Other than basic refractive error, amblyopia is the most common cause of pediatric vision loss.1
A recent meta-analysis found the worldwide prevalence of amblyopia to be 1.36%, although it has been reported to be anywhere from 0.05% to 7.54%.2
Any eyecare provider who sees primary care patients is almost guaranteed to see amblyopic patients, and it is important to know how to educate patients and parents about the condition and their treatment options.
Overview of amblyopia risk factors
Amblyopia is classically defined as “a decrease in visual acuity in one eye when caused by abnormal binocular interaction in one or both eyes, as a result of pattern vision deprivation during visual immaturity, for which no cause can be detected during the physical examination of the eye(s), and which in appropriate cases is reversible by therapeutic measures.”3
Modern definitions have expanded to include risk factors such as abnormal refractive error, strabismus, or deprivation, as well as visual abnormalities other than reduced visual acuity.
For non-optometrists, this definition can appear overwhelming. To simplify it, amblyopia can be described as an eye (or eyes) that cannot see 20/20 even with the best prescription due to a weak eye-brain connection.
To cause amblyopia, the inciting factor must be present early. While the timing of the “sensitive period” is debated, it is generally agreed that amblyopia does not develop after 8 years of age.
Non-ocular risk factors for amblyopia include prematurity, a first-degree relative with amblyopia, and Hispanic ethnicity. Most studies have not found a relationship between gender and amblyopia, although different studies have found a predilection for either gender.3
The three types of amblyopia optometrists may encounter
There are three main types of amblyopia—refractive, strabismic, and deprivational. Refractive amblyopia occurs when uncorrected refractive error is significant enough to reduce the visual cortex’s ability to process visual input. It can be anisometropic (unilateral amblyopia) or isoametropic (bilateral amblyopia).
Strabismic amblyopia occurs when a constant unilateral eye turn results in the affected eye being suppressed. By definition, strabismic amblyopia can only be unilateral.
Deprivational amblyopia results from obstruction of the visual axis via aptosis, corneal opacity, cataract, or vitreous hemorrhage. It is typically the most severe form of amblyopia—but also the least common—likely constituting less than 3% of all amblyopia.
Table 1 details the refractive errors likely to result in refractive amblyopia.4
| Anisometropia | Age | ||
|---|---|---|---|
| < 1 year | 1 to 2 years | > 2 years | |
| Myopia | -4.00 or more | -4.00 or more | -3.00 or more |
| Hyperopia | +2.50 or more | +2.00 or more | +1.50 or more |
| Astigmatism | 2.50 or more | 2.00 or more | 2.00 or more |
| Isoametropia | Age | ||
|---|---|---|---|
| < 1 year | 1 to 2 years | > 2 years | |
| Myopia | -5.00 or more | -4.00 or more | -3.00 or more |
| Hyperopia | +6.00 or more | +5.00 or more | +4.50 or more |
| Astigmatism | 3.00 or more | 2.50 or more | 2.00 or more |
Table 1: Courtesy of the American Academy of Ophthalmology.
Amblyopia presentation in pediatric patients
Amblyopia symptoms vary depending on the etiology. Children may seem clumsier than normal for their age, likely due to reduced depth perception. Other symptoms can include squinting or excessive blinking, head tilting or turning, or fully closing one eye during certain activities.5
Patients with unilateral refractive amblyopia may be asymptomatic until the sound eye is occluded, at which point they may complain or attempt to un-occlude the eye. Further, bilateral refractive amblyopes may not complain when either eye is occluded, but will have bilateral reduced acuity even when best corrected.
Depending on the severity of the eye turn, strabismic amblyopes can be more evident on presentation, although small angle tropes can also result in amblyopia. Patients may present with a head tilt to try to compensate for the strabismus.
Pearls for diagnosing amblyopia
Visual acuity is the primary diagnostic test for amblyopia. For nonverbal patients, this can be measured through behavioral tests such as response to occlusion. Once a patient is able, recognition testing should be done to quantify the degree of amblyopia.
Diagnostic tools to identify amblyopia
Retinoscopy and cover testing should be done on all suspected amblyopes. When doing retinoscopy on a patient with strabismus, it is important to scope in line with their visual axis. For patients who are capable, a detailed refraction to obtain their best acuity should be done.
Stereopsis testing is a helpful diagnostic tool for suspected amblyopes. Global forms on Randot stereo testing require the use of both foveas; if a patient is unable to appreciate these images with best correction, something is affecting the sensitivity of their macula.
Remember that amblyopia is a diagnosis of exclusion. Practitioners must conduct a thorough dilated eye exam to ensure that there is no underlying disease process. If no amblyogenic factor is present, further investigation is required to determine the cause of the patient’s reduced vision.
Amblyopia treatment and management
Optical correction alone often results in improved acuity for refractive amblyopia. If acuity plateaus before achieving 20/20, optical penalization of the non-amblyopic eye should be instituted. Penalization options include patching, atropine eye drops, and blur filters.
Vision therapy can encourage binocular training during and after penalization therapy, as well as improve performance in other higher-order functions affected by amblyopia, such as visual attention and visual search.6
The Pediatric Eye Disease Investigators Group (PEDIG) has published numerous amblyopia treatment studies to determine the best management protocols for amblyopia.7,8
Major findings from the PEDIG for managing amblyopia include:
- Glasses wear is successful in improving amblyopia in nearly ½ of patients.
- Patching is an effective treatment for amblyopia.
- For moderate amblyopia, 2 hours of patching a day is sufficient for improvement.
- For severe amblyopia, 6 hours of patching a day is sufficient.
- Atropine is as effective as occlusion, and patients demonstrated better compliance with a drop one to two times a week compared to daily patching.
- Treatment is most effective with patients under 7 years of age, but patients up to 13 years old saw significant improvement with patching.
