The Eye & Visual Field Defects Flashcards
Define the terms ‘placode’ and ‘pharyngeal apparatus’
Placode - thickened ectodermal patches on the developing head
Pharyngeal apparatus - series of extension ridges and furrows with corresponding internal pouches
Outline the developmental processes involved in maturation of the eye
Out pocketing of forebrain –> optic placode
Hyaloid artery degenerates distally
Proximal portion becomes central artery of the retina
Optic cup –> retina, iris, ciliary body
Describe the innervation of the eye
Sensory = optic nerve (begins as optic stalk) Movements = oculomotor, trochlear, abducens
Explain some common eye development defects
Congenital cataracts: Opacity of the lens Genetic, teratogenic (e.g. Rubella infection) Detached retina: Intraretinal space occurs Coloboma: Failure of choroid fissure to close
Outline the developmental processes involved in maturation of the external ear
1st Ph cleft –> external auditory meatus
1st + 2nd Ph arches –> auricles
Develop initially in neck, as mandible grows, ears ascend
Outline the developmental processes involved in maturation of the middle ear
Derived from pharyngeal pouch and pharyngeal arch cartilage
Meckel’s cartilage –> malleus, incus
Reichert’s cartilage –> stapes
1st Ph pouch –> tympanic cavity, auditory tube
Outline the developmental processes involved in maturation of the inner ear
Optic placodes –> auditory (otic) vesicles –> membranous labyrinth
Saccule –> cochlea
Utricle –> semilunar canals
Describe the innervation of the ear
Vestibulocohlear
Trigeminal (V3) - tensor tympani
Facial - stapedius
Trigeminal + cervical spinal nerves - sensory
Explain some common ear development defects
Ear defects common in most disabilities
Congenital deafness - middle ear (Ph arch 1+2)’ inner ear (teratogens –> maldevelopment of organ of corti
Describe the visual pathway
Eye –> optic nerve –> optic chiasm –> optic tract –> lateral geniculate nucleus –> optic radiation –> visual cortex
Understand the term ‘photoreceptors’
Rods - not in central retina, photosensitive, dark adapt
Cones - concentrated in fovea, high acuity, day vision, colour vision, red/blue/green
Describe the process of ocular reflexes
Parasympathetic pathway
Constriction of pupil in response to light
+ consensual pupillary reaction
Account for disturbed reflexes in a patient
Problem with parasympathetic pathways
Disruption to sympathetic pathway - sympathetic nerve inner step dilatator pupillae
List the three clinical signs of Horner’s syndrome
Partial ptosis
Anhydrosis
Miosis
Explain the role of cranial nerves 3, 4, 6 in the control of eye movements
CN3 (oculomotor) - all other eye muscles
CN4 (trochlear) - superior oblique muscle
CN6 (abducens) - lateral rectus muscle
Account for palsy of the eye muscles
Oculomotor palsy - exotropia, depression (down and out), ptosis, mydriasis
Trochlear palsy - hypertropia
Abducens palsy - esotropia
Define the term ‘amblyopia’ and list some different types
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
List some common abnormal retinal developments
Fovea hypoplasia --> nystagmus Retinal dystrophy Relative afferent pupillary defect Amblyopia Retinal detachment Optic nerve damage --> glaucoma
Name some ways of examining the eyes
Slit lamp examination - detects cataracts
Fundscopy - raised ICP
Optic coherence tomography
Describe the type of defect in the visual field of a lesion of the optic nerve and list some causes of this
Monocular loss (ipsilateral to lesion) Causes - trauma, MS, optic nerve glioma/retinoblastoma (children), optic sheath meningioma (middle aged)
Describe the type of defect in the visual field of a disturbance at the optic chiasm and list some causes of this
Bitemporal hemianopia (tunnel vision) Causes - pituitary adenoma, anterior communicating artery aneurysm
Describe the type of defect in the visual field of a lesion of the optic tract and list some causes of this
Homonymous hemianopia (contralateral to lesion) Causes - vascular disease, head injury, cerebral tumour, neoplasia
Describe the type of defect in the visual field of a lesion of the inferior optic radiation and list some causes of this
Homonymous superior quadrantanopia
Causes - stroke, SOL, temporal lobe lesion
Describe the type of defect in the visual field of a lesion of the superior optic radiation and list some causes of this
Homonymous inferior quadrantanopia
Causes - parietal lobe lesion
Describe the type of defect in the visual field of a lesion of the optic radiation and list some causes of this
Homonymous hemianopia with macular sparing (contralateral to lesion)
Causes - lesion at occipital lobe
Name the components of the eye and their functions
Retina - processes light
Ciliary body - connects choroid to lens
Lens - focuses light
Iris - contractile diaphragm that regulates light that hits retina
Explain why macular sparing can occur
Occipital lobe has dual supply (PCA, occipital pole of MCA)
Large cortical representation
Describe the accommodation reflex
Convergence (medial rectus)
Pupillary constriction (constrictor pupillae)
Convexity (ciliary muscle)
–> lateral geniculate nucleus –> occipital lobe (visual cortex)