theory Flashcards
afferent and efferent pupillary pathways are
Afferent pathway
Optic nerve – chiasm – optic tract – pretectal nucleus (dorsal midbrain)
Efferent
Parasympathetic and sympathetic input to iris muscles
light reflex what nucleus is involved
pretectal nucleus
what are the pupillary light reflexes
Control of pupil diameter based on light intensity
Increased light intensity leads to a reflex pupillary constriction (miosis)
Direct reflex – pupillary constriction in response to light entering the ipsilateral eye
I.e. Light shone in right eye leads to miosis in right eye
Consensual reflex – pupillary constriction in response to light entering the contralateral eye
I.e. Light shone in right eye leads to miosis in left eye
what are the afferent and efferent light reflex pathways
Control of pupil diameter based on light intensity
Increased light intensity leads to a reflex pupillary constriction (miosis)
Direct reflex – pupillary constriction in response to light entering the ipsilateral eye
I.e. Light shone in right eye leads to miosis in right eye
Consensual reflex – pupillary constriction in response to light entering the contralateral eye
I.e. Light shone in right eye leads to miosis in left eye
what is the near reflex
Pupillary constriction when fixating on near target (i.e. accommodation)
Less clearly defined pathway than light reflex
describe the near reflex
Convergence
Increased thickness of lens
Pupillary constriction for better focus (allows less peripheral ”distracting” light surrounding object of interest from entering the eye)
describe the oculosympathetic pathway
Pain, fear, excitatory inputs in general lead to pupillary dilation through the sympathetic innervation of the dilator pupillae muscle
3-neuron arc
1st order – from posterior hypothalamus, down the spinal cord, and synapse at the ciliospinal centre of Budge (at level C8-T2)
2nd order (preganglionic) – from ciliospinal centre of Budge, leaving spinal cord via ventral spinal roots, passing over apex of lung and joining the paravertebral cervical sympathetic chain to ascend and finally synapse at the superior cervical ganglion
3rd order (postganglionic) – from superior cervical ganglion, travelling up along the internal carotid artery, entering cranial cavity (via carotid canal), joining CN V1, and reaching the ciliary muscle and dilator pupillae via the nasociliary nerve and long posterior ciliary nerves
how to examine the pupils
General observation – size, shape, position, colour of iris
Start with ambient light
If anisocoria, check if anisocoria worse in dim or bright conditions
Assess light reflex – both direct and consensual responses
Swinging light test – ?RAPD
Check near reflex
how to assess aniosocoria
worse in dim light , implies failure of dilation and small pupil is therefore abnormal
worse in bright light
implies failure of constriction and large pupil is therefore abnormal
same regardless of light conditions - physiological anisocoria
components of the parasympathetic pathway
Efferent preganglionic parasympathetic fibers travel from the Edinger Westphal nucleus of CN III along the oculomotor nerve before synapsing in the ciliary ganglion
Postganglionic fibers then travel from the ciliary ganglion to the ciliary muscles and sphincter pupillae via the short ciliary nerves
cranial nerve 3rd palsy characteristics
LR (CN VI) and SO (CN IV) only left working
Eye therefore down (SO) and out (LR and SO)
Complete ptosis (loss of levator palpebrae superioris action)
Diplopia due to eye misalignment
Pupil involvement usually indicates a surgical cause
Causes include:
Microvascular disease (e.g. diabetes, hypertension)
Compression from mass effect (tumours, posterior communicating artery aneurysm)
surgical third nerve palsy
B. Microvascular disease (medical CN III palsy) – affects blood supply in vasa nervorum, but tends to spare the outer parasympathetic fibers hence pupil not affected
External compression of CN III affects those parasympathetics, leading to failure of pupillary constriction. Hence a fixed dilated pupil is seen
what is a relative afferent pupillary defect
Light intensity perceived differently by each eye (i.e. the intensity of light relative to the other eye is different)
Only the afferent limb of the light reflex is affected (i.e. sensory perception of light)
Efferent limb normal, i.e. normal pupillary constriction in response to light
However, because one eye is perceiving less light relative to the other, when light is shone in that eye, there is pupillary dilation
what is RAPD due to
Asymmetrical retinal or optic nerve pathology
causes of an RAPD
Optic nerve disease
Multiple sclerosis (demyelinating disease)
Ischaemic optic neuropathy (e.g. due to giant cell arteritis)
Glaucoma
Optic nerve compression (e.g. idiopathic intracranial hypertension)
Retinal disease
Ischaemia – e.g. retinal artery occlusion, ischaemic retinal vein occlusion
Ocular ischaemic syndrome
Retinal detachment
how do media opacities cause RAPD
