Strabismus

Question 1

What is strabismus?

Answer 1

This is a condition characterized by misalignment of the eyes when looking at an object.

Question 2

What is a visual axis?

Answer 2

is an imaginary line that that connects the center of fovea to an object being fixated in space

Question 3

What is binocular single vision?

Answer 3

is the ability to use both eyes together so that separate and slightly dissimilar images arising in each eye are appreciated as a single image by the process of fusion in the brain

Question 4

Characteristics of binocular vision?

Answer 4

It is acquired and reinforced during the first few years of life.
Requires three factors for its development;
1. Clear vision in both eyes
2. The ability of the visual areas in the brain to promote fusion
3. Precise coordination of the two eyes for all direction of gaze

Question 5

Orthophoria?

Answer 5

refers to perfect ocular alignment in the absence of any stimulus for fusion.

Question 6

Heterophoria?

Answer 6

a tendency of the eyes to deviate when fusion is blocked
- Also known as a latent squint.

Question 7

Heterotropia?

Answer 7

manifest deviation in which the visual axes do not intersect at the point of fixation.

Question 8

Muscles of the eye and their innervation?

Answer 8

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Question 9

Pathophysiology of strabismus?

Answer 9

• In order for the eyes to move fully and together, there has to be correct functioning of the extraocular muscles, cranial nerves III, IV and VI, and the higher cortical centres, which control the speed of eye movements.
• Problems in the function of any of these can lead to the development of strabismus or a squint.
• Strabismus describes the appearance of the eyes when the visual axis fails to meet at the fixation point.

Question 10

Epidemiology of strabismus?

Answer 10

• Strabismus is one of the most prevalent ocular problems among children
• Although strabismus can occur at any age, but most of the cases occur before the age of 6 years with a peak onset of about 3 years

Question 11

Classification of strabismus?

Answer 11

1. Apparent(pseudo-strabismus)
2. Latent (heterophoria)
3. Manifest (heterotopia)

Question 12

What is latent strabismus?

Answer 12

AKA intermittent strabismus
- it involves misalignment that occurs intermittently, typically when the eyes are not focusing on any object, such that the eyes may appear aligned most of the times
- but the misalignment can become evident under certain circumstances such as when the person is tired, stressed, or viewing objects at a closer distance for an extended period.

Question 13

Apparent or pseudo strabismus?

Answer 13

• This is the condition where the eye appear misaligned due to factors other than true misalignment
• This can be created by certain morphological features of the face including the eyelids.
  e.g. Prominent epicanthal folds, Eyelids larger than normal or a wide nose bridge

Question 14

What is manifest strabismus?

Answer 14

• AKA constant strabismus
• involves a consistent misalignment of the eyes which is present all the time
• In this condition one eye may turn inward (esotropia), outward ( exotropia), upward (hypertropia), or downward (hypotropia) relative to the other
• This can further be classified into concomitant and paralytic strabismus

Question 15

Concomitant strabismus?

Answer 15

Concomitant strabismus, the angle of deviation remains the same in all directions of gaze, misalignment is consistent regardless of where the person is looking, occurs early in childhood.

Question 16

Paralytic strabismus?

Answer 16

• Strabismus caused by partial or complete paralysis of the EOM
• The angle of deviation alters depending on the direction of gaze. however, the abnormality may occur in the brainstem, nerve, neuromuscular junction, muscles
• Can be congenital but its mostly acquired and caused by cranial nerve palsies, muscle dysfunction or orbital diseases, demyelinating diseases eg MS, trauma
• Compensated by head tilting

Question 17

What is Esotropia?

Answer 17

• Esotropia is a manifest inward deviation of the eyes
• It is the most common form of childhood strabismus
• It may be primary, secondary (most commonly due to poor vision)
• Primary esotropias are classified as accommodative or non accommodative

Question 18

Accomodative esotropia?

Answer 18

• The eyes turn inward when focusing on nearby objects
• Commonly associated with refractive errors of hyperopia.
• Usually presents between 1 and 5 years of age
• Usually intermittent at onset and becomes constant
• Diplopia may occur but disappears with suppression

Question 19

Types of accomodative esotropia?

Answer 19

It can be refractive or non refractive
- Happens when a farsighted individual, is trying to focus on a nearby object the eyes work harder than usual as there will be excessive effort of accommodation resulting in inward deviation of the eye
- It is often hereditary

Question 20

Non accommodative esotropia?

Answer 20

Form of strabismus characterized by inward deviation of the eye regardless of whether the person is focusing on near or distant objects.
Subtypes:
1. Essential Infantile Esotropia (congenital esotropia)
- occurring before the age of 6 months
2. Late onset (acute)

Question 21

Infantile esotropia?

Answer 21

• Early-onset (congenital, essential infantile) esotropia is an idiopathic esotropia thought to be caused by visual-cortical maldevelopment
  developing within the first 6 months of life in an otherwise normal infant with no significant refractive error and no limitation of ocular movements.
• Associated with positive family history of strabismus
• Most common

Question 22

Acute esotropia?

Answer 22

• Late onset
• Around 5–6 years of age.
• No significant refractive error
• Sudden onset of diplopia.
• The sudden diplopia may result from an underlying and potentially life-threatening disease process
• Associated with 6th nerve palsy
• Constant for distant and near vision

Question 23

What is exotropia?

