AaM Refractive error & Emmetropisation

Question 1

The 2 ocular structures that the human eye refracts at??

Answer 1

Cornea & Lens

Question 2

cornea: & refraction power in the eye

Answer 2

fixed focusing power
counts for 2/3rds of total refraction of eye 40D

Question 3

lens:: & refraction power in the eye

Answer 3

accommodation changes lens shape to focus on objects at diff distances
counts for 1/3rd of total refraction of eye 20D

Question 4

Total Eye Power

Answer 4

+60D

Question 5

eyes ability to focus light determined by:

Answer 5

shape of cornea
length of eyeball
power of lens

Question 6

emmetropia

Answer 6

normal vision/ no refractive error where light focuses correctly on the retina w/o need for corrective lenses

Question 7

ametropia??

Answer 7

any refractive error in the eye where light does not focus properly on retina causing blurred vision required correction w/ glasses, contact lenses or surgery

Question 8

main types of ametropia????

Answer 8

myopia (nearsightedness)
hyperopia (farsightedness)
astigmatism (distorted vision due to irregular corneal curvature)
presbyopia (age-related difficulty focusing on close objects)

Question 9

far point??

Answer 9

furthest distance an object can be seen w/o help of lenses or glasses

Question 10

far point for normal eye (emmetropia)??

Answer 10

infinity (6 metres)

Question 11

far point for eye w/ myopia (nearsightedness)

Answer 11

closer than infinity/ some distance in front of the eye

Question 12

far point for eye w/ hyperopia (farsightedness)

Answer 12

point farther away than infinity/ some distance behind the eye

Question 13

focal point??

Answer 13

where parallel light rays meet(converge) after passing thru a lens

Question 14

focal point for normal eye (emmetropia)??

Answer 14

on the retina (light rays from distant object parallel)

Question 15

focal point for eye w/ myopia (nearsightedness)

Answer 15

in front of retina

Question 16

focal point for eye w/ hyperopia (farsightedness)

Answer 16

behind the retina

Question 17

focal length??

Answer 17

distance from the lens/ mirror to the focal point

Question 18

reasons for refractive ametropia in a myopic eye

Answer 18

cornea is TOO CURVED (increases refractive power & focuses light too soon)
lens is TOO POWERFUL (focal point is then in front of retina)

Question 19

reasons for axial ametropia in a myopic eye

Answer 19

the eye is too big (causing light rays to focus in front of the retina)

Question 20

reasons for refractive ametropia in a hyperopic eye

Answer 20

cornea TOO FLAT (reducing its refractive power)
lens TOO WEAK (leading to insufficient bending of light)

Question 21

reasons for axial ametropia in a hyperopic eye

Answer 21

eye is too short (causing light to focus behind the retina instead of on it)

Question 22

astigmatism

Answer 22

usually occurs w/ myopia/ hyperopia, refractive error caused by irregular curvature of the cornea/ lens light rays focus in different locations (2 focal points)

Question 23

Convex Lenses

Answer 23

positive lenses, converge light rays entering eye to move focal point up to the plane of the retina

Question 24

Concave lenses

Answer 24

negative lenses, diverge light rays entering eye to move focal point back to the plane of the retina (myopia)

Question 25

correcting astigmatism

Answer 25

due to 2 focal points:
correct on w/ SPHERICAL lens
correct second w/ CYLINDRICAL LENS