You probably have heard the term “Lazy eye” or “Amblyopia”. Are you interested to gain in-depth knowledge about lazy eye? This article is all about amblyopia.
You will grab detailed information about the lazy eye, it’s causes, symptoms and current trend in the management of amblyopia in the next 10 minutes.
What is a lazy eye?
According to the old definition, amblyopia is a reduction in visual form perception without any structural deficits of the visual system, not correctable by optical means.
But the current definition of lazy eye is a unilateral or bilateral reduced visual acuity caused by pattern or form vision deprivation or abnormal binocular interaction for which no obvious causes can be detected by any physical examination of the eye and it cannot be corrected by optical or surgical means but in appropriate cases is reversible by therapeutic measures.
The word “amblyopia” is derived from Greek words; “amblyos” means dullness or blunt and “Ops” means vision. It is the condition in which the examiner sees nothing and patients see very little.
It is found that around 1-5 percent (WHO 2015) of the global population has some degree of amblyopia. Similarly, 0.9 to 1.8 percent Nepalese population and 2 to 3 percent of the U.S. population is affected by lazy eye. It is estimated that amblyopia is 4 times more common in premature children and 6 times more frequent in children with delayed milestones.
Smoking and the use of drugs and alcohol during pregnancy have been associated with the risk of amblyopia in a newborn baby.
Lazy eye condition commonly begins during infancy and early childhood (birth up to age 7 years). It is the leading cause of partial or total blindness among children in all countries. Although amblyopia can occur in both eyes, in most cases it affects only one eye.
If amblyopia is detected early in life and promptly treated, reduced vision can be avoided or regained, otherwise there will be a permanent vision deficit in the child’s amblyopic eye.
The eye with poorer vision can usually be corrected with proper and timely prescribed eyeglasses and contact lenses, occlusion (patching) therapy, in combination with other active or passive vision therapies.
Although we use the term “Lazy eye”, the eye is not lazy. It is a developmental problem in the cortical region of the brain which is associated with vision, not any intrinsic, organic neurological abnormality in the eyeball itself.
Signs and symptoms of lazy eye
Many people who have mild forms of amblyopia are not aware they have the problem until tested at older ages as they have good vision in their better eye. People with lazy eye typically show one or a combination of the following signs and symptoms:
- Blurred vision (in one or both eyes)
- Double vision
- Poor stereo acuity (vision)
- Poor depth perception: difficulty seeing 3D images, movies
- Reduced contrast sensitivity
- Abnormal binocular summation
- Squinting of eye (upward, downward, outward or inward)
- Abnormal head posture (head tilt, face turn or chin up-down)
Children need to have a vision check-up at an early age because they can’t tell others about the problem. But parents and teachers can notice the abnormal visual behaviors in the children.
Risk factors for amblyopia: when to see a doctor
Some children have a lazy eye(s) when they are born while others develop it later. The risk factors are:
- Premature birth
- Low birth weight
- Family history of crossed eyes, amblyopia, or other ocular conditions associated with amblyopia
- Developmental delay
- Systemic conditions in which eyes get affected like Marfan syndrome (MFS), Weill Marchesani syndrome
It is especially important to have an early eye check-up in cases of the aforementioned conditions.
What causes lazy eye in children and in adults?
Different developmental and visual causes lead to amblyopia. But in some cases, it is harder for optometrists to determine the exact cause of lazy eye.
Although the reasons are less understood, the brain suppresses the images coming from the weaker eye. Here are some possible conditions that can lead to amblyopia:
- Strabismic amblyopia: by misalignment of eyes
- Refractive amblyopia: by anisometropia or iso-ametropia. Anisometropia is a difference in refractive error (either myopia, hyperopia or astigmatism) in both eyes. Iso-ametropia is an almost equal refractive error in both eyes.
- Deprivational amblyopia: obstruction in the visual pathway due to disorders like congenital cataract, corneal opacity, etc.
The Current trend in management of amblyopia
Goal of treatment of lazy eye
If a lazy eye is left untreated, it produces a range of functional deficits along with compromised binocular function. The presence of lazy eye condition and its treatment impact on educational attainment and career opportunities, self-confidence and overall quality of life.
There is a huge emotional impact associated with amblyopia. Hence the effective treatment is necessary to have an overall growth of individuals with amblyopia emotionally and socially.
The prime goal of lazy eye treatment is to restore normal vision in the amblyopic eye. To achieve this goal, two strategies need to be adopted: present clear retinal image and eliminate the cause of visual deprivation.
The steps towards the treatment of amblyopia are proper correction of refractive errors and intensive use of amblyopic eye (poorer eye).
The same treatment modality may not work well for every child. So, the recommended treatment should be based on the age of child, current visual acuity status, compliance with previous treatment, and physical, social and psychological status of the child.
