Optic Nerve Head and Glaucoma

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Questions and Answers

Which region of the optic nerve is located above the lamina cribrosa?

Surface nerve fibre layer

Optic disc

Neuro-retinal Rim

Pre-laminar region (correct)

Which of the following statements best describes the ISNT rule related to the optic nerve?

It suggests that the expected thickness of the neuro-retinal rim follows a specific sequence. (correct)

It states that the temporal rim is thicker than the nasal rim.

It requires assessment of retinal vascularization.

It implies that all optic nerves conform to the same measurement.

What is the primary characteristic of glaucoma?

It is strictly related to external ocular conditions.

It often (but not always) involves raised intraocular pressure. (correct)

It affects only younger populations.

It leads to non-progressive retinal detachment.

What role does the lamina cribrosa play in the optic nerve's structure?

It provides nutrition and structural support to nerve fibre bundles. Signup and view all the answers

Which of the following is NOT a common risk factor for the development of glaucoma?

Low blood pressure Signup and view all the answers

What percentage of aqueous humor exits the eye through the trabecular pathway?

90% Signup and view all the answers

Which structure is primarily involved in draining aqueous humor through the uveoscleral pathway?

Ciliary muscle Signup and view all the answers

After leaving the trabecular meshwork, where does the aqueous humor go next?

Into collector channels Signup and view all the answers

What is the primary route for aqueous humor to exit the eye?

Trabecular pathway Signup and view all the answers

Which of the following correctly describes the final destination of aqueous humor that exits via the uveoscleral pathway?

Vortex veins Signup and view all the answers

In which part of the eye does aqueous humor drain into after entering the anterior chamber?

Schlemm canal Signup and view all the answers

Which term describes the drainage system of aqueous humor primarily associated with the ciliary body?

Uveoscleral pathway Signup and view all the answers

Which of the following statements is true regarding aqueous humor circulation in the eye?

Fluid drains through the Schlemm canal into the episcleral venous system. Signup and view all the answers

What defines ocular hypertension?

Consistently elevated intraocular pressure above 21 mmHg without optic nerve damage. Signup and view all the answers

What percentage of individuals with untreated ocular hypertension may develop primary open angle glaucoma within 5 years?

10% Signup and view all the answers

Which examination method is used to assess elevated intraocular pressure?

Goldmann Applanation Tonometry Signup and view all the answers

Which assessment is essential for evaluating the optic nerve head in patients with ocular hypertension?

Slit lamp examination Signup and view all the answers

Which of the following is NOT a symptom associated with ocular hypertension?

Blurry vision Signup and view all the answers

What is the expected prevalence of ocular hypertension in individuals aged 80 years and older?

8% Signup and view all the answers

Which methodology is used to assess central visual fields in patients with suspected ocular hypertension?

Sita 24-2 Signup and view all the answers

What is the main reason to treat ocular hypertension?

To prevent optic nerve damage leading to glaucoma. Signup and view all the answers

What is the primary modifiable risk factor for the development of glaucoma?

Raised IOP Signup and view all the answers

Which of the following techniques is NOT typically used for central visual field assessment in glaucoma work-up?

Magnetic resonance imaging (MRI) Signup and view all the answers

Which visual field defect is characterized by a loss of vision at the paracentral area?

Paracentral scotoma Signup and view all the answers

What does an increase in the cup-to-disc (C:D) ratio typically indicate?

Progression of optic nerve damage Signup and view all the answers

What type of changes in the optic disc is NOT characteristic of glaucoma?

Positive slam disc sign Signup and view all the answers

Which of the following statements accurately describes the pathogenesis of glaucoma?

It is a combination of mechanical and ischaemic damage. Signup and view all the answers

Which vascular change is commonly observed near the optic disc in glaucoma patients?

Splinter haemorrhages Signup and view all the answers

What is the significance of measuring pachymetry in the context of glaucoma?

Assessing the thickness of the cornea Signup and view all the answers

What does the presence of the Beta zone indicate in relation to glaucoma?

It indicates a risk factor for glaucomatous progression. Signup and view all the answers

Which statement accurately describes the Alpha zone?

It signifies superficial RPE changes and is more common in glaucomatous eyes. Signup and view all the answers

What type of hemorrhage is characterized by feathered margins and occurs from the NRR to the retina?

Disc hemorrhage. Signup and view all the answers

What does bayoneting refer to in the context of vascular changes due to glaucoma?

Double angulation of a blood vessel entering the optic disc. Signup and view all the answers

When should a referral to an ophthalmologist be considered in relation to glaucoma?

