Amblyopia

1
(No Transcript)
2
Amblyopia
American Academy of Ophthalmology (section 6)
2002-2003
Design by Shafei Rahimi (Medical
Student) rahimi_at_doctor.com
3

• Unilateral or less commonly, bilateral reduction
  of best corrected visual acuity that can not be
  attributed directly to the effect of any
  structural abnormality of the eye or the
  posterior visual pathway. Defect of central
  vision

4
Resulting from one of following

• Strabismus
• Anisometropia or high bilateral refractive error
  (Isoametropia)
• Visual deprivation

5

• Prevalence 2-4 in the North American
  population
• Commonly unilateral
• Nearly all amblyopic visual loss is preventable
  or reversible with timely detection and
  appropriate intervention.
• Children with amblyopia or at risk for amblyopia
  should be identified at a young age when the
  prognosis for successful treatment is best.
• Role of screening is important

6

• Amblyopia is primarily a defect of central
  vision.
• There is a critical period for sensitivity in
  developing amblyopia.
• The time necessary for amblyopia to occur during
  critical period is shorter for stimulus
  deprivation than for strabismus or anisometropia.

7
Neurophysiology

• Cells of the primary visual cortex can completely
  lose their innate ability or show significant
  functional deficiencies
• Abnormalities also occur in neurons in the
  lateral geniculate body
• Evidence concerning involvement at the retinal
  level remains inconclusive

8
(No Transcript)
9
(No Transcript)
10
(No Transcript)
11
Classification

• Strabismus Amblyopia
• Anisometropia Amblyopia
• Amblyopia Due to bilateral high refractive error
  (isometropia)
• Deprivation Amblyopia

12
Strabismus Amblyopia

• The most common form of amblyopia
• Strabismic amblyopia is thought to result from
  competitive or inhibitory interaction between
  neurons carrying the nonfusible inputs from the
  tow eye.
• Which leads to domination of cortical vision
  centers by the fixating eye and chronically
  reduced responsiveness to the nonfixating eye
  input.

13
Anisometropia Amblyopia

• Second in frequency
• It develops when unequal refractive error in the
  tow eyes causes the image on the one retina to
  be chronically defocused.
• This condition is thought to result
• Partly from the direct effect of image blur in
  the development of visual acuity.
• Partly from intraocular competition or inhibition

14
(No Transcript)
15

• Mild hyperopic or astigmatic anisometropia (1-2D)
  ? mild amblyopia
• Mild myopia anisometropia (less than -3D) usually
  doesn't cause amblyopia
• unilateral high myopia (-6D) ? sever amblyopia
  visual loss.
• The eye s of a child with anisometropic amblyopia
  look normaly to the family and primary care
  physician.

16
Amblyopia Due to bilateral high refractive error
(isometropia)

• isometropia amblyopia result from large,
  approximately equal, uncorrected refractive error
  in both eyes of a young child.
• Hyperopia exceeding 5D myopia excess of 10 D ?
  risk? bilateral amblyopia

17

• Merdional amblyopia
• Uncorrected bilateral astigmatism in early
  childhood may result in loss of resoling ability
  limited to chronically blurred meridians.

18
Deprivation Amblyopia

• It is usually caused by congenital or early
  acquired media opacity.
• This form of amblyopia is the least common but
  most damaging and difficult to treat.
• In bilateral cases acuity can be 20/200 or worse.

19
(No Transcript)
20

• In children younger than 6 years, dons congenital
  cataract that occupy the central 3 mm. or more of
  the lens must be considered capable of causing
  sever amblyopia.
• Similar lens opacities acquired after 6 years are
  generally less harmful.

21

• Small polar cataracts lamellar cataracts may
  cause mild to moderate amblyopia or may have no
  effect on visual development.
• Occlusion amblyopia is a form of deprivation
  caused by excessive therapeutic patching.

22
Diagnosis

• Characteristics of vision alone cannot be used to
  reliably differentiated amblyopia from other form
  of visual loss.
• The crowding phenomenon is typical for amblyopia
  but not uniformly demonstrable.
• Afferent pupillary defect are Characteristic of
  optic nerve disease but occasiinally appear to be
  present with amblyopia

23

• Multiple assessment using a variety of tests or
  performed on different occasions are sometime
  required to make a final judgment concerning the
  presence and severity of amblyopia.

