Physiology - Vision Flashcards
How would you describe the sclera and cornea?
Tough connective tissue continuous with the dura
What is the visible sclera and what is it covered by?
White of the eye
Covered with conjunctiva membrane
What is the cornea and its function?
Transparent
Responsible for 2/3 of eye total refraction
What is the function of the ciliary muscle?
Controls lens shape (accommodation for near visions)
What is the function of the iris?
Defines pupil diameter (light reflex)
What secretes acqueous humor?
Ciliary body
What is the difference between aqueous and vitreous humour?
Aqueous humour - water like, anterior chamber
Vitreous humour - jelly like, posterior chamber
What is the function of the choroid?
Blood supply for the receptor cell (deep) layer of the retina
Describe the supply of the retina.
Internal layer has retinal blood vessels (blood supply for middle and superficial layers of retina from central retinal artery, enters via optic disc)
Outer part of retina relies on choroid (receptor layer)
What is special about the fovea?
No blood vessels at fovea, relies on choroid for diffusion of oxygen and glucose (do not want BV to obstruct view since the fovea has the greatest visual acuity)
List some examples of disorders with typical retinal appearances.
Damaged from raised intraocular pressure (glaucoma) - pressure in front of eyeball
Increased vascularization in diabetes
Bulging of optic disc (papilloedema) in raised ICP (increased pressure behind eyeball)
What is the difference between conjugate and convergence gaze?
Conjugate gaze - eyes move together
Convergence - squint/come together
Describe the movements of the eyes.
Altering fixation - moves in saccades
Smooth pursuit - fixed on moving target
At rest - microsaccades, constant motion on retina, not fixed
Describe how images change when formed on the retina.
Images formed on the retina are upside down and reduced (inverted and switched left/right)
What adjusts the lens and why?
Ciliary body for accommodation
What is the name given to the stiffening of the lens with age?
Presbyopia - less able to accommodate
Describe what controls the shape of the lens.
Contraction state of the ciliary muscles determines the amount of tension that the zonular fibres exert on the lens.
Describe the contraction state of the ciliary muscles and lens shape.
Contracted ciliary muscle = lower tension on zonular fibres and more rounded lens
Relaxed ciliary muscle = higher tension on zonular fibres and more flattened lens
List the processes occurring with near vision.
Accommodation
Convergence
Pupillary constriction
Describe the process of near vision.
Increased firing of parasympathetic nerves to ciliary muscle
Contraction of ciliary muscle
Relaxation of zonular fibres
Relaxation of the lens so that it becomes more spherical
Near objects brought into focus
What is wrong in nearsightedness vs farsightedness?
Nearsightedness - eyeball too long
Farsightedness - eyeball too short
What causes glaucoma?
Drainage canal becomes blocked or extra aqueous humor is produced resulting in increased eye pressure
Increased eye pressure causes damage to the blood vessels and optic nerve
Optic nerve looks caved in/cupped
Describe the characteristic pattern to loss of visual field - scotoma.
Rim of optic nerve becomes thinner as disc caves in and becomes more cupped.
