The Human Eye Flashcards
Sclera
Tough white layer to resist punctures
Cornea
Bends image, no blood vessels, 90% of focus power
Iris
Circular muscle, controls pupil size, coloured part of eye
Ciliary Muscles
Controls lens shape for focusing
Choroid
Blood rich, dark inky layer to darken eyeball
Lens
Focuses & inverts image, 10% of focus power
Aqueous Humour
Clear fluid between cornea and lens, fluid is renewed every half an hour, nourishes cornea
Vitreous Humour
Clear pressurized fluid to maintain eyeball shape
Retina
Contains photoreceptors (rods & cones)
Fovea Centralis
90% of cones, colour vision, central & clarity/ sharpness of vision
Blind spot
Where optic nerve leaves the eye, no room for photoreceptors
Optic nerve
Contains 1 million axon to occipital lobe
Rods
Peripheral located, black & white contrast, motion sensitive, night vision, 1 kind, pigment= Rhodopsin
Cones
Centrally located, colour sensitive, clarity & detail, bright light (day), 3 kinds (RBG), Pigment=Iodopsin
Eyebrows
Deflect water & debris
Blinking
Keeps eye moist
Glaucoma
Issue with Aqueous Humour & Retina
Due to increased fluid pressure in the aqueous humour. Blockage of drainage ducts causing pressure to rise.
Cataract
Issue with lens
Lens becomes cloudy as we age
Light & images do not pass clearly
Lens proteins have been denatured due to UV light exposure
Astigmatism
Issue with cornea
Normal cornea is smooth & symmetrical
Sometimes cornea adopts an irregular shape
Light entering the eye gets scattered rather than focused on the retina
Myopia (nearsightedness)
Issue with cornea, lens & retina
Close up objects are seen well
Far away object are blurred
Image comes into focus in front of the fovea rather than on it.
Hyperopia (farsightedness)
Issues with cornea, lens & retina
Far away objects are seen well
Close up object are blurred
Image is unable to focus on fovea. Focuses behind the eye
