population)

statistics show low value, 21mmHg = not as reliable figure


how many % of patients have IOP in the normal range at diagnosis and what do you call this type of glaucoma

- 40 - 50% of patients have IOP in the normal range at diagnosis

- Normal tension glaucoma

- IOP may rise with time but not at a faster rate than in normals


what is the risk of normal tension glaucoma causing POAG

- Risk of P(C)OAG increases with IOP, BUT risk is there at levels at or below 21mmHg (and most patients have IOPs


what is high tension glaucoma

a glaucomatous optic neuropathy with IOP outside the statistically normal range normal tension glaucoma (NTG)


what are the 3 types of primary angle closure glaucoma and how much % of primary glaucomas does it make up in the UK, also what is the prevalence of this type of glaucoma in caucasians aged over 40

- acute
- sub-acute
- chronic

- makes up 15% of primary glaucomas in the UK
- prevalence of 0.4% in Caucasians aged over 40


in which parts of Asia is primary angle closure glaucoma more prevalent in compared to POAG and give values for both types from 2 countries

- In China (Beijing) POAG = 0.03%, CAG = 1.4%
(But this is only one study)

- In India one study (Vellore) POAG = 0.4%, CAG = 4.3%
(Other studies disagree)

so proportions of open and closed angle glaucoma differs in the world


what is the prevalence of congenital glaucoma of the primary glaucomas in the UK and why is this type of glaucoma important

- makes up less than 0.5% of primary glaucomas in UK

- Important because:
is responsible for 2.5 - 10% of all registered child blind


what is another name of congenital glaucoma and why does it develop

- infantile - alternative name buphthalmos
- develops as result of a maldevelopment in the outflow system of the eye in utero (of aqueous to escape the eye not developed properly)

juvenile - occurs later in childhood


list 4 points that describes what ocular hypertension OHT is

- IOP >21 mm Hg
- Normal optic discs
- Normal visual fields
- Open anterior chamber angle 

i.e. dont have glaucoma


what is the prevalence of OHT in the adult population and what does NICE (2009) state about OHT

- Prevalence of OHT in the adult population is between 2.7 and 7.5%

- NICE (2009) state that between 3 to 5% of those over 40 have OHT


what is the prevalence of genetics in glaucoma and what has there found to be when it comes to family history and glaucoma

- 10 – 50% of POAG patients report a family history

- there is undoubtedly significant under-reporting of family history

- It is likely that many genes are involved
They may interact to cause the variations that occur in individuals with COAG

- Several genes have been identified:
But these are responsible for uncommon types of glaucoma


describe the genetic link between monozygotic twins and glaucoma

if a monozygotic twin develops POAG there is a 98% chance of concordance [i.e. both affected] between the twins = strong genetic trait


describe the detection of POAG and list the 3 main tests that are used, explain the reliability of these screening tests

POAG is asymptomatic until the late stages of the disease

Three main tests used are:
- Measurement of Intraocular Pressure
- Assessment of visual fields
- Examination of the Optic Disc

In any screening test there are invariably errors and misclassifications, even if the examiner is highly skilled
- No test is perfect
- There are numerous factors affecting the accuracy of tonometry, fields, and disc assessment