amblyopia (lazy eye)

That darn lazy eye...

What is a "lazy eye?"
The term "lazy eye" is most often used to refer to a condition called amblyopia. Amblyopia is reduced vision in one eye, or less frequently both eyes, due to abnormal vision development in childhood (1). 

What causes amblyopia?

In simple terms, functional amblyopia occurs when something prevents the eye from focusing clearly. Any of the below factors can disrupt the normal development of the visual pathway and visual cortex: 

• Deprivation: This type of amblyopia is a result of an obstruction in the line of sight, like a cataract or a lid droop. The first step in treating this type of amblyopia is to remove the obstruction as early as possible. 
• Strabismus: This is the fancy name for an eye turn. When one eye is constantly misaligned, the brain is receiving two dissimilar images. So in order to prevent double vision, the brain ignores the visual input from the misaligned eye, which causes amblyopia. Some cases of strabismic amblyopia require surgery as a part of the treatment plan. Amblyopia can also occur when the eye turn is intermittent or alternating, but that is less frequent and less severe. 
• Refractive error: Refractive amblyopia occurs when there is unequal (anisometropic) refractive error or, less often, high equal (isoametropic) refractive error between the two eyes that goes uncorrected. If one eye is seeing significantly more clearly than the other, the brain will disregard the blurrier eye, causing amblyopia. This is especially difficult to detect because the eyes look normal and the child often won't complain about blur because he/she can see out of one eye. That's why eye exams are crucial!! Optometrists and ophthalmologists are trained to know what kind of prescriptions can cause amblyopia. 

The visual pathway is developing from birth to age 6-8, so amblyopia occurs during this time.

Many of the studies we'll discuss refer to amblyopia in terms of severity. This classification is based on the best correct distance visual acuity, which is how far down the eye chart a patient can read THROUGH their best prescription.

• Mild amblyopia: best corrected distance vision better than 20/40
• Moderate amblyopia: best corrected distance vision 20/40-20/80
• Severe amblyopia: best corrected distance vision worse than 20/80

How is amblyopia treated?
There are many valid answers to this question, and many theories that are currently being studied. We will focus on the evidence-based methods for treating amblyopia. Much of what we know about treating amblyopia is thanks to a group of optometrists and ophthalmologists known as the Pediatric Eye Disease Investigator Group, or PEDIG. This group has conducted numerous Amblyopia Treatment Studies, or ATS. 

Amblyopia treatment is dependent on many factors, such as the severity and type of amblyopia as well as the age and compliance of the patient, so treatment needs to be patient-specific. That being said, here's a general guideline for treating most cases of amblyopia. 

1. OPTICAL CORRECTION: The first line of treatment in most cases of amblyopia is correction of refractive error. Translation: glasses or contact lenses that correct vision to provide equally clear images to the retinas. Your eye doctor will likely use a dilating drop called cyclopentolate to assess the refractive error of the eye. Cyclopentolate relaxes the focusing system and gives the eye doctor a better idea of a patient's true prescription. Because of this, vision up close remains blurry for around 24 hours after the appointment.

Once the eye doctor determines the appropriate prescription, the prescription is written for full-time wear (that can be tricky with young children, but it is imperative). The eye doctor will follow-up every 4 to 6 weeks to check how vision is improving. 

Just having the optical correction in place makes a big difference, so don't underestimate the power of glasses! Glasses can improve vision even if the child still has a crossed eye with the glasses on.

In some cases, optical correction is all your need. But often, more therapy is involved.

2. DEPRIVATION: If further vision improvement is needed after full-time wear of glasses/contacts, deprivation of the better-seeing eye is added to the treatment regimen to encourage the use of the amblyopic eye. This deprivation is often achieved via patching, atropine, or Bangerter filters.      

• Patching
• Patching therapy involves using a patch (over the prescribed glasses/contacts) to cover the non-amblyopic or "good" eye, forcing use of the amblyopic eye. This can be done using an adhesive patch that goes on around the eye, or a soft patch that slides over the glasses.

