Psychology 4051 Amblyopia

Amblyopia Lazy Eye: a substantial reduction in vision in the absence of any detectable optical or retinal abnormalities. Can exist bilaterally but is usually unilateral. Defined as a two-line difference or more (i.e., 0.2 logMAR) on a visual acuity test. While wearing best correction.

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

Types of Amblyopia Caused by vision disorders that disrupt normal visual experiences during the critical period. There are three types of amblyopia. Classified by the cause of amblyopia Amblyogenic factor

Types of Amblyopia Strabismic 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.

Types of Amblyopia The 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.

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

Types of Amblyopia In 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.

Summary Amblyopia 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.

Summary 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.

Treatment of Amblyopia The first step of treatment is to correct the amblyogenic factors. Strabismic amblyopia The strabismus is treated first. This can be treated by muscle surgery. Some patients have accommodative esotropia due to high hyperopia.

Treatment of Amblyopia They 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 Amblyopia The 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 Amblyopia Accommodative esotropia is treated with glasses

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

Treatment of Amblyopia Severe ptosis can be treated surgically.

Treatment of Amblyopia In 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 Amblyopia This 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 Amblyopia Full-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. This may not be appropriate for severe cases of amblyopia.

Treatment of Amblyopia Another 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 Amblyopia A 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 Amblyopia There 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 amblyopia Patients 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 Onset Cases that exist early tend to show poorer outcomes. Duration of Deprivation The 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.