The Visual System - the Eye and Retina Flashcards
what are some basic importance of vision?
to detect prey,
detect predators,
detect mates,
communicate.
define wavelength:
distance between peaks or troughs in waves.
define frequency:
number of waves per second.
define amplitude:
difference between wave peak and trough.
light rays interact in 3 ways:
reflection - off surface,
absorption - gives objects colour,
refraction - bending light.
what does the pupil in the eye do?
lets light into the eye.
what does the iris in the eye do?
contains muscles to control amount of light entering the eye.
what does the sclera in the eye do?
forms the tough, protective wall of the eyeball to give it shape.
what does the cornea in the eye do?
the transparent covering of the pupil and iris that refracts light.
what do the extraocular muscles in the eye do?
move the eyeball, controlled by the oculomotor nerve.
what does the optic nerve do?
carries axons from the retina to the brain.
what does the optic disk do?
it is the blind spot - the origin of blood vessels and the optic nerve.
what is the Macula in the eye?
region of retina for central vision - high visual acuity.
what is the Fovea in the eye?
the centre of the Macula - highest visual acuity.
what is the retina in the eye?
contains the sensory receptor cells and afferent neurons.
what is the lens in the eye?
suspended by suspensory ligaments attached to ciliary muscle.
how are images formed? (simple)
light rays must be focused on the retina, ideally the fovea.
the degree of refraction is determined by:
differences in refractive indices between two media (such as air and the cornea, or the aqueous humour and the lens),
angle at which light hits the interface between these two medias.
describe refraction by the cornea:
light arrives at the cornea,
light travels slowly through the water of the cornea allowing refraction to occur,
light that hits the cornea directly perpendicular moves straight on to the retina.
define focal distance:
distance form refractive surface to convergence of parallel light rays.
describe accommodation by the lens, for distant objects:
the light rays are pretty much parallel and the cornea provides sufficient refraction to focus the image on the retina.
describe accommodation by the lens, for closer objects:
light rays aren’t that parallel so requires additional refraction to focus image on the retina, provided by the fattening of the lens.
what is emmetropia?
when vision is happening correctly.
what is hyperopia?
‘far-sightedness’ - we can see distant objects well but cannot refract near objects to form a clear object.
