Diagnosing and treating amblyopia is a critical responsibility of the optometrist to provide the most potential for maximum visual acuity (VA) in patients. (See “Amblyopia: An Overview,” below.) What’s more, failure to do so can result in deprived vision, which can have negative effects in the classroom and throughout a patient’s life.

Here, I discuss diagnostic and treatment interventions for amblyopia, so the OD can intervene.

Diagnosis

While dry retinoscopy or refraction can be used as a guideline for prescribing considerations, knowledge of the full cycloplegic refractive error of the patient is imperative (and the gold standard method) to arrive at a diagnosis of 1 of the 3 forms of amblyopia.

As a refresher, these forms are (1) refractive amblyopia, (2) strabismic amblyopia, and (3) visual deprivation amblyopia.

Proper cycloplegic refraction requires the use of agents such as atropine sulphate, homatropine hydrobromide, cyclopentolate hydrochloride, or tropicamide.

1.Refractive amblyopia. Refractive amblyopia comes in 2 forms, anisometropia and isoametropia.

The former is a unilateral amblyopia that occurs due to unequal refractive correction and goes undetected during the critical period of brain development. The critical period of brain development is debatable, but the brain it is generally thought to be the most plastic prior to age 7. 

Specifically, the eye that has the higher prescription is given less preference in image clarity on the retina due to rivalry or interocular competition. This then halts the visual development of that eye.

Reduced VA is the hallmark symptom of anisometropia, though decreases in contrast sensitivity and amplitude of accommodation are often also noted.

Although the severity of the amblyopia can correspond to the magnitude of the interocular difference, this is not always the case in that a mild anisometropic difference can result in a deep and severe amblyopia. The severity often corresponds to the age at which amblyopia was diagnosed, and when refractive error management was initiated. The earlier the diagnosis and initiation of proper refractive correction, the better the outcome in the affected eye and more potential for improved binocularity. 

Isoametropic amblyopia is bilateral amblyopia that occurs from a symmetric high refraction. Specifically, the eyes cannot accommodate or focus properly to provide the smaller refined letters of perfect VA.

Symptoms can include blurry vision and asthenopia, however young patients often do not complain. Instead, we hear symptoms noticed by their parents or caregivers. These symptoms: decreased depth perception or clumsiness, closing an eye while reading or doing near work, holding near material very close, or tilting/turning of the head at times.  

Knowing the degree of interocular difference (see Table 1) the patient can tolerate and to what degree is critical for patient care.

2. Strabismic amblyopia. This formcan develop in a constant tropia that does not alternate and can occur in both horizontal and vertical deviations, as well as in small magnitude deviations, otherwise termed micro strabismus. 

As a result of the deviation of the eye, the visual cortex begins to inhibit or suppress the activation of the retinocortical pathway to prevent diplopia. This causes a restructuring of the visual cortical circuits, which, in turn, leads to this type of amblyopia.

The symptoms of strabismic amblyopia are highly affected stereopsis, though a smaller effect on contrast sensitivity vs anisometropic amblyopia or visual deprivation amblyopia. 

3. Visual deprivation amblyopia. This isthe least common cause of amblyopia and is caused by the complete or partial obstruction of the visual axis due to a media opacity, degraded image, or lid blockage from ptosis of the eyelid. While this is the least common form of amblyopia, it is often the most severe and difficult to treat. This is because this form constantly blocks the delivery of visual information.

Treatment

While early treatment is the goal of all amblyopia management, the OD should offer treatment to patients of all ages, especially if they have not been treated previously. This is because plasticity of the brain is life-long. Specifically, cortical regeneration can be seen on functional magnetic resonance imaging after recovery from trauma in an adult brain, and improvements in acuity in older amblyopes can be achieved. The treatments for all 3 forms of amblyopia:

• Refractive correction. According to a randomized control trial, continued wear of refractive correction alone for 18 weeks can improve VA in the amblyopic eye by 2 or more lines in at least two-thirds of children ages 3 to 7 who have untreated anisometropic amblyopia.¹  

Another study in children ages 7 to 17 shows that amblyopia improved 2 or more lines with refractive correction alone in about one-fourth of the children.²  A drawback to this method: Compliance to spectacle wear can be difficult.

