Lazy Eye (Amblyopia): A Childhood Problem That Progresses Silently

Despite what its name suggests, lazy eye is not a problem of the eye itself but a developmental problem in the centres of the brain where seeing is learned. Known in medicine as amblyopia, this condition develops in infancy and early childhood when the image reaching the brain from one eye is not clear, or when the images from the two eyes do not match. Over time the brain suppresses the eye sending the blurred or conflicting signal; even though that eye is structurally sound, its visual acuity falls behind. Seen in roughly two or three of every hundred children, amblyopia is regarded as the most common cause of reduced vision in one eye during childhood. Its most insidious feature is that it gives no sign that would draw a family's attention — no pain, redness or watering; because the child sees comfortably with one eye they feel no deficiency and do not mention the problem themselves. In this article we look at why amblyopia develops, which signs families should watch for, how the diagnosis is made, and why timing is so decisive in treatment.

What Is Lazy Eye?

Vision is not a process completed simply by the eye perceiving light; the actual image is formed when the signals leaving the retina are processed in the visual centres of the brain. These centres begin to develop at birth and reach maturity at around eight to ten years of age; throughout this period they need to receive regular, clear input from both eyes. If the image from one eye is blurred for any reason, or if the two eyes cannot focus on the same point, the brain chooses to suppress the information from the weaker eye in order to prevent double vision and blurring. Although this suppression may look like a solution that works in the short term, the development of the unused pathways stops and that eye's visual capacity falls permanently behind. This is what is called amblyopia, or lazy eye; it usually appears in one eye and, less often, may affect both. The most critical aspect of the condition is that the brain's capacity for this learning — its plasticity — decreases rapidly with age. For this reason amblyopia is largely reversible at an early age, but can turn into permanent reduced vision in later years.

Why Does Lazy Eye Develop?

The causes underlying amblyopia fall into three main mechanisms that impair the quality of the image reaching the brain. The first and most common is strabismus: when an eye turns inward or outward because of an imbalance between the muscles that position the eyes, the images from the two eyes do not overlap and the brain disables the deviating eye. The second mechanism concerns refractive errors; a marked difference in prescription between the two eyes — anisometropia in medical terms — can cause a child to develop amblyopia without showing any outwardly noticeable sign. Likewise, high hypermetropia, myopia or astigmatism in both eyes that is not corrected with glasses can result in bilateral amblyopia. The third mechanism consists of conditions that physically prevent light from reaching the retina: congenital cataract, corneal opacities, drooping of the eyelid (ptosis) and congenital glaucoma fall into this group and generally produce the most severe cases. Two or three of these mechanisms may be present together in the same child; for example, it is by no means rare for an eye with a high prescription both to see blurred and to deviate over time. Premature birth, low birth weight, developmental delays and a family history of strabismus or lazy eye are the main factors that increase the risk.

Which Signs Should Families Watch For?

The most difficult aspect of lazy eye is that in most children it progresses without giving any visible sign; in cases due to a difference in prescription in particular, no abnormality can be noticed from outside. Even so, there are clues that a family's careful observation can catch, foremost among them one of the eyes turning inward or outward, and this deviation becoming more marked when the child is tired or short of sleep. The child moving too close to the television or a book, squinting when looking at something, or constantly tilting or turning their head in the same direction are also behaviours that should not be overlooked. Weakness in depth perception may show itself as stumbling on stairs, misjudging the distance when reaching for a glass, or difficulty catching a ball. In school-age children, avoiding reading, skipping lines, tiring quickly, headaches and loss of interest in lessons may sometimes be the only sign, and are often mistaken for an attention problem. The child becoming markedly distressed when one eye is covered, while showing no reaction when the other is covered, is a simple but valuable observation suggesting a difference in vision between the two eyes. When any of these signs is noticed, an eye specialist should be consulted without waiting for a more obvious finding such as strabismus to appear.

How Is the Diagnosis Made?

The diagnosis of amblyopia rests on a comprehensive eye examination carried out with methods appropriate to the child's age, and assessment is possible even before the child can speak. In infants the physician looks at whether both eyes follow a moving object in a coordinated way, at the response to light, and at the difference in the child's reaction when each eye is covered in turn. The red reflex returning from the pupil being equal and clear in both eyes is a fundamental step in ruling out problems such as cataract that obstruct vision. To measure refractive error reliably, drops that dilate the pupil and temporarily relax the focusing muscle are generally used; the blurring and light sensitivity these drops cause pass by themselves within a few hours. While prescriptions are determined by autorefractometer measurement and retinoscopy, visual acuity tests with letter, symbol or picture cards are carried out in children who can speak; the difference in acuity between the two eyes reveals the degree of amblyopia. The presence and angle of strabismus are assessed with cover tests, and the retina and optic nerve are examined by fundus examination. Even in the absence of symptoms, it is recommended that every child have a first eye examination in infancy, with further checks repeated in the preschool period and on starting school; these screenings are the step at which amblyopia is caught earliest, not latest.

