educational ppt in ophthalmology subspeciality squint

1. Amblyopia
V.Chandrasekhar Reddy
Hyderabad .INDIA
drvcreddy@gmail.com

2. • Amblyos-------Dull
• Opia------------Vision

3. Amblyopia Definition
• : Reduced vision in one eye or occasionally
both eyes caused by pattern vision deprivation
or abnormal binocular interaction for which no
causes can be detected by physical
examination of the eye and which in
appropriate cases is reversible by therapeutic
measures ( von Noorden).

4. • Mono------2 line differance.
• Bil -------<6/12

5. • Functional (Reversible)
• Organic (Irriversible)

6. Prevalence
• 1% to 5% of children.
• most common cause of monocular
(one eye) visual impairment among
young and middle-aged adults.
• Up to age 40, amblyopia causes poor
vision in more people than all ocular
diseases or trauma combined.

7. Mechanism
Basically visual system is not being
used & incompatable in its
developemental period due to
• Abnormal binocular interaction
• foveal pattern deprivation

8. Facts
• Unilateral amblyopia is associated with
strabismus in 50% of cases and with
anisometropia in a somewhat smaller
percentage.
• Amblyopia is more than four times in
infants who are premature, who have a
first degree relative with amblyopia.

9. • Neurodevelopmental delay sixfold
greater than in healthy, full-term
infants.
• Socioeconofic factors no role

10. Other factors
• Lower birthweight may indicate a
greater susceptibility of the developing
visual pathways.
• Genetic

11. • In full term infants whose mothers
smoke, abuse alcohol or drugs, the
risk of strabismus and amblyopia is
similar to that of premature babies.

12. Pathophysiology
• Very important research about visual
development was done by David Hubel
and Torsten Wiesel and for their work,
they were awarded the Nobel prize for
medicine in 1981for their work on
information processing in the visual
system

13. • children born with cataracts did not develop
normal vision after removal of the cataracts
what happens to the brain's visual processing
system when one eye was occluded by closing
the lid. Wiesel and Hubel found that when an
animal lacked vision in one eye during a critical
early period of development, cells in the brain's
primary visual cortex expanded into the areas
that normally would have received signals from
that eye. This research showed that early in life
there is a brief span of time during which the
neural connections present at birth can be lost
or modified if they are deprived of stimuli.

14. In a dark field autoradiograph of striate
cortex in a normal monkey (top), the
labeled columns from one eye are white;
those from the other eye are dark. The
image at bottom shows how the columns of
the open eye (white) have expanded as the
columns of the eye deprived of light (black)
have shrunk.

15. • Differentiation, Development &
organisation of visual pathways is not
complete at birth.

16. • The visual pathways continue to
develop from birth to approximately age
10, most rapid in infancy.
• Potential for the development of
amblyopia persists to approximately
age 10, at which time plasticity of the
visual pathways ceases.

17. Retina
• X. Ganglion cells—Fovea—High spacial
• Y. Whole ---Low spacial
Reduction of X cells

18. LGN
• In the LGN, some shrinkage
of cells is seen in layers
associated with the deprived
eye.

19. Visual cortex changes
• Reduction in no; of cortical cells
recieving inputs from amb. Eye
• Neurons associated with the temporal
hemi-retina (non-crossing fibers) are
more severely affected .

20. • The ERG of amblyopic eyes are normal. In
contrast, VER reduced in amplitude
• fMRI
• Positron emission tomography(PET)
• Magnetencephalography(MEG)
Reduced levels of activation in the visual
cortex

21. Positron emission tomography(PET)
Left showingLeft showing gulcose metabolismgulcose metabolism

22. Ambliogenic factors
Anisometropia (spherical or cylindrical)
>1.50 D
Any manifest strabismus
Hyperopia >3.50 D in any meridian
Any media opacity >1 mm in size
Astigmatism >1.5 D at 90° or 180° > in
oblique axis (>10° eccentric to 90° or
180°)
Ptosis ≤1 mm margin reflex distance

23. Critical period
• Begins about 4months .earlier for
stimulus deprivation.
• Peak by 2yrs
• Disappears by 9 -12yrs

24. Primary causes of
amblyopia:
• Pattern deprivation
• Strabismus
• Optical defocus

25. Pattern deprivation is the
most severe form of visual
deprivation.
Light reaches the retina, but
all spatial detail (high and
low spatial frequencies) is
lost.
The most common cause of
pattern deprivation is
infantile cataract
• corneal opacity.ptosis
medial opacities
• blepharospasm. obstuction
of visual axis.

