optics and low light

Question 1

what is emmetropia?

Answer 1

no refractive error; light focussed onto retina
e.g. normal vision in terms of refraction

Question 2

what is ametropia?

Answer 2

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

Question 3

what is anisometropia?

Answer 3

significant difference between right and left ametropia

Question 4

what are the 2 types of ametropia?

Answer 4

myopia (light focused in front of the retina)
hypermetropia (light focused behind the retina)

Question 5

what is myopia?

Answer 5

short sightedness (need glasses for seeing far away)

Question 6

what is hypermetropia?

Answer 6

long sightedness (need glasses for seeing close up - reading classes)

Question 7

does myopia have + or - lenses?

Answer 7

-

Question 8

does hypermetropia have + or - lenses?

Answer 8

+

Question 9

what is astigmatism?

Answer 9

Eye has unequal refractive powers at different meridia (rugby ball eyes)
Causes distorted vision
Cylindrical lenses

Question 10

describe presbyopia

Answer 10

the reduction in ability of the eye to accommodate for close-work with age. This requires a supplementary converging or positive lens (reading glasses) in order to focus light from a near object onto the retina

Question 11

what would a spherical prescription look like (no astigmatism)?

Answer 11

Rx: -5.25DS (1 number)

Question 12

how do astigmatism prescriptions look?

Answer 12

Rx: +3.00 / -1.00 x 180
Sphere/ cylinder x axis

Question 13

what is visual acuity?

Answer 13

smallest letter on the chart that px can read, with best spectacle or contact lens correction

Question 14

what is the criteria for being sight impaired?

Answer 14

vision worse than 6/60 with both eyes open

Question 15

what is the criteria for being severely sight impaired?

Answer 15

vision worse than 3/60 with both eyes open