Vision 1 & 2 Flashcards
What is refraction?
The bending of light as it passes from one medium to another
Which structures in the eye allow for refraction?
Cornea and lens
What is accommodation?
The changes occurring in both eyes as it focuses from a distant object to a close object
What three things comprise accommodation?
Lens change shape, pupil constricts and eyes converge
Which muscle allows the lens to become thicker
ciliary muscles
What effect does thickening the lens have on the focus?
It allows focusing on close objects
Which nerve fibres causes ciliary body contraction
Parasympathetic
What is convergence?
The turning in of the eyes when focussing on an object up close
Which muscles are responsible for convergence of the eyes?
Medial rectus muscles
What is myopia?
Short-sightedness
What is hyperopia?
Long-sightedness
What is astigmatism?
Non spherical curvature of the cornea or lens
What is presbyopia?
Long-sightedness of old age
What happens to a persons vison in shortsightedness?
Close objects look clear and distant objects appear hazy
What is the most common cause of short-sightedness?
Eyeball is too long, making the image form in front of the retina
What are the symptoms of short-sightedness?
Headaches, not able to see distant objects, divergent squint in infants and preverbal children and loss of interest in sports/people in adults
How is short-sightedness corrected?
Biconcave lenses (glasses or contact lenses) or laser eye surgery
What happens to a persons sight in far-sightedness?
Close objects look hazy and distant objects appear clear
What is the cause of far-sightedness?
Eyeball too short or cornea + lens too flat making the image appear behind the retina
What are the symptoms of far-sightedness?
Eyestrain and convergent squint in children/toddlers
How is far-sightedness corrected?
Biconvex glasses, contact lenses or laser eye surgery
What happens to a person’s vision in astigmatism?
Close and distant objects appear hazy
What is the cause of astigmatism?
The surface of the eye has different curvatures in different mediums
What happens to vision in presbyopia?
Seeing near objects becomes difficult
What is the cause of presbyopia?
With age the lens gets less mobile/elastic and when the ciliary muscle contracts it is less able to change shape
How is presbyopia corrected?
Biconvex “reading glasses”
What is phototransduction?
The conversion of light energy to an electrochemical response by the photoreceptors (rods and cones)
What is rhodopsin made up of?
Opsin + 11-cis Retinal
How does bleaching of the visual pigment result in phototransduction?
Phototransduction
What role does vitamin A play in the visual pigment?
Visual pigment regeneration
Where do all fibres from the eye pass?
Through the optic nerve to the optic chiasm
What happens to the fibres at the optic chiasm?
The medial/nasal fibres cross to the opposite side
What fibres does the optic tract contain?
Fibres from the temporal half of the ipsilateral eye and the nasal fibres from the contralateral eye
Where do the optic radiation fibres go?
Primary visual cortex in the occipital lobe
Name the six extrinsic ocular muscles of the eye
Medial rectus, lateral rectus, inferior rectus, superior rectus, superior oblique and inferior oblique
Where do the recti muscles of the eye arise from?
An annular fibrous ring at the apex of the orbit
Where does the superior oblique muscle arise from?
Roof of the orbit posteriorly
Where does the inferior oblique muscle arise from?
Floor of the orbit anteriorly
What does the levator palpebrae superioris do?
It elevates the upper eyelid
Which muscle is supplied by the trochlear nerve?
Superior oblique
Which muscle is supplied by the abducent nerve?
Lateral rectus
Which nerve innervates the extrinsic muscles of the eye (apart from LR and SO)?
Oculomotor nerve
Where is constrictor pupillae found?
At the pupillary border in the iris
Where does the dilator pupillae lie?
Radially in the iris
What is the innervation of the ciliaris and constrictor pupillae muscles?
Parasympathetic fibres from the oculomotor nerve
What is the innervation of the dilator pupillae muscle?
Sympathetic fibres
