Errors Of Refraction

Question 1

What is Ametropia

Answer 1

Refractive errors of any kind that does not allow for proper focusing of images on the retina.

Question 2

What is Emmetropia

Answer 2

This is the absence of any refractive errors this images are formed/focused on the retina.

Question 3

What is the natural history of refractive errors?

Answer 3

• Newborns are HYPEROPIC
• At age 1 they are EMMETROPIA
• Between ages 6 - 12 years, MYOPIA may start

Question 4

What’s the total refractive per of the eye?

Answer 4

60 Diopters (D)

• 2/3 (40 D) by the cornea
• 1/3 (20 D) by the lens

Question 5

What is the normal axial length of the eye

Answer 5

22 - 25mm

Question 6

What are the three types of myopia?

Answer 6

• Refractive (index) myopia:- Increased diopteric power of the eye eg in Keratoconus (bulging of cornea), nuclear sclerosis.
• Axial myopia:- Globe > 25mm
• Curvature myopia:- Increased cornea curvature, increased convexity of the lens

Question 7

What are some of the symptoms of myopia

Answer 7

• Straining
• Headache
• Can’t see far
• Poor academic performance cos they can’t see the board
• Child prefers to play indoors as a form of compensatory mechanism

Question 8

What are the treatment options for myopia

Answer 8

1) Spectacles:- Divergent lens (concave lens)

2) Contact lens

3) Surgery:- This is the definitive management of myopia. LASIK (laser assisted in situ keratomileusis), Radical keratectomy

Question 9

What are the types of refractive errors

Answer 9

Myopia
Hyperopia (hypermetropia)
Astigmatism
Presbyopia

Question 10

What are the types of hyperopia

Answer 10

1) Axial hyperopia:- Eyeball <22mm

2) Refractive error hyperopia:- Inadequate diopteric power

3) Curvature hyperopia:- Reduced curvature of the cornea.

Question 11

What are the symptoms of hyperopia?

Answer 11

1) Inability to see both near and far objects properly

2) Eye aches

3) Headaches

4) Watery eyes due to accommodation

NB:- All these symptoms (2-4) are called asthenopic symptoms (from eye straining.

Question 12

What is the problem in Astigmatism

Answer 12

The refractive power of the eye varies in different meridian (sturm’s conoid). This is usually due to irregular shape of the cornea or lens.

Question 13

What are the types of astigmatism

Answer 13

• Regular:- Principal meridian are at 90 degrees to each other
• Irregular:- Principal meridian are not at 90 degrees to each other
• Oblique:- Principal meridian are not at 90 or 180 degrees and do not lie at 90 degrees to each other.
• Compound
• Mixed

Question 14

What are the symptoms of astigmatism

Answer 14

1) Doubling of words or texts while reading
2) Relatively stable blurry vision
3) Inability to focus on both near and far objects

Question 15

What are the treatment options for astigmatism

Answer 15

1) CORRECTIONAL:- Use of cylindrical spectacles or contact lens.

2) SURGICAL:- Reshaping of the cornea using contact lens that is worn at night or with laser surgery.

Question 16

Presbyopia is a refractive error.

True or False?

Answer 16

False

It is a decline in amplitude of accommodation with age.

Question 17

What are the major causes of presbyopia

Answer 17

Sclerosis of crystalline lens
Changes in lens capsule

Question 18

What is the age of onset of presbyopia

Answer 18

35-40 years

Question 19

What are the symptoms of presbyopia

Answer 19

• Difficulty seeing in dim light
• Receeding near point

Question 20

What are the treatment options for presbyopia

Answer 20

1) Spectacles:- convex lenses (reading only, bifocal, varifocal)

2) Contact lenses

3) Surgical correction using multifocal intraocular lens

Question 21

What is anisometropia

Answer 21

Difference in refraction in the 2 eyes