What was the aim of the review?
We examined the available evidence regarding occlusion treatment for stimulus deprivation amblyopia (SDA) with respect to vision at the end of treatment.
There is a lack of evidence from randomized controlled trials (trials in which participants are randomly assigned to one treatment group or another) regarding the effects of occlusion treatment for SDA.
What was studied in the review?
Amblyopia or 'lazy eye' occurs when vision does not develop normally in early childhood. SDA is a type of amblyopia that occurs due to blockage of vision in the eye (for example, by a cloudy lens or droopy eyelid). Eye doctors consider this type of amblyopia to be the most difficult to treat. Although about 1% to 5% of people have some type of amblyopia, SDA is much less common, affecting 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 cause has been 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, 'three-dimensional' 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 three-dimensional 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.
What are the main results of the review?
We found no randomized controlled trials 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.
How up-to-date is the review?
The review authors searched for studies that had been published up to December 2018.
We found no evidence from RCTs or quasi-randomized trials on the effectiveness of any treatment for SDA. RCTs 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.
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 high-income countries, most people present under the age of one year; in low- to middle-income countries, people are likely to be older at the time of presentation. The mainstay of treatment is correction of the obstruction (e.g., 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.
To evaluate the effectiveness of occlusion therapy for SDA in an attempt to establish realistic treatment outcomes and to examine evidence of any dose–response effect and assess the effect of the duration, severity, and causative factor on the size and direction of the treatment effect.
We searched CENTRAL (2018, Issue 12), which contains the Cochrane Eyes and Vision Trials Register; Ovid MEDLINE; Embase.com; and five other databases. We used no date or language restrictions in the electronic searches. We last searched the databases on 12 December 2018.
We planned to include randomized controlled trials (RCTs) and controlled clinical trials of participants with unilateral SDA with visual acuity worse than 0.2 LogMAR or equivalent. We specified no restrictions for inclusion based upon age, gender, ethnicity, comorbidities, medication use, or the number of participants.
We used standard Cochrane methodology.
We identified no trials that met the inclusion criteria specified in the protocol for this review.