optics and low vision

Question 1

what does emmetropia mean?

Answer 1

no refractive error; light focussed onto retina
no glasses needed

Question 2

what does ametropia mean?

Answer 2

refractive error present; light focussed in front of or behind retina

Question 3

what does anisometropia mean?

Answer 3

significant difference between right and left ametropia

Question 4

what are the two types of ametropia?

Answer 4

myopia- light focused before the retina (short sighted, so far away is blurred)
hypermetropia- light focused behind the retina (long sighted, so up close is blurred)

Question 5

what lenses are needed for myopia and hypermetropia

Answer 5

myopia- negative lenses
hypermetropia- positive lenses

Question 6

what is astigmatism?

Answer 6

Eye has unequal refractive powers at different meridia
Causes distorted vision
Cylindrical lenses

Question 7

what is presbyopia?

Answer 7

This describes the reduction in ability of the eye to accommodate for close-work with age
tends to require reading glasses

Question 8

how is a prescription for astigmatism worked out?

Answer 8

sphere/cylinder x axis

Question 9

what are some common causes of low vision?

Answer 9

Wet and dry macular degeneration
Glaucoma
Diabetic eye disease

Question 10

what is the definition of being sight impaired?

Answer 10

Sight impaired (previously termed ‘partially sighted’)
(if full field needs to be worse than 6/60 with BOTH EYES OPEN)

Question 11

what is the definition of being severely sight impaired?

Answer 11

Severely sight impaired (previously ‘termed blind’)
(if full field needs to be worse that 3/60 with BOTH EYES OPEN)