Glaucoma and Ocular Hypertension Flashcards
Glaucoma definition:
• Progressive optic neuropathy
• and associated characteristic visual field loss
• lOP only known modifiable risk factor and is used when classifying glaucon
• However, low IOP does not mean that glaucoma is not present!
Glaucoma Aetiology: Theories
• Imbalance between aqueous production + drainage leads to increase IOP
• Increased IOP causes mechanical dkg to retinal nerve fibres; laminar cribosa; mechanical theory
• However people diagnosed with normal tension glaucoma
• Compression of blood vessels in optic nerve lead to ischaemia, can occur in absence of high pressure in predisposed individuals - Ischaemia theory
Classification of Glaucoma:
• Open or Closed Angle
• Normal vs High IOP - NTG vS POAG VS OHT
• Primary and Secondary Glaucoma
- Primary - Glaucoma with absence of other disease processes
- Secondary - Glaucoma secondarily to another disease process / mechanism causing : outflow to be impeded
- e.g Pseudoexfoliation or Pigment Dispersion syndrome
Congenital or Juvenile
• Congenital - Primary Glaucoma
• Juvenile - Secondary Glaucoma in childhood
Classification of Glaucoma: Types
• POAG - Primary open angle glaucoma
• PCAG - Primary closed angle glaucoma
• NTG - Normal tension glaucoma
• OHT - Ocular hypertension
• Secondary OAG
• Secondary CAG
Describe IOP measurements linked to Glaucoma: OHT, POAG, NTG, PCAG
• Repeatable measurement of IOP >21mmg defined as High IOP
• Ocular Hypertension (OHT) is IOP >21mmHg when no other signs of glaucoma are present
• In the presence of other glaucomatous signs e.g. ONH changes and/or characteristic visual field loss is defined as POAG
• POAG pressure generally between 21-35mmHg
• ONH changes and/or changes in the visual field with repeatable IOP <21mmHg defined as NTG
• PCAG pressure can be 50-100mmg during an acute attack
Describe Ocular Hypertension:
Definition for the NICE glaucoma guideline
- “Consistently or recurrently elevated IOP (greater than 21 mmHg) in the absence of clinical evidence of optic nerve damage or visual field defect.”
3 Causes of SOAG:
• Pre-trabecular
- A membrane covers the trabeculum blocking drainage E.g. - fibrovascular tissue causing neovascular glaucoma
• Trabecular
- “Clogging up” of the trabeculum, Eg. - pigment particles causing pigmentary glaucoma
- Pseudoexfoliative material causing pseudoexfoliative glaucoma
• Post-trabecular
- Aqueous outflow is impaired due to elevated episcleral venous pressure, E.g. Sturge Weber Syndrome
Closed angle mechanisms:
Pupillary block and non-pupillary block mechanisms - often a mixture of both mechanisms together
Two types of SCAG:
• With pupil block
- Seclusio Pupillae 360 degree posterior synechaie, usually as a result of recurrent uveitis
- E.g. uveitic glaucoma
• Without pupil block
- Causes of peripheral anterior synechaie (abnormal adhesion between the iris and angle)
- E.g. uveitic or traumatic glaucoma
Glaucoma: Symptoms
• Most often none!
• So is your History and symptoms useful when diagnosing glaucoma?
- Yes!
- Advanced cases patients may report being more clumsy, knocking things over, tripping, falling
- History and symptoms will help assess px risk of developing glaucoma
• Angle closure - headache (often around the eye/temporal), photophobia,
nausea
POAG - Risk factors
• Age (over 40 at risk, increases with age)
• Ethnicity - (African descent 4x more likely)
• Family history - 1st degree relative, 3x
• Peripheral vascular disease
• Diabetes
• Hypertension
• Myopia >6D
NTG - Risk Factors
• Age
• Family History
• Ethnicity - Japanese 4-12x increased risk of
•Raynauds Phenomenon
•Migraine?
CAG - Risks
• Age
• Family History
• Ethnicity - South East Asian
• Hyperopia >2D
Hx and Sx for acute/chronic CAG:
• If Acute
- Poor VA in affected eye
- Haloes around lights
- Ocular/periocular headache
- Gl symptoms including abdominal pain
• If Chronic
- Symptoms more subtle
- Mildly reduced VA intermittently
- Haloes around lights - especially in the evening when watching TV in a darkened
room
- NONE!
Common causes of secondary Glaucoma:
• Uveitis
• Steroid Induced Glaucoma
• Pigment Dispersion syndrome
• Pseudoexfoliation
How is the anterior chamber angle investigated:
• Van herricks or gonsioscopy
• Referral if van herricks grade 2, due to risk of ACAG; but narrow angle doesn’t mean they definitely have CAG
Classification of closed angle vs open angle glaucoma:
• If signs of glaucoma and grade 1 or zero - classified as closed angle glaucoma
• If signs of glaucoma and grade 2 or above OAG classified as open angle glaucoma
What signs are looked for in the anterior chamber?
