Amblyopia Treatment

and Yi Ning J. Strube²

(1)

Wright Foundation for Pediatric Ophthalmology and Adult Strabismus Medical Center, Los Angeles, CA, USA

(2)

Queen’s University, Kingston, Ontario, Canada

Keywords

AmblyopiaVertical prism induced tropia testStrabismus fixusRefractive error requiring correctionAnisometropiaHypermetropiaMyopiaAstigmatismOcclusion therapyPatchingAtropinePenalization therapy

Amblyopia is poor vision caused by abnormal visual stimulation during early visual development. The abnormal visual stimulation disrupts neurodevelopment of visual centers in the brain. Abnormal stimulation can arise from a blurred retinal image, or strabismus with strong fixation preference for one eye and cortical suppression of the nondominant eye. Children under 8 years of age are capable of strong cortical suppression and hence can eliminate double vision. Children who alternate fixation and use either eye will alternate suppression and do not develop amblyopia. The vertical prism induced tropia test can be used to determine fixation preference and diagnose unilateral amblyopia in preverbal children with straight eyes or small-angle strabismus [1]. This test is performed by placing a vertically oriented 10 PD prism over one eye, either base down or base up. The vertical prism induces a hypertropia, allowing evaluation of fixation preference. Strong fixation preference for one eye is indicative of amblyopia [2]. Amblyopia can be bilateral in children with bilateral blurred retinal images (e.g., bilateral congenital cataracts, or bilateral high hypermetropia >+5.00 sphere).

Vision is the foremost priority in ophthalmology, so strabismic children with amblyopia should have the amblyopia treated prior to strabismus surgery. After strabismus surgery, the parents often assume that all is well, and will default follow-up appointments. Thus our best chance for treating amblyopia is before strabismus surgery. An exception to this rule is amblyopia associated with large-angle esotropia, with the amblyopic eye fixed in adduction (strabismus fixus) so the visual axis is occluded. Part of the amblyopia treatment is to operate on the amblyopic eye to bring it into primary position, to clear the visual axis and allow occlusion therapy.

Amblyopia therapy works best when initiated in children under 3 years of age, but even older children up to 8 or 9 years of age can show visual acuity improvement with diligent amblyopia therapy. Visual acuity improvement has been documented when children are treated in late childhood, after 8 years of age, especially in those children with no history of prior amblyopia treatment [3]. It is also important to monitor children after strabismus surgery for the development of amblyopia until the ages of 8–9 years. There are two basic strategies to treat amblyopia:

Provide a clear retinal image.

Correct ocular dominance.

1.1 Clear Retinal Image

The first goal of amblyopia therapy is to ensure the presence of a clear retinal image. A careful cycloplegic refraction is required for all children with amblyopia and strabismus. Topical cyclopentolate 1 % with tropicamide 1 % given twice can achieve adequate cycloplegia for most patients. Patients with densely pigmented irides may require multiple drops, or even atropine 1 % given twice a day for 3 days if retinoscopy shows variable readings.

Table 1.1 lists refractive errors that are potentially amblyogenic and need correction. Prescribing spectacles for patients with accommodative esotropia is covered in Chap. 4. Patients with straight eyes and anisometropic amblyopia usually have some degree of peripheral fusion. These patients often show significant improvement of visual acuity with optical correction alone, even without occlusion therapy. As a rule, give the full hypermetropic correction to the amblyopic eye, because amblyopic eyes do not fully accommodate. If the good eye is mildly hyperopic (+0.75 to +1.50 sphere) it is advisable not to give the full plus to the good eye, as doing so will blur the vision and the child may not wear the spectacles (see Example 1.1). The key is that the spectacles must be worn full time—even in the bathtub or swimming pool!

Table 1.1

When is a refractive error amblyogenic?

Type of amblyopia

Refractive error requiring correction^a

Only gold members can continue reading. Log In or Register to continue