- Recurrence is common after discontinuing penalization treatment, especially when treatment is not tapered.
- Near-work activities with patching resulted in more improvement compared to not performing near work.
Binocular treatments for amblyopia
Researchers are looking into how binocular (or dichoptic) treatments can be implemented to improve higher-order functions affected by amblyopia (i.e., binocularity, fixation instability, visuomotor activities, etc.).
PEDIG has conducted research on dichoptic treatment, including one study comparing patching to playing a binocular falling blocks game. While this study found patching was superior, compliance with the game was an issue, as the children were not interested in the game. There is hope that with more engaging protocols, dichoptic treatment may be an alternative to penalization.
Patients with strabismic amblyopia who are also surgical candidates should be treated prior to surgery in order to maximize the chances of surgical success. Treatment of strabismic amblyopia is the same as refractive amblyopia. For deprivational amblyopia, once the obstruction has been removed, the treatment is also the same as it is for refractive amblyopia.
Discussing amblyopia with pediatric patients
As eyecare providers, it is our responsibility to synthesize this information into something children and their parents can understand. Oftentimes, amblyopic children have never noticed that their eyes are different.
It is important to be sympathetic and empathetic when discussing their diagnosis and treatment.
Sample scripts for describing amblyopia treatments
For younger children, the initial conversation can be as simple as:
OD: “One of your eyes is a little different than the other, so it has trouble seeing. Let’s get you glasses to help even them out, and then I’ll see how you’re doing with your glasses in a few weeks.”
Older children may be resistant to glasses, especially if they are asymptomatic and seeing well uncorrected. Motivating them with other possible improvements resulting from treatment can help.
OD: “For you to see as clearly as possible, it is important to wear your glasses all the time, even if you don’t notice a big difference. The more you wear them, the better your eyes will work together, and the easier time you’ll have with sports and art projects.”
Explaining penalization treatment for amblyopia
When penalization treatment is needed, the child may be hesitant. Being cognizant of the child’s feelings about treatment and letting them be a part of the decision, if appropriate, is important. For example, while some children may be excited to be called a pirate when wearing an eyepatch, others may feel self-conscious, reducing their compliance.
OD: “To help your eye get even better, we’re going to have it work by itself, so we have to keep your other eye from doing all the work. We can do that using eye drops you take once or twice a week, or by using something to cover your other eye. Which one do you think would be easier?”
Remember to keep up a positive energy. Patients may experience anxiety with coming to a doctor’s office or may be discouraged if treatment plateaus. Reminding them of how far they have come and how well they are doing, whether that means they’re improving or just being more compliant with glasses wear, can go a long way in reducing their anxiety.
Reviewing ocular health and safety tips
For patients who do not improve with treatment, or who are diagnosed at a later age and are not interested in pursuing treatment, the conversation may shift to ocular health and safety. Because these patients are functionally monocular, they should be educated on the importance of eye protection.
Ideally, they should be in glasses full-time with shatterproof lenses, and a prescription should be written for them that provides the most comfortable vision (potentially a balance or plano lens).
OD: “If you are comfortable with your vision, we don’t have to correct your amblyopic eye. We should make sure that we keep your other eye as safe as possible, so I want you to wear your glasses all the time, or at least when you’re doing anything that could result in something hitting your eyes.”
Discussing amblyopia with parents
When discussing amblyopia with a caregiver, one of the most important things to emphasize is that amblyopia is often asymptomatic and difficult to detect without a vision screening or eye exam.
Sample scripts for explaining amblyopia to parents
Some parents may ask if they could have done anything to prevent it or notice it sooner, and the answer is often no. This can be a segue to remind them to schedule exams for their other children or talk to their friends about the importance of pediatric eye exams.
OD: “Your child has a condition called amblyopia in one (or both) eye(s), meaning that their eye-brain connection is weak and needs assistance to develop. Our first line of treatment is getting them the best prescription glasses and having them wear them all the time. Some patients require more treatment, which we can discuss if that time comes.”
Describing amblyopia treatments to parents
Should the patient require further treatment beyond glasses, both patching and atropine should be offered to the parent as options. Parents know their children’s tolerances and with which treatment their child is most likely to be compliant.
OD: “It looks like we’ve gotten as much improvement as we can just wearing glasses. To help them improve further, they can either wear a patch over the better-seeing eye for 2 (or 6) hours a day, or we can put a drop in their better eye once (or twice) a week to make it very blurry.
The drop will dilate their pupil for several days, so it will look bigger than their amblyopic eye, and they may be light sensitive. Which do you think will work better for them?”
Discussing dichoptic training with parents
Some parents may have questions about dichoptic training. Practitioners interested in offering these treatment options can research the myriad of start-ups offering dichoptic therapy for amblyopic patients and select which program to utilize.
Amblyopic patients can also be good candidates for vision therapy; if they do not offer in-office vision therapy, practitioners should network with other offices to determine to whom they can refer patients.
If a patient resists treatment, parents should be reminded that they can only do so much, and their child may benefit from deferring treatment until they have matured more.
OD: “I know how hard you have been working, but right now may be a good time to take a break and just focus on wearing glasses all the time. We can look at starting again after their next appointment in a few months.”
Offering tips to help encourage treatment compliance can be beneficial.
OD: “If there is a game that your child enjoys playing on a tablet or game console, that would be a good time to have them wear their eye patch. Rewarding them for a consistent week of patching with a special dinner or activity may also encourage them.”
Conclusion
If an eyecare provider sees pediatric patients, they are sure to encounter amblyopia at some point in practice.
Even if they plan on referring patients to a pediatric or binocular vision specialist, being knowledgeable about the causes of amblyopia, the methods of treatment, and how to talk to patients and their parents about this condition is critical.
