Extraocular muscles
Extraocular adduction muscles
Superior rectus
Medial rectus
Inferior rectus
Extraocular abduction muscles
Inferior oblique
Lateral rectus
Superior oblique
Extraocular muscle innervation
CN III (oculomotor)
EXCEPT
- lateral rectus: CN VI
- superior oblique: CN IV
Trochlear nerve palsy
CN IV: superomedial deviation
Abducens nerve palsy
CN VI: medial deviation
Oculomotor nerve palsy
CN III: ptosis and deviation
- down and out
Nerve of vision
CN II (optic)
Sensation and lacrimation innervation
Trigeminal nerve (CN V)
3 layers of the eyeball
- Fibrous:
* sclera
- provides shape and resistance
- tough and opaque
* cornea
- transparent - Vascular: Uvea
* choroid - lines most of the sclera
* ciliary body - provides attachment and control for lend
* iris - contractile diaphragm
* sphincter pupillae - circular fibers - parasympathetic control –> constriction
* dilator pupillae - radial fibers - sympathetic control –> dilation - Inner
* retina
- optic part: light sensitive
- nonvisual retina: no light sensitvity
- optic disc: optic nerve and vessels enter the eye, blind spot
- macula of the retina: visual acuity; fovea centralis
Path of light
- Cornea: clear extension of the sclera
- Anterior chamber: filled with watery fluid
- Pupil: dilates and constricts
- Lens: accommodates distances of image
- Vitreous humor: gel, provides support
- Retina: where light is transduced
The photoreceptor cells are embedded in what layer of the retina?
pigmented layer
Rods and cones
Rods: activated by low intensity light; one type
Cones: activated by high intensity light; three types
- lack of cones = color blindness
Colorblindness
Cones are sensitive to only one range of light
- red - blue - yellow-green
Red-green deficiency: most common
Blue-yellow deficiency: more rare
What happens after light enters the eyeball and travels through the lens to the retina?
Light stimulates the photoreceptors.
First order neurons transmit signals to second order neurons.
Photoreceptors
light energy transduced into electrical energy
1st order neurons
bipolar cells
2nd order neurons
ganglion cells which form the optic nerve
- alpha
- beta
Light stimulates a sensory signal which travels the following path:
optic nerve
optic chiasm
optic tract
LGN of thalamus
Optic radiations
Visual cortex
Visual pathways//visual fields
The R visual field is transmitted to L cerebral hemisphere.
Lower visual fields are carried in upper optic radiations.
Therefore vision loss of lower field of vision corresponds to damage of upper optic radiations.
Visual field deficits
- Optic nerve lesion: monocular vision loss
- Chiasm lesion: bitemporal hemianopsia
- Optic tract lesion: contralateral homonymous hemianopsia
- Optic radiation lesion: contralateral, upper or lower
- visual cortical lesions: depends on location of injury
ADD PIC
Secondary: subconscious vision
Midbrain:
1. superior colliculus: saccadic eye movement
2. pretectal area: autonomic reflexes (dilation and constriction)
- hypothalamus: circadian rhythms
- reticular formation: arousal/vision
Pupillary light reflex - constriction
PSNS
Afferent: CN II (optic)
Efferent: CN III (oculomotor)
1. light –> optic nerve/ optic tract
2. pretectal midbrain –> bilateral Edinger-Westphal nucleus
3. bilateral ciliary ganglia –> constrictor muscles
Shine light in left eye, both should constrict
Pupillary light reflex - dilation
SNS
1. hypothalamus
2. spinal cord
3. superior cervical ganglia
4. internal carotid artery plexus
5. dilator muscles