What are the features of perfect amblyopia therapy? Lazy eye therapy should be effective and acceptable to children and their parents. Similarly, it should have good compliance and should be quick, easy to administer and well maintained.
The success and failure of any treatment are determined by its cost. So, amblyopia treatment should be cost-effective and affordable for every individual.
Treatment of amblyopia
To achieve the goal of treatment, the following choices are used alone or in combination:
The child experiences a change in visual stimulation without any conscious effort. Passive therapies are:
- Proper refractive correction
It is designed to improve vision with a child’s conscious involvement in a sequence of specific and controlled visual tasks. Periodic feedback is expected for the achievement of a goal. Active therapies are:
- Near activities
- Active stimulation therapy using CAM vision stimulator
- Syntonic phototherapy
- Perceptual learning
- Binocular stimulation
- Software-based active treatments
- Exposure to darkness
Proper refractive correction
Proper refractive correction in amblyopia aims to provide sharp images and hence establish the optimal environment for amblyopia therapy. Proper optical correction alone is sufficient to treat most cases of amblyopia.
That is why optical correction alone is prescribed initially for a short period of about 6-8 weeks before the initiation of other therapy. A progressive improvement in visual acuity is seen within 16-22 weeks of refractive correction in some patients with refractive amblyopia(Stewart C. et al 2004).
Improvement in visual acuity has seen in 25-33 percent of anisometropic amblyopia and also in strabismic amblyopia.
Similarly, PEDIG study of 2006 has concluded that amblyopia improves with optical correction in 77 percent and resolved in 27 percent cases of lazy eye.
Likewise, Chen et al (AJO 2007) concluded that optical correction alone is sufficient to improve amblyopia in 93 percent cases while it resolved in 45 percent cases.
Studies have suggested that penalization and patching therapy is required only if the vision doesn’t improve with optical correction alone for 4 months.
Occlusion therapy (patching therapy) has remained the mainstay of treatment of lazy eye since the 18th century to till now. It is the most effective and powerful means of treating amblyopia. We all must keep this in mind that occlusion therapy is highly effective until 8 years of age.
Although new studies have shown improvements up to 24 years of age, it is not as effective as it is under 8 years of age. In patching therapy of lazy eye, a good eye is covered with an occluder (patch) to stimulate a poorer eye. The success rate is variable ranging from 30-92 percentage
In the lazy eye, penalization is a therapeutic technique performed by optically defocusing the better eye by using cycloplegia (Atropine eye drop) or altering the eyeglass lens. Penalization is indicated in certain conditions as given below:
- When there is no compliance for patching of lazy eye
- In case of mild degree of amblyopia penalization can be done but it has poor results with dense amblyopia
- As a maintenance therapy after occlusion penalization is used
- Penalization has good results in anisometropic amblyopia
Penalization is cheap and has better compliance compared to occlusion in certain types of lazy eyes. But there might be side effects of drugs used in penalization due to systemic absorption.
Another demerit of penalization is the risk of occlusion amblyopia if not done in the strict guidance of optometrist. This treatment is not advised unless penalization decreases the vision of better eye below the lazy eye.
Types of penalization
In this type of penalization, the fixing eye is atropinized and fully corrected for distance whereas the amblyopic eye is overcorrected with +2.00 to +3.00 Diopter lenses.
Here fixing eye is atropinized and overcorrected and the amblyopic eye is fully corrected.
In total penalization, fixing eye is atropinized and under-corrected by 4.00 to 5.00 Diopter and the amblyopic eye is fully corrected.
According to PEDIG study, for children age less than 7 years and with visual acuity 6/12 to 6/30, daily atropine produces a similar effect as 6 hours patching.
It is designed to improve vision with a child’s conscious involvement in a sequence of specific and controlled visual tasks.
The word “pleaoptics” means “full vision” in Greek. In amblyopia therapy, pleoptics is used for active stimulation of the fovea (central sensitive part of the retina where the image is formed) to overcome eccentric fixation and thereby improves the vision.
In this technique, the peripheral retina of the lazy eye is dazzled with an intense light protecting the foveal region. The fovea functions better after the light source is turned off because the surrounding retinal region is in a state of hypofunction due to intense light.
Immediately, the fovea is stimulated by pleoptophore (Bangerter’s method) or indirectly by producing after image (Cupper’s method).
This technique is complex and demands the co-operation of the child and intelligence to appreciate after image. So, it is abandoned nowadays. It is rarely indicated in a co-operative and intelligent child older than 6 years having eccentric fixation.
According to a study done by Verlee DL, Conventional patching therapy is found to be better than pleatoptics treatment.
Active stimulation therapy using Grating stimuli: CAM vision stimulator
In this active therapy of amblyopia, a better eye is occluded and the lazy eye is stimulated for 7 minutes by slowly rotating high contrast square-wave grating of different spatial frequencies. It is carried out once in every week for 3-4 weeks.
