Amblyopia

What is Amblyopia?

Amblyopia, often referred to as “lazy eye,” is a condition that happens in your early childhood and affects your vision. It is caused by changes in the brain’s visual development, which may lead to abnormal vision in one or both eyes. In simple terms, the visual system in one eye, sometimes both, doesn’t develop the way it should. If amblyopia isn’t treated, it can result in permanent vision loss in the affected eye, even if the eye problem causing it is fixed later on.

Amongst children and young adults, amblyopia is the most frequent reason for decreased vision in one eye, affecting about 2 to 4% of children. Factors such as lack of proper visual stimulation, complications in the interaction between the two eyes, and visual deprivation during childhood development are often associated with developing this condition. Patients with amblyopia usually show reduced vision, even after correction, which can’t be explained by changes in the eye’s structure.

Amblyopia happens early in life when the developing visual system fails to send a clear and focused image to the part of the brain responsible for vision. Various issues like media opacities (clouding of the eye), cataracts, strabismus (eyes that don’t align properly), or an unequal degree of short or long sightedness in the two eyes, which put one eye at a disadvantage, can cause amblyopia. While it is commonly seen in one eye, rare cases involve both eyes, especially if cataracts or high degrees of sightedness errors are present in both. The visual experiences during infancy and childhood are crucial in forming adult vision.

Doctors diagnose amblyopia by finding a reduction in vision in one or both eyes that is more than what should be expected from a physical abnormality of the eye, and by ruling out other vision disorders. The process often involves identifying a significant difference in vision between the two eyes when glasses or contact lens are used to correct vision errors. In the case of young children, it can be challenging to measure vision, but it can be estimated by observing how they react when one eye is covered, such as their ability to track objects with a single eye.

What Causes Amblyopia?

Amblyopia, also known as lazy eye, is a condition that can be classified into four main types based on its different causes: refractive, strabismic, visual deprivation, and reverse (occlusion) amblyopia.

Refractive Amblyopia:

Refractive amblyopia happens when there are optical issues in one or both eyes that aren’t corrected, such as far-sightedness, astigmatism, or near-sightedness. Normally, it often occurs in eyes with far-sightedness or astigmatism more than near-sightedness, because near-sighted eyes can still focus on nearby objects clearly.

Anisometric amblyopia is a form of this condition that takes place when one eye has a different focusing problem than the other. This causes a blurry image for the weaker eye and can happen with or without the eyes being misaligned. Research shows that the size of the difference between the two eyes, along with the type of focusing problems, affects how severe the amblyopia can become.

On the other hand, bilateral refractive amblyopia, though it’s rare, occurs when severe and uncorrected optical issues in both eyes cause them to consistently receive blurred images. People with this condition are usually treated by first evaluating their vision and then prescribing corrective lenses to treat the underlying issues.

Strabismic Amblyopia:

Strabismic amblyopia happens when the eyes are not aligned correctly. In children, the brain sometimes avoids double vision by ignoring the visual input from one eye, which can impact how that eye develops. This affects the eye’s ability to work together and merge images from both eyes. Even though treatments like surgery or prism glasses can help correct the misalignment, amblyopia might still persist. This makes it necessary to treat it separately in order to restore vision in the affected eye.

Visual Deprivation Amblyopia:

Visual deprivation amblyopia is caused by any condition that blocks the visual pathway, causing blurred or unclear images to hit the retina. Several factors like early-onset or congenital cataracts, corneal opacity, inflammation inside the eye, vitreous hemorrhage, retina damage, optic nerve conditions, or ptosis (drooping eyelid) can contribute to this obstruction.

Though it’s the least common type of amblyopia, it tends to be the worst and the hardest in terms of treatment. However, outcomes usually improve if the treatment begins early, specifically in cases involving cataracts or any cause of eye opacity.

Occlusion (Reverse) Amblyopia:

Occlusion amblyopia is rare, resulting often from the healthy eye being deprived of vision for a long period, generally due to a patch or eye drops that blur vision in the good eye. Vision normally gets back to normal when the patch or eye drops are stopped, and corrective glasses are worn on the healthy eye.

It is crucial to monitor and manage occlusion amblyopia promptly to ensure the best outcomes for vision. Keep in mind that the severity of amblyopia can worsen if the degree of visual deprivation is high. Also, treating amblyopia gets harder the later it starts because the main period for visual development is in the first 7 years of life, with the first few years and months being especially crucial.

Therefore, surgeries to treat conditions like dense congenital monocular cataracts must often be done as early as a week after discovery. Even a few months of having a congenital cataract can result in irreversible amblyopia. However, in cases of binocular cataracts where both eyes are equally affected, intervention can be done within a few weeks.

