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Magazine
Look at your eye
Dr. MURALI ARIGA
Dr. N. R. RANGARAJ
Ms. P. SUBHADRA
Ms. NANDINI L. SHAH
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Therapy for amblyopia, or lazy eye, is difficult for patient, parent and doctor and requires patience and understanding. Improvement occurs gradually over a period of time.
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SIX-YEAR-OLD Ranjitha's right eye had a squint since she was three years old. But, her parents did not seek treatment because the squint was considered lucky and they believed that it would go away. Only when the child started moving close to the television while watching programmes that they took her for an eye examination. The child was found to have significant myopia in both eyes with its manifestation in one eye being more than the other.
The cause? Amblyopia or lazy eye that had developed as a result of the unequal myopia. Glasses were prescribed for constant wear, which improved her vision significantly.
Besides, she was also recommended eye exercises and occlusion of the normal eye, to stimulate the lazier right eye. The therapy was continued and, after one month, Ranjitha's vision had improved significantly; enough to do her school work comfortably.
Amblyopia is decreased vision in one or both eyes in the absence of an obvious eye disease. Because using both eyes in the presence of squint/refractive error would cause significant eye-strain and double vision, the brain ignores the image from the squinting eye, resulting in amblyopia.
The most common cause is squint or cross-eyes. One eye turns either in or out and the squint may be present at all times or occasionally, when the child is tired or day-dreaming. A squint could occur at birth or develop any time in childhood. It is often ignored in the hope that the child would outgrow it and is commonly considered lucky by superstition.
The fact is that a child, however young, with a squint should be evaluated in detail to rule out near-sightedness, far-sightedness or astigmatism. If present, early treatment should be started.
The second most common cause of amblyopia is refractive error, especially if it occurs in only one eye. In such a case, the patient is able to use the normal eye for routine tasks and does not notice the poor vision in the other eye.
If not recognised and treated early, this could result in amblyopi because the eye with the refractive error never takes part in the process of seeing.
Eye diseases like cataract or opacity in the cornea are less common causes.
Amblyopia can be prevented if the factors causing it are identified and treated before eight years of age, although satisfactory results have been obtained in older children. All children above the age of three years should be examined in detail even if there are no symptoms to suggest poor vision.
Unless there is an obvious squint, or a significant refractive error in both eyes to permit good vision, amblyopia is often asymptomatic. A few patients may complain of headache, eye pain or nausea, but many do not. Therefore, amblyopia is often diagnosed during a routine eye test at school or when the patient seeks treatment for other reasons like injury or infection. Those children who do complain of eye-strain or difficulty in seeing the black-board should be taken for a comprehensive examination. In very young children, poor vision should be suspected if the child goes very close to objects of interest or is unable to identify familiar objects shown at a distance.
Watching television or working on the computer for long hours does not cause refractive error or amblyopia. If, after a thorough eye evaluation, the child is found to be normal without refractive error or squint, he (or she) should be left alone. Treatment guidelines include: Glasses; Contact lenses; Occlusion; Atropinisation; Surgery and Exercises
Glasses/spectacles: Treatment begins with the correction of refractive error with the use of spectacles. In some patients, this is sufficient to improve vision to near normal and reduce the degree of squint. Where a large difference exists in near or far-sightedness between the two eyes, contact lenses are preferred. This is because the difference in thickness and image sizes between the two eyes may be too great to permit comfortable vision with spectacles.
Occlusion: Occlusion, or patching of the sound eye, is the mainstay of treatment for amblyopia and is done to force the lazier eye into use. The patient wears his or her spectacles, and a black rubber occluder is stuck over the glass in front of the amblyopic eye. The child is now forced to use the lazier eye for all his/her routine tasks. The degree of visual improvement and the duration of occlusion depends on the age at which treatment was started, the nature of refractive error and, if present, the degree of squint. Inverse amblyopia/amblyopia of the previously sound eye, as a result of prolonged unmonitored occlusion, occurs rapidly in infants. For this reason, infants and very young children should be seen periodically to assess improvement and to prevent inverse amblyopia.
Atropinisation: Atropine is a drug that is used to dilate the pupil. Recent studies have confirmed that it is effective in the treatment of amblyopia and works by inhibiting the stimulation to the eye for near vision.
As a result, the patient's amblyopic eye is forced into use for all tasks involving near-vision. In patients with far-sightedness, the drug makes the normal eye's vision worse than that of the lazy eye. Thus, by application of atropine and by modifying the spectacles, the patient is made to see with his amblyopic eye.
Surgery: Surgery is an important treatment option. A large degree of squint does not usually respond well to other means of therapy but can be corrected completely or to near-normal levels by surgery. Surgery is the only treatment of choice and should be performed early in children who have developed lazy eye due to diseases like cataract (congenital/after injury).
Eye exercises: To facilitate the comfortable use of both eyes, exercises are also recommended. These could be simple ones that can be done at home (drawing, colouring and reading) for young children and more sophisticated exercises in the clinic in older children, who require more aggressive therapy. However, eye exercises are only an additional means of therapy and are not a substitute for spectacles/occlusion.
Therapy for amblyopia is difficult for all concerned (patient, parent, doctor) and requires patience and understanding. Improvement occurs gradually over a period of time. A high degree of motivation is required on the part of the parent and the patient to comply with treatment.
If full-time occlusion is warranted but the child refuses it for fear of being teased, the teacher should talk to the class about the need for occlusion and its benefits.
The final outcome of the treatment of amblyopia depends on the age of the patient, the degree of squint or refractive error and the ability to comply with the treatment schedule.
Improvement could occur within a few weeks, especially in younger children and in whom treatment has been started early, but in others it could take even months. After the initial results, the patient is put on a maintenance therapy programme for a few more weeks to sustain the improvement.
If the patient shows consistently good vision and good co-ordination between the eyes, therapy is discontinued and the patient followed up periodically.
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