AMBLYOPIA: the importance of screening
Amblyopia is the medical term for the colloquial expression “lazy eye” and it means that the visual acuity of at least one of the eyes is below normal values. In most of the cases, it affects only one eye, but it can be bilateral.
The main causes are strabismus and uncorrected refractive errors. Other causes, rarer but more serious, include congenital cataract and other alterations capable of obstructing the visual axis.
VISION IMPLIES APPRENTICESHIP!
At birth, the structure of the visual system is completely developed. Nevertheless, the visual function is very poor and its improvement requires appropriate visual stimuli. This evolution occurs at brain level, but it depends on the good functioning of the eye during the period of time in which the brain has plasticity to learn how to see.
This period, in which vision can progress, is called CRITICAL PERIOD. Afterwards, the development of vision becomes impossible, even when ocular alterations are corrected.
When does the critical period end?
It varies with the different aspects of the visual function. Although cerebral plasticity diminishes more or less linearly with age, the critical period ends around the age of 6 – 7 years. Nevertheless, it is much easier to treat amblyopia at the age of 2 than of 5 years. In the cases of obstruction of the visual axis (cataract), the critical period can end very precociously in the first months of life.
What should be screened: the presence of amblyopia or the factors of risk for its development?
The age usually advised for screening children’s vision is 4 years old, because there is then a greater probability of cooperation, necessary to obtain and to register visual acuity.
99% OF THE CASES OF AMBLYOPIA ARE DUE TO REFRACTIVE ERRORS AND/OR STRABISMUS!
Even without cooperation to evaluate visual acuity, it is possible to identify the factors of risk of amblyopia and to correct them before amblyopia is present.
AT THE AGE OF 4 YEARS, MOST OF THE TIMES AMBLYOPIA IS ALREADY PRESENT!
SCREENING SHOULD START AT BIRTH AND CONTINUE DURING CHILDHOOD!
What should be screened by paediatricians and family physicians?
At birth and during the first months of life, it is fundamental to check up the presence of normal pupillary reflex and the absence of ocular morphologic alterations.
From the age of 2 – 3 months onwards, they should also check the infants’ capacity to fix the eyes on human faces, lights and objects, and to follow their movement.
At 4 – 6 months of age, the physicians should check the ocular alignment and the reaction to the occlusion of each eye.
At what age should refractive errors be screened?
From the age of 12 – 15 months onwards, it is important to screen the existence of refractive errors, because they represent the most frequent cause of amblyopia and are many times related to the appearing of strabismus.
IDEALLY, THE FIRST OPHTHALMOLOGICAL SCREENING SHOULD BE CARRIED OUT BETWEEN THE AGES OF 12 AND 15 MONTHS!