Refraction

Question 1

emmetropia

Question 2

in any eye, how does the distance of objects to the eye affect where on the back of the eye they fall

Answer 2

the nearer objects come to the eye, the further back their image falls

Question 3

myopia

Answer 3

short-sighted

The eyeball is too long. Only close objects focus on the retina (cos the nearer objects come to the eye the further back their image falls) unless concave (diverging) spectacles are worn

Question 4

how does myopia progress with age

Answer 4

in normal growth, changes in eyeball and lens curvature compensate for the eye getting longer as it grows, but in myopic children such compensations may not be occurring, so the myopia worsens with age

most dont become myopic until around the age of 6 and it will then continue to worsen into late teens

changes stop usually below 6 dioptres

Question 5

how must myopic eyes be handled

Answer 5

eyes checked reguarly

avoid over compensation as this can make eyes worse

Question 6

astigmatism

Answer 6

shape correction factor

present if the cornea of lens don’t have the same degree of curvature in the horizontal and vertical planes

light is focused at several points on the retina meaning vision is blurred at all distances

can occur alone, or with myopia or hypermetropia

Question 7

hypermetropia

Answer 7

the eye is too short, even distant objects when the eye is at rest are focused behind the retina, but the eye can correct this

cose objects are focused even further behind the retina, which the eye sturggles to compensate for

this can produce tiredness of gaze, and sometimes, convergent squint in children

corrected by convex (converging) lenses to bring the image forward to focus on the retina

Question 8

presbyopia

Answer 8

ageing of lens and ciliary muscles causes the lens to stiff and so cannot get as convex for focusing on near objects as it used to be able to

• long sightedness