Optic Disc Anatomy and Physiology Assessment

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Questions and Answers

What percentage of glaucoma patients have pressure within normal limits?

10%

20%

30% (correct)

40%

What is the purpose of the Circle of Zinn in the optic disc?

Supporting the lamina cribrosa

Forming the scleral ring

Regulating aqueous fluid dynamics

Blood supply to the optic nerve head (correct)

What is the characteristic of the cup in a normal optic disc?

Triangular

Slightly vertically oval

Circular

Slightly horizontally oval (correct)

What is a potential cause of increased intraocular pressure (IOP) in glaucoma?

All of the above Signup and view all the answers

What is the purpose of the scleral ring in the optic disc?

To distinguish the neuro-retinal rim from the cup Signup and view all the answers

What is a common feature of the cup edge in the optic disc?

It can be sloped or vertical Signup and view all the answers

What is the recommended approach to define the edge of the cup?

Rely on vessels and stereo cues Signup and view all the answers

What is a characteristic feature of an overhang in the disc?

A sudden disappearance of a blood vessel Signup and view all the answers

What is the primary mechanism of angle closure glaucoma?

Pupil block leading to bowing of the iris forward Signup and view all the answers

What is the recommended action for all angles of grade 1 (Van Herick)?

Refer all urgently for gonioscopy assessment Signup and view all the answers

What is a key distinguishing feature of a glaucomatous defect?

Corresponding ONH changes Signup and view all the answers

What is a potential limitation of auto-perimetry?

High plus or trial lens artefact Signup and view all the answers

What is a characteristic feature of an arcuate defect?

Para-central defect Signup and view all the answers

What is the recommended approach to confirm a glaucomatous defect?

Exclude alternative diagnoses Signup and view all the answers

What is a complication of CRAO?

Iris neovasculation Signup and view all the answers

What is a characteristic feature of a small disc?

Smaller CD ratios Signup and view all the answers

What is the primary mechanism that can give rise to increased intraocular pressure?

Imbalance in anterior fluid dynamics Signup and view all the answers

What is the characteristic shape of the normal optic disc?

Slightly vertically oval Signup and view all the answers

What is the function of the Short Posterior Ciliary Arteries?

Supply blood to the optic nerve head Signup and view all the answers

What is the characteristic appearance of the neuro-retinal rim tissue?

Pink Signup and view all the answers

What is a potential sign of glaucoma?

Enlargement of the cup Signup and view all the answers

What is the purpose of using a 78 or 90D lens and slit-lamp?

To visualize the optic nerve head Signup and view all the answers

What is the primary reason for not relying solely on the colour change from the pink of the rim to the pallor of the cup to define the edge of the cup?

The edge of pallor is not necessarily the edge of the cup in some situations. Signup and view all the answers

In what type of angle closure glaucoma is the mechanism of pupil block relieved by iridotomy/iridectomy?

Primary angle closure glaucoma Signup and view all the answers

What is the primary purpose of referring all angles of grade 1 (Van Herick) for gonioscopy assessment?

To assess the risk of angle closure Signup and view all the answers

What is the characteristic feature of a nasal step defect in a visual field?

Wedge-shaped defect in the nasal field Signup and view all the answers

What is the recommended approach to exclude alternative diagnoses in a patient with a glaucomatous defect?

All of the above Signup and view all the answers

What is the primary reason for using retinal vessels to define the edge of the cup?

The retinal vessels are a reliable guide to the cup edge Signup and view all the answers

What is the primary purpose of monitoring grade 2 angles (Van Herick) regularly?

To detect the progression of glaucoma Signup and view all the answers

What is the characteristic feature of a diffuse field loss in a visual field?

A general reduction in visual sensitivity Signup and view all the answers

What is the primary purpose of considering the statistical analyses of the visual field machine?

To assess the reliability of the visual field test Signup and view all the answers

What is the recommended approach to defining the edge of the cup in cases where there are no vessels as a guide?

Use stereo cues to visualize the cup edge Signup and view all the answers

Study Notes

Optic Disc Assessment and Anatomy

30% of glaucoma patients have pressure within normal limits, and large numbers of fibers can be lost before a visual field defect can be demonstrated.
Tools used to assess the optic disc: 78 or 90D lens and slit-lamp, and direct ophthalmoscope.
The normal optic disc head is slightly vertically oval, and a normal cup often appears slightly horizontally oval.

Blood Supply to the Optic Nerve Head

Short Posterior Ciliary Arteries
Circle of Zinn
Ophthalmic Artery
Central Retinal Artery
Lamina Cribrosa

Aqueous Fluid Dynamics and Glaucoma

An imbalance in anterior fluid dynamics can give rise to increased IOP.
Examples: angle closure/narrowing, pseudoexfoliation, PDS, anterior chamber inflammation, trauma.

Signs of Glaucoma

Enlargement of the cup
Localized loss of neuroretinal rim (NRR)
Pallor
Vessel deviations
PPA (peripapillary atrophy) disc hemorrhages
Nerve fiber layer defect
Lamina cribrosa

Defining the Edge of the Cup

The inner edge of the neuroretinal rim (=cup edge) may be sloped (especially on the temporal side of the disc) or vertical.
Use small to medium-sized blood vessels to define the cup edge by tracing their path across the scleral ring and then over the rim tissue.

Additional Points

Larger discs (>2mm) tend to display larger cup-disc ratios.
Cupping in small discs increases the risk of BRVO (branch retinal vein occlusion).
Proliferative diabetic retinopathy and carotid artery obstruction are related to CRAO (central retinal artery occlusion).

Angle Closure Glaucoma

Primary: 0.5% prevalence in age >40, associated with pupil block, causing bowing of the iris forward leading to angle closure.
Secondary: variety of mechanisms other than pupil block (not relieved by iridotomy/iridectomy).
Refer all angle closure urgently, and consider referral of all angles of grade 1 (Van Herick) for gonioscopy assessment.

Visual Fields Revision

Glaucomatous defect: look for corresponding optic nerve head changes.
Exclude alternative diagnoses.
NICE guidelines: look for unequivocal, suspicious, and early signs of glaucoma.

NICE Guidelines on Fields

Threshold or suprathreshold: glaucomatous changes of the visual field that reflect nerve fiber bundle loss.
Unequivocal signs: arcuate scotomas, nasal steps, altitudinal scotomata, focal defects, and absolute defects.
Suspicious signs: generalized defect, relative defect, and enlarged blind spot.
Early stages: mean defect >-6dB, 5% probability level defect for.

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Description

Test your knowledge of the optic disc's anatomy and physiology, including its assessment and blood supply. Learn about the normal optic disc shape and cup appearance, and how to use tools like the direct ophthalmoscope. Ideal for students of ophthalmology and optometry.