Risk Factors and Frequency for Amblyopia

Amblyopia, sometimes called “lazy eye,” is a global health concern due to its common occurrence and risk of permanent vision problems if not treated quickly. It’s been known to affect up to 3% of people, with a 1.2% lifetime chance of vision loss because of it. However, recent data suggests that globally, it may affect closer to 1.1% to 1.8% of people.

Studies show that the prevalence of amblyopia can vary. Estimates show between 0.7% to 2.6% of children aged 30 to 70 months, and 1.0% to 5.5% of older children have it. These percentages can vary based on factors like age, race, ethnicity, how amblyopia is defined, how the study was conducted, and other influences.

A detailed analysis of global data covering over 1.8 million patients across 60 studies found an average prevalence rate of 1.44%, ranging from 1.17% to 1.78%. The rates differed across continents, with Europe, North America, Asia, and Africa reporting rates of 2.90%, 2.41%, 1.09%, and 0.72%, respectively. It’s estimated that about 99.2 million people across the world had amblyopia in 2019, with projections showing an increase to 175 million by 2030 and 220 million by 2040.

Amblyopia usually affects one eye, but there can be cases where it affects both eyes if visual changes are seen during early development. The majority of amblyopia cases are due to anisometropia, followed by mixed anisometropia and strabismus, strabismus, and visual deprivation. The percentages of amblyopia types are approximately 50% due to anisometropia, 19% related to strabismus, 27% caused by both, and 4% as a result of deprivation.

The chance of developing amblyopia increases depending on certain factors. If the difference in how each eye focuses (refractive error) is between 1D to 2D, the odds are 4.5 times higher. The risk increases by 40 times if the difference is more than 2D. In terms of strabismus, the risk for amblyopia can be 3 to 18 times higher than people without strabismus. Mixed and strabismic amblyopia is typically diagnosed earlier (average age of 7.4 years) compared to anisometropic amblyopia (average age of 12.7 years). The likelihood of amblyopia is about the same for both eyes, and doesn’t favor any particular gender.

Various risk factors can contribute to the development of amblyopia:

• Ptosis (drooping or falling of the upper eyelid)
• Strabismus (condition in which the eyes do not properly align with each other)
• Childhood glaucoma (a group of eye diseases that damage the optic nerve)
• Early-onset cataracts
• Uveitis (eye inflammation)
• Systemic conditions with ocular manifestation (body-wide conditions that affect the eye)
• Being born small for gestational age
• Low birth weight (less than 1500 g)
• Premature birth (born before the 30th week of pregnancy)
• Developmental delay
• Having a close relative with the condition
• Mother’s smoking, alcohol or drug use during pregnancy

Signs and Symptoms of Amblyopia

When doing a full medical check for patients, it’s important to look into their health history right back to when they were children. Sometimes patients might not remember everything about their past health, so it’s helpful to ask their parents or other family members. Some important details to know include:

• Their age, race, and ethnicity
• Their history from birth (like their birth weight, days of pregnancy, and any history of alcohol or drug use by the mother)
• When they first noticed issues with their vision
• Any glasses or contact lens prescriptions they’ve had
• Any eye injuries or diseases
• Any treatment they had for lazy eye (amblyopia)
• Any eye surgeries
• Any other health issues
• Any medications they are taking

It’s also important to know if there’s any family history of eye disease.

If a patient might have lazy eye, they should get a full eye exam. The eye doctor will need to check their vision in each eye. This can be tricky because people often think their vision is better than it really is in the eye with lazy eye. A helpful tool for this is ‘bracketing’, which uses a sequence of visual targets. The doctor will also check the patient’s depth perception, which is often not as good in people with lazy eye.

All patients with reduced vision should have an eye prescription check. For young patients, eye doctors often give eye drops first to make the test more accurate. This is known as a ‘cycloplegic refraction’ test and it can reveal hyperopia (farsightedness).

The doctor will also shine a light into the patient’s eyes to see how the pupils respond and look carefully for any relative afferent pupillary defect. This can be done with a ‘swinging flashlight test’. All patients who are able to should have eye pressure measurement, although it might need to be skipped for some people, like children. Eye movement and field of vision should be tested. To see if the cause of the lazy eye is strabismus (crossed eyes), the doctor will do cover-uncover and alternate-cover tests.