If optic nerve head damage is observed. Signup and view all the answers

What does 'collaterals' refer to in the vascular changes associated with glaucoma?

Uncommon shifts between two veins at the disc. Signup and view all the answers

What is the significance of disc hemorrhages in glaucoma patients?

They can reveal areas of potential visual field loss. Signup and view all the answers

Which condition is NOT associated with systemic vascular diseases that may exhibit disc hemorrhages?

Glaucoma. Signup and view all the answers

What is the first-line treatment for elevated intraocular pressure (IOP) in patients with glaucoma?

Selective Laser Trabeculoplasty (SLT) Signup and view all the answers

Which of the following characterizes Normal Tension Glaucoma (NTG)?

IOP consistently ≤ 21mmHg Signup and view all the answers

What is the purpose of a dilated slit lamp exam in glaucoma diagnosis?

To assess the optic nerve head and fundus Signup and view all the answers

Which risk factor is NOT associated with Normal Tension Glaucoma?

Active smoking Signup and view all the answers

When managing a patient with a high IOP who opts out of SLT, which treatment is typically prescribed first?

Prostaglandin analogue eye drops Signup and view all the answers

What specific symptom should be inquired about during the history taking for a patient suspected of having Normal Tension Glaucoma?

History of hypovolaemic shock Signup and view all the answers

Which type of eye drop is considered the second choice in managing elevated IOP for glaucoma patients?

Topical beta blockers Signup and view all the answers

What technique can be performed if gonioscopy is not possible to evaluate anterior chamber configuration?

Van Herick technique Signup and view all the answers

Study Notes

Optic Nerve Head

The optic nerve head is the intra-ocular segment of the optic nerve. It is composed of 3 segments:
- Surface nerve fibre layer: Convergence of retinal ganglion cell axons onto the optic nerve head.
- Pre-laminar region: Nerve fibres form into bundles to pass through the lamina cribrosa.
- Lamina Cribrosa: Connective tissue with multiple openings. Provides nutrition to the nerve fibre bundles. The pores are larger in the superior and inferior lamina cribrosa due to larger nerve fibre bundles.

Optic Disc

Optic disc: Optic cup + Neuro-retinal rim (NRR).
Small disc size: 2.2mm.
Large discs: More likely to be damaged, particularly in Normal Tension Glaucoma.
ISNT Rule: Expected thickness: Inferior > Superior > Nasal > Temporal. High sensitivity in detecting early glaucomatous changes (81%). However, healthy optic nerves may not always follow this rule.

Glaucoma

Group of conditions causing chronic progressive optic neuropathy.
Often associated with raised intraocular pressure (IOP). This is a key modifiable factor.
Aqueous humour: Fluid that circulates in the eye.
Aqueous drainage pathways:
- Trabecular pathway: 90% of aqueous exits through this route.
- Uveoscleral pathway: 10% of aqueous exits through this route.

Retinal Nerve Fibre Layer Defects

Types of defects:
- Focal: Localized wedge-shaped defects.
- Diffuse: Widespread defects.
Appearance: Easier to see in red-free illumination.
Significance: Subtle defects that precede optic nerve head changes and visual field loss.

Laminar Dot Sign

Definition: Visible lamina cribrosa pores or increased lamina cribrosa pore size due to loss of retinal ganglion cell axons.
Prevalence: Observed in 70% of patients with Primary Open Angle Glaucoma.

C:D Ratio Asymmetry

Definition: Discrepancy in cup to disc ratio (C:D ratio) between the two eyes due to differences in disc size.
Significance: Can be a sign of glaucoma.

Aqueous Drainage

Aqueous humor exits the eye via two pathways: trabecular pathway (90%) and uveoscleral pathway (10%)
Trabecular pathway: Aqueous flows through the trabecular meshwork, Schlemm's canal, collector channels, and then into the episcleral venous system.
Uveoscleral pathway: Aqueous drains into the space between the ciliary body and sclera, exits through veins in the ciliary muscle and anterior choroid, and then drains into vortex veins.

Optic Nerve Recap

The optic nerve head is the intraocular segment of the optic nerve.

Glaucoma Overview

Glaucoma is a group of eye diseases that damage the optic nerve, which can lead to blindness.
Primary Open-Angle Glaucoma (POAG) is the most common type and involves a gradual increase in intraocular pressure (IOP) due to blockage of the trabecular meshwork.
Normal Tension Glaucoma (NTG) is characterized by glaucomatous optic neuropathy and visual field loss despite normal IOP.
Ocular Hypertension refers to consistently elevated IOP (>21 mmHg) without optic nerve damage.

