the eye

pupil

hole through which light enters the eye

cornea

transparent to let light into the eye, helps focussing

iris

controls size of pupil

aqueous humor

clear fluid that provides nutrients to the eye in lieu of blood, and allows cornea to expand during accommodation

lens

clear disc that focusses light rays onto the retina

ciliary body/muscle

contracts to change shape of the lens

suspensory ligaments

holds the lens in place

sclera

tough outer layer of eye

retina

contains light sensitive cells

optic nerve

carries impulses to the brain from the retina, made up of nerve axons bundled

vitreous humor

composed of water and collagen - less fluid, more gel-like when young, maintains eye shape and protects retina

how do eyes adjust to bright light

circular muscles contract, radial muscles relax, pupil constricts

how do eyes adjust to dim light

ciruclar muscles relax, radial muscles contract, pupils dilate

how do eyes adjust to nearby objects

ciliary muscles contract, suspensory ligaments slacken, low muscle tension on lens, lens thickens so more convex

how do eyes adjust to far away objects

ciliary muscles relax, suspensory ligaments pulled tight, high muscle tension on lens, lens thinner so more concave

myopia

cannot focus on far away objects as point of focus is too short of retina, happens if lens refracts light too much or if eyeball is too long, need glasses with a concave lens

hyperopia

unable to focus on near objects as lens doesn’t refract light enough or the eyeball is too short, need glasses with a convex lens

different types of cone cells

l-cone (red-sensitive opsin, long wavelength), m-cone (green-sensitve opsin, medium wavelength), s-cone (blue-sensitive opsin, short wavelength)

rod cells

rhodopsin pigment, thinner than cones, important in dim light, uninmportant for colour vision, distributed throughout retina but least dense in fovea, more abundant than cones, low acuity due to high convergence (several rod cells attached to 1 bipolar cell), high snesitivity (1 photon of light will result in a response)

cone cells

3 iodopsin pigments, thicker than rod cells, unimportant in dim light, important for colour vision, densely packed in fovea, less abundant than rods, high acuity due to no convergence (each cone cell has own bipolar cell), low sensitivity (high levels of light needed to stimulate response)

protanopia (type of colour blindess)

1% in males, 0.01% in females, missing l-cones, cannot perceive red light, sees world in vibrant blues and yellows

deuteranopia (type of colour blindness)

1.5% in males, 0.01% in females, missing m-cones, cannot perceive green light, sees world in vibrant blues and yellows but can see red hues

tritanopia

0.008% in both males and females, missing s-cones, cannot perceive blue light, difficult to see yellow and blue colours