Patients who might have lazy eye should also have an eye exam with dilated pupils. During this exam, the doctor will look closely at the eye parts – the cornea, lens, retina, and optic nerve – that are important for vision. In general, a comprehensive eye test will include:

• Checking both eyes and depth perception
• Binocular red reflex test
• Checking eye alignment, holding gaze, and eye movement
• Checking the eye prescription and best corrected visual acuity
• Checking the front part of the eye
• Mesuring eye pressure when there are risk factors present
• Cycloplegic refraction or retinoscopy
• Checking the inside of the eye on the back side

Testing for Amblyopia

If a doctor is checking you for amblyopia, which is a condition that can cause your vision to be blurry or incomplete, they might need to do additional tests. These could include tests like looking at your visual fields (your full range of vision), taking pictures of the back of your eye (fundus photography), or doing an electroretinogram (ERG), which measures your eye’s response to light. If the doctor is worried about something pushing on your nerves for vision, they might also do some imaging, like a CT scan or an MRI, of your brain and eye sockets.

However, amblyopia is usually diagnosed based on your symptoms and how your eyes look when the doctor examines them. They don’t usually need to do specific tests unless they are looking for other eye conditions. Some studies have shown that people with amblyopia might have a smaller visual cortex, which is the part of your brain that processes what you see. These results were found using an MRI scan of the brain, but these scans are not usually part of the regular testing for amblyopia.

Screening for Amblyopia

Amblyopia is a common global issue and the most common reason for reduced vision in one eye among children. However, if the condition is caught early and treated in a timely manner, it can help prevent or reduce the impact of long-term vision problems. That’s why many countries have public health programs that include regular screening for amblyopia.

How and when screening is done can vary widely between different countries, and even within the same country, for a range of reasons. However, many countries have developed their own guidelines for screening for amblyopia. Here are a few examples:

* In Canada, certain provinces have rolled out amblyopia screening programs for children aged 3-5. However, some provinces, like Ontario and Quebec, do not follow these national programs.

* In the United States, despite the American Medical Associations recommending it, not all states have official programs for screening children for amblyopia. In some states, though, vision screening tests are a must for kids in school, usually from kindergarten through to grade 12.

* The recent rules in France suggest children with risk factors for amblyopia should have eye checks in their first year of life. They recommend a full eye assessment, which includes checking eyesight and eye movement, at age 3. If amblyopia is suspected, the child is then referred to an eye specialist.

* The UK’s National Screening Committee recommends checks by eye specialists for children aged 4-5.

* In Singapore, kids 4-5 years old undergo their first vision screenings, which continue each year until age 14. If amblyopia is suspected or if the child needs glasses, they are then referred to an eye doctor.

* South Korea has had country-wide screening programs for babies and toddlers as part of their national health programs since 2008.

Treatment Options for Amblyopia

The first step in treating amblyopia, also known as “lazy eye”, usually depends on what’s causing it in the first place. Here’s how it typically works:

– Deprivation amblyopia: If your lazy eye is due to an underlying issue that’s stopping you from seeing clearly, your doctor will propose a treatment to fix this problem. This could include eye surgeries like cataract surgery, retinal detachment repair, corneal surgery, or other kinds of eye treatments.

– Refractive amblyopia: Sometimes, your lazy eye can get better if you correct your vision with glasses or contact lenses. This can often be enough to “reverse” the condition.

– Strabismic amblyopia: If your lazy eye is caused by strabismus, which is when your eyes aren’t aligned properly, you might need interventions to fix the alignment of your eyes. This alone typically doesn’t fully fix the lazy eye, but it can help.

The main goal of treating lazy eye is to avoid permanent vision loss while the eyes are still developing. If we catch it early and start treatment during childhood, we can usually improve the vision in the lazy eye, which is better for eye movements, depth perception, focus, contrast sensitivity (the ability to tell the difference between shades of gray), and overall quality of life in the long run.

Usually, treating lazy eye involves making the unaffected eye work a little less. This forces the lazy eye to work harder, which makes it stronger. We usually do this by putting a patch over the unaffected eye (like a pirate!). This can be for a couple of hours a day, or even all day, depending on how bad the lazy eye is. While the patch is on, doing activities that need good vision, like reading or playing video games, can help strengthen the lazy eye. This method of treatment is nothing new – it’s been used since the 16th century!

If the patient can’t use the patch regularly, there is another option that involves eye drops. A drug called atropine can help to blur the vision in the good eye, which in turn encourages the lazy eye to work harder. This could be easier than wearing a patch all day. However, for patients whose eyes can focus well without having to adjust (such as those who are nearsighted or have perfect vision), this method might not work.

As the patient gets older, the chance of completely fixing the lazy eye becomes less likely because the brain’s ability to rewire itself decreases. It’s not exactly clear what age is the cutoff for effective treatment, but research has shown that treatment can still help children aged 7 to 12, while those older than 13 typically show little improvement with treatment.