Ocular Hypertension

4.5-9.4% of individuals over 40 years old have ocular hypertension.
10% of patients with untreated ocular hypertension develop POAG within 5 years.
45.5% of individuals with ocular hypertension develop POAG within 20 years.
Symptoms: Asymptomatic
Signs: Elevated IOP (>21mmHg) measured by Goldmann Applanation Tonometry (GAT).

Primary Open Angle Glaucoma (POAG)

Prevalence: 4% in individuals over 40
Increases with age: ~1% at 40 years old, ~3% at 60 years old, ~8% at 80 years old

POAG Risk Factors

Raised IOP: Main modifiable risk factor.
Increasing age
Family history of POAG
Ethnicity
Corticosteroid use
Type 2 Diabetes
Myopia
Vascular disease
Ocular perfusion pressure (difference between arterial blood pressure and IOP)

POAG Aetiology & Pathogenesis

Aetiology: Increased resistance to drainage through the trabecular meshwork, leading to progressive optic neuropathy.
Pathogenesis:
- Mechanical damage: Retinal nerve fibers are damaged at the optic nerve head (ONH) as they pass through the lamina cribrosa.
- Ischaemic damage: Compression of blood vessels supplying the ONH.

POAG: Work Up

Central visual field assessment: Using standard automated perimetry (full or suprathreshold).
Optic nerve head assessment: Slit lamp and OCT.
IOP measurement: Goldmann-type applanation (or Perkins).
- IOP threshold value: ≥24mmHg.
- Pachymetry.
Peripheral anterior chamber depth and configuration: Van Herick, OCT, or Gonioscopy.

POAG: Visual Field Defects

Paracentral scotoma: Central blind spot near the fovea.
Nasal step scotoma: Step-like depression in the nasal field.
Arcuate scotoma: Arc shaped defects in the visual field.
Ring scotoma: Ring-like defects in the visual field.

POAG: Optic Disc Changes

Notching: Focal or diffuse indentations in the optic nerve rim.
Asymmetry in the C:D ratio: Differences in the cup-to-disc ratio between the two eyes.
Neuroretinal rim (NRR) thinning: Thinning of the rim surrounding the optic cup.
RNFL defects: Deficiencies in the retinal nerve fiber layer.
Lamina dot sign: Grey dot-like fenestrae in the lamina cribrosa become visible.
Peripapillary atrophy: Atrophy of the tissue surrounding the optic disc.
- Alpha Zone: Superficial RPE changes, outer zone.
- Beta Zone: Inner zone, chorioretinal atrophy, larger in glaucoma, signifies a risk of progression.
Vascular changes:
- Splinter hemorrhages: Near the optic disc, may also occur in systemic vascular conditions.
- Baring of circumlinear blood vessels: Early sign, gap between NRR and superficial blood vessels.
- Bayoneting: Double angulation of a blood vessel.
- Collaterals: Vessels connecting two veins at the disc.

POAG Referral

Refer if any of the following are present:
- Optic nerve head damage.
- Visual field defect consistent with glaucomatous damage.
- IOP ≥24mmHg.

POAG Management (covered in more depth in next week's lecture)

First-Line treatment:
- Selective Laser Trabeculoplasty (SLT).
If IOP > 24mmHg and SLT is unsuitable/declined:
- Prostaglandin analogue eye drops (first choice)
- Topical beta blocker (second choice)
- Carbonic anhydrase inhibitors
- Combination therapy.

Normal Tension Glaucoma (NTG)

Characteristics:
- Glaucomatous optic neuropathy.
- Characteristic visual field loss.
- IOP consistently ≤ 21mmHg.
- Open anterior chamber angle.
- No signs of secondary glaucoma.

NTG Risk Factors:

Age: Patients tend to be older than those with POAG.
Race
Family history of NTG
Thin central corneal thickness
Systemic hypotension: Including dips in blood pressure at night.
Abnormal vaso-regulation: In patients with migraine or Raynaud's syndrome.
Low cerebrospinal fluid pressure

NTG Work Up:

History and symptoms:
- History of migraine, Raynaud's phenomenon, episodes of hypovolemic shock, headaches, neurological symptoms, intermittent steroid use, and systemic beta-blockers.

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Description

This quiz covers the anatomy of the optic nerve head, including its segments and the optic disc. It also explores the implications of optic disc size in glaucoma, particularly the ISNT rule and its sensitivity in detecting glaucomatous changes. Test your knowledge on these critical aspects of ophthalmology.