visual system Flashcards
where is the lacrimal system located?
within the orbit, latero-superior to the globe
where are tears produced?
lacrimal gland
outline the path taken by tears
produced by lacrimal gland, drain through the two puncta, flow through superior and inferior canaliculi then gather in tear sac. exit tear sac via tear duct into nasal cavity
what are ‘puncta’ (lacrimal system)?
opening on medial lid margin
What are the three types of tear stimulus?
basal, reflex and emotional
What afferent nerves are associated with the lacrimal system?
cornea, trigeminal nerve - opthalmic division (V1)
what efferent nerves are associated with the lacrimal system?
parasympathetic
what neurotransmitter is used within the lacrimal system?
acetylcholine
what is a reflex tear?
increased tear production in response to ocular irritation
what is a basal tear?
produces tears at a constant level, even in the absence of irritation or stimulation
what is the name of the thin layer of fluid that constantly covers the cornea?
The tear film
outline the functions of the tear film
maintenance of a smooth cornea-to-air surface
Why is the smooth cornea-to-air surface important?
important to maintain clear vision, to remove debris during blinking and is a source of oxygen and nutrient supply to the anterior segment
What are the three layers of the tear film?
lipid layer, aqueous tear film, mucinous layer
what is the role of the lipid layer of the tear film?
protects the tear film from evaporation
how is the lipid layer of the tear film produced?
secreted by the Meibomian glands situated along the eyelid margins
What is the function of the aqueous tear film?
Delivers oxygen and nutrient to the surrounding tissue, contains factors against potentially harmful bacteria
Which layer of the tear film forms the bulk of the tear film?
aqueous tear film
what is the function of the mucinous layer of the tear film?
ensures that the tear film sticks to the eye surface, renders the surface of the eye ‘wettable’. mucin molecules act by binding water molecules to the hydrophobic corneal epithelial cell surface
Which layer in the tear film protects the tear film from rapid evaporation?
lipid layer
What is the conjunctiva?
thin, transparent tissue that covers the outer surface of the eye. begins
Where does the conjunctiva begin?
outer edge of cornea, covers the visible part of the eye and lines the inside of the eyelids.
How is the conjunctiva perfused?
is nourished by tiny blood vessels that are nearly invisible to the naked eye
The coat of the eye is composed of three layers, what are these layers called?
Sclera, choroid, retina
what is the function of the sclera?
responsible for protecting the eye,
and maintaining the shape of the eye.
what is the sclera?
outer fibrous opaque layer of the eye
what is the function of the choroid?
responsible for providing circulation to the eye,
and shielding out unwanted scattered light
what is the choroid?
middle pigmented layer of the coat of the eye
what is the retina?
innermost neurosensory layer of the coat of the eye
what is the function of the retina?
responsible for converting light into neurological impulses,
to be transmitted to the brain via the Optic Nerve.
Which layer of the coat of the eye has the highest water content?
sclera
What is the cornea?
the transparent, dome-shaped window covering the front of the eye
what property of the cornea allows it to provide 2/3 of the eyes focusing power?
is a powerful refracting surface
How much of the eyes focusing power can be attributed to the cornea?
2/3
What are the five layers of the cornea?
Epithelium, Bowmans membrane, stroma, descemets membrane, endothelium
What is the function of the endothelium layer of the cornea?
pumps fluid out of cornea and prevents corneal oedema
what is the name given to the vascular coat of eyeball that lies between the sclera and the retina?
the uvea
what is the Uvea?
Vascular coat of eyeball and lies between the sclera and retina.
What are the three parts of the Uvea?
iris, ciliary body and choroid
what is the consequence of a disease in one part of the uvea?
the layers of the uvea are intimately connected so a disease affecting one layer will affect all three layers though not necessarily to the same degree
What is the function of the Choroid?
provides blood supply and absorbs light rays
What is the function of the iris?
controls light levels inside the eye
What property of the iris allows it to constrict/ dilate the pupil size
embedded with tiny muscles
The human lens is responsible for ? of the refractive power of the eye.
