Vision 1 Flashcards
define -
light rays bend to form a sharp image on the retina?
refraction
define -
changing the shape of the len by the ciliary body to focus on far away/near objects by refraction?
accommodation
what three mechanisms are involved in accommodation ?
- changing lens shape
- pupils constrict
- eyes converge
how does the lens thicken?
- ciliary body contracts making the ciliary body bulge
- space in the middle decreases
- suspensory ligaments become
- lens is no longer under stretch so lens becomes thicker
what shape does the lens become when it is relaxed?
more spherical
when do the pupil constrict ?
when we are looking at an object up close and need to sharp focus
what muscle is used to constrict the pupils ?
pupillary constrictor
what autonomic response constricts pupils
parasympathetic response
what cranial nerve constricts the pupil?
occulomotor nerve
what extrinsic eye muscles are responsible for converging the eyes?
medial rectus
what muscles tend to be thicker
- medial recti
- lateral recti
medial rectus
what is myopia?
short sightedness
what is hyperopia ?
long sightedness
what is astigmatism ?
non-spherical curvature of cornea
- increased curvature
what is presbyopia ?
long sightedness of old age
what is emmetropia?
perfect vision
what is the most common cause of myopia?
eye ball is too long
in myopia,
is the image focused infront or behind the retina?
in front
myopia
- do close things look clear or hazy?
clear
what are the common symptoms of myopia in toddlers?
loss of interest in sports/people. More interest in books, pictures.
what are the common symptoms of myopia in infants ?
divergent squint
what type of lens is used in glasses to correct myopia ?
biconcave to decrease the power of bending
can laser eye surgery be used to treat myopia?
yes
in hyperopia do close objects look hazy or clear?
hazy
what are the anatomical differences in hyperopia?
eye ball is too short and lens is too flat
in hyperopia, what kind of squint would a child have?
convergent
why does children with hyperopia have to be treated immediately ?
to prevent a lazy eye
where does the image focus during astigmatism?
the image is focused in two locations which causes double vision
during astigmatism do close and distant objects appear clear or blurry?
distant and close objects appear hazy
what type of glasses are used to correct astigmatism?
cylindrical glasses
what is the cause of presbyopia?
the lens becomes less mobile with old age
what type of glasses are used to correct presbyopia?
biconvex
what is phototransduction ?
The energy in light waves need to stimulate photoreceptor cells on the retina
conversion of light energy to electrical energy by rods and cones
what is the shape of the outer segment of the
- rod
- cones
rod
- rod shaped outer segment
cones
- cone shaped outer segment
is a thin or thick lens more powerful?
thick
name the two photoreceptors in the eye
rods
cones
How does bleaching of the visual pigment result in phototransduction?
Phototransduction cascade.
What role does Vitamin A play in the visual pigment?
visual pigment regeneration
what channel closes as a result of the phototransduction casade ?
Na channels
what are three symptoms which can be caused by vitamin A deficiency ?
- night blindness
- abnormal conjunctiva and corneal epithelium
is Vit A water or fat soluble?
fat soluble
what are two clinical signs of a Vitamin A deficiency ?
Bitots spots on conjunctiva
corneal ulceration
describe the basic mechanism of a photon landing on a photoreceptor
- photon lands on Rhodopsin
- 11-cis isomer changes to all-trans isomer
- this results in bleaching of a visual purple colour
- Na channels close
- results in hyper polarisation of the cell
- Hyperpolarisation increases Ca ions which stimulates the retinal cells