Slide-on patches by OKeye on Etsy

A couple of adorable kids showcasing their adhesive patches.
@patchwithgus on the left, @chipperspiratedays on the right

• Patching has been used as amblyopia treatment for decades, but the way it is used has changed thanks to PEDIG's Amblyopia Treatment Studies (ATS). The ATS 2 study found the effectiveness of 6 hours of patching/day for severe amblyopia to be similar to full-time occlusion (2). Secondly, they found the effectiveness of 2 hours of patching/day for moderate amblyopia to be similar to 6 hours of patching (3). 
• That is where we get our recommendation of 2 hours of patching a day for moderate amblyopia and 6 hours of patching a day for severe amblyopia. Some children with severe amblyopia respond to as little as 2 hours of patching, so any amount is better than nothing!
• Both of the above studies involved at least an hour of near work during the patching hours, because that was thought to stimulate the visual system. Interestingly, the ATS 6 study found similar results in those that were assigned near tasks vs those that were assigned distance tasks.  There was a greater improvement in visual acuity in the near-task group among those with severe amblyopia, but it did not reach statistical significance. Worth noting: the study looked at "common" near tasks like reading or using the computer (4). There is reason to believe that specific near tasks designed to enhance focusing, improve tracking, fixation, etc. can improve outcomes other than visual acuity, though that was not studied.
• Another PEDIG study (ATS 15) showed that if visual acuity stops improving after 12 weeks of 2 hours/day patching therapy, increasing to 6 hours/day was more effective than continuing at 2 hours/day for another 10 weeks (5).

• Atropine
• Atropine therapy involves instilling a drop of atropine to the non-amblyopic or "good" eye to make vision blurry, forcing use of the amblyopic eye.  
• The ATS 1 study found patching and atropine therapy to be similarly effective initial treatments for moderate amblyopia in children age 3 to 7 years old (6). Another study found similar findings in children age 7 to 12 years old (7).
• Any parent of a child that is patching can attest to some difficulty with compliance, so atropine may be a less fussy option for kids (and parents). 
• The ATS 4 study found similar effectivity between daily use of 1% atropine and use only on the weekends in children age 3 to 7 with moderate amblyopia (8). Weekend atropine may also be effective for severe amblyopia, though improvements may be greater in younger children (9). 
• That is where we get our recommendation of 1 drop of 1% atropine instilled in the AM twice per week. It has been shown to be effective for moderate and severe amblyopia. 
• Atropine does have some systemic side effects, including dryness, flushing of skin, fever, confusion, unusual behavior, and irritability. Those rarely occurred in the studies.

• Bangerter filter
• Bangerter filters are translucent filters that are applied full time to the lens in front of the good eye, and they are available in different densities to degrade the image to different levels. Since this doesn't occlude vision entirely, it may help reduce suppression (10). 

Bangerter filter on a pair of glasses via Fresnel Prism and Lens Co

• The ATS 10 study compared the improvements in visual acuity between those treated with Bangerter filters and those with 2 hours of patching in moderate amblyopes age 3 to 10. The average difference between the two groups was less than half a line on the eye chart, but the study concluded that the filters were "not non-inferior" to patching. What does that mean in laymen's terms? The study did not conclude that the filter treatment effect was similar to that of patching, but it also didn't conclude that patching was definitely superior to filters. The study did show that the filters had less of a "negative impact" on patients and parents in terms of social stigma, compliance, etc (11). 

As you can see, there are multiple ways to go about occluding or depriving the "good eye." There are even other forms of occlusion that we did not mention here, including flicker glasses and occluder contact lenses. What works for one child may not be the best treatment for another, so it's great to have options that have been proven effective. Also, if one of these treatments isn't producing the expected results, we have the option of switching to another.