1/3
outline the structure of the lens
It is composed of an outer acellular thin capsule,
encasing a core of regular elongated cell fibres.
What may happen to the human lens with age?
May lose transparency resulting in cataracts
What is the function of the human lens?
Transparency
Regular structure
Refractive Power
1/3 of the eye focusing power - higher refractive index than aqueous fluid and vitreous
Elasticity
What is the function of the retina?
Responsible for capturing the light rays that enter the eye, These light impulses are then sent to the brain for processing, via the optic nerve.
What is the retina?
the very thin layer of tissue that lines the inner part of the eye
Outline the function of the optic nerve
transmits electrical impulses from the retina to the brain
what name is given to the visible portion of the optic nerve?
optic disc
Where does the optic nerve connect to the eye?
connects to the back of the eye at the macula
How is the blind spot of the eye formed?
at the point where the optic nerve meets the retina there are no light sensitive cells
Where is the macula located?
in the centre of the retina, temporal to the optic nerve
What is the macula and what is its function?
Small and highly sensitive part of the retina responsible for detailed central vision.
What name is given to the very centre of the macula and what does this structure allow for?
The fovea, allows us to appreciate detail and perform tasks that require central vision such as reading
What is the most sensitive part of the retina?
the fovea
Describe the distribution of rods and cones in the fovea
highest concentration of cones, but a low concentration of rods
What part of the eye is the only part to have a concentration of cones high enough to perceive in detail?
the fovea
What is the corresponding anatomic landmark for the physiological blind spot?
the optic disc
what is the canthus?
corner of the eye
what is the limbus?
border between cornea and sclera
what is central vision (fovea vision)?
the fovea has the highest concentration of cone receptors therefore central vision describes detail day vision and colour vision. used for reading and facial recognition
how is central vision assessed?
visual acuity assessment
Why is it important that the tear film delivers oxygen?
the cornea is avascular so must get its oxygen from the tear film
what does loss of foveal vision lead to?
poor visual acuity
why do the blood vessels of the conjunctiva become visible during conjunctivitis?
infection leads to inflammation leads to increased blood flow
What is meant by peripheral vision?
shape, movement, night vision
how is peripheral vision assessed?
visual field assessment
what can occur as a result of loss of peripheral vision ?
extensive loss of visual field, unable to navigate in environment
what are the two functions of the ciliary body?
produces aqueous humour and contains ciliary muscles
The cornea having a high water content is pathological or physiological?
pathological
Where can one find the highest concentration of Rod photoreceptors in the retina?
20-40 degrees away from fovea
what does the retina consist of?
an outer thin layer of Retinal Pigment Epithelium,
situated right in front of the Choroid, a middle layer
and an inner thicker layer called the Neuroretina.
what is contained within the outer layer of the retina?
photoreceptors (first order neurones) responsible for the detection of light
what is the function of the retinal pigment epithelium?
transports nutrient from the choroid to the photo-receptor cells,
and removes metabolic waste from the retina.
what is contained in the middle layer of the retina?
Bipolar Cells (2nd order neuron)
Local signal processing to improve contrast sensitivity, regulate sensitivity
What is contained within the inner layer (neuroretina)?
Retinal ganglion cells (3rd order neuron)
Transmission of signal from the eye to the brain
What are the two main classes of photoreceptors?
rods and cones
outline the structure and function of rod cells
Longer outer segment with photo-sensitive pigment
100 times more sensitive to light than cones
Slow response to light
Responsible for night vision (Scotopic Vision)
are there more rod cells or cone cells in the eye?
