Amblyopia

Amblyopia -
Definition, Classification, Pathophysiology, Factors, Types, Clinical features, Management - prevention and treatment.

2. ▪DEFINITION
▪CLASSIFICATION
▪TYPES OF AMBLYOPIA
▪PATHOPHYSIOLOGY OF AMBLYOPIA
▪CLINICAL CHARACTERISTICS / CLINICAL FEATURES
▪VISUAL ACUITY IN AMBLYOPIC EYE
▪MANAGEMENT OF AMBLYOPIA

3. ▪It refers to partial loss of sight (vision) in one or both eyes, in the
absence of any organic disease of ocular media, retina and visual
pathway.
▪It is caused by abnormal visual development secondary to abnormal
visual stimulation in the absence of ophthalmoscpic or other marked
objective signs.
▪Literally, speaking, amblyopia is a spectrum of visual loss, range from
missing a few letters on 6/6 line to the hand motion vision.

4. 1.) ORGANIC AMBLYOPIA VERSUS FUNCTIONAL AMBLYOPIA –
ORGANIC AMBLYOPIA –
▪It is irreversible condition.
▪It refersto a partial visual loss causedby undetectable organic
lesions in the eye or in the visual pathway.
▪E.g. –toxic amblyopia.
FUNCTIONAL AMBLYOPIA –
▪It refers to obligatory psychical suppression of the retinal images.
▪It is a reversible condition.
▪Depending on the cause, may be anisometropic, strabismus,
meridional or stimulus deprivation.

5. 2.)AMBLYOPIA OF ARREST VERSUS AMBLYOPIA OF EXTINCTION –
AMBLYOPIA OF ARREST –
▪Amblyopia caused by a stage of visual development early in life.
▪It is not known that a 6/6 visual acuity in an infant is reached in 6 months of
age, amblyopia of arrest would be caused by an interference with the
fixation reflex that begins before 6 months of age . E.g. During critical
period of development.
AMBLYOPIA OF EXTINCTION –
▪Amblyopiaresulting from the suppression of an already existing visual
acuity.
▪This is usually possible in children up to 6 years of age.
▪In other words, it can be concluded that any strabismus or visual
deprivation b/w 6 months of age & 6 years, would result in amblyopia of
extinctionor so called suppression amblyopia.

6. 3.) CONGENITAL VERSUS ACQUIRED AMBLYOPIA -
CONGENITAL AMBLYOPIA –
▪These term had been used in the literature for the patient’s
having low vision, nystagmus and poor colour vision.
▪It is also used for patients having reduced visual acuity in
whom no obvious cause, such as strabismus and ametropia, is
present.
▪These patients do not respond to treatment.E.g. Organic
amblyopia.
ACQUIRED AMBLYOPIA –
▪It is a non informative term which encompasses all other
cases with amblyopia such as strabismus, anisometropia and
disuse. Etc.

7. There are many types of amblyopia –
▪Strabismic amblyopia
▪Stimulus deprivation amblyopia
▪Anisometropic amblyopia
▪Meridional amblyopia
▪Isoametropic amblyopia
▪Idiopathic amblyopia
▪Amblyopia secondary to nystagmus

8. 1.) STRABISMIC AMBLYOPIA –
▪The term Strabismic amblyopia is used for the amblyopia seen
in those children patients with unilateral constant squint who
strongly favour one eye for fixation.
▪Strabismic amblyopia is a common form of amblyopia.
▪Strabismic amblyopia is seen far more often in esotropia than
the exotropes.
▪Strabismic amblyopia occurs very rarely in patients with
hypertropia.
▪Patients with alternative Strabismus ( squint) do not have
amblyopia but they have abnormal binocular functions.

9. 2.)STIMULUS DEPRIVATION AMBLYOPIA / AMBLYOPIA OF
DISUSE / AMBLYOPIA EX ANOPSIA –
▪This term has been discarded in relation to Strabismus.
▪It should be reserved for those conditions only where in one eye is
totally excluded from seeing early in life.
▪Such conditions include –monocular congenital or traumatic
cataract, compete ptosis, corneal opacity and prolonged patching of
the normal eye for the treatment of amblyopia.
▪It is least common but most damaging and difficult to treat form of
amblyopia.
▪NOTE –Bilateral deprivational amblyopia may develop in small
children with bilateral media opacities, such as –Bilateral congenital
cataract, Bilateral corneal opacity and Bilateral vitreous
haemorrhage.