3) COMPUTER PROGRAMS AND ACTIVE VISION THERAPY: The most recent buzz around amblyopia treatment is reducing suppression by taking a binocular approach. Research is being done on the efficacy of dichoptic games, which involve simultaneous and separate stimulation of both eyes (unlike occlusion of one eye). High-contrast images are presented to the amblyopic eye and low-contrast images to the "good" eye. This type of therapy was found to be effective in adults (12). However, in a study (ATS 18) comparing 1 hour of binocular iPad game to 2 hours of patching a day in children 5 to 13 year old with amblyopia, the improvement after 16 weeks was better in the patching group (13). Participants lost interest in the game, and compliance wasn't great, so that may have contributed to the poor results. More studies need to be done to determine what types of anti-suppression therapy may produce better results. 

Adding vision therapy to amblyopia treatment is helpful in improving visual skills and binocularity. Vision therapy involves activities designed to reduce suppression and improve deficiencies in accommodation, form discrimination, and fixation, all of which are skills that are often poor in patients with amblyopia (14). 


Can you treat amblyopia in older kids? 
YES! In the ATS 3 study, PEDIG found that using either 2 hours of daily patching or weekend atropine as the initial treatment can be effective in improving vision for amblyopes age 7 to 12 years old, even if they've had prior treatment (15). That being said, amblyopia is MORE responsive to treatment in younger children, so this is one of the key reasons to have children see an optometrist EARLY!


Can amblyopia recur after treatment?
YES! According to ATS 2C, nearly 25% of amblyopic children under 8 years old experienced regression within a year of discontinuing treatment. The recurrence rate was similar in patients who stopped patching vs those that stopped atropine, and most cases occurred within 3 months of discontinuing treatment (16). The ATS 3 study showed that only 7% of 7 to 12 year olds studied experienced recurrence (17). The risk is much greater when those patching 6-8 hrs were stopped abruptly, so tapering off (ie: going from 6 hrs to 2 hrs) is advised, especially with younger children.  Because recurrence is possible, following up with your eye doctor is critical!


CliffsNotes: The first step in treating most cases of amblyopia is to correct vision, either with glasses or contacts. Surgical intervention may be needed in some cases. Occlusion therapy may be needed to improve vision beyond what is achieved by optical correction alone, and it's never a bad idea to enroll in vision therapy to improve eye teaming and visual skills. Amblyopia treatment may vary depending on the type and severity of the amblyopia as well as the age and compliance of the patient. Early intervention is key, so get your kids in to see their optometrist ASAP!


Additional Recommended Resources:

• All About Vision: Amblyopia
• AOA: Amblyopia

Helpful resources for ODs and OMDs: 

• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5396957/
• https://www.aoa.org/documents/optometrists/CPG-4.pdf

vision & learning

Not only is August back-to-school time for most kids, but it is also National Children's Vision and Learning month.  I discussed the importance of eye examinations in school-aged children in the previous post.  Here, I will go into a little more detail on how a child's vision and learning are related.

Learning, particularly in the form of reading, requires a combination of many visual skills.  A thorough eye exam is needed to evaluate these skills.

• Visual acuity refers to the clarity or sharpness of vision.  Typically, distance visual acuity is measured at 20 feet, and near visual acuity is measured at 40 centimeters.  A child can see 20/20 but still have issues with any or all of the skills below.

• Accomodation, or focusing, refers to the ability to keep things clear at varying distances.  For instance, when a child is copying something from the board to his/her paper, the accomodative system is responsible for shifting focus quickly and easily so as to maintain clear images far away and up close.  If this system is over- or under-worked, it can result in blur, headaches, and/or eyestrain.  Issues with accomodation are typically addressed with appropriately prescribed glasses, or the use of vision therapy to train the system, or a combination of both.    

• Eye teaming refers to the ability of the eyes to work in tandem to produce a single, fused image with depth.  The most common eye teaming deficiency is called Convergence Insufficiency (CI).  When doing near work, the eyes must converge, or move inwardly.  In CI, a person's eyes tend to rest in an outward position, resulting in an inability to converge normally and comfortably.  People with CI have to exert extra effort to keep the eyes aligned to maintain a clear and single image.  This extra effort can lead to eye strain, headaches, fatigue, difficulty concentrating, and problems with comprehension when doing near work for even a short period of time.  If this extra effort is exhausted, a person with CI may see double (if the eyes drift outward), or the brain may suppress the image from one eye to avoid seeing double.  According to a scientific research study by the National Eye Institute, office-based vision therapy is the most successful treatment for this condition (1).

