eye

Question 1

how do we see

Answer 1

light rays from an object enter the front of eye through cornea
cornea and lens in the eye refract light rays causing them to converge at a point on retina
image formed on the retina is upside down and reversed
when message carried from eye to brain brain adjusts image so it is right side up and round
cones in retina work in high light intensities allowing a person to see in colour
the rods in retina work in low light intensities allowing a person to see in black and white only

Question 2

explain accommodation

Answer 2

process by which the shape of the lens changes to allow a person to see near and distant objects clearly
the lens changes shape as a result of changes in the ciliary muscles

Question 3

what occurs if the shape of the lens is altered

Answer 3

extent to which light rays are refracted is affected

Question 4

what kind of lens is in the eye

Answer 4

convex which cause light rays to converge

Question 5

how do we view distant objects

Answer 5

light rays from the distant object enter the eye reaching convex lens in eye
ciliary muscle relaxes increasing its circumference
this causes suspensory ligaments to pull on the lens at either end causing the lens to become longer and thinner
this results in the lens refracting light rays less causing them to converge on the retina producing a clear image

Question 6

how do we view near objects

Answer 6

light rays from the near objects enter the eye reaching convex lens in the eye
ciliary muscle contracts decreasing its circumference
this causes the suspensory ligaments to push on the lens at either end causing lens to become shorter and wider
this results in the lens refracting light rays more causing them to converge on the retina producing a clear image

Question 7

explain pupil reflex

Answer 7

in dim light the circular muscles of the iris relax and radial muscles contract causing pupil to dilate/widen
allows maximum light to enter the eye
in bright light circular muscles of iris contract and radial muscles relax causing pupil to constrict or become smaller
reduces amount of light entering the eye protecting structures in the eye for example the retina from being damaged

Question 8

list sight defects

Answer 8

short sight
long sight
astigmatism
old sight
glaucoma
cataracts

Question 9

explain short sight

Answer 9

ability to see near objects clearly but distant objects appear blurred
light from near objects focused on retina
light from distant objects converge at a point before retina

cause
eyeball too long
lens too curved

correction
diverging/concave lens bends light rays outward before reaching eye so that they will converge on retina

Question 10

long sight

Answer 10

ability to see distant objects clearly but near objects appear blurred
light from distant objects focused on retina
light from near objects converge at a point behind/after retina

cause
eyeball too short
lens too flat

correction
converging or convex lens bends light rays inward before reaching eye so that they will converge on retina

Question 11

astigmatism

Answer 11

light rays in one plane focus on retina to give clear image while light rays in another plane do not focus on retina so image is blurred

cause
surface of lens and or cornea curved irregularly

correction
corrective lenses which are irregularly cured to compensate for irregular curvature in eye

Question 12

glaucoma

Answer 12

painful inflamed tender eye
halo around objects in visual field

cause
blockage in the flow of aqueous humour causes an increase in pressure within eye

treatment
eye drops to relieve pressure
oral medication to relieve pressure
surgery to open drainage canals

Question 13

cataracts

Answer 13

light cannot pass through lens so objects not seen

cause
lens becomes opaque

treatment
remove lens and wear strong spectacles or contact lenses
replace lens with artificial lens
clear lens with laser treatment

Question 14

old sight

Answer 14

person becomes progressively more long sighted with age
short sight improves with age

cause
lens loses elasticity
ciliary muscle becomes weaker with age
both of these result in the lens being less able to curve

correction
converging convex lens