lecture 25 - vision Flashcards
What is the term for the ‘white of the eye’?
Sclera
What muscle controls lens shape for accomodation?
Ciliary muscle
What structure in the eye defines pupil diameter?
Iris
What is the function of the ciliary body?
Secretes aqueous humor
What fluid is found within the anterior chamber of the eye?
Aqueous humor
What fluid is found within the posterior chamber of the eye?
vitreous humor
Why does the retina need a good blood supply?
Relies on oxidative metabolism, so relies on a good supply of oxygen and gluocse
What is the function of the choroid of the eye?
Contains lots of blood vessels that provides blood to the deep retina
Where is the location of the deep retina?
At the back of the eye, on the outer part of the eyeball, but is deep to the light source that comes from the anterior
What condition arises when there is damage from raised intraocular pressure?
Glaucoma
What are the findings on ophthalmoscopy in diabetes?
Increased vascularisation
What are the findings on ophthalmoscopy in papilloedema?
Optic disc bulges
What are the 6 extraocular muscles that control eye movement?
Superior oblique, Inferior oblique, Lateral rectus, medial rectus, superior rectus, inferior rectus
Which cranial nerves control eye movement?
Oculomotor (III), trochelar (IV), abducens (VI)
Which extraocular muscles are controlled by the oculomotor nerve?
Superior rectus, Inferior rectus, medial rectus, inferior oblique
Which extraocular muscles are controlled by the trochlear nerve?
Superior oblique
Which extraocular muscles are controlled by the abducens nerve?
Lateral rectus
What is the relationship between the contraction state of the ciliary muscles and the shape of the lens?
Contracted muscles = lower tension and more rounded lens
Relaxed muscles = higher tension and more flattened lens
What is the action of the ciliary muscles during near vision?
They contract to relax the zonular fibres and relax the lens so it becomes thicker and more spherical
What is the pathophysiology of glaucoma?
There is build of aqueous humor in the front of the eye due to excessive production or blocked drainage. This increases pressure which damages eye blood vessels and the optic nerve.
What are the steps in the pathway of visual information from the retina to the optic nerve?
Photoreceptor cells (rods/cones), bipolar cells, ganglion cells, axons of ganglion cells converge to form optic nerve
What are the basic steps in the pathway of visual information from the optic nerve to the visual cortex?
optic nerve, optic chiasm, optic tract, lateral geniculate body, optic raditation
What visual field defect occurs when there is a single optic nerve lesion?
mononuclear blindness (loss of vision in the ispilateral eye)
What visual field defect occurs when there is an optic chiasm lesion?
Bitemporal hemianopia
What type of visual field defect will often arise in patients with a pituitary tumor?
Bitemporal hemianopia (loss of peripheral vision) due to pressure on the optic chiasm
What visual field defect occurs when there is a lesion to the optic tract?
Homonymous hemianopia (loss of vision on half of each each eye on the side opposite to the lesion)
What visual field defect occurs when there is a lesion affecting Meyer’s loop?
Upper quadrantic anopia
What visual field defect occurs when there is a partial lesion of the optic radiation?
Lower quadrantic anopia
What visual field defect occurs when there is a PCA infarct?
Homoonymous hemianopia with macular sparing (vision in the centre of each eye is intact)
What is the purpose of the retino-hypothalamic tract?
Convey information about light for circadian rhythm, body clock, sleep-wake cycles
What is the function of the superior collicullus-visual pathway?
Role in unconscious automatic control of orientation to visual stimuli
What are the 2 types of light-sensitive receptors in the retina?
Cones, rods
What is the function of cones in the eye?
Colour vision - each cone can absorb different wavelengths of light
What is the function of rods in the retina?
Grey-scale vision - vision in low light levels
Which type of light receptor cell operates in higher light intensity?
Cones - can only see colour at high light density
Which type of light receptor cell is more sensitive?
Rods
Where in the retina is the highest density of cones?
Fovea
How are cones adapted to see different wavelengths of light?
There are 3 different types of cones, with 3 different cone opsins that have sensitivity to red, blue and green