Cones (120 million in comparison to 6 million)
outline the structure and function of cone cells
Less sensitive to light, but faster response
Responsible for day light fine vision and colour vision (Photopic Vision)
where are photopigments synthesized?
the inner photo-receptor segment, then transported to the outer segment
what is the outer segment of photoreceptors composed of?
stacks of discs
what happens to the distal discs in the outer segment of photoreceptors?
they have deactivated photo-pigments which are shedded from the tips and phago-cytosed by the retinal epithelial cells
how are deactivated photopigments regenerated?
regenerated inside the retinal epithelial cells and then transported back onto photo-receptors
What are the three types of photoreceptor and what colours do they capture?
S-cones: blue, M-cones: green, L-cones: red
Are rods specific for colour?
Roads are used for night vision and spatial recognition and are not really sensitive to any particular colour
What is the most common form of colour blindness?
Deuteranomoly also known as daltonism
What is deuteranomoly?
Not completely colour blind but don’t perceive the colour red
What term describes full colour blindness?
Achromatopsia
As light goes from one medium to another, what happens (refraction)?
The velocity changes, the path changes
What exactly happens when light reaches a new medium?
Some of the light reflects off the boundary and some of the light refracts through the boundary
What are the two basic types of lenses?
Convex: converging lens that takes light rays and brings them to a point.
Concave: diverging lens takes light rays and spreads them outwards
What is the difference between emmetropia and ametropia?
Emmetropia= adequate correlation between axial length and refractive power. Parallel light rays fall on the retina
Ametropia = refractive error caused by a mismatch between axial length and refractive power meaning the light rays do not fall on the retina
What are the four types of ametropia?
Myopia, hyperopia, astigmatism, presbyopia
What is myopia?
Near-sightedness. Parallel rays converge at a focal point anterior to the retina
what is the eitiology of myopia?
Not clear, genetic factor
What are the causes of myopia?
Excessive long globe (axial myopia) or excessive refractive power (refractive myopia)
Which is the most common type of myopia: axial or refractive?
Axial
What are the symptoms associated with myopia?
Blurred distance vision, headaches, squinting in an attempt to improve uni or reacted visual acuity when gazing into the distance
What are the three treatment options for myopia?
Correction with diverging lenses, correction with contact lens, correction by removing the lens to reduce the refractive power of the eye
What is hyperopia?
Parallel rays converge at a focal point posterior to the retina
What is the etiology of hyperopia?
Not clear, inherited causes
What are the causes of hyperopia?
Excessive short globe (axial hyperopia) or insufficient refractive power (refractive hyperopia)
Is axial hyperopia or refractive hyperopia more common?
Axial hyperopia
What are the symptoms associated with hyperopia?
visual acuity at near tends to blur relatively early
•nature of blur is vary from inability to read fine print to near vision is clear but suddenly and intermittently blur
•blurred vision is more noticeable if person is tired , printing is weak or light inadequate
•asthenopic symptoms : eyepain, headache in frontal region, burning sensation in the eyes, blepharoconjunctivitis
•Amblyopia – uncorrected hyperopia > 5D
What are the treatment options for hyperopia?
Correction with converging lenses, correction with converging lenses + cataract extraction, correction with contact lens, correction with intraocular lens
What is astigmatism?
Parallel rays come to focus in 2 focal lines rather than a single focal point
What is the etiology of astigmatism?
Hereditary
What is the cause of astigmatism?
Refractive media is not spherical so refract differently along one meridian than along meridian perpendicular to it
What are the symptoms associated with astigmatism?
Headache and eye pain, blurred vision, distortion of vision, head tilting and turning
What are the treatment options for a regular vs an irregular stigmatism?
Regular astigmatism : cylinder lenses with or without spherical lenses (convex or concave), Sx
Irregular astigmatism : rigid cylinder lenses, surgery
What is the near response triad?
Adaptation for Near Vision
Near Response Triad
•Pupillary Miosis (Sphincter Pupillae) to increase depth of field
•Convergence (medial recti from both eyes) to align both eyes towards a near object
•Accommodation (Circular Ciliary Muscle) to increase the refractive power of lens for near vision
What is presbyopia?
Naturally occurring loss of accommodation (focus for near objects)
Onset from age 40 years
Distant vision intact
How is presbyopia treated?
