Refractive Errors

Question 1

What is a refractive error?

Answer 1

A refractive error occurs when the shape of the eye prevents light from focusing directly on the retina to form a clear image

Question 2

Refractive media of the human eye?

Answer 2

Human eye has 4 refractive media
1. cornea
2. aqueous humor
3. lens
4. vitreous humor
- Normal size, shape and curvature of these is critical in achieving clear vision
- Anterior surface of the cornea does the maximum refraction
- Total refractive power of the eye is 63 D

Question 3

Emmetropia?

Answer 3

light is focused onto the retina

Question 4

Ametropia?

Answer 4

an abnormal refractive eye condition in which images fail to focus upon the retina
- e.g. myopia, hyperopia, astigmatism

Question 5

What is myopia?

Answer 5

• Light rays focus in front of the retina
• Difficulty in seeing distant objects clearly (Nearsightedness)

Question 6

Causes of myopia?

Answer 6

1. Mainly caused by increase in axial length of the eye ball
2. Increased curvature of the cornea
3. Increased refractive index of the eye

Question 7

Risk factors for myopia?

Answer 7

1. A family history of myopia
2. Prolonged near work activities
   e.g. reading, screen time
3. Low outdoor activity
   - especially in childhood

Question 8

Types of myopia?

Answer 8

1. Congenital myopia: present at birth, progressive, severe
2. Simple myopia: typically develops in childhood, correctable with glasses
3. Degenerative myopia: severe, with an increased risk of complications

Question 9

Management of myopia?

Answer 9

1. Concave lenses in the form of glasses or contact lenses
2. Refractive surgery

Question 10

Complications of myopia?

Answer 10

1. Retinal detachment
2. Open angle glaucoma
3. Macula hole

Question 11

What is hypermetropia?

Answer 11

• Light focuses beyond the retina
• Blurred near vision and clear far vision
• Causes discomfort and strain on eyes - headaches and eye fatigue

Question 12

Causes of hypermetropia?

Answer 12

1. Smaller axial length of the eye
2. Flatter cornea
3. Decreased refractive index

Question 13

Risk factors for hypermyopia?

Answer 13

1. Genetic predisposition
2. Prematurity and low birth weight
3. Maternal smoking during pregnancy

Question 14

Management of hypermyopia?

Answer 14

1. Appropriate convex lenses in the form of spectacles or contact lenses
2. Refractive corneal surgery

Question 15

Complications of hyper myopia?

Answer 15

1. Closed angle glaucoma
2. Early onset of presbyopia
3. Amblyopia

Question 16

What is Astigmatism?

Answer 16

• Refraction varies in different meridian of the eye
• Ray of light entering the eye can not converge to a point focus but form focal lines
• Usually due to unequal curvature of the cornea
• Blurred vision at all distances
• Corrected by toric lenses or surgery
• Early onset increases risk for ambylopia

Question 17

What is presbyopia?

Answer 17

• Loss of accommodative ability
• Usually in older patients, from age of 40
• Difficulty reading small prints, patients usually hold reading material at a distance
• Corrected by concave lenses

Question 18

Other refractive error manifestations?

Answer 18

1. Pain in the eyes
2. Headache
3. Strabismus

Question 19

Assessment of refractive errors?

Answer 19

1. Objective
   - Retinoscope
   - autorefractor
2. Subjective
   - Different lenses put in front of patient until clearest vision

Question 20

Refractive anomalies in children?

Answer 20

Visual system still developing in early childhood (up to six years)
- The visual system needs visual signals to mature
- Any interruption of visual signals lead to irreversible visual impairment (amblyopia)