26. Research with monkeys has established
two of the basic requirements for
successful treatment and prevention of
amblyopia, in cases of form
deprivation:
• surgery before the age of 4 months
• occlusion

27. Strabismic amblyopia
• Most common.
Strabismus can lead
to amblyopia since
the eyes receive
uncorrelated retinal
images.
• The result is arrested
development of visual
function (including
visual acuity) and
amblyopia.

28. • Commonly seen
in non alternating
ET.
• Neutral density
filter effect
• Eccentric fixation

29. Optical defocus
• Next common.
• Optical defocus is less damaging to
visual development than pattern
deprivation as defocus removes
high spatial frequencies (fine detail,
sharp edges, etc.) from the retinal
image, but low spatial frequencies
(large shapes) remain.

30. The most common cause of this kind
of amblyopia is anisometropia.
Ametropia ..Bil Amb
• very high myopia, >6D
• more hyperopic eye.>4D
• Astigmatism >2D

31. • To prevent amblyopia is to correct the
refractive error as early as possible;
• > +2.50 diopters of hyperopia or
astigmatism, 75% amblyopic without
treatment, but only 25% developed
amblyopia who were corrected

32. Causes Abnormal
Binocular
Interaction
Deprivation of Form
Vision
Strabismus
Anisometropia
Visual deprivation
Uni
Bil
+
+
+
_
_
--
+
+

33. Organic /relative
• Organic cause with amblyogenic
factors like anomalies of retina,medial
opacities ,optic nerve
• Improve with patching

34. Diagnosis
• Reduced V.A uni or Bil.
• Amblyogenic factors like vision
deprivation, Strabismus, optical
defocus
• Alternative causes for visual loss have
to be ruled out

35. Abnormalities associated
with amblyopioa
Decreased
• V.A.
• Grating acuity
• Vernier acuity
• Contrast sensitivity
• Brightness perception
• Contour interaction
• Binocular percption
• Pupil reaction

37. Visual Acuity

38. Preverbal
Grating acuity tests
1.Teller acuity cards
2.Forced preferential looking (PFL)
6/240 at birth
6/60 at 3mths

39. Optokinetic nystagmus
(OKN) test
Smallest stripe that
produces nystagmus
6/120 at Birth
6/60 in 6mths child

40. Fixation preference test
• CSM method
Central
Steady
Maintained
• Child wont allow to cover normal eye
• Alt fixation ..No amb

41. Sweep VEP
• Records cortical potentials to visual stimuli
• 6/120…1 mth
• 6/6 at 6 mths

42. 2-4yrsVerbal children
Matching tests
• Illeterate E
• Pictures
• Symbols
• Numbers
• 6/9
Bust vision tests

43. METHOD 1mth 2mths 6mths Age 6/6
OKN
Preferential
looking
VEPsweep
6/120 6/60 6/36 20-30mths
6/120 6/60 6/36 24-36mths
6/120 6/60 6/6-6/12 6-12mths

44. 4-6yrs
Conventional subjective tests
• Snellens

45. Crowding
phenomenon
• Single letter acuity better than line acuity
• This is due to “spatial interference effects
seeing a visual contour that is produced
by a near by adjacent contour
• For followup..single acuity improves
faster than line
• If line acuity not achieved regression is
high on discontinuation of therapy
• typically found in strabismic amblyopia
[Bonneh, Y., Sagi, D., & Polat, U. (2004a)

46. • A pattern can be difficult to identify
when surrounded by a “crowd” of
flanking patterns, a phenomenon called
“crowding” (Stuart & Burian, 1962). A
briefly flashed pattern can be difficult to
identify when surrounded in time
(before and/or after) by other patterns (
Breitmeyer, 1984), forming a “temporal
crowding” situation

47. • This reduction in acuity is due to an
interference effect by the flanking
patterns, and it depends on their
distance from the central pattern . The
critical distance for crowding increases
with eccentricity, extending as far as
half the retinal eccentricity of the target
and at the periphery it appears to be
independent of the size of the target

48. Three tasks.
Levi D M et al. J Vis 2007;7:21
©2007 by Association for Research in Vision and Ophthalmology

49. The central field of amblyopes is similar to
the normal periphery in many respects (e.g.,
Levi, 1991; Levi & Klein, 1985, Levi et al.,
1985; Levi et al., 1994a, 1994b, but see Levi
et al., 2002a). The similarity suggests that
amblyopia (or at least some aspects of
amblyopia) might be explained on the basis
of an “equivalent eccentricity”, that is, an
eccentricity in the normal periphery where
performance is equivalent to that of the
amblyopic fovea.

