Neuro-ophthalmology

update

Neuro-ophthalmology Update

Professor Helen Danesh-MeyerDepartment of Ophthalmology

Of which fundus is this a diagram?

A. Right

B. Left

C. Could be either

The axons of which cells are represented in the optic nerve?

• A. Bipolar cells

• B. Retinal ganglion cells

• C. Amacrine cells

• D. Muller cells

Image formation on the retina• Light rays are refracted by the cornea and the lens so that they

are focused on the retina• These images are inverted and right and left are reversed

Image formation on the retina• Close objects require more refraction to bend the divergent light rays on to the retina

Image formation on the retina• Lens shape made more convex by contraction of the ciliary muscle - accommodation.

Principal function of the retina

To absorb photons of light

Translate light into biochemical message

Translate biochemical message into electrical impulse

Transmit electrical impulse to brain via ganglion cells

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Direction of

Retinal structure & integration

Three layers of retinal neurons: photoreceptor, bipolar and ganglion cell layers

These 3 layers separated by outer & inner synaptic layers

Ganglion cells plus amacrine & horizontal cells modify signals from photoreceptors

The Retina – normal appearance

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1. Visual Acuity

Best Corrected

Pinhole

Near Vision

Visual FieldsV/A 6/6 V/A 6/6

Right Left

Right Left

Bilateral Disc Swelling: Papilloedema

2. Colour vision in compressive lesions

• Optic neuropathy has decreased colour out of proportion to VA.

• Red desaturation classic for compressive optic neuropathies

• Tests:• Ishihara• Red target

2. Colour Vision

• Test in brightly lit room

• Monocular

• With reading add

Control Plate

Red perception

• Test in brightly lit room• Ask:

1.Is bottle top equally red in both eyes?

2.If it is 100% red in this eye (or worth 100 dollars) then how many percent (or how many dollars) is the redness of the bottle top in the other eye?

Red perceptionOS OD

100% ?

3. Pupil abnormalities

Pupil Size• Miosis = small pupil

• Mydriasis = large pupil

• Anisocoria = difference in size

• Polycoria = multiple apertures

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Pupil reflexes

• Light reflex – direct/consensual

• Near reflex – miosis / accommodation / convergence

• Relative afferent pupil defect

• Pathologic pupil defects

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3. Relative Afferent Pupillary Defect

• Objective sign of optic nerve compromise

• Can be used to monitor progression

• Provides a comparison of the two optic nerves

Relative Afferent Pupillary Defect (RAPD)

• Test in dim room with pt looking at the distance

• Use bright source of light about 30cm from pt’s eyes

• Swing light b/w the eyes (2-3 sec on each eye)

• Make your decision within 2-3 swings

TESTING RAPD VIDEO

Circumstances when RAPD assessment difficult

• Both pupils dilated

• Dark irides

• Elderly- small constricted pupils

• Damage to iris by surgery (cataract)

• Presybopic examiner

Surrogate Tests for RAPD

• Brightness sense

• Red perception

Brightness sense• Test in dim room with pt looking directly at the light

• Use bright source of light

• Ask:1. Is light equally bright in both eyes?2. If light is 100% bright in this eye (or worth 100 dollars) then how many percent

(or how many dollars) is it in the other eye?

Other important Pupil abnormalities

Diagnosis

Horner’s Syndrome

Sympathetic System and the Eye

Horners triad

• Ptosis• Miosis• Anhidrosis

Test for Horners

Diagnostic Drop Tests

• Cocaine 4% or 10%• Horners pupil will not dilate because of lack of noradrenaline while normal

pupil dilates because of blockage of reuptake

• Apraclonidine (alpha agonist)• Upregulation of alpha-1 recepters by denervated pupillae

Apraclonidine: Dilates Horners pupil

Cocaine and apraclonidine in Horners

Causes of Horner’s

• Brainstem disease• Spinal Cord tumour• Carotid dissection

• Painful Horners

• Tumour at lung apex• Neck lesions

Sympathetic System and the Eye

Another case

Mr DP: 75 year old with diplopia

Presenting complaint:

• Sudden onset

• Same day developed headache

• Later the same day developed diplopia

What is the abnormality?

Oculomotor Nerve Palsy

• Ptosis (partial or complete)

• Pupil dilation

• Limitation of upgaze/downgaze and adduction

Important causes

• Intracranial aneurysm• Need MRI/MRA

• Giant cell arteritis• Over the age of 60• Associated with systemic constitutional symptoms• Do ESR/CRP• Temporal artery biopsy is gold standard

Pupil Summary

• RAPD is critical in diagnosis unilateral optic neuropathy• Anisocoria

• Usually benign• If associated with lid abnormalities

• Horners (miosis and ptosis)• Oculomotor nerve palsy (mydriasis and ptosis)

Visual pathway

1. Optic Nerve2. Chiasm3. Optic tract4. Lateral geniculate

nucleus5. Optic radiation6. Visual cortex

Localising lesions by type of visual field defect 1

Left eye Right eye

Left eye Right eye

Localising lesions by type of visual field defect 2

Left eye Right eye

Localising lesions by type of visual field defect 3

Left eye Right eye

Localising lesions by type of visual field defect 4

Left eye Right eye

Localising lesions by type of visual field defect 5

Left Right

The EndMaterial contained in this lecture presentation is

copyright of The Department of Ophthalmology, New Zealand National Eye Centre, University of Auckland, and should not be reproduced without first obtaining

written permission