Amblyopia Clinical Presentation

Updated: Apr 05, 2016
  • Author: Kimberly G Yen, MD; Chief Editor: Hampton Roy, Sr, MD  more...
  • Print
Presentation

History

Elicit any previous history of patching or eye drops as well as past compliance with these therapies. Elicit any previous history of glasses wear.

Document previous ocular surgery or disease.

In addition to the routine information, obtaining a family history of strabismus or other ocular problems is important because the presence of these ocular problems may predispose a child to amblyopia.

Next:

Physical

Visual acuity

Diagnosis of amblyopia usually requires a 2-line difference of visual acuity between the eyes; however, this definition is somewhat arbitrary and a smaller difference is common.

Crowding phenomenon

A common characteristic of amblyopic eyes is difficulty in distinguishing optotypes that are close together. Visual acuity often is better when the patient is presented with single letters rather than a line of letters.

Diagnosis is not an issue in children old enough to read or with use of the HOTV test.

Testing in preverbal children

If the child protests with covering of the sound eye, amblyopia can be diagnosed if it is dense.

Fixation preference may be assessed, especially when strabismus is present.

Induced tropia test may be performed by holding a 10-prism diopter before one eye in cases of an orthophoria or a microtropia.

In infants who cross-fixate, pay attention to when the fixation switch occurs; if it occurs near primary position, then visual acuity is equal in both eyes.

Caution should be used when obtaining Teller acuity in children, as grating acuity may be less reduced than Snellen acuity, especially in strabismic amblyopia.

Contrast sensitivity

Strabismic and anisometropic amblyopic eyes have marked losses of threshold contrast sensitivity, especially at higher spatial frequencies; this loss increases with the severity of amblyopia.

Neutral density filters

Patients with strabismic amblyopia may have better visual acuity or less of a decline of visual acuity when tested with neutral density filters compared to the normal eye. This was not found to be true in patients with anisometropic amblyopia or organic disease.

Binocular function

Amblyopia usually is associated with changes in binocular function or stereopsis.

Eccentric fixation

Some patients with amblyopia may consistently fixate with a nonfoveal area of the retina under monocular use of the amblyopic eye, the mechanism of which is unknown. This can be diagnosed by holding a fixation light in the midline in front of the patient and asking them to fixate on it while the normal eye is covered. The reflection of the light will not be centered.

Refraction

Cycloplegic refraction must be performed in all patients, using retinoscopy to obtain an objective refraction after full cycloplegia. In most cases, the more hyperopic eye or the eye with more astigmatism will be the amblyopic eye. If this is not true, one needs to investigate further for ocular pathology or to confirm the refraction.

Rest of examination

Perform a full eye examination to rule out ocular pathology.

Preschool vision screening

Preschool vision screening techniques have included the SureSight Autorefractor and the Randot Preschool Stereoacuity Test. One study has found the Pediatric Vision Scanner (PVS), a laser scanner capable of directly detecting amblyopia or strabismus in preschool children, to be more accurate than either of these, achieving a sensitivity of 98% and a specificity of 88%. [8]

Previous
Next:

Causes

Many causes of amblyopia exist; the most important causes are as follows: [1, 2]

Anisometropia

Inhibition of the fovea occurs to eliminate the abnormal binocular interaction caused by one defocused image and one focused image.

This type of amblyopia is more common in patients with anisohypermetropia than anisomyopia. Small amounts of hyperopic anisometropia, such as 1-2 diopters, can induce amblyopia. In myopia, mild myopic anisometropia up to -3.00 diopters usually does not cause amblyopia.

Hypermetropic anisometropia of 1.50 diopters or greater has been shown to be a long-term risk factor for deterioration of visual acuity after occlusion therapy.

Strabismus

The patient favors fixation strongly with one eye and does not alternate fixation. This leads to inhibition of visual input to the retinocortical pathways.

Incidence of amblyopia is greater in esotropic patients than in exotropic patients.

Strabismic anisometropia

These patients have strabismus associated with anisometropia.

Visual deprivation

Amblyopia results from disuse or understimulation of the retina. This condition may be unilateral or bilateral. Examples include cataract, corneal opacities, ptosis, and surgical lid closure. [9]

Organic

Structural abnormalities of the retina or the optic nerve may be present. Functional amblyopia may be superimposed on the organic visual loss.

Previous