Ocular anatomy and dysfunction

Question 0

Wilbrand’s knee

Answer 0

Where fibres from the inferior nasal retina of one eye loop back up into the other optic nerve after reaching the optic chiasm for up to 3mm before continuing down the optic tract.
It’s existence in normal people has been questioned

Question 1

Visual pathway anatomy

Answer 1

Retina–> optic nerve –> join at the optic chiasm where the fibres from the nasal retina of each eye cross–> continue in optic tracts accounting for the contra-lateral half of visual space –> these terminate at the lateral geniculate body/nucleus –> optic radiations connect this to the primary visual cortex

Question 2

General rules for localising visual field defects

Answer 2

Lesions anterior to the chiasm produces unilateral defects
Posterior to the chiasm –> contra-lateral homonymous defects
Lesions at the chiasm produce bitemporal defects
Generally more congruous the defect in each eye the further back the lesion

Question 3

Total monocular blindness indicates a lesion where?

Answer 3

Unilateral optic nerve compression/lesions

Question 4

Bitemporal homonymous hemianopia indicates a lesion where?

Answer 4

Midline sagittal chiasm lesion/compression - full coronal lesion of the chiasm would produce total blindness
Mostly neoplastic-> pituitary expansion->increasing compression
Initially incomplete and asymmetric, becoming more complete with increasing compression

Question 5

Monocular Nasal hemianopia indicates a lesion where?

Answer 5

Unilateral perichiasmal lesion - damaging the temporal retina fibres of that eye

Question 6

Homonymous hemianopia

Answer 6

Contralateral lesion of the optic tract - Or - lesion to the visual cortex (occipital lobe) –> posterior to the chiasm
Loss effecting the same half of the visual field in both eyes
The more symmetrical the defects in each eye the closer to the occipital lobe the lesion

Question 7

Optic radiations

Answer 7

Visual information from the LGN to the primary visual cortex
Nasal retinal fibres decussate at the chiasm so that each tract and radiation deal with the contralateral half of visual space
Divide into Meyer’s loop (more vulnerable) and superior optic radiation (Baum’s loop)

Question 8

Meyer’s loop

Answer 8

Half of the optic radiation on each side where fibres from the inferior contralateral retina travel laterally through the temporal lobe to the primary visual cortex
Carry information on superior contralateral visual space
Damage produces a homonymous contralateral superior quadrantanopia

Question 9

Baum’s loop

Answer 9

The superior part of the optic radiation–> LGN up through the parietal in the retrolenticular limb of the internal capsule
Carry information from the contralateral superior retina on contralateral inferior visual space
Damage causes contralateral homonymous inferior quadrantanopia

Question 10

Superior homonymous quadrantanopia indicates a lesion where?

Answer 10

Meyer’s loop contralaterally

Question 11

Inferior homonymous quadrantanopia indicates a lesion where?

Answer 11

Baum’s loop contralaterally

Question 12

Bitemporal superior quadrantanopia

Answer 12

Indicates a compression of chiasm –> often first sign of pituitary tumour
Defects can often be asymmetric and respect the vertical midline but not the horizontal -> progress to hemianopia as tumour grows
May produce eventual optic neuropathy

Question 13

Central visual field defects

Answer 13

Most commonly due to AMD –> monocular
May also be - optic nerve disease –> bilateral, progressive and sub-acute, can be toxic/metabolic, nutritional or genetic
Usually have associated colour vision and acuity defect
Can also be due to trauma –> eg laser burn

Question 14

Diplopia

Answer 14

Double vision –> occurs when the eyes become mis-aligned
Normal at extremes of vision
Can be vertical, horizontal or oblique

Question 15

Causes of Diplopia

Answer 15

Physical displacement of the globe –> tumours, trauma or infection/inflammation (orbital cellulitis)
Cranial nerve palsies –> 3rd,4th and 6th (extra-ocular muscles)
Muscle fatigue –> myasthenia gravis/decompensation of squint
Thyroid eye disease

Question 16

For Diplopia in children consider

Answer 16

Birth history
Any history of amblyopia and patching treatment
Any family history of strabismus

Question 17

Amblyopia

Answer 17

loss of visual acuity due to problems in the visual cortex
Often occurs in children as the visual cortex is still developing, if one eye is used less due to illness or weakness the other is used more and becomes stronger
Treated by patching the good eye to force the other to catch up

Question 18

Strabismus

Answer 18

A misalignment of one of the eyes from fixating straight ahead
Often congenital –>Will cause Diplopia acutely but when young the brain will adapt to misalignment allowing single vision
Can be surgically corrected but if done after childhood the brain is unable to adapt to new alignment

Question 19

Abnormal head posture

Answer 19

Indicates possible new onset Diplopia
Often due to muscle problem limiting movement of one eye
This produces a Diplopia which can be corrected by changing head position
Position may indicate something about the nature of the problem