Media opacities include cataracts, vitreous haemorrhage, corneal opacities
Media opacities lead to a scattering of light on the retina, leading to unfocused/blurred images…
However TOTAL light intensity detected by retina is unaffected
Therefore in the absence of optic nerve or retinal pathology, media opacities (almost) NEVER lead to an RAPD
what is Horners syndrome and what is the Triad ie.e what would you expect
Disruption along the sympathetic chain
Classic triad of
Miosis – dilator pupillae affected
Partial ptosis – Muller’s muscle affected (but levator muscle still working)
Ipsilateral anhydrosis – inability to sweat
causes of horners
Preganglionic causes
Pancoast tumour – lung apex tumour
Neck lesions
central causes: Stroke
Tumour
Cervical spinal cord lesion
Postganglionic causes
Internal carotid artery dissection (PAINFUL)
Cavernous sinus lesion
what are the pharmacological tests caused Horners syndrome
10% cocaine eyedrops
Blocks reuptake of norepinephrine (sympathetic)
Normal pupil will dilate
If sympathetic pathway is disrupted – norepinephrine is not released anyway and therefore no effect seen
Therefore in Horner’s there is no dilation with cocaine drops
0.5% apraclonidine (alpha1 agonist – sympathetic)
Very dilute and has no effect on a normal pupil
In sympathetic lesions, the iris dilator muscles develop denervation hypersensitivity (i.e. they become extremely sensitive to whatever stimulation they can get in an effort to work normally)
Therefore in Horner’s there is pupil dilation with dilute apraclonidine drops
what is adies tonic pupil
Denervation of postganglionic parasympathetic supply to ciliary muscle and sphincter pupillae
May follow viral illness
May be inherited
Sluggish response to light, but better response to accommodation (light-near dissociation – another cause is Argyll-Robertson pupil)
Vermiform movement may be seen
Once contracted, the pupil is very slow to redilate (tonic)
differentials for a fixed dilated pupil
Denervation of postganglionic parasympathetic supply to ciliary muscle and sphincter pupillae
May follow viral illness
May be inherited
Sluggish response to light, but better response to accommodation (light-near dissociation – another cause is Argyll-Robertson pupil)
Vermiform movement may be seen
Once contracted, the pupil is very slow to redilate (tonic)
what are some systemic conditions with iris signs
uveal melanoma
Brushfield spots- associated with trisomy 21
coloboma - located in the inferior nasal quadrant
result of failed or incomplete closure of the choroidal fissure during development
kayser - fleshier ring - brown ring around theconeea
due to copper deposition in part of the cornea (descements membrane)
Wilsons disease - abnormal copper handling by the liver resulting in copper accumulation In the body
characteristics of bacterial conj
S.epidermidis, S.aureus, S.pneumoniae, H.influenzae, C.trachomatis
Red eye, FB sensation, stuck eyelids, often bilateral, itchy
Purulent discharge
Antibiotics as appropriate
characteristics of viral conj
Adenovirus (serovars 3, 4, and 7 – pharyngoconjunctival fever; serovars 8, 19, and 37 – epidemic keratoconjunctivitis), herpes simplex, poxvirus (molluscum)
Red itchy watery eye, often starts with one eye and then both
Watery discharge, oedema
Often conservative, avoid contact, aciclovir if herpes
characteristics of allergic conj
Seasonal (summer), perennial (throughout – dust mites…), atopic, vernal (esp in dry hot countries)
Red eye, itchy, may have other symptoms of atopy
Papillae, scarring of conjunctiva in advanced cases
Mast cell stabiliser, antihistamines, identify allergen and avoidance, steroids
what is vernal keratoconjuctivits
Recurrent bilateral immune-mediated disease
Affects young boys predominantly
Usually seasonal (worse in spring often)
Usually resolves in teenage years
VKC can be
Palpebral
Limbal
Mixed
May need immunomodulation – e.g. with steroids/ciclosporine
what would you see in limbal viral kertatoconjuctivis
horner- truants spots
what is atopic keratconjuctivits
Typically presents in adults
Often they have had a long hx of atopy
Some may have had VKC as children
Presents as a much more sever form of VKC
Usually perennial (i.e. year-round)
Corneal involvement can lead to blindness if untreated
what is a pingeglum
Actinic damage to conjunctiva
Often present on nasal limbus, but does NOT encroach on limbal/corneal surface
Rarely requires treatment, unless for cosmesis
If inflamed, short course of topical steroids usually sufficient
what is a pterigium
Fibrovascular subepithelial growth of degenerative bulbar conjunctival tissue
Cross limbus and encroaches onto cornea
(C.f pinguecula spares limbus)
No treatment if asymptomatic
If symptomatic excision
differences between scleritis and episcleritis
scleritis - very painful , deep vascular plexus , no blanching with phenelpherine ,
episceleritis - not usually painful, red (superficial vascular plexus) , blanches with phenylephrine