10. 3.) ANISOMETROPIC AMBLYOPIA –
▪It refers to the amblyopia occuring in an eye having
higher degree of the refractive error than the fellow (
other ) eye.
▪This type of amblyopia is more common.
▪It is of a higher degree in patients with
anisohypermetropia than those in anisomyopia.
▪Even 1-2D. Hyperopic anisometropia may cause
amblyopia while up to 3 D myopic anisometropia usually
does not cause amblyopia.

13. It can be discussed Under following headings-
1.) Amblyogenic factors
2.) Role of retina in the development of amblyopia
3.) Active cortical inhibition

14. 1.) AMBLYOGENIC FACTORS -
These are as follows –
A.) Deprivation of form vision
B.) Light deprivation
C.) Abnormal binocular interaction

15. A.) DEPRIVATION OF FORM VISION—
a.) Monocular deprivation of form vision –
▪It occurs the critical period of visual development results in
amblyopia in the deprived eye.
▪Monocular visual deprivation works as an amblyogenic factor in
strabismic, Anisometropic,and stimulus deprivation amblyopia.
b.) Binocular deprivation of form vision –
▪It occurs the critical period of visual development results in bilateral
deprivational amblyopia.
▪It plays the role of amblyogenic factors in children with bilateral
cataract, ametropia and bilateral high refractive errors.

16. B.) LIGHT DEPRIVATION –
▪Light deprivation works as an amblyogenic factor in children with
unilateral as well as Bilateral complete cataract.
C.) ABNORMAL BINOCULAR INTERACTION –
▪Abnormal binocular interaction is highly amblyogenic.
▪It plays the role of amblyogenic factor in children with strabismic,
anisometropic and unilateral stimulus deprivation amblyopia.

17. 2.) ROLE OF RETINA IN THE DEVELOPMENT OF AMBLYOPIA
–
▪There is some evidence that the retina itself is abnormal in
amblyopia.
▪Retinal abnormality is the effect of cause of amblyopia is
debatable.
▪Retinal threshold and sensitivity have been affected in amblyopia.
▪It is, however, widely believed and proved experimentally that
there is a decreased sensitivity of foveal cones in amblyopia.
▪Decreased rod and cones in the affected eye cause certain
neurophysiological changes, transmitted aberrantly to the CNS
which triggers the onset of amblyopia.

18. 3.) ACTIVE CORTICAL INHIBITION –
▪Active cortical inhibition are the two fundamental
mechanisms for development of amblyopia.
A.) PHYSIOLOGIC EVIDENCE
B.) PHARMACOLOGIC EVIDENCE

19. ▪Decreased in Binocular visual acuity –binocular visual acuity
20/40 or worse in amblyopia eye or worse with atleast 3
logMAR line difference.
▪Crowding phenomenon –(separation difficulty) refers to the
inability of an amblyopic eye to distinguish letters crowded
together.
▪Neural density filter effect –with reduced illumination, acuity
of an amblyopic eye declines less sharply than that of a normal
eye. This means that amblyopic eye can act under mesopic
condition.

20. CLINICAL FEATURES -
▪Fixation patterns –central, eccentric, or no fixation.
▪Contrast sentivity –reduced.
▪Accommodation –defective.
▪Visual field -largest acuity losses in esotropia & amblyopia occur in
the temporal field.
▪Colour vision –impaired only if visual acuity is below 6/36.
▪Pupillary light reflex –generally normal.
▪ERG & EOG –ERG is normal but EOG shows unsteadiness of fixation.

21. 1.) PREVERBAL CHILDREN –
▪CSM METHOD –
▪C-location of corneal light rerlex under monocular condition.
▪S –Steadiness of fixation on target.
▪M –Maintenance of fixation.
▪Preverbal/ nonverbal patients with strong fixation in one eye should be suspected
of having an amblyopia in other eye.

22. 2.) VERBAL CHILDREN –
PRE-LITERATE CHILDREN-
▪HOTV, Illetrate E charts, lea symbols, Allen picture cards.
LITERATE CHILDREN-
▪Snellen’s visual acuity chart, logMAR chart.

26. B.) TREATMENT OF AMBLYOPIA –
Goal of amblyopia treatmentis to maximise and potentially normalise
visual acuity.
Strategy of treat amblyopia it includes –
▪Elimination of the cause of visual deprivation and provision of clear
retinal image in amblyopic eye.
▪Correction of ocular dominance.
▪Perceptual training.