Corrected by reading glasses - convex lenses to increase refractive power of eye
What are the disadvantages and complications associated with contact lenses?
Careful daily cleaning and disinfection, expense.
Complications = infectious keratitis, giant papillary conjunctivitis, corneal vascularisation, severe chronic conjunctivitis
What are intraocular lenses?
Replacement of cataract crystalline lens, give best optical correction for aphakia, avoid significant magnification and distortion caused by spectacle lenses
Which statement is false for Myopia?
•A) May be associated with large globe
•B) Light ray converges behind the retina
•C) May be associated with increased corneal curvature
•D) Unable to see objects clearly at distance without glasses or other optical correction
B: light ray converges behind the retina
In accommodation, which one of the following events does not take place?
•A) Relaxation of Circular Ciliary Muscle
•B) Relaxation of Zonules
•C) Thickening of Lens
•D) Increase of Lens Refractive Power
•A) Relaxation of Circular Ciliary Muscle
where does the visual pathway transmit signals to and from?
From the eye to the visual cortex
What are the seven visual pathway landmarks?
Eye
•Optic Nerve – Ganglion Nerve Fibres
•Optic Chiasm – Half of the nerve fibres cross here
•Optic Tract – Ganglion nerve fibres exit as optic tract
•Lateral Geniculate Nucleus – Ganglion nerve fibres synapse at Lateral Geniculate Nucleus
•Optic Radiation – 4th order neuron
•Primary Visual Cortex or Striate Cortes – within the Occipital Lobe
What are the first order neurons in the visual pathway retina?
Rod and cone retinal photoreceptors
What are the second order neurons in the visual pathway retina?
Retinal bipolar cells
What are the third order neurons in the visual pathway retina?
Retinal ganglion cells
Which cranial nerve is associated with the visual pathway?
The optic nerve (CN2)
Where does dessucation of the optic nerve pathway happen?
53% of ganglion fibres cross at the midline
Lesions anterior to the optic chiasma affect what?
Visual field in one eye only
Lesions posterior to optic chiasma affect what?
Affect visual field in both eyes
Crossed fibres originate from ______ and are responsible for what?
Originate from nasal retina and responsible for temporal visual field
Uncrossed fibres originate from _____ and are responsible for what?
Originate from temporal visual retina and responsible for nasal visual field
A lesion at the optic chiasma damages which ganglion fibres and causes what kind of optic deficit?
Damages crossed ganglion fibres from nasal retina in both eyes resulting in temporal field deficit in both eyes (bitemporal hemianopia)
A right sided lesion posterior to the optic chiasma causes what type of visual field defect?
Left homonymous hemianopia in both eyes
A left sided lesion posterior to the optic chiasma results in what type of visual field defect?
Right homonymous hemianopia in both eyes
What is an example of a lesion that would cause unilateral field loss in left eye ?
Left optic nerve compression
what is an example of a lesion that would result in a bitemporal hemianopia?
Chiasmal compression from pituitary tumour
What is an example of a lesion that will result in a right homonymous hemianopia ?
Left cerebrovascular event
What are the six disorders of the visual pathway?
Monocular blindness, bitemporal hemianopia, nasal hemianopia, homonymous hemianopia, quadrant-anoxia, macular sparing
What is monocular blindness?
Loss of visual field in one eye
What is right nasal hemianopia?
Loss of nasal visual field in right eye
What is a homonymous hemianopia?
Loss of either right or left half of visual field in each eye
What is quadrant-opia?
Loss of 1/4 quadrants of vision in both eyes
What is macular sparing?
Macular sparing is visual field loss that preserves vision in the center of the visual field,
What causes homonymous hemianopia with macular sparing?
Damage to Primary Visual Cortex
•Often due to stroke
•Leads to Contralateral Homonymous Hemianopia with Macula Sparing
•Area representing the Macula receives dual blood supply from Posterior Cerebral Arteries from both sides
What is the pupillary function?
