Amblyopia

Abdul Fahma FirmanaI11109026

AmblyopiaThe Physician sees nothing and the Patient very little

AmblyopiaAmblyopia, by definition, refers to a partial loss of vision in one or both eyes, in the absence of any organic disease of ocular media, retina and visual pathway.Most Common Know as the Lazy-Eye.Can exist bilaterally but is usually unilateral.

AmblyopiaMost common cause of monocular vision loss in children.Prevalence is between 0.2 and 5.5%Approximately 5% in Newfoundland.

PathogenesisAmblyopia is produced by certain amblyogeneic factors operating during the critical period of visual development (birth to 6 years of age). The most sensitive period for development of amblyopia is first six months of life and it usually does not develop after the age of 6 years.

Amblyogenic factors include :Visual (form sense) deprivation as occurs in anisometropia,Light deprivation e.g., due to congenital cataract,Abnormal binocular interaction e.g., in strabismus.

Types of AmblyopiaCaused by vision disorders that disrupt normal visual experiences during the critical period.There are four types of amblyopia.Classified by the cause of amblyopia

Types of AmblyopiaStrabismic Amblyopia: caused by strabismus. The most common form of amblyopia.A misalignment of the eyes.Esotropia: One or both eyes are misaligned in the inward position.Exotropia: One or both eye are misaligned in the outward direction.

2. Stimulus deprivation amblyopiaDevelops when one eye is totally excluded from seeing early in life as, in congenital or traumatic cataract, complete ptosis and dense central corneal opacity.

Types of AmblyopiaImage Deprivation Amblyopia: caused by an optical obstruction that prevents the formation of a sharp, clear image in one eye.Cataracts and Ptosis

3. Anisometropic amblyopiaoccurs in an eye having higher degree of refractive error than the fellow eye. It is more common in anisohypermetropic than the anisomyopic children. Even 1-2D hypermetropic anisometropia may cause amblyopia while upto 3D myopic anisometropia usually does not cause amblyopia.

Anisometropic AmblyopiaThe misaligned eye receives a completely different image.Can lead to diplopia.Anisometropic Amblyopia: Caused by anisometropia.Anisometropia: Unequal refractive error between the eyes.Have a strong eye and a weak eye.Usually refers to a difference of 1.0 to 1.5 D.

4. Isometropic amblyopiaThe kind of bilateral amblyopia occurring in children with bilateral uncorrected high refractive error.

Types of AmblyopiaIn each case, the image from the affected eye (weaker or misaligned) eye is suppressed.Cortical connections from the affected eye regress.The suppression becomes permanent.There is a reduction in the number of binocular cortical cells.Leads to a lack of stereopsis or poor stereoacuity.Also leads to reduced visual acuity and contrast sensitivity.

AmblyopiaAmblyopia is caused by the existence and persistence of a monocular visual problem during the period of plasticity.This affected eye is placed at a disadvantage in the formation and preservation of neural connections to the visual cortex.The anatomical/physiological result is that few cells in the visual cortex will be driven by the amblyopic eye.

Furthermore, few cells will be binocular.The visual effects are reduced visual acuity, contrast sensitivity, vernier acuity, and stereopsis/stereoacuity.Because the effects are cortical in nature, these problems will persist even when the amblyogenic factor is treated.

Vision for Someone with Amblyopia

Examination for AmblyopiaAcuity testing- age appropriate (Crowding Phenomena test)Tests of stereopsis and binocular function (ex. Worth 4 dot testing)External examination (looking for ptosis, lid hemangioma or other lesion which could affect visual development)Anterior segment examination (looking for any media opacity, or irregularity)

Treatment of AmblyopiaThe first step of treatment is to correct the amblyogenic factors.Treatment of amblyopia should be started as early as possible (younger the child, better the prognosis).

Treatment of AmblyopiaStrabismic amblyopiaThe strabismus is treated first.This can be treated by eye muscle surgery.Some patients have accommodative esotropia due to high hyperopia.

Treatment of AmblyopiaThey are so severely hyperopic that their lenses must accommodate to see relatively distant objects.There is a relationship between how much we accommodate and how much the eyes converge.Patients with accommodative esotropia accommodate so much that their eyes over-converge.

Treatment of AmblyopiaThe patient attempts to fixate the x.Because he/she is excessively hyperopic, each lens must accommodate to see the object.Because of the relationship between accommodation and convergence, the eyes will converge.Based on the amount of accommodation, the eyes will over-converge.

Treatment of AmblyopiaAccommodative esotropia is treated with glasses

Treatment of AmblyopiaAnisometropic amblyopiaCorrected with glasses.Image Degradation amblyopia Cataracts are removed by removing the lens.An intraocular lens (IOL) can be implanted.

Treatment of AmblyopiaSevere ptosis can be treated surgically.

Treatment of AmblyopiaIn some cases the amblyopia will resolve in response to spectacle correction alone.In more severe cases however, subjects must undergo occlusion therapy.The unaffected eye is patched to force the use of the previously deprived eye.

Treatment of AmblyopiaThis should allow cortical connections to be re-established leading to improvements in spatial vision.Young children are averse to patching.Thus, children and parents are often not compliant.This makes it difficult for children to show visual improvement and for researchers to determine how effective patching is.

Treatment of AmblyopiaFull-time occlusion does not allow the formation of binocular cells.Patient is patched during most of the waking hours.As a result, good stereoacuity is unlikely.A better option may be part-time occlusion.Eg. The patient is patched two hours per day.This may allow for stereopsis.Patching can be done at home.

Patching for the treatment of AmblyopiaPatching: training the brain to use the eye that has weaker vision. This allows vision to develop normally in that eye.

Treatment of AmblyopiaAnother type of treatment is penalization.The unaffected eye is treated with a pharmacologic agent such as atropine.Prevents accommodation.A sharp image can not be formed on the retina.However, administration of eye drops in young children is very difficult.

Treatment of AmblyopiaA relatively new treatment is to provide the patient with levadopa.Levodopa (L-dopa) is the metabolic precursor of dopamine.L-dopa may re-establish a period of plasticity in the visual cortex.Allow cortical cells to be open for the formation of new connections.

Treatment of AmblyopiaThere is evidence that L-dopa leads to visual improvements even in adults.It is not known whether these improvements are long-lasting.Also, L-Dopa may produce improvements in both eyes.There may be a persistent difference between the eyes.

When is Treatment Effective?The success of treatment depends on three factors.

The depth of amblyopiaPatients with more severe amblyopia tend to show poorer outcomes.Rarely reach 20/20 or 20/25 in the amblyopic eye.

When is Treatment Effective?Age of OnsetCases that exist early tend to show poorer outcomes.

Duration of DeprivationThe longer the deprivation, the poorer the outcome.

When is Treatment Effective?The last two factors are closely linked.It appears that the duration of deprivation is the more important of the two.These last two factors indicate that the prompt, early detection of amblyopia is critical as early treatment leads to better outcomes.

Danke

**********Patients with unilateral amblyopia are often asymptomatic. Occasionally, patients will complain that one eye is blurry, or younger children may report discomfort in the affected eye. Torticollis occurs infrequently. Poor depth perception or clumsiness may be noted. **********Atropines effect comes from blurring the vision of the better seeing eye for near work. Therefore, the drops will not effectively treat amblyopia if the child is wearing a bifocal. The child will still be able to use the bifocal to see well at near despite the use atropine.******