Answer 23

• Exotropia is a manifest outward deviation of the eye.
• Constant or intermittent
• It may be primary, secondary
• Exotropia may occur from time to time
• AKA divergent squint or wall eyes
• Associated with 3rd cranial nerve palsy
• Other accommodative types are: hypertropia, hypotropia

Question 24

Risk factors for strabismus?

Answer 24

1. Family history of strabismus
2. Cerebral palsy
3. Infections (meningitis, encephalitis, measles)
4. Head injury
5. Genetic disorders i.e. down syndrome
6. Low birth weight or prematurity
7. Prenatal drug exposure i.e. alcohol

Question 25

Clinical presentation of strabismus?

Answer 25

1. Ocular discomfort 2. Headaches 3. Abnormal head posture 4. Inability to read properly 5. Asthenopia (eyestrain) 6. Double vision (diplopia) - This occurs when the brain receives two different images from the eyes. 7. Suppression - The brain may ignore the image from the misaligned eye to avoid double vision, which can lead to amblyopia (lazy eye).

Question 26

DDx for strabismus?

Answer 26

1. Pseudo-strabismus 2. Nystagmus Related to pathology e.g 3. graves disease 4. duanes syndrome 5. brown syndrome 6. mysthenia gravis

Question 27

Investigations for strabismus?

Answer 27

1. Hirschberg test 2. Krimksy test/prism test 3. Cover-uncover test 4. Worth 4-dot test

Question 28

What is the Hirschberg test?

Answer 28

- Detects Heterotopia and Heterophoria. - A very important simple test that can be done with a pen torch - Estimates the angle of deviation - Observe corneal reflections & assess fixation in the deviating eye - Use a light source, such as a penlight or Finhoff transilluminator.

Question 30

Describe the Hirschberg test?

Answer 30

1. Use a light source, such as a penlight or Finhoff transilluminator. 2. Instruct the patient to focus their gaze on your light source. 3. From a distance of 2 feet, shine your light source equally into the patient’s eyes at midline. 4. Observe the reflection of light off the cornea, which should appear as a pin-point white light near the center of the pupil in each eye

Question 31

Describe the Krimsky test?

Answer 31

1. Initial Observation – The doctor shines a light at both eyes and observes the reflection in the cornea - Any misalignment is noted. 2. Prism Placement – A prism is placed in front of the deviated eye to shift the reflection - The strength of the prism is gradually increased. 3. Alignment Assessment – The doctor continues adjusting the prism power until the reflections in both eyes are aligned. 4. Measurement of Deviation – The prism power required for alignment gives an estimate of the degree of eye misalignment.

Question 32

Describe the cover-uncover test?

Answer 32

The cover-uncover test is useful to differentiate manifest and latent strabismus 1. Cover one of the patient’s eyes and closely observe the uncovered eye for corrective movement. 2. When (fixating) the normal eye is covered, (a manifest) the abnormal eye must move from its deviated position and take up correct fixation (position). 3. Accordingly, movement indicates that manifest strabismus is present in the uncovered eye (a tropia). The cover test is repeated on each eye

Question 33

Describe the worth 4 dot test?

Answer 33

1. Place glasses or polarized Worth 4-dot glasses on the patient 2. The red lens goes over the right eye. 3. The patient is shown a flashlight or wall-mounted target with 4 illuminated dots 4. The test is performed at both 33 cm and 6 m.

Question 34

Results of worth 4 dot test?

Answer 34

1. Four dots: This indicates a normal result in patients with normal alignment during testing 2. Two red dots: Left eye suppression 3. Three green dots: Right eye suppression 4. Five dots with red on the right and green on the left: Uncrossed diplopia. This is expected in esotropia and indicates ARC in exotropia patients. 5. Five dots with green on the right and red on the left: Crossed diplopia. This is expected in exotropia and indicates ARC in esotropia patients. 6. In patients with manifest strabismus during testing, this indicates anomalous retinal correspondence (ARC).

Question 35

Non-surgical management of strabismus?

Answer 35

Vision Therapy Eye Exercises Computerized Programs Occlusion Therapy Patching Atropine Drops Correct refractive errors Glasses or Contact Lenses Prism Lenses

Question 36

Surgical management of strabismus?

Answer 36

1. Strabismus Surgery - Repositioning of muscles - Tucking - Myectomy - Adjustable Sutures 2. Post-Treatment Care - Follow-Up Visits - Additional Treatments

Question 37

Prognosis of strabismus?

Answer 37

1. Early Detection and Treatment 2. Better Prognosis in Children <5 3. Critical Period: The first few years of life are critical for visual development 4. Better prognosis when identified and treated early 5. Strabismus must be treated before 6- 10 years of age

Question 38

Potential complications of untreated strabismus?

Answer 38

1. Amblyopia - If strabismus is left untreated, especially in children, it can lead to amblyopia, where the brain favors one eye over the other, resulting in reduced vision in the weaker eye. 2. Vision Loss - Untreated amblyopia can lead to permanent vision loss in the weaker eye. 3. Double Vision - In some cases, strabismus can cause double vision, especially in adults. 4. Cosmetic Concerns - The appearance of strabismus can also be a cosmetic problem, potentially impacting self-esteem