27. 1.) ELIMINATION OF THE CAUSE OF VISUAL DEPRIVATION AND
PROVISION OF CLEAR RETINAL IMAGE –
#)MEDIA CLEARANCE –
▪Media clearance, whenever required, is the first step of amblyopia
management.
▪Childhood cataract, when present, should be operated as early as
possible with appropriate corrections.
▪Severe congenital ptosis should be corrected at the earliest.
▪Corneal opacity should be treated by penetrating keratoplasty.

28. #) CORRECTION OF REFRACTIVE ERROR SND SPECTACLE
ADAPTATION –
▪Refractive error, if any, should be fully corrected as
determined with cycloplegic refraction before starting the
amblyopia therapy.
▪Spectacles adaptation for 3-4 weeks should be tried
anisometropic amblyopia before starting occlusion therapy.

29. 2.) CORRECTION OF OCULAR DOMINANCE –
It is done by stimulating the amblyopic eye with the use of following
modalities alone or in combination.
▪Occlusion therapy
▪Penalization
▪Active stimulation
▪Pleoptics
▪Pharmacological manipulation

30. 1.) OCCLUSION THERAPY –
▪Occlusion of the sound eye ( normal eye) is the most powerful means
of treating amblyopia by forcing the patient to use amblyopic eye.
Methods of Occlusion –
▪Occlusion can be accomplished by an adhesive patch on skin, gauze
pad and tape, use of Doynes rubber occluded which can be stuck to
the spectacle lens, opaque contact lens, adhesive tape on glass or any
method that excludes the use of occluded eye.
▪Adhesive skin patch is the best method.
▪Some problems may arise in children with sensitive skin.
▪If application of tincture of benzoin before the patch is applied on the
skin also does not help than other methods may be tried as a
substitute for a patch.

32. DIRECT VERSUS INDIRECT (INVERSE) OCCLUSION –
▪Direct Occlusionrefers to occlusion of the sound eye.
▪Indirect Occlusionrefers to Occlusion of the amblyopic eye.
FULL TIME VERSUS PART TIME OCCLUSION –
▪Full tine occlusioninvolves placing the occluded over the eye as soon
as the child gets up in the the morning and removing only after the
child goes to bed at night.
▪Part time Occlusioninvolves use of the occluded for short time each
day.

34. HOW TO GO ABOUT OCCLUSION -
▪Complianceis the keyword of success in Occlusion therapy and
should be ensured by motivating the child and parents.Once the near
vision then the distance vision, start improving.
▪Active vision exercisesby the amblyopic eye during occlusion
therapy, may enhance the success of Occlusion.
▪Simple taskslike dotting, joining dots to make drawing, tracing,
threading beads, watching television, reading comics and story
books may be quite useful and enhance the recovery.
▪Computer games, a very useful in occlusion therapy.
▪In patients with improvement in visionassessed at monthly follow up
visits, the occlusion should be continued till amblyopic eye has not
only developed equal vision but also equal preference of fixation
compared to the normal eye.
▪In patients with no improvement with occlusion, on three consecutive
follow up visits, further occlusion unlikely to be fruitful.

35. MAINTENANCE OCCLUSION TREATMENT –
▪Once the vision has been equalized, the Maintenance Occlusion
should be continued till the amblyogenic age i.e.Up to atleast 9
years of age and sometimes even till the child has reached early
teens.
▪Maintenance Occlusion is accomplished by a part time Occlusion
for 2-3 hours in a day with active vision exercises at home.

36. 2.) PENALIZATION-
PRINCIPLE –
▪The word penalization literally means to punish or to inhibit.
▪The principle is to force the amblyopic eye to a greater use
for distance, near or both by penlizing the sound eye for
distance, near or both with the help of glasses or a
cycloplegic drug.
▪The eyes should be straight.
▪It is the best method used in anisometropic amblyopia.

38. 4.) PLEOPTICS-
▪Pleoptics means full vision.
▪Used for active stimulation of the fovea to overcome eccentric
fixation and improves the visual acuity.
▪In this technique, the peripheral retina is dazzled with an intense
light protecting foveal area.
▪After the light source is turned off, the fovea functions better.
▪This can be followed by direct stimulation of fovea by pleoptophore
or indirectly by producing after image.

39. DEMERITS –
▪The technique is complex and requires an absolute
cooperation of the patient and intelligence to appreciate after
images.
▪Daily sitting for a longer period of time is required.
▪Since Occlusion of the sound (dominant) eye is a very
successful, simple and inexpensive method of treating
eccentric fixation, so the use of Pleoptics method is abandoned.
▪Only indication is cooperative and intelligent child older than
6 years having eccentric fixation.