Eye Flashcards
Myopia
- Short sighted
- Light focuses at a point before the retina
- Connected with concave lens
- Larger eye
Hypermetropia
- Long sighted
- Light focuses at a point beyond the retina
- Smaller eye
- Corrected with a convex lens
Describe the properties of rods
- 120 million in the retina
- High convergence to ganglion cells
- Very light sensitive
- Widespread in the retina
- Broad spectral sensitivity
- One type - vision in greyscale
Describe the properties of cones
- 6 million in the retina
- Low convergence to ganglion cells
- 3 types: blue, red, green
- 1/30th sensitivity of rods
- concentrated in the macula
- narrow spectral sensitivity
Lesion of right optic nerve
Right eye vision loss
Lesion of the optic chiasm
Bitemporal hemianopia
Lesion of right lateral geniculate nucleus
Left hemianopia
Lesion of the parietal lobe
Inferior quadrantinopia
Lesion to the temporal lobe
superior quadrantinopia
Lesion of the right primary visual cortex
Left hemianopia
What is Meyer’s loop?
- Inferior optic radiation that goes through the temporal lobe
- Information from the upper part of the visual field
What are the two streams of vision?
- Dorsal stream: ‘where’ , parietal lobe, allows us to see one thing among many
- Ventral stream: ‘what’, temporal lobe, helps us to recognise objects/faces etc.
What is the role of the occipital lobe in vision
Primary vision cortex
What is the role of the temporal lobe in vision?
- Ventral stream (What pathway)
* Hosts our visual library
What is the role of the parietal lobe in vision?
- Dorsal stream
* Serves function of attention
What is the role of the frontal lobe in vision?
• Execution of a plan
Peri-ventricular leucomalacia
- Holes in the Brian caused by death of cells around the ventricles
- Ischaemic damage
What is simultanagnosia?
- Difficulty finding one thing amongst many
* Bilateral parietal brain damage from cerebrovascular accident
What is achromatopsia?
- Unable to see colour - everything is grey
* Bilateral anterior occipital brain damage
What is visual acuity
the ability of the visual system to resolve a gap between two objects- spatial resolution
How can you test visual acuity?
- Snellen chart
- 6 metre distance
- Cover one eye, read then switch eyes
- Result recorded as 6/x
What is driving vision
• Better than or equal to 6/12
Pupil pathway
• Light -> retina
• Optic nerve
Efferent: Oculomotor
What is RAPD
- Relative afferent pupillary defect
- Pupils respond different to stimuli shone in one eye at a time due to unilateral or asymmetrical disease of retina or optic nerve
What are the causes of RAPD?
Unilateral or assymetrical disease of the retina or optic nerve: • Optic neuritis • Anterior ischaemic optic neuropathy • Trauma, pressing on the optic nerve • Glaucoma - most common
What can cause the appearance of a swollen disc?
• Pseudo swelling: - small disc - calcium deposits 'drusen' • Genuine swelling: - optic neuritis (VA reduced: associated with MS) - Idiopathic intracranial hypertension - hydrocephalus
Nerve supply to the eye muscles
- Most = oculomotor
- Superior oblique: glossopharyngeal
- Lateral rectus = accessory
3rd Cranial nerve palsy
- Vertical diplopia
- Eye down and out
- Dilated pupil and ptosis
- Can be associated with aneurysm - needs urgent brain scanning and angiogram
4th cranial nerve palsy
- Oblique diplopia
- Head tilt away from the side of the lesion
- Diplopia worse away from the side of the palsy if unilateral
- Common after a head injury
- If bilateral, may be congenital
6th Cranial nerve palsy
- Horizontal diplopia
- Worse in far distance
- Worse towards side of palsy if unilateral
- If bilateral, concerned about raised ICP
Which cranial nerve palsy is a medical emergency?
3rd Cranial nerve - oculomotor
• Associated with aneurysm