24

• Binocular fixation pattern
• It is a test for estimating the relative level of
  vision in the tow eyes for children with
  strabismus who are under the age of about 3.
• This test is quite sensitive for detecting
  amblyopia but results can be falsely positive.
• Showing a strong preference when sision is equal
  or nearly equal in the tow eyes, particularly
  with small angle strabismic deviations.

25

• The modified Snellen technique directly measures
  acuity in children 3-6 years old.
• Often, however, only isolated letters can be
  used, which may lead to under estimated amblyopia
  visual loss.
• Croding bar may help alleviate this problem.

26

• Crowding bar, or contour interaction bars, allow
  the examinator to test the crowing phenomenon
  with isolated optotype. Bar surrounding the
  optotype mimic the full of optotype to the
  amblyopia child.

27
Treatment

• Treatment of amblyopia involves the following
  steps
• Eliminating (if possible) any obstacle to vision
  such as a cataract
• Correcting refractive error
• Forcing use of the poorer eye by limiting use of
  the better eye.

28
Cataract removal

• Cataracts capable of producing amblyopia require
  surgery without unnecessary delay.
• Removal of significant congenital lens opacities
  during the first 2-3 months of life is necessary
  for optimal recovery of vision.
• In symmetrical bilateral cases, the interval
  between operations on the first and second eyes
  should be no more than 1-2 weeks.
• Acutely developing severe traumatic cataracts in
  children younger than 6 years should be removed
  within a few weeks of injury, if possible.

29
Refractive correction

• In generally, optical prescription for amblyopic
  eyes should correct the full refractive error as
  determined with cyclopagic.

30
Occlusion and optical degradation

• Full time occlusion of the sound eye
• Defined as occlusion for all or all but one
  waking hour.
• It is the most powerful means of treating of
  amblyopia by enforced use of the defective eye.
• The patch can either be left in place at night or
  removed at bedtime.
• Spectacle-mounted occluser or special opaque
  contact lenses can be used as an alternative to
  full-time patching if skin irritation or poor
  adhesion proves to be a significant problem

31
(No Transcript)
32
(No Transcript)
33

• Full time patching should generally be used only
  when constant strabismus eliminates any
  possibility of useful binocular vision because ?
  full time patching runs a small risk of
  perturbing binocularity.

34

• Part-time occlusion
• Defined as occlusion for 1-6 hours per day.
• The children undergoing part time occlusion
  should be kept as visually active as possible
  when the patch is in place.
• Compliance with occlusion therapy for amblyopia
  declines with increasing age.

35

• Penalization
• A cyclopagic agent (usually atropine 1 or
  homatropine 5 )? once daily to the better eye
• This form of treatment has recently been
  demonstrated to be as effective as patching for
  mild to moderate amblyopia.

36
Complication of therapy

• Full time occlusion carries the greatest risk of
  this complication and requires close monitoring,
  especially in the younger child.
• The first follow up visit after initial treatment
  should occur within 1 week for an infant and
  after interval corresponding to 1 week per year
  of age for the older child.
• Part time occlusion optical degradation methods
  allow for less frequent observation but regular
  follow up is still critical

37

• The time required for completion of treatment
  depends on the following
• Degree of amblyopia
• Choice of therapeutic approach
• Compliance with the prescribed regimen
• age of the patient

38
Unresponsiveness

• Complete or partial Unresponsiveness to treatment
  occasionally affect younger children but must
  often occurs in patients older than 5 years.
• Primary therapy should generally be terminated if
  there is a lock of demonstrable progress over 3-6
  months with good compliance.
• Refraction should be carefully rechecked and the
  macula and optic nerve critically inspected for
  subtle evidence of hypoplasia or other
  malformation that might have been previously
  overlooked.

39
Recurrence

• When amblyopia treatment is discontinued after
  fully or partially successful completion,
  approximately half of patients show some dgree of
  recurrence,
• Maintenance therapy
• Patching for 1-3 hours per day
• Optical penalization with spectacles
• Pharmacologic penalization with atropine 1 or 2
  day per week.
• This may require periodic monitoring until age
  8-10.

40
(No Transcript)