Glaucoma and Ocular Hypertension Flashcards by Bradley Brown

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!

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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

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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

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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

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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

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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.”

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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

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Closed angle mechanisms:

Pupillary block and non-pupillary block mechanisms - often a mixture of both mechanisms together

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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

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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

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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

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NTG - Risk Factors

• Age
• Family History
• Ethnicity - Japanese 4-12x increased risk of
•Raynauds Phenomenon
•Migraine?

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CAG - Risks

• Age
• Family History
• Ethnicity - South East Asian
• Hyperopia >2D

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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!

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Common causes of secondary Glaucoma:

• Uveitis
• Steroid Induced Glaucoma
• Pigment Dispersion syndrome
• Pseudoexfoliation

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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

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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