The Eye & Visual Field Defects

Question 1

Define the terms ‘placode’ and ‘pharyngeal apparatus’

Answer 1

Placode - thickened ectodermal patches on the developing head
Pharyngeal apparatus - series of extension ridges and furrows with corresponding internal pouches

Question 2

Outline the developmental processes involved in maturation of the eye

Answer 2

Out pocketing of forebrain –> optic placode
Hyaloid artery degenerates distally
Proximal portion becomes central artery of the retina
Optic cup –> retina, iris, ciliary body

Question 3

Describe the innervation of the eye

Answer 3

Sensory = optic nerve (begins as optic stalk)
Movements = oculomotor, trochlear, abducens

Question 4

Explain some common eye development defects

Answer 4

Congenital cataracts:
Opacity of the lens 
Genetic, teratogenic (e.g. Rubella infection) 
Detached retina:
Intraretinal space occurs 
Coloboma:
Failure of choroid fissure to close

Question 5

Outline the developmental processes involved in maturation of the external ear

Answer 5

1st Ph cleft –> external auditory meatus
1st + 2nd Ph arches –> auricles
Develop initially in neck, as mandible grows, ears ascend

Question 6

Outline the developmental processes involved in maturation of the middle ear

Answer 6

Derived from pharyngeal pouch and pharyngeal arch cartilage
Meckel’s cartilage –> malleus, incus
Reichert’s cartilage –> stapes
1st Ph pouch –> tympanic cavity, auditory tube

Question 7

Outline the developmental processes involved in maturation of the inner ear

Answer 7

Optic placodes –> auditory (otic) vesicles –> membranous labyrinth
Saccule –> cochlea
Utricle –> semilunar canals

Question 8

Describe the innervation of the ear

Answer 8

Vestibulocohlear
Trigeminal (V3) - tensor tympani
Facial - stapedius
Trigeminal + cervical spinal nerves - sensory

Question 9

Explain some common ear development defects

Answer 9

Ear defects common in most disabilities

Congenital deafness - middle ear (Ph arch 1+2)’ inner ear (teratogens –> maldevelopment of organ of corti

Question 10

Describe the visual pathway

Answer 10

Eye –> optic nerve –> optic chiasm –> optic tract –> lateral geniculate nucleus –> optic radiation –> visual cortex

Question 11

Understand the term ‘photoreceptors’

Answer 11

Rods - not in central retina, photosensitive, dark adapt

Cones - concentrated in fovea, high acuity, day vision, colour vision, red/blue/green

Question 12

Describe the process of ocular reflexes

Answer 12

Parasympathetic pathway
Constriction of pupil in response to light
+ consensual pupillary reaction

Question 13

Account for disturbed reflexes in a patient

Answer 13

Problem with parasympathetic pathways

Disruption to sympathetic pathway - sympathetic nerve inner step dilatator pupillae

Question 14

List the three clinical signs of Horner’s syndrome

Answer 14

Partial ptosis
Anhydrosis
Miosis

Question 15

Explain the role of cranial nerves 3, 4, 6 in the control of eye movements

Answer 15

CN3 (oculomotor) - all other eye muscles
CN4 (trochlear) - superior oblique muscle
CN6 (abducens) - lateral rectus muscle

Question 16

Account for palsy of the eye muscles

Answer 16

Oculomotor palsy - exotropia, depression (down and out), ptosis, mydriasis
Trochlear palsy - hypertropia
Abducens palsy - esotropia

Question 17

Define the term ‘amblyopia’ and list some different types

Answer 17

Amblyopia - lazy eye caused by abnormal binocular input early in life
Strabismus - esotropia, exotropia, hypertropia, hypotropia
Anisometropia - uncorrected difference in refractive power between the two eyes

Question 18

List some common abnormal retinal developments

Answer 18

Fovea hypoplasia --> nystagmus
Retinal dystrophy
Relative afferent pupillary defect
Amblyopia
Retinal detachment
Optic nerve damage --> glaucoma

Question 19

Name some ways of examining the eyes

Answer 19

Slit lamp examination - detects cataracts
Fundscopy - raised ICP
Optic coherence tomography

Question 20

Describe the type of defect in the visual field of a lesion of the optic nerve and list some causes of this

Answer 20

Monocular loss (ipsilateral to lesion) 
Causes - trauma, MS, optic nerve glioma/retinoblastoma (children), optic sheath meningioma (middle aged)

Question 21

Describe the type of defect in the visual field of a disturbance at the optic chiasm and list some causes of this

Answer 21

Bitemporal hemianopia (tunnel vision) 
Causes - pituitary adenoma, anterior communicating artery aneurysm

Question 22

Describe the type of defect in the visual field of a lesion of the optic tract and list some causes of this

Answer 22

Homonymous hemianopia (contralateral to lesion) 
Causes - vascular disease, head injury, cerebral tumour, neoplasia

Question 23

Describe the type of defect in the visual field of a lesion of the inferior optic radiation and list some causes of this

Answer 23

Homonymous superior quadrantanopia

Causes - stroke, SOL, temporal lobe lesion

Question 24

Describe the type of defect in the visual field of a lesion of the superior optic radiation and list some causes of this

Answer 24

Homonymous inferior quadrantanopia

Causes - parietal lobe lesion

Question 25

Describe the type of defect in the visual field of a lesion of the optic radiation and list some causes of this

Answer 25

Homonymous hemianopia with macular sparing (contralateral to lesion) Causes - lesion at occipital lobe

Question 26

Name the components of the eye and their functions

Answer 26

Retina - processes light Ciliary body - connects choroid to lens Lens - focuses light Iris - contractile diaphragm that regulates light that hits retina

Question 27

Explain why macular sparing can occur

Answer 27

Occipital lobe has dual supply (PCA, occipital pole of MCA) | Large cortical representation

Question 28

Describe the accommodation reflex

Answer 28

Convergence (medial rectus) Pupillary constriction (constrictor pupillae) Convexity (ciliary muscle) --> lateral geniculate nucleus --> occipital lobe (visual cortex)