Ophthalmology
PUPIL
- Allows light to enter eye lens retina optic nerve
- Controls amount of light entering eye
o Contraction = miosis
o Dilation = mydriasis
- Autonomic control
IRIS
- Contractile (controls size of pupil)
- Mainly smooth muscle
o Circular group: sphincter pupillae
o Radial group: dilator pupillae
MIOSIS – CONTRACTION
PNS control
Neuron pathway:
Edinger-Westphal nucleus (in midbrain near CNIII nucleus) orbit (enters with CNIII)
ciliary ganglion synapses at CG short ciliary nerves sphincter pupillae muscarinic
receptors stimulated by Ach
Rule of the pupil – down and out presentation
- Lesion of CNIII = eye down and out + pupil dilation
- Pupil dilation: Parasympathetic nerves impacted
- PNS fibres run outside of CNIII so can be easily compressed
- No pupil dilation: Suggests ischemia of CNIII but sparing of superficial fibres to pupil
e.g diabetes
MYDRIASIS – DILATION
SNS control
Neuron pathway
Hypothalamus spinal cord superior cervical ganglion dilator pupillae stimulated by
NAd
Horner Syndrome
- Disruption of sympathetic chain to the face
- Causes miosis due to loss of SNS innervation
- Eyelid droop (ptosis) due to supply of superior tarsal muscle from SNS
- Absence of sweat on one side of the face (anhidrosis)
- Can cause anisocoria (difference in pupil size, large = abnormal)
, Causes:
- Apical lung tumour
- Aortic dissection
- Carotid dissection
- PICA stroke (lateral medullary syndrome)
PUPILLARY REFLEXES
1. Light
Shine light in one eye both eyes should constrict
Light signals pretectal nucleus in the midbrain bilateral EW nucleus
Marcus Gunn Pupil
- Relative afferent pupillary defect
- Light shone in one eye produces less constriction
o Should constrict equally on both sides with light shone into either eye
- Diagnosed by the swinging light test
- Caused by a lesion in the afferent light reflex limb (problem sensing light)
o Optic neuritis (most common cause) inflammatory demyelinating disorder
common in multiple sclerosis, causes complete vision loss in one eye
2. Accommodation
- Changes optical power to focus on near objects
- Ciliary muscles change the shape of the lens
- Associated with miosis (constriction)
Accommodation Reflex
Convergence: eyes move medially to track an object
Accommodation: shape of lens changes and focal point is maintained on the retina
Miosis: pupil constricts to block the entry of divergent rays from the near object
Argyll Robertson Pupil (Prostitute’s Pupil)
- Strongly associates with tertiary neurosyphilis
- Bilaterally small pupils that don’t constrict in response to light
- Pupils will constrict with the accommodation reflex
o Involves the pretectal nucleus which is not a part of the accommodation
reflex but is involved in the light reflex
PUPIL
- Allows light to enter eye lens retina optic nerve
- Controls amount of light entering eye
o Contraction = miosis
o Dilation = mydriasis
- Autonomic control
IRIS
- Contractile (controls size of pupil)
- Mainly smooth muscle
o Circular group: sphincter pupillae
o Radial group: dilator pupillae
MIOSIS – CONTRACTION
PNS control
Neuron pathway:
Edinger-Westphal nucleus (in midbrain near CNIII nucleus) orbit (enters with CNIII)
ciliary ganglion synapses at CG short ciliary nerves sphincter pupillae muscarinic
receptors stimulated by Ach
Rule of the pupil – down and out presentation
- Lesion of CNIII = eye down and out + pupil dilation
- Pupil dilation: Parasympathetic nerves impacted
- PNS fibres run outside of CNIII so can be easily compressed
- No pupil dilation: Suggests ischemia of CNIII but sparing of superficial fibres to pupil
e.g diabetes
MYDRIASIS – DILATION
SNS control
Neuron pathway
Hypothalamus spinal cord superior cervical ganglion dilator pupillae stimulated by
NAd
Horner Syndrome
- Disruption of sympathetic chain to the face
- Causes miosis due to loss of SNS innervation
- Eyelid droop (ptosis) due to supply of superior tarsal muscle from SNS
- Absence of sweat on one side of the face (anhidrosis)
- Can cause anisocoria (difference in pupil size, large = abnormal)
, Causes:
- Apical lung tumour
- Aortic dissection
- Carotid dissection
- PICA stroke (lateral medullary syndrome)
PUPILLARY REFLEXES
1. Light
Shine light in one eye both eyes should constrict
Light signals pretectal nucleus in the midbrain bilateral EW nucleus
Marcus Gunn Pupil
- Relative afferent pupillary defect
- Light shone in one eye produces less constriction
o Should constrict equally on both sides with light shone into either eye
- Diagnosed by the swinging light test
- Caused by a lesion in the afferent light reflex limb (problem sensing light)
o Optic neuritis (most common cause) inflammatory demyelinating disorder
common in multiple sclerosis, causes complete vision loss in one eye
2. Accommodation
- Changes optical power to focus on near objects
- Ciliary muscles change the shape of the lens
- Associated with miosis (constriction)
Accommodation Reflex
Convergence: eyes move medially to track an object
Accommodation: shape of lens changes and focal point is maintained on the retina
Miosis: pupil constricts to block the entry of divergent rays from the near object
Argyll Robertson Pupil (Prostitute’s Pupil)
- Strongly associates with tertiary neurosyphilis
- Bilaterally small pupils that don’t constrict in response to light
- Pupils will constrict with the accommodation reflex
o Involves the pretectal nucleus which is not a part of the accommodation
reflex but is involved in the light reflex
