Treatment for amblyopia caused by obstructed vision

Review question

We examined the available evidence regarding occlusion treatment for stimulus deprivation amblyopia (SDA) with respect to vision at the end of treatment.


Amblyopia or 'lazy eye' occurs when vision does not develop normally in early childhood. Stimulus deprivation amblyopia (SDA), the type that occurs due to blockage of vision in the eye, for example by a cloudy lens or droopy eyelid, or unequal refractive error in the two eyes (unequal focus of the images, for example one eye is nearsighted and the other eye is farsighted). Eye doctors consider this type of amblyopia to be the most difficult to treat successfully. Although about 1% to 5% of people have some type of amblyopia, SDA is much less common, about 3% of all people with any type of amblyopia. Usually SDA is diagnosed after parents observe a whitish pupil or a droopy eyelid before a baby's first birthday. SDA is often diagnosed after the problem causing these signs is treated and refractive correction (for example, wearing spectacles) is prescribed.

The goal of treatment of SDA is to improve vision in the affected eye and to provide stereopsis, that is, '3-D' vision and depth perception. Treatment may last for several months in order to assure that the affected eye gains as much vision as possible. Also, participation in sports and future employment may be affected by poor vision in one eye or loss of 3-D vision. A common treatment is to occlude or cover the unaffected eye, often with an adhesive patch, in order to force the amblyopic eye to be used. Because young children find occlusion confusing or uncomfortable, occlusion therapy may be difficult for their parents to implement.

Key results

We found no randomized controlled trials (trials in which participants are randomly assigned to one treatment group or another) that evaluated the effectiveness of occlusion therapy for SDA. Thus, well-designed research studies of SDA are needed before we have the information we need to make treatment decisions.

Authors' conclusions: 

We found no evidence on the effectiveness of any treatment for SDA. Future randomized controlled trials are needed in order to evaluate the safety and effectiveness of occlusion, duration of treatment, level of vision that can be realistically achieved, effects of age at onset and magnitude of visual defect, optimum occlusion regimen, and factors associated with satisfactory and unsatisfactory outcomes with the use of various interventions for SDA.

Read the full abstract...

Stimulus deprivation amblyopia (SDA) develops due to an obstruction to the passage of light secondary to a condition such as cataract. The obstruction prevents formation of a clear image on the retina. SDA can be resistant to treatment, leading to poor visual prognosis. SDA probably constitutes less than 3% of all amblyopia cases, although precise estimates of prevalence are unknown. In developed countries, most patients present under the age of one year; in less developed parts of the world patients are likely to be older at the time of presentation. The mainstay of treatment is removal of the cataract and then occlusion of the better-seeing eye, but regimens vary, can be difficult to execute, and traditionally are believed to lead to disappointing results.


Our objective was to evaluate the effectiveness of occlusion therapy for SDA in an attempt to establish realistic treatment outcomes. Where data were available, we also planned to examine evidence of any dose response effect and to assess the effect of the duration, severity, and causative factor on the size and direction of the treatment effect.

Search strategy: 

We searched CENTRAL (which contains the Cochrane Eyes and Vision Group Trials Register) (The Cochrane Library 2013, Issue 9), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to October 2013), EMBASE (January 1980 to October 2013), the Latin American and Caribbean Literature on Health Sciences (LILACS) (January 1982 to October 2013), PubMed (January 1946 to October 2013), the metaRegister of Controlled Trials (mRCT) ( ), ( and the WHO International Clinical Trials Registry Platform (ICTRP) ( We did not use any date or language restrictions in the electronic searches for trials. We last searched the electronic databases on 28 October 2013.

Selection criteria: 

We planned to include randomized and quasi-randomized controlled trials of participants with unilateral SDA with visual acuity worse than 0.2 LogMAR or equivalent. We did not specify any restrictions for inclusion based upon age, gender, ethnicity, co-morbidities, medication use, or the number of participants.

Data collection and analysis: 

Two review authors independently assessed study abstracts identified by the electronic searches.

Main results: 

We did not identify any trials that met the inclusion criteria specified in the protocol for this review.