Amblyopia

See Also

Definitions

Amblyopia
1. Greek: "Dullness of Vision"
2. Poor Vision in one eye not correctable with eyeglasses developing in early childhood
  1. Best corrected Visual Acuity not attributed to a structural abnormality of the eye or Visual Pathway

Epidemiology

Prevalence
1. North America: 2.4%
2. Worldwide: 1.4%
3. Fu (2020) Br J Ophthalmol 104(8):1164-70 [PubMed]
Occurs in children up to age 6 to 7 years old
1. Most common childhood cause of monocular Vision Loss
2. Reversible with early detection and treatment before age 7 years
Cause of permanent Vision Loss in 2.9% of adults in U.S.
1. Most common cause of monocular impaired Vision in ages 20 to 70 years old

Pathophysiology

Visual blur at level of Retina coinciding with visual development in early childhood
Occurs in developmentally immature eye
1. During first 6 months of life
2. Acuity normally improves rapidly 20/400 => 20/80
3. Eye fully matures by age 9 years
Normal maturity
1. Requires clear, equal, aligned image for each eye
2. Conflicting data with
  1. Strabismus (2 competing images)
  2. Anisometropia (1 clear, 1 blurred image)
3. Brain suppresses information from the "bad" eye in children
  1. Contrast with adults, who are unable to suppress conflicting images and therefore experience Diplopia
4. Continued suppression leads to permanent Vision Loss
  1. Loss of binocular Vision and depth Perception

Causes

Strabismus (most common cause of Amblyopia, 50% of cases)
1. Misalignment of eyes
2. Eyes are deviated inward or crossed (Esotropia) or outward (Exotropia)
3. One eye is suppressed to prevent Diplopia, and disuse results in Amblyopia
Refractive Amblyopia (17% of cases)
1. Concurrently present in up to 30% of patients who also have Strabismus
2. Isometric Amblyopia (Ametropic Amblyopia)
  1. Severe, equal Refractive Errors (results in bilateral Amblyopia)
3. Anisometropia
  1. Large difference in Refractive Error between eyes
  2. Causes
    1. Bilateral Hyperopia or far sightedness (most common)
      1. Myopia is less likely to result in Vision Loss
    2. Severe unilateral Hyperopia or Myopia
    3. Astigmatism
    4. Induced Astigmatism
      1. Eyelid Ptosis
      2. Periorbital Capillary Hemangioma
      3. Mild Congenital Cataract
Deprivation Amblyopia or Physical Occlusion (least common, <3% of cases)
1. Congenital Cataract
2. Retinoblastoma
3. Corneal scarring
4. Vitreous opacity
5. Severe Ptosis
6. Optic atrophy
7. Iatrogenic excessive patching

History

Wandering eye
Squinting or closure of one eye (associated with eye wandering or Exotropia)
Torticollis (child tilts head to better re-align the eyes, or to decrease Nystagmus)
Nystagmus
Strabismus
Family History
1. Congenital Cataracts
2. Congenital Glaucoma
3. Amblyopia

Exam

Vision
1. See Pediatric Vision Screening
Exam for associated ocular disease
1. Ptosis
2. Cataracts or Corneal opacities
3. Pupil exam
4. Extraocular Movement
Test for eye alignment abnormality (Strabismus)
1. Corneal Light Reflex
2. Cover-Uncover exam
3. Bruckner Test (Red Reflex)
4. Fixation and following
Differentiate Refractive Error from Amblyopia
1. Pinhole Test
Photoscreeners
1. Red Reflex evaluated in digital flash photograph taken of both eyes
2. Uncorrected Refractive Error can be inferred from the image
3. Iphone Application (gocheckkids) costs ~$150 per month per phone
4. Test Sensitivity 65% and Test Specificity 83%
5. Arnold (2018) Clin Ophthalmol 12:1533-7 [PubMed]
6. Matta (2009) Arch Ophthalmol 127(12):1591-5 [PubMed]

Management
Indications to Refer to Pediatric Ophthalmology

Family History
1. Sibling requiring glasses before age 2.5 years
2. Amblyopia Family History
3. Strabismus Family History (esp. parental history, which increases child's risk four fold)
4. Congenital Cataract Family History
5. Congenital Glaucoma Family History
Infant Findings
1. Retinoblastoma Family History
2. Abnormal Red Reflex
3. Abnormal eye tracking after age 3 months
4. Strabismus
5. Chronic eye tearing or discharge
6. Gestational age <30 weeks
7. Birth weight <1500 g (3 lb 5 oz)
8. Cerebral Palsy
9. Down Syndrome and other syndromes with eye involvement
Childhood findings
1. Strabismus
2. Ptosis
3. Two-line difference between eyes
4. Age 3 to 4 years
  1. Vision worse than 20/50 in either eye
5. Age 4 to 5 years
  1. Vision worse than 20/40 in either eye
6. Age >5 years
  1. Vision worse than 20/30 in either eye
  2. Child not reading at grade level

Management
General

Treat underlying cause early
1. Address Congenital Cataracts and Refractive Error if present
2. Correct Strabismus if present
Previously, encouraged children to write or draw while good eye obscured
1. However near activities have not been found to improve Amblyopia
Force child to use amblyopic eye by obscuring good eye
1. Approach
  1. Late presenting, older children with more significant Amblyopia typically receive more aggressive approach
    1. Sustained glasses and patching
  2. Patching for 2 hours daily is as effective as 6 hours daily in moderate Amblyopia (20/40 to 20/80)
  3. Patching for 6 hours daily is as effective as 23 hours daily in severe Amblyopia (20/100 to 20/400)
2. Manual methods
  1. Patch "good", dominant eye (usual course)
  2. Opaque Contact Lenses
  3. Cloth over glasses on good eye side or prescription glasses to blur good eye
    1. However, glasses are less effective since child may still see around the edges of the glasses
  4. Bangter Filter (graded adhesive applied to glasses lens over the good eye)
    1. Indicated in moderate Amblyopia
    2. As effective as 2 hours of patching daily
3. Atropine (0.5-1%)
  1. Indicated in children noncompliant with patching or glasses
  2. Dosing: 1 drop daily to good eye for 2-7 days per week
  3. Mechanism
    1. Drops applied to good eye to dilate pupil
    2. Prevents accommodation and causes Vision blurring
  4. Efficacy
    1. Used 2 consecutive days per week (e.g. weekends) is as effective as daily use in moderate Amblyopia
    2. Daily Atropine is as effective as daily, 6 hour patching in moderate Amblyopia
    3. Most effective in far sightedness

Prognosis

Early, aggressive, and consistent therapy is critical
1. Most responsive before age 3-5 years old
2. Good outcomes when treated at age <7 years
Amblyopia recurs in 24% after 1 year
1. Be vigilant about surveillance
Amblyopia nearly irreversible after age 9 years
1. New studies suggest teens may benefit from therapy
2. Scheiman (2005) Arch Ophthalmol 123:437-47 [PubMed]

Resources
Patient Education

Information from your Family Doctor
1. http://www.familydoctor.org/handouts/460.html

References