Physics of the Eye Flashcards
What is the function of the cornea?
Protect the eye and focus light onto retina via refraction. (most refraction is done here)
What is the function of the iris?
To control the amount of light that can enter the eye by changing the diameter of the pupil.
What is the function of the pupil?
To allow light to enter the eye.
What is the function of the lens?
To focus light onto the retina via refraction.
What is the function of the ciliary muscles?
To change the thickness of the lens to focus on objects of differing length from the lens.
What is the function of the retina?
To form a real image when light rays from an object hit the photosensitive cells.
What is the function of the optic nerve?
To carry nerve impulses from the retina to the brain.
What is the blind spot?
The point where the optic nerve connects to the retina. There are no photosensitive cells, so no image will be formed.
What is the function of the suspensory ligaments?
To support and hold the eyeball in its place.
What is the sclera?
The protective outer layer of the eyeball containing collagen and elastic fibre.
What is the vitreous humour?
The clear gel that fills the space between the retina and the lens. It holds the shape of the eyeball.
What is the aqueous humour?
The clear gel that fills the space between the lens and the cornea. It maintains pressure and provides nutrition to eye tissue.
What humour is constantly refreshed?
Aqueous humour.
What humour is there from birth?
Vitreous humour.
What is the fovea?
The small highly concentrated area of cones on the back of the eyeball.
What is the fovea responsible for?
Sharp central vision.
What is the choroid?
The layer that lies between the retina and the sclera.
What is the bulbar conjunctiva?
The fine membrane that encases the eyeball.
When does refraction occur?
When light moves between two mediums that each have a different density.
When does light bend towards the normal?
When moving from a lower to higher density, it also slows down.
When does light slow down?
When moving from a lower to higher density, it also bends towards the normal.
When does light bend away from the normal?
When moving from a higher to a lower density.
When does light speed up?
When moving from a higher to a lower density, it also bends away from the normal.
How much of the refraction occurs in the cornea?
60%
What is the refractive index when moving from A to B?
refractive index = speed of light in A / speed of light in B
What is a converging lens?
A convex lens.
What is a diverging lens?
A concave lens.
What do the rays do when a converging lens is used?
Converge on focal point.
What do the rays do when a diverging lens is used?
Diverge from the focal point?
What is myopia?
Short sighted-ness. The image is focused before the retina.
What is hypermetropia?
Long sighted-ness. The image is focuses beyond the retina.
What is the focal length?
The distance between the centre of the lens and the focal point.
What lenses are used to correct myopia? How?
Diverging lenses. Spreads light out which pushes focal point back.
What lenses are used to correct hypermetropia? How?
Converging lenses. Bends light inwards which brings focal point forward.
What is the lens power equation?
P = 1/f
What sign is used for the power of a diverging lens?
-
What sign is used for the power of a converging lens?
+
What is the unit for power?
Diopters (D)
In what case is a real image formed using a converging lens?
If the object is further away than the principal focus.
In what case is a virtual image formed by a converging lens?
If the object is closer than the principal focus.
What lens always forms virtual images?
Diverging lens.
What image is larger than the object?
Virtual.
What image is smaller than the object?
Real.
What is the lens formula?
1/f = 1/u + 1/v
f = focal length u = object distance v = image distance
What is the magnification produced by a lens?
m = v/u
m = magnification v = image distance u = object distance
What are the two types of photoreceptors in the retina?
Rod and Cones.
What are the rods responsible for?
Vision at low light levels. (Scoptic vision)
What are the cones responsible for?
Vision at high light levels (Photopic vision) and all high resolution vision.
Which photoreceptors are responsible for colour vision?
Cones.
What are the three types of cone and what are they responsible for?
Short wavelength (S-cone) - blue light Medium wavelength (M-cone) - green light Long wavelength (L-cone) - red light
What is the light level at which both rods and cones are being used?
Mesopic.
Which photoreceptors are most sensitive?
Rods.
Which photoreceptors detect the most detail?
Cones.
How many rods are in the retina?
120 million
How many cones are in the retina?
6-7 million
Where are cones most concentrated?
The central fovea (0.3mm)
What colour cones are most concentrated in the central fovea?
Red and green.
What cones are the most sensitive?
Blue cones.
Where are blue cones mostly found?
Outside the fovea.
Which of the three cones are the least in numbers in the retina?
Blue.
What is colour blindness?
When one or more coloured cones are missing from the retina.
What is protanopia?
No red cones.
What is deuteranopia?
No green cones.
What is tritanopia?
No blue cones.
What is monochromacy?
Missing two types of cones.
What is achromatopsia?
All colour cones missing or defective.
Where are rods more predominant?
In the peripheral vision.
What sensitive photopigment is used in the rods?
Rhodopsin.
What is spatial resolution?
The eye’s ability to see detail. It is dependant on the spacing of rods and cones in the retina.
What is the persistence of vision?
Flicker fusion. When a cone detects light, the signal takes 50-80 milliseconds and when a rod detects light the signal takes 300 milliseconds.
What is astigmatism?
A condition where the cornea curvature is large or irregular. The image on the retina is unevenly focused.
What lens is used to correct astigmatism?
Cylindrical lens.
