The Fundamental Requirements For Normal Visual Development In The Child Are :
- A clear retinal image in each eye.
- Visual acuity equal or very similar in both eyes.
- Accurate eye alignment.
If any of these requirements fail, amblyopia (more commonly known as lazy eye) occurs. Lazy eye is the unilateral or bilateral decrease of visual acuity, without a detectable organic cause and that occurs during the sensitive or critical period of the development of the vision, by alteration of it. In order to diagnose lazy eye in a child, the following diagnostic criteria must be met:
Visual acuity less than 20/30 (see at 20 feet what a normal person sees at 30), in both eyes, in cases of bilateral lazy eye or two fewer lines of board vision in the affected eye, in relation to the another, in cases of unilateral lazy eye. All this, evaluated with the appropriate optical correction, according to the child’s refraction. (Normal visual acuity is 20/20).
- Absence of other organic pathologies that explain poor visual acuity.
- Appearance during the critical period of development of visual acuity.
How Do Glasses Correct A Lazy Eye?
The importance of lazy eye lies in the fact that it is a highly prevalent condition, estimating that 4% of the most frequent causes of lazy eye are, from better to worse prognosis:
Bilateral Ametropia: That is, the presence of a refractive defect in both eyes. Lazy eye is more frequent in high hyperopia (greater than +4.0 diopters), or astigmatism greater than 3 diopters.
Strabismus: In this pathology, the fovea of one eye is stimulated by an image, while in the other eye occurs by a different image producing; therefore, adaptive mechanisms that lead to the suppression of the image of the deviated eye, and the consequent lazy eye of that eye, due to the abnormal binocular interaction.
Anisometropia: When the refractive vice is present in only one eye, or in both, but of different magnitude, if it is not corrected properly with glasses, lazy eye will occur with greater ametropia, since the brain will prefer the healthy eye.
Visual Deprivation: By depriving the brain of a clear vision of the forms, it “chooses” the eye through, which it receives the clearest images, and suppresses those that come from the problematic eye. This occurs in cases of impaired transparency of the ocular media, such as cataracts, corneal opacifications, and vitreous hemorrhages, among others.
If a child has lazy eye, the visual prognosis will depend on the etiology of the lazy eye, the age of onset (the earlier it will be more severe), the duration of this and the age of initiation of treatment. This last point is critical, since the later the treatment starts, the fewer the possibilities of visual recovery, due to the lower plasticity in the child’s visual system.
After 9 years, it is very difficult to treat. Hence the importance of awareness, in the medical community of the need to refer to every child to their first ophthalmological examination at four years old, although no obvious pathology is observed.
Methods For The Treatment Of Lazy Eye
Ocular occlusion with a patch is the most effective, cheapest and most widely used method to stimulate the amblyopic eye.
Another useful method in the management of lazy eye is the optical glass penalty. This consists in adding a glass lens of +1 to +1.5 diopters to the dominant eye with the objective that this one sees blurry (the dominant eye “is penalized”), this is done for the amblyopic eye sees better. It is used when there is a rejection of the occlusion by the child, but only in mild lazy eye.
Using the same principle above, there is a pharmacological penalty, by which, instead of lenses, atropine is instilled in the dominant eye.
Other methods to correct lazy eye are pleoptic exercises, use of red filters and prisms. It is known that the establishment of an appropriate treatment at 4 years is effective (87% success), especially methods of penalizing the healthy eye such as pharmacological and optical penalization (prescribe glasses with unnecessary graduation to cause blurred vision in the healthy eye).
- American Association for Pediatric Ophthalmology and Strabismus (AAPOS): “Amblyopia (Lazy Eye).” Source: https://aapos.org/glossary/amblyopia Detailed information on amblyopia, its causes, diagnosis, and treatment methods from the AAPOS.
- Cleveland Clinic: “Amblyopia (Lazy Eye).” Source: https://my.clevelandclinic.org/health/diseases/8583-amblyopia-lazy-eye Concise overview of amblyopia, its prevalence, and the importance of early diagnosis and treatment.
- National Eye Institute: “Amblyopia.” Source: https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/amblyopia Information on amblyopia from the National Eye Institute, including its causes and treatment options.