Lec. 7: Introduction to Amblyopia and Strabismus

What is amblyopia?

Vision loss in which the visual pathways are intact and normal at birth, but fail to develop normally due to abnormal visual experience during the critical/sensitive period

Critical period

Birth to 6 months

Sensitive period

6 months until 6-8 years

Is amblyopia usually unilateral or bilateral?

Unilateral

Moderate amblyopia

20/40 to 20/80

Severe amblyopia

> 20/80

How common is amblyopia?

Not very common but also not rare. About 1-5% of children

When does amblyopia begins?

<5 years old

Different types of amblyopia

All

What is form deprivation amblyopia?

• Lack of near image and inadequate stimulation of the fovea

• Neural connections not stimulated (FOVEA)

What is abnormal binocular interactions amblyopia?

• Unequal/conflicting input in each eyes leading to diplopia or confusion —> suppression

• Different images being seeing by each eye

Is amblyopia a disease?

No, it is a syndrome

What is the worst nightmare for an amblyope?

Crowding phenomenon

How to stimulate crowding phenomenon when taking single letter visual acuity?

Crowding bars around the letters

What is not a cause of amblyopia?

Genetic

Isoametropia vs Anisometropia

Isometropia refers to a condition where both eyes have equal refractive power, while anisometropia is where the refractive powers are different between the two eyes.

Isoametropia astigmatism:

> 2.50

Isoametropia Hyperopia

> 5.00

Isoametropia Myopia

>8.00

Anisometropia Astigmatism

>1.50

Anisometropia Hyperopia

>1.00

Anisometropia Myopia

>3.00

Which is more often to run into?

Anisometropia

Is isoametropia one or both eyes?

Bilateral refractive amblyopia (both eyes are bad)

Is anisometropia one or both eyes?

Unilateral refractive amblyopia (one good and one bad eye)

What is the most common type of amblyopia?

Refractive

What is strabismus amblyopia missing?

Absence of bifoveal fixation

What is not a strabismus etiology type?

Bilateral

What is pseudoesotropia?

An appearance of esotropia while there is no actual eye turn

What is not a cause of pseudoesotropia?

Wide PD

When does the nose bridge become more prominent and epicanthal fold more displaced?

2 years

Feature of infantile esotropia

Large angle esotropia (>40 PD) & occurs during first 6 months

What is not a refractive accommodative esotropia feature?

Uncorrected myopes

How to treat a hyperopic and/or high AC/A accommodative esotropia?

Bifocals

You prescribe single vision plus glasses to a little girl that has constant esotropia. She comes back for her 3 months follow up and you repeat cover test, she seems ortho at distance. However, Near cover test reveals some residual esotropia with her spectacle Rx. What is the next step from there?

Prescribe add power for near to relax the accommodation and help her diverge.

Infantile XT Presentation

All of the above

What can an infantile XT develop?

Strabismus amblyopia (abnormal binocular interaction)

Deprivational Amblyopia

Physical obstruction along the lone of sight preventing the formation of a clear retinal image

What is the age cut off to consider deprivational amblyopia?

Before 6 years

What is not a potential cause of deprivational amblyopia?

Strabismus

What is the most common form of mixed mechanism amblyopia?

Anisometropia & constant unilateral strabismus

How to detect refractive amblyopia?

Cycloplegic refraction

How to not detect strabismus?

Cycloplegic refraction

How to not detect derivational amblyopia?

Cover test

When is the best time to remove unilateral congenital cataract?

6-8 weeks

When is the best time to remove bilateral congenital cataract?

6-10 weeks

Most common treatment for refractive amblyopia?

Glasses

Which type of refractive amblyopia do you patch for?

Anisometropia

How long to patch for if pt has moderate amblyopia?

2 hours

How long to patch for if pt has severe amblyopia?

6 hours

How many times is equivalent to Atropine 1% daily?

Twice a week

How many hours is equivalent to atropine 1%?

6 hours