The Eye Flashcards
where is the eye located
bony sockets of the skull called orbits, and have muscles attached to move them
orbit
protects the back of each eye from damage
eyelids and eyelashes
protect the front from foreign particles by blinking, involuntary action
tears
produced by tear glands above each eye,
keep the eyes moist, wash away foreign particles and contain an enzyme (LYSOZYME) that destroys micro-organisms, prevnting infections
conjunctiva
thin, transparent
layer continuous with the lining
of the eyelids. Protects the cornea
conjunctivitis- inflammation and irritation of the conjunctiva causing the eye to appear reddish or pink, virus, illness, fungi, air pollution
cornea
transparent front
part of the sclera. Refracts
(bends) light rays onto the retina
aqueous humour
Colourless fluid. Maintains the shape of the cornea
lens
– transparent, elastic, biconvex structure. Makes fine adjustments
to focus light rays on the retina
pupil
hole in the centre of the
iris. Allows light to enter the eyeball
iris
coloured disc composed of
muscle. Controls the amount of
light entering the eye
suspensory ligament
attaches
the lens to the ciliary body
ciliary muscle
– circular ring of muscle
running through the ciliary body. Alters the shape of the lens during
accommodation
vitreous humour
jelly-like fluid.Maintains the shape of the eyeball
sclera
– tough,white,fibrous coat.Protects the eyeball
choroid
contains blood vessels which supply the retina with food and oxygen, and melanin to prevent reflection of light inside the eye
fovea
contains cones only.The most sensitive part of the retina, most light rays are focused here
retina
contains light-sensitive cells called rods and cones.Where the image forms
optic nerve
carries impulses from the retina to the brain
blind spot
point where theoptic nerve leaves the eye. No light-sensitive cells are present
Image formation
In order to see, light rays from an object must berefracted (bent) as they enter the eye so that they form a clear image of the object on the receptor cells of the retina. Being convex in shape, both the cornea and the lens refract the light rays.
Detection of light intensity and colour by the eye
The retina is composed of two types of specialised light-sensitive cells or photoreceptors:
Rods role in image formation
Rods function in low light intensities. They are responsible for detecting thebrightness of light andare located around the sides of the retina. Images falling on the rods are seen in shades of blackand white only.
Cones role in image formation
Cones function in high light intensities. They are responsible for detecting colour and fine detail, and are mainly located around the back of the retina. The fovea is composed entirely of cones which are packed closely together. There are three types that detect either the red, green or bluewavelengths of light.
Short sight, myopia
OPEN V-SHAPED
LENS ARE DIVERGING, CONCAVE CAVE IN
A person with short sight can see near objects, but distant objects are out of focus. Light rays from near objects focus on the retina; light rays from distant objects focus in front of the retina. Short sight occurs if the eyeball is too long
from front to back or if the lens is too curved (thick). It is corrected by wearing diverging (concave) lenses as spectacles or contact lenses.
Long sight (hypermetropia)
A person with long sight can see distant objects, but near objects are out of focus. Light rays from distant objects focus on the retina; light rays from near objects focus behind the retina. Long sight occurs if the eyeball is too short from front to back or if the lens is too flat(thin). It is corrected by wearing converging (convex) lenses as spectacles or contact lenses.
CONVERGING CONVEX POUTS OUT
DIAGRAM HAS LIGHT RAYS THAT ARE QUADILATERAL
Old sight (presbyopia)
As a person ages, the lens loses its elasticity and the ciliary muscles weaken. The lens is less able to curve and the person finds it increasingly difficult to see near objects. It is corrected by wearing converging lenses for looking at near objects.
Glaucoma
Glaucoma is a condition in which the pressure of the fluid within the eye increases due to the flow of aqueous humour from the eye being blocked.
If left untreated, the optic nerve becomes damaged and it can lead to blindness. The most common type develops slowly and causes a gradual loss of peripheral (side) vision.
Glaucoma is treated with:
eye drops to reduce fluid production or improve the flow of fluid from the eye,
or by laser treatment
or an operation to open the drainage channels