It is advantageous over the conventional patching therapy in the sense that the better eye remains open between the weekly treatment sessions.
CAM vision stimulator is based on the assumption that rotating grating provides stimulation tor cortical neurons. Although it is easier to carry out compared to occlusion therapy, it has failed to replaced time tested conventional patching therapy for the treatment of the lazy eye.
But some optometrists still use this technique as supplementary to occlusion therapy in co-operative children with supportive parents who can carry out the treatment at home.
Recently, a new treatment has been devised based on a similar principle. It is computer-based treatment and is hoped to supplement patching therapy, particularly in the adult population.
A computer game is designed to view on a monitor against the background of a low spatial frequency drifting sine-wave grating. The effectiveness of treatment is higher if this therapy is done in conjunction with conventional occlusion therapy.
Syntonic phototherapy in the treatment of amblyopia
Syntonic is the branch of science dealing with different color filters. In the treatment of lazy eye, red and orange filters are used. It is highly inspired by the work of Spitler who applied syntonic phototherapy to treat amblyopia. However, there are no published studies on the efficacy of this treatment method.
Role of perceptual learning in amblyopia treatment
Many studies have suggested that perceptual learning may provide an important new technique for the treatment of the lazy eye. It is reported to operate based on the principle of reduction of neural noise or through more efficient use of stimulus information by returning the weighting of the information.
Perceptual learning utilizes a visual discrimination task such as positional acuity, contrast sensitivity and stereo-acuity.
Many studies found significant improvement in visual acuity and contrast sensitivity. Although the role of perceptual learning in the treatment of lazy eye is still controversial, it provides a new potential option for lazy eye treatment in adult amblyopes.
Binocular stimulation in the treatment of lazy eye
During occlusion therapy, binocular vision is not encouraged as the non-amblyopic eye is completely occluded. But binocular stimulation may be important in the treatment of the lazy eye.
Recent studies have indicated that binocular stimulation encourages binocular cortical connections during the recovery phase of deprivational amblyopia.
Two existing approaches based on this principle are the use of Bangerter foils in amblyopia and atropine penalization. In both scenarios vision is binocular in the sense that both eyes get light stimulation without impeding peripheral resolution (Wang YZ).
Although this method alone doesn’t offer a significant advantage over occlusion, the combination approach provides significant results.
Software-based active treatments for amblyopia
The Ambp iNet program is marketed by Home Therapy Solutions. The system has 12 treatment programs, 6 of which are randomly assigned for 5 days per week. This game involves activities like ‘letter jumping’, among others. It involves a visual search of a certain target.
“Not a lazy eye, but a lazy brain” is another software-based therapy which is introduced by Revital Vision. It is designed for home therapy and done 2-3 times per week. Each session of 40 minutes is assigned for a total of 40 sessions.
Studies have shown that visual acuity improvement by this software-based game alone is not as good as with 2 hours of patching therapy but can provide significant improvement if used in combination with conventional patching therapy of the lazy eye.
The two most extensively studied drugs in the treatment of amblyopia are Levodopa and Citicoline. It is based on the principle of neural plasticity of the visual system. A Precursor of catecholamine dopamine, a neurotransmitter, is known to influence visual systems at the cortical and retinal levels.
Catecholamine based medicines have been studied to improve vision in the lazy eye by either extending or reactivating the visual system’s sensitive period of neural plasticity.
A study by Leguire and co-workers concluded that a combination of levodopa and occlusion improves visual function more than levodopa-carbidopa alone in a lazy eye.
Pharmacological therapy has many advantages over conventional patching therapy of the lazy eye. It improves compliance and speeds up the recovery of visual functions. Similarly, is reduces the cost and duration of treatment of amblyopia.
Near activities used in the treatment of amblyopia
This involves paper-based near activities such as reading, writing and word puzzles. Von Noorden and co-workers found that 1 hour of occlusion per day in combination with near activities is beneficial in the treatment of lazy eye for older children.
In the absence of reliable evidence, it is not prescribed solely for the treatment of amblyopia but the combination with occlusion provides better outcomes.
Lazy eye occurs early in life due to abnormal visual experience. Proper optical correction alone is prescribed for a short time (6-8 weeks) before starting other active or passive therapies.
Part-time occlusion of the non-amblyopic eye is the mainstay of treatment since the 18th century to till now. For moderate and severe amblyopia, 2 hours and 6 hours of patching are prescribed respectively.
Atropine penalization is also used in children with poor compliance. Trial of occlusion can be given in adults up to the age of 17 years.
Similarly, perceptual learning, pharmacological manipulation, binocular stimulation, software-based treatment and other methods have shown potential areas in the treatment of amblyopia.
Till now, most of these therapy methods have good results when used together with conventional patching therapy.
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