mnsr 33 Flashcards
— is a dark membrane which absorbs stray light.
choroid
the – is the outer protective coating of the eyeball and is made from tough dense connective tissue
scalera
Light enters the eyeball through the—- and passes through a fluid filled chamber containing —-
Conner, aqueous humour
is the coloured ring behind the corner which regulates the amount of the light that enter through the —
iris, pupil
the pupil varies in diameter from
7-8 to 2-3 mm
then the light enter the —- of the eye, the shape is controlled by —-
crystalline lens, cillary muscles
accomodation is the
ability of the ciliary muscles to change the shape of the lens to focus objects at different distances onto the retina
Behind the lens is a jelly-like substance is
vitrous humour
the most sensitive at small retinal depression in the eye is the
yellow spot and the central position is the fovea centralis - 0.35 mm diameter and densly packed w cones. Responsible for direct vision . the eyeball normally rotates so that objects under examination are imaged directly onto the fovea.
the most bending occurs when incoming light enters the
cornea
the function of the crystalline lens is
provide fine adjustments to the refractive power of the eye to focus on objects at different distances. [The normal relaxed eye will focus parallel light onto the retina].
light rays from an object as close as — to the eye is —-
6 metre is parallel, normal, and relaxed and can view sharp objects from 6m to infitinty without having to focus
in the process of accommodation we need to
change the focal length to view objects closer than 6m for example bc the eyes have to focus
the further away the near point is
the more difficult to see
the near point varies depending on
the age
- child: few cm
- ppl in their 40s ~ 20cm
- age depend bc of the gradual decrease of elasticity of the lens and the hardening of the cillary muscle
refers specifically to the numerical difference between the refractive power of the eye when relaxed (far point) and when fully accommodated (near point), i.e. maximum focussing power.
power of accommodation
light is absorbed by the
photoreceptors cells which causes photochemical reaction and initiates an action potential. Rods are more sensitive than cones ( 350-550 nm)
we can discriminate between different colours bc
we have thee different types of cones w/ different wavelengths.
L: long , red
M: med , green
S: short, blue
different colours are included by
-different proportions of active.
-Our brain corrects for this interdependence of cones. Its decoding of the cone activity patterns is called the chromaticity diagram and restores the full colour range normally seen in an RGB colour mixing triangle
we have extensive field of vision bc
-retina covers most of the back half of the eye
-The foveal field corresponds to the size of only-
a thumbnail at an arm’s length- a
35 cm diameter disk in 10 meter distance
cones have excellent resolution bc
each cone in the fovea is connected directly to visual cortex
the reason why rods have poor resolution
many rods are connected to the same nerve fiber
the max density of rods are in an angle of
20 degree from the axis of vision and rods are not disturbed evenly in the retina
cones are only active in — while rods are
- light adapted eye
- active all the time
why do we see all cats gray at night?
the fovea is the most sensitive part of the retina in daylight conditions but can result in night time blindspot in our direct vision bc no rods are in the fovea even though our peripheral vision in the dark is good
in bright light the iris reduces the pupil size to
3-4mm in 5 seconds , parasyptahtic, circular pillary sphincter constricts
in dim light the iris needs
300 sec aka 5 minutes to open the pupil to 8 mm
the reduction of the pupil in the bright condition will reduce
lens defects ( spherical aberration ) and improve the depth of focus
optical illusions
1-. Like most sensory nerves, the nerve cells in the eye stop sending signals in the presence of a steady stimulus, that’s why our eyes jiggle to overcome this.
( the reason why we can see the blood vessels in our retina is bc of the steady supply of blood )
2-The eyes can play funny tricks in interpreting contrast between adjacent blocks of colour or toneThis perception is due to the interaction between adjacent groups of light sensors in the eye.This effect works to our advantage in discerning borders in X-ray images for example (note, the effect is diminished when the contrast is poor).In addition, our perception of darkness or brightness of an object also depends on the background colour behind the object, e.g.
3- Persistence of Vision.
4-Stereoscopic Vision:allows us to have ‘depth of field’, i.e. the ability to identify structures as being 3-d and to differences in distance from the eye.The brain processes the two images and fuses them together so that the combined image has components of both separate images and has a 3-d appearance( w/ slightly different angles )
5- perspection