Treatment: First the Cause, Then the Amblyopia

Treatment of lazy eye is built on a two-stage logic: first the problem preventing a clear image from reaching the brain is removed, then work begins on making the weaker eye function. For this reason, if there is a refractive error, glasses or contact lenses of the appropriate prescription are prescribed and the child is helped to wear them continuously; in some cases significant gains are achieved within months with glasses alone. In conditions such as congenital cataract, severe drooping of the eyelid or strabismus that cannot be corrected with glasses, surgery is required, and the timing of these operations directly affects the outcome; in congenital cataract in particular it is of great importance that the intervention be carried out in the first weeks of life. The main method of the second stage is patching: by covering the better-seeing eye with a patch for a set period, the brain is obliged to use the signal from the weaker eye. The duration of patching is determined by the physician according to the child's age and the degree of amblyopia, and is readjusted through regular check-ups throughout treatment; deciding on this duration on your own may risk an adverse effect on the better-seeing eye. In children who will not accept patching, atropine-type drops instilled into the sound eye temporarily blur its focus and achieve a similar effect. Orthoptic exercises, CAM treatment and near-work activities that challenge hand–eye coordination, such as drawing, jigsaw puzzles and colouring, are complementary methods that support these treatments.

Why Is Timing So Important?

The strongest factor determining success in amblyopia treatment is the age at which treatment begins. The brain's visual centres carry their capacity for reshaping at its highest level in early childhood; for this reason, complete return of visual acuity to normal is possible in most children when treatment is started between three and six years of age. As age advances, every step gained requires more effort and more time, and after eight to ten years of age the gain that can be achieved is markedly limited. This does not mean that nothing can be done in children over ten or in adults; there are studies reporting some improvement with computer-based visual training programmes that target contrast sensitivity and the two eyes working together. However, the gain provided by these approaches cannot be compared with the results of classical treatment applied in the early period. Another important reason for starting treatment early is that a person with one weak eye is left defenceless against a problem that may arise in the sound eye in future. In addition, a permanent deficiency in depth perception may create limitations in many areas, from the choice of profession to obtaining a driving licence; for this reason amblyopia should not be seen as a problem that can be postponed.

Follow-Up After Treatment

Treatment is not considered complete when visual acuity reaches the target level; amblyopia also carries a risk of recurrence that requires at least as much attention as the diagnosis. If patching or drop treatment is stopped abruptly, the brain may return to its old habit and suppress the weaker eye again, and the vision gained may regress within a few months. For this reason physicians generally end treatment not suddenly but by gradually reducing the patching time and supporting it with a maintenance programme. Since glasses prescriptions will change as the child grows, keeping the glasses up to date is also decisive for the continuity of treatment. Check-ups should be continued regularly, at the intervals set by the physician, until the age at which the visual centres complete their development. The family's attitude is one of the most decisive components of this process, because children do not like having their better-seeing eye covered and securing their cooperation requires patience. Combining patching hours with activities the child enjoys, and making the patch a natural part of the daily routine rather than a punishment, directly increases the success of treatment.

Frequently Asked Questions

Up to what age can lazy eye be treated? The most productive period for treatment is the preschool years and the first years of primary school, while the brain's visual centres are still developing. It is generally accepted that gains are markedly possible up to about eight to ten years of age and decrease rapidly thereafter. Limited improvements have been reported in children above this age and in adults with certain visual training methods. Even so, the best approach is to have the diagnosis made as early as possible rather than waiting until the age limit is approached.

Are glasses alone enough? In many mild and moderate cases due to refractive error, regular use of the correct glasses alone brings significant gains within months. For this reason physicians often prefer to observe for a period with glasses alone first. If the difference between the two eyes has not closed by the end of that period, patching or drop treatment is introduced. Whichever stage is reached, wearing the glasses continuously is the foundation on which the whole of the treatment is built.

Can lazy eye be corrected by surgery? There is no surgical method that directly corrects the amblyopia itself. Surgery is performed to remove the problems that pave the way for amblyopia, such as congenital cataract, drooping of the eyelid and strabismus that cannot be resolved with glasses. The operation removes this obstacle, but patching treatment is then needed for the brain to learn to use the weaker eye again. In other words, surgery is usually the beginning of treatment rather than its end.

Does using phones and tablets cause lazy eye? Screen use can lead to eye strain, a feeling of dryness and headaches, and there are studies linking it to the progression of myopia. However, amblyopia arises not from looking at a screen but from a clear image failing to reach the brain during the developmental period. On the other hand, long periods spent in front of a screen may mask an existing vision problem in a child, because they can be comfortable with one eye when looking at something close. For this reason limiting screen time does not take the place of a regular eye examination.

When should I take my child for an eye examination? Even in the absence of any complaint, it is recommended that children have an eye examination in infancy, in the preschool period and on starting school. If there is a family history of strabismus, lazy eye or high prescriptions, or if there was premature birth or low birth weight, these checks should be carried out earlier and more frequently. When deviation of an eye, tilting the head to one side when looking, or an inability to follow objects is noticed, a consultation should be sought without waiting. An early examination gains the one thing that must not be lost in amblyopia: time.

This article has been prepared for general information purposes only and does not take the place of a medical examination. If you have any concern about your child's vision, please consult an ophthalmologist for assessment, diagnosis and treatment.