MNSR 34 -Eye and Vision Flashcards
Iris function
a coloured ring behind the cornea which adjusts in size to regulate the amount of light entering the eye through the Pupil
where does light enter the eye
enters through crystalline lens
what controls the shape of the crystalline lens
ciliary muscles
an example of accommodation in the eye
The ability of the ciliary muscles to change the shape of the
lens to focus objects at different distances onto the retina
where is the eye most sensitive
most sensitive in small retinal depression called yellow spot or fovea - dencely packed with cones
normal horizontal field of view
60 - 95 degrees L and 95 degrees R
Normal vertical field of vision
135 degrees
60 degrees up
75 degrees down
what does refractive index determine and how does it influence how light travels in the eye.
determines how fast light travels and if it goes from one material to different material with different refractive index
where does most of light bending occur in the eye
most f light bending occurs as light enters the cornea
the greatest difference in refractive index is between light and cornea (refractive index difference = 0.337) greatest difference =greatest bending
what is the function crystalline lens in regards to refractive index
adjusts in accordance to refractive power of the eye to focus on objects at a distance
why does the crystalline lens not have to adjust its shape w/ objects further than 6 metres?
Light rays from an object as close as 6 m to the eye are essentially parallel, so the normal, relaxed eye can view sharp
images of objects from 6 m to infinity without having to focus.
how does accommodation process change with age and explain why?
decreases gradually
due to the loss of elasticity of lens and hardening of ciliary muscles
what does power of accommodation refer to specifically?
numerical difference between refractive power of the eye when relaxed (far point) and when fully accommodated (near point)
2 structural differences between rod and cones
rod - contains membrane lined vesicles in centre
- contains pigment rhodopsin
cone - membrane surface folds in on itself
- contain pigment iodopsin
what photoreceptor cell is more sensitive and in what wavelength range?
rods are more sensitive within 350 - 550 nm range
3 cones in eye
blue (S) cone (short wavelength)
Green (M) cone (Medium wavelength)
Red (L) cone (Long wavelength)
chromaticity diagram
decoding of the cone activity patterns within the cones
restores the full colour range
normally seen in an RGB colour mixing triangle.
cones that detect colour - in corner
how it is perceived - in the centre
what are cones responsible for?
for daytime and colour vision.
for our ability to resolve fine detail.
direct vision - mainly in fovea
how do cones in the eye give excellent resolution
Each cone in the fovea centralis is connected directly to the visual cortex
how come the resolution of the rod much poorer than that of the cones even though there are more rods than cones?
most of the rods are connected to the same nerve fibre
why is the pupil in the centre of the iris black?
because all of the light that enters is
absorbed inside the eye.
how does iris respond to bright and dim light and how long does it take?
does not respond instantly
in bright light - reduces pupil size to 3-4mm in 5 seconds
in dim light - iris opens pupil to 8mm in around 5 mins
purpose of reducing pupil size in bright conditions
to reduce lens defects (spherical aberrations) and
improve depth of focus
why can’t we see blood vessels of retina?
see time stamp of 42 mins
how does eye perceive different brightness
maximises contrast in shades
the intensity may actually be more homogenous than we perceive it to be
due to interaction between adjacent groups of light sensors in the eye
persistance of vision
eye can’t process more than 25 images a second
stereoscopic vision
images taken from both eyes are from different angles
brain combines them and allows image to have depth
how can stereoscopic vision be used
one can take pictures of object at dif angles
show left image at left eye but right image at right eye. - create sense of depth in. examination of tumours