Regulates light input to the eye
What is the affect of pupil constriction?
decreases spherical aberrations and glare
•increases depth of field – see Near Response Triad from Previous Lecture
•reduces bleaching of photo-pigments
•Pupillary constriction mediated by parasymapthetic nerve (within CN III)
What is the effect of pupil dilation?
increases light sensitivity in the dark by allowing more light into the eye
•pupillary dilatation mediated by sympathetic nerve
Outline the afferent pathway of the pupillary reflex
Rod and Cone Photoreceptors synapsing on Bipolar Cells synapsing on Retinal Ganglion Cells
•Pupil-specific ganglion cells exits at posterior third of optic tract before entering the Lateral Geniculate Nucleus
•Afferent (incoming) pathway from each eye synapses on Edinger-Westphal Nuclei on both sides in the brainstem
Outline the efferent pathway of the pupillary reflex
Edinger-Westphal Nucleus -> Oculomotor Nerve Efferent ->
•Synapses at Ciliary ganglion ->
•Short Posterior Ciliary Nerve -> Pupillary Sphincter
what is the difference between the direct vs consensual light reflex?
Direct = constriction of pupil of the light stimulated eye, consensual light reflex = constriction of pupil of the other eye
What is the neurological basis of the pupillary reflex?
Afferent pathway on either side alone will stimulate efferent (outgoing) pathway on both sides
What is the effect of a right afferent defect? e.g. damage to optic nerve
No pupil constriction in both eyes when right eye is stimulated with light
•Normal pupil constriction in both eyes when left eye is stimulated with light
What is the affect of a right efferent defect on pupil constriction?
•No right pupil constriction whether right or left eye is stimulated with light
•Left pupil constricts whether right or left eye is stimulated with light
What is the difference between a unilateral afferent defect and a unilateral
Unilateral Afferent Defect
•Difference response pending on which eye is stimulated
Unilateral Efferent Defect
•Same unequal response between left and right eye irrespective which eye is stimulated
In the swinging torch test both pupils _______ when light swings to undamaged side and both pupils _________ when light swings to damaged side
Both Pupils constrict when light swings to undamaged side
•Both Pupils paradoxically dilate when light swings to the damaged side
Eye movement is facilitated by what muscles and nerves?
Facilitated by the six extraocular muscles innervated by the three cranial nerves (III, IV and VI)
What does the term ‘duction’ mean?
Eye movement in one eye
What does the term ‘version’ mean?
Simultaneous movement of both eyes in the same direction
what does the term ‘vergence’ mean?
Simultaneous movement of both eyes in the opposite direction
What does the term ‘convergence’ mean
Simultaneous addiction (inward) movement in both eyes when viewing a near object
What two terms are used to decide the speed of eye movement?
Saccade= short fast burst
smooth pursuit = sustain slow movement
What are the four types of saccade?
Reflexive saccade to external stimuli, scanning saccade, predictive saccade to track objects, memory-guided saccade
What drives the movement of smooth pursuit?
Driven by motion of a moving target across the retina
How many extraocular muscles are there?
Six
What is the function of the six extraocular muscles?
Attach eyeball to orbit
what two types of movement do the extraocular muscles allow for?
Straight and rotary
What are the names of the four straight extraocular muscles?
1.Superior rectus
2.Inferior rectus
3.Lateral rectus
4.Medial rectus
Where does the superior recuts muscle attach to the eye?
At 12 o’clock
What is the action of the superior rectus muscle?
Moves the eye up
Where does the inferior rectus muscle attach to the eye?
6 o’clock
What is the action of the inferior rectus?
Moves the eye down
What is the other name given to the lateral rectus?
External rectus
Where does the lateral rectus attach to the eye?
Attaches on temporal side of the eye
What is the function of the lateral rectus?
Moves the eye toward the outside of the head
What is the other name given to the medial rectus?
Internal rectus
Where does the medial rectus attach to the eye?
Attached on the nasal side of the eye
What is the action of the medial rectus?
