What is strabismus?
Strabismus is the non-alignment of the visual axes, that is, when one eye is deviated with regard to the other one. Strabismus can be caused by several reasons, especially in the first years of life (up to 9-10 years), when our visual systems is developing:
- Refractive defects. Sometimes, high prescriptions either in one eye or both, can be overlooked and cause a eye misalignment due to the defocusing ot to the effort trying to focus.
- Lack of transparency of ocular media. Congenital cataracts, congenital deformities affecting the pupil or the retina (colobomas), scars etc. can "annul" the vision of one eye with the corresponding loss of fixing. Congenital strabismus due to muscle paresis and neurological disorders affecting good eyesight development.
- Estrabismos congénitos por paresias musculares y/o trastornos neurológicos que afecten al correcto desarrollo de la visión.
Eye movements are controlled by six muscles. Two move each eye left and right and the other four move it upwards, downwards and turn it. For both eyes to be aligned fixed in the same point, all twelve muscles must be balanced, the ones on one side working in line with those on the other side. When this "balance" is lost a misalignment or strabismus takes place.
What is amblyopia or lazy eye?
We call lazy eye or ambliopia a healthy eye with a decreased visual acuity even with the best refractive correction. In children, we can say that the main visual alteration is ambliopia, and it is mainly caused by the prior existence of strabismus,
Ambliopias can be classified according to the causes, finding strabic ambliopias, anisometropic (due to prescription difference between one eye and the other) and/or due to deviation.
The trigger of the cases of anisometropic and isometropic ambliopias is the presence of blurry retinal images due to a refractive error. Yet in the case of anisometropias, unequal retinal images are produced between the two eyes. In strabismus, the images are received in different areas of the retina/fovea due to the deviation of one eye with regard to the fixing point. In ambliopias with deprivation a lack of stimulation is produced as can occur in the cases of palpebral fall or congenital cataract.
The decrease of visual acuity in anisometropy is directly linked to the amount of the refractive error, and the higher the prescription the lower the visual acuity. It is important to mention that a greater refractive error is needed to produce and ambliopia in a person with myopia than with hyperopia. In strabismus, the visual acuity is independent of the deviation angle.
How is amblyopia or lazy eye treated?
The most effective treatment will be the one that not only treats the decrease of the visual acuity, but also the other alterations present. The first step will be to correct the refractive error as much as possible. With this we will achieve a clear retinal image that helps stimulating the fusion. If the rivalry between the "good eye" and the lazy eye is such that the fixing of the "good eye" will always predominate, treatments such as occlusion with patch and/or visual therapy can be added.