deck_3165729 Flashcards
Describe the path of the light reflex
Light activates optic nerve and AP passes alongAxons pass though the LGN and some decussateAxons synapse at the pretectal nucleusAP passes to Edinger-Westphal nucleus and stimulates CN3 fibres of ciliary ganglionStimulate constrictor pupillae
Describe the corneal reflex pathway
Closes eye in response to stimulation of the cornea- AP generated when cornea is stimulated (nasociliary branch)- Stimulates temporal and zygomatic branches of the facial nerve, causing constriction of orbicularis oculi.
Define the vestibulo-ocular reflex
Reflex eye movement that stabilises images on the retina during head movement by producing eye movement in the direction opposite to the head movement
Describe Horner’s Syndrome
Lack of sympathetic innervation to the ipsilateral side of the head. MiosisAnhydrosisFlushingPtosis
Describe retinal detachment
Blow to the eye can cause the layers of the retina to become separated. Pigment cell layer is not firmly attached to the neural layer (it is however firmly attached to the choroid)- complain of flashes of light/speck floating in their vision
Define exopthalmos
Protrusion of the eye- eyelids part more than normal- sclera are visible all around the cornea and the iris.
Causes of exopthalmos
unilateral = aneurysm or haematomabilateral = Grave’s disease
Why do you get papilloedema with raised ICP?
Optic nerve is surrounded my meninges, CSF in subarachnoid spaceIncrease CSF pressure can compress the optic nerve, blood vessels supplying retina which can lead to blindness. Papilloedema is because the vein is occluded before the artery, leading to the oedema of the retina.
Give some different types of strabismus
Extropia = eye turned outEsotropia = eye turned inHypertropia = one eye higher than the otherHypotropia = one eye lower than the other
Where do you find the lateral geniculate nucleus?
Thalamus
Describe the primary visual cortex
Found posteriorly in the occipital lobe2mm thickMade up of 6 layersContains prominent strips of white matter - myelinated axons
Define the focal length of the eye
The distance from the lens to the point of focus
Describe how the strength of a lens is measured
Dioptric strength- the reciprocal of its focal length in metresstrength = 1 / focal length (metres)
What is normal intraocular pressure?
20-25mmHg
How is the intraocular pressure maintained?
The aqueous humour has a greater osmotic strength than the blood, therefore fluid is drawn into the ciliary body. The fluid can escape via the canal of Schlemm
What defines why someone is short-sighted?
The strength of their eye lens system is too strong- axial length of the eye is too long - focus lies in front of the retina
What defines why someone is long sighted?
The strength of their eye lens system is too weak- too short axial length- focus lies behind the retina
Define presbyopia
Age related degeneration of the eyesight- get progressively more long-sighted with age
Define myopic
Short-sighted
Define hyperopic
Long-sighted
Describe accommodation of the eye
The ciliary muscle contracts in order to increase the convexity of the lens, which will add to the dioptric strength of the eye
Why does accommodation occur?
As an object approaches the eyes, the light rays will diverge. The focal point moves backwards as a result and the eye needs to accommodate, by adding to the dioptric strength so that the object can remain in focus.
Define near point
The shortest distance in front of the eye where an object can be maintained in focus.
Define visual acuity
The ability to distinguish between two separate sources of light.
What does visual acuity depend on?
Density of light receptorsSize of receptive field of the receptors in the retina.
Define a cataract
An opacity in the lens, so that light cannot pass through
Give some causes of cataracts
SenilityTraumaMetabolic disturbance e.g. diabetes Congenital
Define scotoma
Pathological blind area