Moves eye toward the middle of the head
Where does the superior oblique muscle attach to the eye?
High on temporal side of the eye
What muscle passes under the superior rectus muscle to attach high on the temporal side of the eye?
Superior oblique muscle
What is the action of the superior oblique muscle?
Moves the eye in a diagonal pattern down and out
The superior oblique extraocular muscle travels through which structure?
The trochlea
Where does the inferior oblique muscle attach to the eye?
Low on the nasal side of the eye
Which extraocular muscle passes over the inferior rectus muscle?
Inferior oblique muscle
What is the action of the inferior oblique muscle?
Moves the eye in a diagonal pattern - up and out
Which cranial nerve is responsible for innervation of the superior rectus muscle?
The superior branch of the oculomotor nerve
Which cranial nerve innervates the levator palpebrae superiporis muscle?
The superior branch of the oculomotor nerve
What is the action of the levator palpebrae superioris muscle?
Raises eyelid
Which cranial nerve innervates the inferior rectus muscle?
Inferior branch of oculomotor nerve
Which cranial nerve innervates the medial rectus muscle?
Inferior branch of the oculomotor nerve
What is the action of the medial rectus muscle?
Adducts eye
Which cranial nerve innervates the inferior oblique muscle?
Inferior branch of oculomotor nerve
What is the action on the eye of the parasympathetic nerve of the inferior branch of the oculomotor nerve?
Constriction of the muscle
Which cranial nerve innervates the superior oblique muscle of the eye?
Trochlear
Which cranial nerve innervates the lateral rectus muscle of the eye?
Abducens (lateral rectus abducts the eye)
Which three cranial nerves are involved in the innervation of the extraocular muscles?
Oculomotor
Trochlear
Abducens
What does the term supraduction mean?
Elevation of one eye
What does the term supraversion mean?
Elevation of both eyes
What does the term infraduction mean?
Depression of one eye
What does the term infraversion mean?
Depression of both eyes
What term describes the movement of both eyes to the right?
Dextroversion
In dextroversion, what is happening to each eye?
Right abduction
Left adduction
What does the term levoversion describe?
The movement of both eyes to the left
In levoversion, what is happening to each eye?
Right adduction
Left abduction
In third nerve palsy, what is the affect on the eye?
The affected eye moves down and abducts
Why do patients with third nerve palsy have a droopy eyelid?
Loss of elevator palpebrae superioris
Why do patients with third nerve palsy look down and out in their affected eye?
Down as Unopposed superior oblique innervated by fourth nerve
Out as unopposed lateral rectus innervated by sixth nerve
What is the presentation of sixth nerve palsy?
Affected eye unable to abduct and deviates inwards
In sixth nerve palsy, what causes the affected eye to be unable to abduct and deviate inwards?
Unopposed medial rectus muscle innervated by oculomotor nerve
What is the affect of sixth nerve palsy on vision?
Double vision that worsens on gazing to the side of the affected eye
In describing eye movement what does the term torsion describe?
Rotation of eye around anterior-posterior axis of the eye
What does nystagmus describe?
Oscillatory eye movement
What does the term optokinetic nystagmus describe?
Smooth pursuit and fast phase reset saccade
What is the optokinetic nystagmus reflex useful for testing?
Visual acuity in pre-verbal children by observing the presence of nystagmus movement in response to moving grating patterns of various spatial frequencies
What does the presence of optokinetic nystagmus in response to moving grating signify?
that the subject has sufficient visual acuity to perceive the grating pattern
58-year-old gentleman has presented to the eye casualty department complaining of inability to open his right eye. You lift his lid up and find that the eye is deviated down and out. He complains of double vision when you do this. On H-test he cannot elevate or adduct his right eye. His left eye has normal movements in all directions. His right pupil is also dilated in comparison to the left. He has an abnormal direct light response in the right eye, but a normal consensual light response in the left eye.
Which cranial nerve may account for this presentation?
