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Amblyopia or lazy eye is a common condition where vision is reduced in one or infrequently in both eyes. Amblyopia develops when an eye does not receive optimal visual stimulation during the early formative years and hence, there is poor development of the brain-eye neural pathways.
A child with amblyopia has little or no symptoms. Hence, screening is essential to detect it. In Singapore, a vision screen is done at the age of four by the polyclinics. Annual vision testing is also performed in schools for children starting from five years and above. Children with poor vision are then referred to either the refraction clinic at the Health Promotion Board or to a paediatric eye clinic.
Early detection and treatment of amblyopia is important when the part of the brain responsible for vision is still developing. Routine eye screenings are essential in prevention of amblyopia. Also, eye checks should be done early if a visual problem is suspected (e.g. if the child appears to have a squint or trouble seeing, or if there is obstruction of vision by droopy eyelids, cataract, etc.)
Delayed treatment is mostly unsuccessful and can lead to permanent poor vision.
Refractive errors: This is the most common cause of amblyopia in Singapore. Refractive errors that might result in amblyopia include high myopia, hyperopia, astigmatism or a significant difference in spectacle degree requirements between each eye (anisometropia). When vision is poor in an eye due to refractive errors, the brain ignores that eye and vision will not develop properly.
Strabismus: The misalignment of eyes, in which one eye may focus straight ahead while the other turns in, out, up, or downwards. To avoid seeing double, the child's brain may ignore the image from the misaligned eye, leading to amblyopia.
Droopy eyelids or early-onset cataract: Blocked vision due to these conditions can cause deprivational amblyopia.
Once a child is referred to the eye clinic, an eye examination will be performed to determine the cause of amblyopia. Eye alignment is checked, glasses power measured with cycloplegic refraction and a thorough eye examination will be performed.
Depending on the cause, the child may be required to wear glasses or commence patching therapy where one eye is patched for a few hours a day. In some cases, surgery might also be indicated (e.g. if there is a visually significant cataract or significant droopy eyelid).
Case example:
Terry, a five-year-old child, was noted to have a vision of 6/6 in the right eye but 6/15 in the left eye during an eye screening in school. The parents and teachers did not express any concern about his vision. After a complete eye examination, he was found to have astigmatism of -2D in the left eye, but his vision only improved to 6/12 with glasses. There was no significant degree in the right eye.
Terry was advised to wear glasses full-time to encourage the amblyopic left eye ('lazy eye') to see better. After wearing glasses for three months, his vision in the left eye had improved to 6/9. In order to stimulate vision development in the amblyopic left eye further, patching of the stronger right eye for two hours each day was started. After four months, Terry had equal and good vision in both the eyes with glasses.