• Pseudoexfoliation
• Pigment Dispersion
» Iris transillumination
» Kruckenberg spindle
• Iridotomy
Describe Pseudo-exfoliation, pigment dispersion syndrome and Iridotomy
• Can cause secondary open angle glaucoma
- Synechie
- Blocks trabecular meshwork
• Iridotomy
- Risk of developing glaucoma in future
CAG - Anterior chamber: Signs
• With pupil block
- Seclusio Pupillae 360 degree posterior synechaie, usually as a result of recurrent uveitis
•E.g. uveitic glaucoma
• without pupil block
- Causes of peripheral anterior synechaie (abnormal adhesion between the iris and anple)
•E.g. uveitic or traumatic glaucoma
ACAG - Anterior chamber: Signs
Only in an acute attack
- Corneal epithelial oedema
- Unreactive mid-dilated pupil
- VA 6/60 to HM
- Conjunctival hyperaema and circumcorneal injection
Why is intraocular pressure measured?
• applanation tonometry
- referrals for glaucoma and ocular hypertension; applanation tonometry used
• IOP used to classify as NTG, POAG, or OHT
• IOP must be considered alongside CCT when considering referral
• IOP is the only modifiable factor when treating glaucoma
How is IOP measured using applanation tonometry ?
• Calibrate, to Establish a baseline
• Minimum of two readings on a single occasion
• Record time, reading and instrument
• Should consider for referral if
- IOP > 25 mmHg irrespective of CCT
- IOP 21-25 AND CCT <555m AND Aged < 65
Monitor in the community if IOP <26 and CCT ≥ 555um and no signs of glaucoma
Why is CTT measured?
• Important independent risk factor for glaucoma
• At increased risk of glaucoma if CCT < 555mm
• Measured using pachymeter
•Record CCT mean and the pachymeter you used
What are the signs present to all glaucomatous conditions?
• Progressive optic neuropathy
• Characteristic visual field defect
• Neither will be present in OHT
Optic disc signs in Glaucoma:
• Focal thinning of the neuroretinal rim
- RIM TO DISC ratio measures narrowest neuroretinal rim
- Focal thinning will cause decrease in RIM TO DISC ratio
• Diffuse thinning of the neuroretinal rim
- CUP TO DISC ratio will increase if diffuse thinning
• Optic disc nerve fibre layer haemorrhage
• Asymmetric cupping
Why is Asymmetry a sign of glaucoma?
• Asymmetry of more than 0.1 can be indicator of glaucoma
• Compare cup to disc ratio in two eyes
• 5-8% of general population have cup to disc asymmetry of >0.1, especially in anisometropic eyes
Which limits are important for glaucoma on a visual field plot?
• Reliability indices
• Glaucoma hemifield test
• Mean Defect
• Pattern standard deviation plot
What are reliability indices?
(Look at a picture for reference)
• Three total: in order
- Fixation loss
- False positives
- False negatives
Good reliability 20% each
What is the Glaucoma hemifield test?
(Look at a picture for reference)
• Can be one of three:
- Normal
- Borderline
- Abnormal
• Compares overall sensitivity of visual field in inferior/superior fields
- Glaucomatous defects are almost always asymmetric between superior/inferior
What is the Mean defect?
(Look at a picture for reference)
• Represents mean threshold across visual field compared to age matched normal
- Negative number represents poor sensitivity compared to age matched norm
• A change in mean defect of -2Db per year can indicate progression of a defect
What is looked for in the pattern standard deviation plot
(Look at a picture for reference)
• A cluster of 3 or more points all of which have a p value less than 1% AND away from the disc AND is repeatable should be viewed as suspicious and potentially referred.
What are the visual field defects characteristic of glaucoma?
• Paracentral defect
• Arcuate defect
• Nasal step
• Temporal wedge
Describe Paracentral defect
- Isolated defect within 15degrees fixation
- superior or inferior hemifield
- more common in NTG
- ARMD can also cause paracentral loss!
Describe arcuate defect
- typically superior first
- extends from optic disc to temporal retina beyond the macula
Describe nasal step
- a change in sensitivity between inferior and superior hemifields where arcuate bundles meet temporal raphe
Describe temporal wedge
- Uncommon
- linked to focal neuro retinal rim loss
Optic disc signs, and visual field loss signs:
• Should always compare visual field findings to optic disc findings
- E.g. superior visual field loss represents a structural change in the optic nerve and a corresponding defect in the inferior neuroretinal rim
Describe OCT in relation to Glaucoma:
• Shows neuroretinal rim thickness and compares to age matched normals
- Can quantify structural changes in the neuroretinal rim
• Can be used to monitor glaucoma progression
Describe Gonioscopy in relation to Glaucoma:
• Technique to investigate the anterior chamber angle
• Refer irrespective of other signs, refer if:
- Gonioscopy shows 270 degrees or more of the angle where the posterior pigmented trabecular meshwork is not visible
• Only for use when practitioner is confident in their abilities
Whats a saying to remember the structures using gonioscopy:
I
Can - Ciliary Body
See - Scleral Spur
The - Trabecular Meshwork
Line - Schwalbe’s Line
How is Glaucoma and OHT managed in community:
• ОНТ
- 21mmHg -25mmg with CCT >555nm with no glaucomatous signs: Monitor in the community
- 21mmHg -25mmg with CCT <555m no glaucomatous signs + age under 65: Refer
- IOP >25 mmHg: Refer
• Glaucomatous optic neuropathy and/or characteristic visual field defect: Refer