Treating lazy eye can involve a lot of different techniques, and each case is unique. Some of the options apart from those mentioned above could include special filters, games that force both eyes to work together, or surgery. There are also some newer treatment options being researched like special training protocols and video games.

Regular check-ups are important to make sure the treatment is working and to make any changes if needed. The main goal is to improve vision in the lazy eye, but it’s also important to check the good eye to ensure that it doesn’t start to become lazy because it’s being covered. The doctor or eye health professional will also check that the prescription for glasses or contacts is up to date, check for any side effects, and look for any signs of the lazy eye coming back after treatment has stopped. If needed, they’ll adjust the treatment plan based on how well it’s working and whether it’s suitable for the patient. These ongoing checks and tweaks are key to getting the best possible outcome from treatment.

What else can Amblyopia be?

Amblyopia, often known as “lazy eye,” is a condition that is only diagnosed after ruling out other possible reasons for poor vision. These might include:

• Eye issues like: refractive errors, cataracts, problems with the cornea
• Retinal disorders
• Diseases of the optic nerve

Most of these conditions can be verified or crossed off the list with a comprehensive eye examination. It’s also vital to rule out brain-related vision problems and functional vision loss, which is a decrease in vision without a clear physical cause.

While routine tests such as OCT (a test that takes detailed images of the retina), visual field testing (a test that measures all areas of your eyesight, including your side vision), and MRI scans are not usually done routinely, they might be ordered in cases where the cause of vision loss is unclear or if other specific factors need to be ruled out.

What to expect with Amblyopia

The outcome of amblyopia, or lazy eye, greatly depends on when treatment starts and how severe the condition is. Amblyopia can seriously affect a person’s sight and is a common reason for sight impairment in one eye. In fact, treatment like patching the stronger eye helps improve vision in approximately 75% of kids. Do keep in mind, though, roughly half of these children may experience a slight decrease in their vision over time.

The best results are usually seen in children who received treatment early in their lives. However, as children grow up, they might notice slight changes in how they view real-life objects.

With appropriate treatment, over 70% of patients have significant improvement in their vision within one year. But, even after treatment is successful, some individuals might experience a minor decrease in vision over the following years. Certain factors might make restoring complete vision more challenging. These elements include the age when treatment began (the older a child is when starting treatment, the less likely for a positive outcome), cases of deprivation amblyopia (a severe form of lazy eye usually caused by cataracts), and very poor vision to start with.

Possible Complications When Diagnosed with Amblyopia

Amblyopia, also known as “lazy eye,” can lead to lifelong problems with vision if left untreated. This includes a whole spectrum of vision problems, like lower-than-average clarity of vision, difficulty in distinguishing fine details and detecting contours, issues with contrast sensitivity, and problems of spatial distortion.

People with amblyopia often have problems with their binocular vision as well, particularly with depth perception and combining the visions from both eyes. While the problems typically center around the lazy eye, it’s not uncommon to find subtle issues in the “good” eye as well.

• Lifelong problems with vision
• Difficulty in distinguishing fine details and detecting contours
• Problems with contrast sensitivity and spatial distortion
• Problems combining the vision from both eyes
• Subtle problems in the good eye

Those with amblyopia may have trouble seeing 3D images that are common in certain types of displays. For example, it can be harder for them to decode images hidden in what are called “autostereograms.” The brighter side, however, is that their sense of depth doesn’t usually get affected when they’re using only one eye.

Notably, children with amblyopia may face difficulties in their academic well-being. They may struggle with slower reading and answering multiple-choice questions. Additionally, amblyopia might also contribute to worsening cross-eye, a condition known as ‘strabismus’, because of difficulties in synchronizing both eyes.

• Difficulties seeing 3D images
• Ability to decipher depth when using one eye typically remains unaffected
• Academic difficulties
• Slower reading and difficulties with multiple-choice questions
• Potential worsening of cross-eye (strabismus)

Preventing Amblyopia

It’s really important for parents to understand the value of getting their children’s vision checked early on. Many a times, it’s at school vision screenings that a condition called amblyopia, or lazy eye, is first suspected. If a child is found to have this condition, parents need to understand that if it isn’t treated, the resulting vision loss is usually permanent. So, therapy for this condition is very important, and this should be made clear to both the child and the parents.

At first, kids might resist wearing glasses or eye patches, part of the common treatment for lazy eye, but parents have to make sure they stick with it. Healthcare professionals, like doctors or nurses, can play a part here by always reminding and encouraging parents during every appointment. This is really important since treatment for a lazy eye can go on for a long time.