Right oculomotor nerve
58-year-old gentleman has presented to the eye casualty department complaining of inability to open his right eye. You lift his lid up and find that the eye is deviated down and out. He complains of double vision when you do this. On H-test he cannot elevate or adduct his right eye. His left eye has normal movements in all directions. His right pupil is also dilated in comparison to the left. He has an abnormal direct light response in the right eye, but a normal consensual light response in the left eye.
What pathologies may cause this?
Micro vascular disease due to HTN
Diabetes mellitus
Surgical lesions in the form of a posterior communicating artery aneurysm
A posterior communicating artery aneurysm to the oculomotor nerve typically compresses which portion of the nerve fibres?
Outer portion which is where the parasympathetic nerves run
In relation to the circle of Willis, where does CN3 run?
In between the posterior cerebral and superior cerebellar artery
58-year-old gentleman has presented to the eye casualty department complaining of inability to open his right eye. You lift his lid up and find that the eye is deviated down and out. He complains of double vision when you do this. On H-test he cannot elevate or adduct his right eye. His left eye has normal movements in all directions. His right pupil is also dilated in comparison to the left. He has an abnormal direct light response in the right eye, but a normal consensual light response in the left eye.
What treatments may be offered for this presentation?
Treatment will depend on the cause of the cranial nerve palsy. In this case, the cause is likely to be a posterior communicating artery aneurysm. Hence a neurosurgical opinion is advised, and assessment of the aneurysm is needed (this may involve clipping).
For patients with microvascular disease, they will need better metabolic control of their condition.
28-year old lady, tonically dilated pupil in the right eye. Upon shining light into the right eye, the pupil is slow to react compared to the left. The left eye reacts when light is shone into the right eye. Addition of pilocarpine drops, however, causes rapid constriction of the right pupil. On further examination, she has an absent knee-jerk reflex and impaired sweating. What is the site of damage causing the pupil defect?
Damage to parasympathetic ciliary ganglion which is involved in the pupillary-light reflex. Parasympathetic fibres travel with CNIII (oculomotor) to synapse at the ciliary ganglion before innervating the iris and ciliary body.
28-year old lady, tonically dilated pupil in the right eye. Upon shining light into the right eye, the pupil is slow to react compared to the left. The left eye reacts when light is shone into the right eye. Addition of pilocarpine drops, however, causes rapid constriction of the right pupil. On further examination, she has an absent knee-jerk reflex and impaired sweating. What is the site of damage causing the absent reflex and impaired sweating?
Dorsal root ganglia of the spinal cord
28-year old lady, tonically dilated pupil in the right eye. Upon shining light into the right eye, the pupil is slow to react compared to the left. The left eye reacts when light is shone into the right eye. Addition of pilocarpine drops, however, causes rapid constriction of the right pupil. On further examination, she has an absent knee-jerk reflex and impaired sweating. How does pilocarpine work?
Pilocarpine is a muscarinic receptor agonist that acts on M3 receptors in the iris sphincter muscle. This results in contraction of the muscle (miosis) and constriction of the pupil. These are independent of the parasympathetic tract, hence the response.
What is pilocarpine?
Pilocarpine is a muscarinic receptor agonist that acts on M3 receptors in the iris sphincter muscle. This results in contraction of the muscle (miosis) and constriction of the pupil.
28-year old lady, tonically dilated pupil in the right eye. Upon shining light into the right eye, the pupil is slow to react compared to the left. The left eye reacts when light is shone into the right eye. Addition of pilocarpine drops, however, causes rapid constriction of the right pupil. On further examination, she has an absent knee-jerk reflex and impaired sweating. What term can be used to describe this defect?
An Adie’s pupil is described as having light-near dissociation. This is due to reinnervation that takes place as a result of damage to the ciliary ganglion. This process involves up regulation of postsynaptic receptors but the reinnervation is aberrant, causing fibres directed for the ciliary body to end up targeting the iris. As a result, the patient develops more meiosis with near accommodation than they do to light.