• Patching/occlusion. A randomized clinical trial reveals that 6 hours of prescribed daily patching produces an improvement in VA that is similar in magnitude to patching prescribed for all but 1 waking hour when treating severe amblyopia in children younger than age 7.³

In addition, a study shows that 2 hours of prescribed daily patching for moderate amblyopes produces an improvement in VA that is similar in magnitude to the improvement produced by 6 hours of prescribed daily patching.⁴

Some drawbacks to patching include skin sensitivity to adhesives, seeing around a fabric or coverlet patch, loss of binocularity, potential for injury if used during activity, cosmetic concerns, and noncompliance.

• Atropine penalization. Prescribing atropine 1% solution can be ideal in children who cannot tolerate occlusion, have poor compliance with patching, and when vision in the amblyopic eye is better than 20/60. Severe or some moderate amblyopia may not qualify for this treatment method because this method does not defocus the nonamblyopic eye enough to give the amblyopic eye preference. The drop is typically instilled once mid-week and once on the weekend.

Of note: Atropine can be combined with optical penalization for a stronger push for maximum VA. This means that when used on patients who have hyperopic anisometropia, the hyperopic prescription of the non-amblyopic eye can be under corrected to increase blur even in the distance when using atropine penalization. A caveat: The optometrist should prescribe this for no more than 6 months with good compliance, so reverse amblyopia is not induced. Some drawbacks to this method: The side effects of pupil dilation, photophobia, and anisocoria.

• Digital interventions. Digital dichoptic treatments using virtual reality headsets for watching television programs or movies, and several computer-based dichoptic game programs using anaglyph glasses are available to treat amblyopia. These treatments promote binocular vision and reduce the suppressive interaction from the visual cortex. Daily treatment is required and depending on the software prescribed can be from 30 minutes to 1 hour per day. Patients are monitored with home compliance, and in-office follow-up appointments are necessary to check VA and binocularity. Drawbacks with this treatment method can include cost and cyber sickness.

Preserving binocularity
Amblyopia can result in lifelong visual loss if left untreated. As a result, diagnosis and treatment using both classic and newer treatments are imperative to giving these patients maximum VA. While earlier diagnosis and spectacle management are key, choice of treatment method depends upon each individual case. Additionally, involving the family in that decision process is critical to the success and compliance of the treatment. OM

References

1. Scheiman MM, Hertle RW, Beck RW, et al. Randomized trial of treatment of amblyopia in children aged 7 to 17 years. Arch Ophthalmol. 2005;123(4):437-447. doi:10.1001/archopht.123.4.437

2. Writing Committee for the Pediatric Eye Disease Investigator Group, Cotter SA, Foster NC, et al. Optical treatment of strabismic and combined strabismic-anisometropic amblyopia. Ophthalmology. 2012;119(1):150-158. doi:10.1016/j.ophtha.2011.06.043

3. Holmes JM, Kraker RT, Beck RW, et al. A randomized trial of prescribed patching regimens for treatment of severe amblyopia in children. Ophthalmology. 2003;110(11):2075-2087. doi:10.1016/j.ophtha.2003.08.001.

4. Repka MX, Beck RW, Holmes JM, et al. A randomized trial of patching regimens for treatment of moderate amblyopia in children. Arch Ophthalmol. 2003;121(5):603-611. doi:10.1001/archopht.121.5.603.

Megan S. Allen, OD, FAAO, is a part-time instructor at the Illinois College and works in private practice. She is a Pediatric Eye Disease Investigative Group researcher, is involved in many myopia management studies, and enjoys treating adult diplopia, post-traumatic brain injury, strabismic and amblyopic cases of all ages.