• Ocular motor skills are involved in keeping the eyes stabilized on a target, and moving the eyes quickly and accurately from target to target.  The act of reading involves a series of eye movements called saccades and fixations.  Saccades are the eye movements that allow us to quickly redirect our line of sight from one location to another.  When reading, saccades allow us to move through a line of text.  The normal reader averages about 7-9 letter spaces per saccade.  Fixations occur when the eye is relatively still.  Regressions are eye movements in the right-to-left direction that occur when we reread a word or section.  They occur 10-15% of the time in skilled readers.  Less skilled readers typically have longer fixations, shorter saccades, and make more regressions than more skilled readers (2).  When these ocular motor skills are deficient, it can lead to one losing their place when reading, skipping words, and reading slowly.  This is also an area that can be trained with vision therapy.

• Visual perception has to do with how we process the information we receive through the visual system.  Some sub-categories of visual perception include visual memory (the ability to recall what is seen), visual-motor integration (the ability to coordinate visual input with motor output), visual closure (the ability to identify a form without its full presentation), and visual-spatial skills (the ability to perceive the position of an object relative to oneself and relative to other objects in space).  There will be a separate post in the future with detailed descriptions and examples of each area of visual perception.   

As you might imagine, a deficiency in any of these areas can have negative effects on a child's learning.  A child that sees double, gets headaches, or loses his/her place when he/she reads may have a short attention span and exhibit frustration and disinterest in school.  Because of similarities in the presenting symptoms and signs, some children that are suspected of having learning or behavioral problems may have an undiagnosed visual problem.  Ruling out vision-related issues as an obstacle to success in school is an important piece of the puzzle.

There are many optometrists out there that specialize in this area of optometry.  To find one in your area, go to www.covd.org, or ask your primary care optometrist to recommend one close to you.

CliffsNotes: Vision and learning are very much connected!

Additional recommended resources:

• Vision and Learning
• COVD: August is Vision and Learning Month

back-to-school eye exams

For many parents, the next few weeks will be filled with orientations, school supply lists, sports physicals, and immunizations.  If you are in that boat, be sure to include a visit to your eye doctor to have your child's eyes examined before starting the school year.  Experts estimate that as much as 80% of learning occurs through the visual system (1), so give your child every possible opportunity to succeed in school.  Learning, particularly in the form of reading, requires a combination of many visual skills.  There is far more to vision than just seeing 20/20.  

Vision screenings at the pediatrician's office and at school, though helpful in flagging some potential problems, usually only assess one or two aspects of vision.  Screenings are limited and non-diagnostic, so they are not a substitute for a comprehensive eye exam.  I regularly see kids who pass school screenings but have vision problems that need to be addressed.  Some states actually require a comprehensive eye exam before entering kindergarten, which is a fantastic idea.  The visual system is not fully developed in young children, and equal input from both eyes is necessary for proper development.  The earlier problems are detected, the better the chance of treatment being successful.  The American Optometric Association (AOA) recommends an eye exam at 6 months old, 3 years old, and again before entering first grade.  While in school, a child/teen should have an eye exam at least every 2 years if no issues exist, or yearly if he/she wears glasses or contact lenses.  Depending on the child and the condition, your eye doctor may recommend more frequent examinations.  

Some common signs and symptoms for parents and teachers to keep an eye out for:

• squinting
• eye(s) turning in or out
• sitting close to the TV 
• holding books close to the face
• complaining of seeing double
• complaining of headaches
• tilting head 
• avoiding reading and/or reading slowly
• losing place when reading and/or skipping words

While some children will have symptoms and signs that parents and/or teachers can pick up on, it is not uncommon to find children with issues that do not report any symptoms at all.  That is why the objective tests done during a comprehensive eye exam are so important for young children.    