50. Neutral density filters
• Does not cause reduction in VA..in
StrabismicAmb
• More specific
• Differentiate organic from functional
Amb & aniso metropic

51. • Contrast sensitivity reduced
• Eccentric fixation
• increase in the foveal thickness of
amblyopic eyes along with a reduced
foveal pit in the horizontal, but not
vertical, meridian.[3]
• Bruce A, Pacey IE, Bradbury JA, Scally AJ, Barrett BT. Bilateral Changes in Foveal Structure in Individuals with Amblyopia. Ophthalmology.
Sep 29 2012;[Medline].
•

52. • Stereopsis decreased
• Light sensitity reduced

53. • Pupillary response..better in
paracentral retina
• VA better in uniocular
• VA better in scotopic

55. • Start treatment immediately
• Earlier ..better results

56. Clearing media
• Corneal opacity
• Cong.cataract
• Vet. Opcities
• Epiretinal membranes
• Subluxated clear lens
• Ptosis

57. Treatment
Optical correction
• Spects
• Contacts
• LASIK
• Phakic IOL

58. Spects
• Accurate optical correction
• Never cut the cylinder
• Deduct hyperopic power equally for
both eyes
• Objective measurement are more imp.
• Prompt correction of aphakia

59. Optical correction
• Acc.ET with amblyoia ::Full + correction
• Non acc ET:: <full +
• Acc. is symmetrical. Fixing eye
determines amount of acc.Any
decrease in + must be symmetrical

60. Optical correction
Ex, RE Amb
• RE -0.75 +1.50 90
• LE +0.75 sphere
• RE -1.50+1.50 90

61. Optical correction
• > 1.50 d sphere or 1.00 cylinder wait
for spects before starting patching
Anisometropia
• Knapps rule..aniseikonia will not occur
if anisometropia is axial

62. Occlusion
• Widely recognised ,time tested method.
• Neither substitute nor shortcut.
• Occlusion with adhesive skin patch is the
most effective means of therapy
• Near vision exercises will hasten
improvement

65. • Occlusion Dose Monitor electronically measures compliance
with the prescribed hours of occlusion so that visual
improvement may be correlated with the actual time patched.

66. Occlusion
• Unaffected eye
• Adhesive patch
• All waking hours
• Tapered gradually

67. • At any age
• Fulltime or part time
• Total coverage of eye
• No fogging or rubber
occluders
• Re-examined at
regular intervals
Younger the patient
greater risk of
occlusion amb

68. Schedule for occlusion
Age
---------------------
0-1yr
2-3yrs
4-6yrs
>6yrs
Occulsion(days)
Better eye
---------------------
3
4
5
6
Amb eye
-------------------
1
1
1
1

69. Techniques of active
treatment
• Mallet Intermittent photic stimulation
• Red filter over amblopic eye
• Euthyscope,Haidingers brushes- foveal fixation
• Chequer board light box with flashes
• Dotting: child fills series of circles
• Colouring pictures within lines,Video games

70. Response to occlusion
Minimum 3 months
• Acceptance
• Compliance

71. Followup
• V.A. VEP fMRI
• Fixation pattern
• Occlusion Amb
1st
yr…Every week
2nd
yr … 2 weeks
3rd
yr…3 weeks

72. When to stop occlusion
• V.A becomes equal
• Fixation is alternating
• No change in V.A. even after 3months

73. Prognostic considerations
• Younger the child better the prognosis
• Most effective in strabismic Amb.
• Myopic better than Hyperopic
• Fulltime occlusion

74. • Central fixation better than eccentric
• Near vision exercises will hasten
improvement
• Better after surgical allighnment

75. Occlusion after 9 yrs Encouraging in
• anisometropic,
• Ametropic
• after squint correction

76. • One study by Levartovsky et al showed
deterioration in 75% of children with
anisometropia of 1.75 diopters or more
after occlusion therapy.[29]
Recidivism
can occur, even several years after the
initial treatment period, and is as high
as 53% after 3 years.

