Refractive errors

Question 1

Optical components

Answer 1

Cornea - fixed
Lens - variable
Axial length

Question 2

Accommodation reflex

Answer 2

1. More light refraction from near objects
2. Ciliary muscle fibres contract
3. Suspensory ligament relaxes
4. Lens becomes thicker

Question 3

Types of refractive error

Answer 3

Myopia - short sighted
Hypermetropia - long sigted
Astigmatism

Question 4

Astigmatism

Answer 4

Different shape of eyeball

Question 5

Causes of myopia

Answer 5

Long axial length with an average cornea (common)

or

High power cornea (steeper) with an average axial length

Question 6

Myopia pathophysiology

Answer 6

Light focus falls short of retina

Question 7

How to correct myopia

Answer 7

Requires a concave lens to correct

Question 8

Hypermetropia pathophysiology

Answer 8

Light focus is past the retina

Question 9

Causes of hypermetropia

Answer 9

Axial length too long with normal corneal power (common)

or

Corneal power is weaker (flatter) with normal axial length

Question 10

How to correct hypermetropia

Answer 10

Convex lens

Question 11

Astigmatism

Answer 11

Anatomical variation where the cornea has 2 axis of curvature giving 2 powers and 2 foci

Question 12

Presbyopia

Answer 12

Loss of elasticity of the lens due to old age therefore less accommodation

Can’t see short distance

Question 13

If sphere value is +

Answer 13

Hypermetropia

Question 14

If sphere value is -

Answer 14

Myopia