According to the American Public Health Association, about one in four school-aged children has a vision problem that interferes with learning.  Here is a brief overview of some eye conditions that are relevant to this age group:

• Hyperopia, myopia, and astigmatism:  These are all types of refractive error.  A refractive error exists when the eye doesn't focus light exactly on the back of the eye (the retina).  An eye doctor measures the refractive error of the eyes and prescribes glasses/contact lenses if needed.  Correcting a child's refractive error when appropriate is the first step in addressing problems with the visual system because it may be the root cause of other vision problems, like those described later in this post.  
• Hyperopia, or farsightedness, is when the eye focuses light behind the retina.  Small amounts of hyperopia are normal in young children.  Kids can often compensate for this by using their eye muscles to bring images into focus.  But when the amount of hyperopia is substantial, it creates an unnecessary burden on the system and can result in blur, fatigue, eye strain, and headaches, especially when reading.  High amounts of uncorrected hyperopia can cause an inward eye turn to develop as well (accomodative esotropia).  
• Myopia, or nearsightedness, is when the eye focuses light in front of the retina.  Those with myopia have difficulty seeing far away.  Myopia is often first detected in school-aged children, and typically progresses through the adolescent years.
• Astigmatism is when the curvature of the cornea and/or the lens of the eye is different in one direction than it is in another, and light gets focused at two different points.  This can cause blur and distortion up close and far away.    
• Strabismus:  Commonly called crossed eyes, strabismus is a misalignment of one or both eyes, present in 2-5% of the general population.  The eye may turn in (esotropia), out (exotropia), up (hypertropia), or down (hypotropia).  It may happen all the time, or it may happen only some of the time (constant vs. intermittent).  The turned eye may be the same eye all the time, or it may alternate between the two (unilateral vs. alternating).  When the eyes are pointing in two different directions, they are sending the brain two different images.  Depending on the frequency and severity of the eye turn, it may cause double vision.  Alternatively, the brain may learn to ignore the image from the turned eye in an attempt to relieve the confusion.  This adaptation is called suppression.  If left uncorrected, strabismus can result in decreased vision in the turned eye (ambylopia) and loss of depth perception.     
• Amblyopia:  Sometimes referred to as lazy eye, amblyopia affects 2-3% of the general population.  Amblyopia is defined as reduced vision in one eye, or less commonly both eyes, in the absence of disease or structural abnormalities.  It can be caused by an eye turn (strabismic amblyopia), or a high prescription in one or both eyes that hasn't been corrected (refractive amblyopia), or something physically obstructing the line of sight (deprivation amblyopia).  Amblyopia occurs in the brain during the developmental stage, and it is often a preventable and treatable cause of vision loss.  The sooner it is diagnosed and treated, the better the chance of achieving normal visual function.  This is a big reason why eye exams are recommended early in life. 
• Ocular motor dysfunction (OMD):  Patients with OMD have problems keeping their eyes on a target (fixation), moving their eyes quickly and accurately from one target to another (saccades), and following a moving target with their eyes (pursuits).  These eye movements play an important role in reading and sports.  OMD usually does not present by itself; a child with OMD may also have issues with focusing and/or eye teaming.  The primary treatment here (assuming the appropriate glasses prescription has been given) is vision therapy.    

Vision therapy is a program of activities designed to help correct deficiencies and improve efficiency of the visual system.  Vision is a developed skill, and thus can be enhanced with guided training.  Vision therapy can be prescribed to help treat some conditions I mentioned above, as well as others relating to focusing and/or eye coordination.  Not all optometrists offer vision therapy, but all optometrists can direct you to one in your area that does provide such services.

CliffsNotes: Be sure to add a comprehensive eye exam to your child's yearly back-to-school checklist.  Clear, comfortable, single vision is important to a child's academic success!

     Additional recommended resources:

• Vision and Learning
• College of Optometrists in Vision Development

(1) Gazzaniga MS, Ivry RB, Jangun CR. Cognitive Neuroscience, the Biology of the Mind. New York, NY; WW Norton & Co, 1998.