77. Alternative methods
• Penalisation
• ,Levo-dopa 0.5-0.12mg/Kg
• ,citicoline
• Pleoptics& Red filter stimulation
• CAM stimulator
• Drugs..Strychnine
• ethnol

78. PENALISATION
• Atropine 1% drops one drop instilled once
daily by the mother in the sound eye
• Cosmetically acceptable,good compliance
• Not as effective as patch
• Useful in moderate and not dense
amblyopia
• NIH- randomised clinical trial: succes rate
patch 79%, penalisation 74%

79. • OPTICAL PENALISATION
Can be achieved by over correction with
+3DS equivalent to decrease dist vision of
better eye
EW CONTACT LENS used in infants

80. PHARMOCOLOGICAL
THERAPY
• Levadopa and Carbidopa are used
• Levadopa is a precursor of dopamine which
is nuerotransmitter at retinal level and also in
the visual cortex
• Carbidopa is a peripheral decarboxylase
inhibitor that prevents breakdown of
levadopa
• L- dopa administration showed changes in b
wave in ERG, oscillatory potentials, implicit
time of VEP

81. Prevention
• Screening for V.A ,Corneal reflex test,
refraction,&Stereopsis
• Team effort: parents,teachers,family
physician,paediatrician,ophthalmologist
• Surgical dressing.
• Hyphema
• Lid edema

82. New ideas
Perceptual learning >9yrs
• Gabor signal gratings.set of 3
contrasting dark &light ovals that form
Basic unit of visual perception

83. Implantable collamer lens
(ICL)
• Refractive Amblyopia not respondinfg
to patching with spects or contacts
Reversibility
High errors
Thin corneas

84. Recent studies
Amblyopia Treatment Study(ATS)
by Paed.Eye Disease Investgator
Group (PEDIG)
ATS1..
• Penalistion vs occlusion..moderate
Amb..Results showed similar response
after 6 months.In occlusion results are
faster.near vision activities must

85. ATS2… Dosage of occlusion
• 2hrs/day vs 6hrs/day for mod.Amb
• 6hrs/day vs fulltime occlusion in severe
Amb
• After 6 mths effect same

86. ATS 3
• Regular treatment for7-12 yrsand 13-
17yrs is encouraging
ATS 4
• Weekend atropine vs daily atropine for
mod. Amb
Amb treatment advice will be consistant
around the world and evidence based.

87. • After controlling baseline refractive error,&
alignment a decrease in hyperopia of
amblyopic eye . This shift toward
emmetropia was associated with ocular
alignment, supporting the idea that better
motor and sensory fusion promote
emmetropization.
• Marjean T. Kulp,1
Nicole C. Foster,2
Jonathan M. Holmes,3
Raymond T. Kraker,2
B. Michele Melia,2
Michael X. Repka,4
and D. Robbins Tien5
, on behalf of the
Pediatric Eye Disease Investigator Group

88. • 6 hours daily rather than 2 hours yield
greater improvement at 10 weeks. intense
patching protocol suggests that this strategy
is worth considering in children with residual
amblyopia.
• stable residual amblyopia after 12 weeks of
2-hour patching, an increase to 6-hour
patching c bring further improvement
• to achieve the best result in the shortest
amount of time, it may be worthwhile to
bypass 2-hour patching and start with 6-hour
patching instead

89. Trial of Patching vs Acupuncture for
Anisometropic Amblyopia in Children
Aged 7 to 12 Years
Jianhao Zhao, MD; Dennis S. C. Lam, MD, FRCOphth; Li Jia Chen, PhD; Yunxiu Wang, BMed; Chongren Zheng, DEpid; Qiaoer
Lin, DN; Srinivas K. Rao, FRCS; Dorothy S. P. Fan, FRCS; Mingzhi Zhang, MD; Ping Chung Leung, MD; Robert Ritch, MD,
FRCOphthArch Ophthalmol. 2010;128(12):1510-1517. doi:10.1001/archophthalmol.2010.306.

90. Most cases of amblyopia are
reversible if detected and treated
early,
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