lecture 2: classifications, screening and genetics of glaucoma Flashcards
What is the definition of glaucoma?
Ocular conditions that produce a characteristic optic neuropathy
How can you classify glaucoma?
primary
-open-angle: normal tension, high tension
85% of cases, not easy to detect
-angle closure: acute, aub-acute, chronic
15% of cases, easy to detect
-congenital
secondary
-open angle
-angle closure
What is primary glaucoma?
What is secondary glaucoma?
the condition is not associated with any other ocular disorder (95% of cases)
an increase in IOP occurs secondary to another ocular or non-ocular disorder e.g., steroid induced glaucoma
What is the definition of open angle glaucoma?
a form of chronic injury to the axons of the retinal ganglion cells and the 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
*Raised IOP is an important risk factor
What is the pathogenesis of glaucomatous optic neuropathy?
- Mechanical (IOP mediated)
-Nerve Axons pass through the pores of the lamina cribrosa
-Axon damage occurs due to pressure induced deformation or bending of the lamina cribrosa
-This results in retinal ganglion cell death (apoptosis) - Vasogenic (vascular)
-The quality of the blood supply to the ONH is impaired
-This leads to hypoxia and reduced nutrition to the ONH
-This leads to retinal ganglion cell death
What types of visual field defects can you get in moderate open-angle glaucoma?
What else can cause this vf defect?
-You get a sharp cut off at the nasal step.
-Arcuate shape extending from blind spot to nasal step
-Follows the distribution of nerve fibres on the retina
MS
optic disc drusen
What type of visual field testing should you do to detect early glaucoma?
central 24 to pick up early signs of glaucoma
glaucoma first affects the central part of the field
What are the risk factors for open angle glaucoma?
age
IOP
race (African)
FH
myopia
genetics
corneal thickness
smoking
low diastolic blood presssure
DM
Migraine
Raynuads disease
History of acute volume loss or blood transfusion
What is normal tension glaucoma?
A gluacotmous optic neuropathy with IOP within the statically normal range (below 21 mmHg)
How is the mean IOP worked out?
16mmHg (mean IOP) + 2 standard deviations
SD: 2.5mmHg
IOP is not normally distributed
What is high tension glaucoma?
A glaucomatous optic neuropathy with IOP outside the statistically normal range
What is the prevalence of congenital glaucoma?
When is the onset?
-0.5% primary glaucoma
neonatal (0-1 month)
infantile (1-24 months)
late onset (>2 years): caused by maldevelopment of anterior chamber angle du e to incomplete development of the TMW. can show bupthalmos
What is ocular hypertension?
*They don’t have glaucoma
*They have IOPs more than 21 mmHg consistently or recurrently
*Normal optic discs, normal visual fields, open anterior chamber angle
need monitoring
Is there genetics involved in glaucoma?
*10 – 50% of OAG patients report a family history,
*If someone reports FH of glaucoma, it’s important to ask what type of glaucoma, when was it diagnosed etc.
*if a monozygotic (identical) twin develops OAG there is a 98% chance of other twin developing glaucoma [i.e., both affected] between the twins
What can identification of specific gene defects lead to?
*Better understanding of the mechanisms of the disease
*Better conventional treatments
*Widespread screening for disease, especially in affected families. Early identification of “at risk” members of families may reduce the risk of visual loss later in life
What is health screening?
*The process of distinguishing those individuals who are healthy from those who would benefit from further investigation
*In optometric practice the procedure adopted with open angle glaucoma is “case finding” or “opportunistic surveillance” rather than screening
What are the 3 main tests used in the detection of open angle glaucoma?
1.Measurement of Intraocular Pressure
2.Assessment of visual fields
3.Examination of the Optic Disc
Why is a patient not referred based on one test alone?
normal patients being included in referrals (FALSE POSITIVES)
many people who would have benefited from referral not being detected (FALSE NEGATIVES)
What is sensitivity and specificity?
*sensitivity: the proportion of all diseased patients who are correctly classified as diseased by the test (we want this to be 100%)
*specificity: the proportion of all normal patients who are correctly classified as normal by the test (we want this to be 100% too)
What are the risk factors for Acute angle closure glaucoma?
Age
Ethnicity (0.4% European populations, 0.8% in Chinese populations >40 years)
Female gender
Hypermetropia
Anticholinergic drugs