Question 20

Monocular Diplopia

Answer 20

Double vision which persists when one eye is covered
Indicates a refractive error problem which is uneven across the lens/cornea - corneal scarring, cataract, untreated refractive error
Usually described as ‘ghosting’

Question 21

Binocular Diplopia

Answer 21

Indicates the eyes are misaligned or become so in certain gaze positions
May be due to muscle palsies
Must investigate –> acuity, any abnormal head posture, eye movements and refraction

Question 22

4th nerve (trochlear) palsy and Diplopia

Answer 22

Supplies the superior oblique –>rotates the eye down and in
Patients complain of Diplopia when reading or going down stairs
Diplopia may be vertical, diagonal or rarely torsional
May tilt head away from the lesion, and eye will deviate upwards as it moves toward the nose

Question 23

4th nerve (trochlear) palsy - causes

Answer 23

May be congenital or acquired and bilateral or unilateral
Acquired may be due to diabetes or hypertension, or demyelination (MS)
Other causes : giant cell arteritis, tumours, aneurysms
Most common cranial nerve to be injured by trauma

Question 24

4th nerve (trochlear) palsy - treatment

Answer 24

In children - treat any amblyopia and refractive error
Prisms may be useful in adapting the patient in preparation for surgery or to produce functional monopia
Surgery is used to treat Diplopia and in some cases for cosmetic reasons –>careful with adults with neurally compensated Diplopia

Question 25

6th nerve (abducent) palsy - diplopia

Answer 25

Supplies the lateral rectus –> palsy causes a failure of abduction to the affected side –> causes horizontal Diplopia which is worse when looking to the affected side
May hold head turned to affected side to minimise diplopia

Question 26

6th nerve (abducent) palsy - causes in children

Answer 26

May occur transiently in neonates or occur benignly 1-3 weeks post-viral

Question 27

6th nerve (abducent) palsy - causes in adults

Answer 27

Hypertension/diabetes if >50yrs, MS, tumours, trauma, infections

Raised intracranial pressure (6th is particularly sensitive because of intracranial course)

Question 28

6th nerve (abducent) palsy - treatment

Answer 28

Investigate for cause with MRI/blood tests and orthopic tests (Hess test to identify weak muscles)
Treat with prisms or surgery if does not resolve spontaneously or with treatment of cause

Question 29

3rd nerve (oculomotor) - function

Answer 29

Supplies the superior, inferior and medial rectus and inferior oblique –> failure gives ‘tramp’s palsy’ as eye is ‘down and out’
Sympathetic to levator palpebrae superioris (failure>partial ptosis)
Parasympathetic to iris via cillary ganglion (failure causes fixed dilated pupil)

Question 30

3rd nerve (oculomotor) palsy - causes

Answer 30

Diabetes and hypertension can cause a micro-vascular palsy which will spare the pupil (parasympathetic fibres are superficial and so spared from ischaemic/metabolic injuries)
Other causes–> trauma, neoplasm, migraine, giant cell arteritis

Question 31

A painful unilateral 3rd nerve palsy with dilated pupil may be due to

Answer 31

Posterior communicating artery aneurysm

Requires an urgent neurological assessment/imaging

Question 32

Optic nerve disease/swelling can cause

Answer 32

Reduced visual acuity
Visual field defects
Reduced colour vision/red desaturation
Loss of pupillary reflexes/RAPD

Question 33

Unilateral Optic nerve swelling can be caused by

Answer 33

Central retinal vein or artery occlusion
Non-arteritic anterior ischaemic optic neuropathy (occlusion of short posterior cillary arteries) - Or - Arteritic anterior ischaemic optic neuropathy (temporal arteritis)
Papillitis or neuroretinitis

Question 34

Papillitis or neuroretinitis

Answer 34

Inflammation of the optic nerve head, or nerve head and surrounding retina
Idiopathic

Question 35

Bilateral Optic nerve swelling can be caused by

Answer 35

Raised intracranial pressure due to mass or blockage of CSF drainage –> will cause visible papilloedema on fundoscopy
Malignant hypertension —> rapidly rising hypertension, optic disc swelling indicates grade 4 hypertension
Optic disc drusen

Question 36

Optic disc Drusen

Answer 36

Drusen are calcified deposits–> can occur at the optic disc or deeper
When they are behind the disc they can give the appearance or swelling –> can cause visual field defects, usually asymptomatic
No treatment is avaliable

Question 37

Optic disc swelling - examination

Answer 37

Full ophthalmic, neurological and systemic history

Must rule out –> raised intracranial pressure, hypertension and giant cell arteritis

Question 38

Idiopathic intracranial hypertension is associated with

Answer 38

Obesity
Pregnancy
Oral contraceptives
Steroids 
Not Amiodarone