In October 2014 edition of the Institute of Child Health Monthly Seminar, Dr. O.M Uhumwangho (Senior Lecturer/ Consultant Ophthalmologist, University of Benin/ University of Benin Teaching hospital, Benin City) discussed about squint in children.
Squint is a condition where the eyes do not look together in the same direction. While one eye looks forwards to focus on an object, the other eye turns either inwards, outwards, upwards or downwards. The medical name for squint is strabismus. Strabismus can be present at birth or develop in childhood usually between 1 and 4 years of age. In most cases, the cause is unknown, although kids with a family history of strabismus, cerebral palsy and Down’s syndrome have an increased risk. It is normal for a necorn’s eyes to wander or cross occasionally during the first few months of life. By the time a baby is up to 5 months old, the eyes usually straighten out. If one or both eyes continue to wander, even intermittently, it is probably a strabismus.
Understanding eye muscles (Extraocular muscles)
The movement of each eye is controlled by six muscles that pull the eye in specific directions. These are: the lateral rectus which pulls the eye outwards, the medial rectus which pulls the eye inwards, the superior rectus mainly responsible for upwards movements, the inferior rectus which mostly pulls the eye downwards and, the superior and inferior oblique muscles which help to stabilize eye movements especially for looking downwards and inwards, or upward and outward. Both eyes are kept straight by the drive to keep the image of the object being viewed in the centre of the macula – the centre part of eye with best vision. The tone in the extraocular muscles is constantly being readjusted to maintain this fixation. If vision is impaired in one or both eyes, this constant readjustment cannot occur and one eye may wander. A squint develops when the eye muscles do not work in a balanced way and the eyes do not move together correctly.
Signs and Symptoms
Many children with squint do not complain of eye problems. It is usually a family member or teacher who notices a misalignment of the eyes. Some kids may complain of double vision (seeing two objects when there’s only one in view) or have trouble seeing things in general. Younger children who are not yet able to verbalize their vision problems may squint frequently and turn or tilt their heads in an attempt to see more clearly.
Why a Squint is important
When we are born, our eyes are well formed but light needs to focus on the retina – the light sensitive layer of tissue that lines the inside of the back of the eye that transmits light to the brain for interpretation of images seen. A squint is important because it may show that the vision of the eye is impaired from treatable conditions such as a cataract (opacity of the lens) or a refractive error which cause a blur image on the retina such as hypermetropia (long sightedness), myopia (shortsightedness) and astigmatism. If not corrected early in childhood, it can make the eyes become lazy (amblyopia). Longstanding eye misalignment also might impair the development of depth perception (stereopsis) or the ability to see in 3D. It is especially important in a child because unlike the vision of an adult, a child’s vision may be irreversibly impaired if treatment is not given in time. The visual pathways in the brain that receive information from an abnormal eye fail to develop normally. The resulting depressed brain function leads to amblyopia, commonly called a “lazy” eye. A squint may be a sign of a life threatening condition as it is a common presentation in a child with retinoblastoma- a type of cancer in the eye that occurs in children which is treatable if the child presents early.
When detected early on, strabismus is curable through a variety of safe and effective treatment options. However, it is important for kids to be treated early waiting too long or overlooking treatment completely can lead to permanent vision loss. The condition usually is corrected with either glasses or eye muscle surgery. There is no such thing as being too early for a child to wear glasses as it prevents the development of amblyopia, a condition difficult to treat. The myth that early use of glasses or surgery for cataract in children causes worsening of the eyes is untrue and should be discouraged. A child who has amblyopia as well as strabismus might be prescribed eye patches to be worn over the unaffected or straight eye or atropine eye drops for some period of time. These block out all light and force the misaligned or weaker eye to do the “seeing” Over time, consistent patching may strengthen the vision in the weaker eye. For parents of babies and toddlers with strabismus, enforcing the use of an eye patch can seem challenging. But after the initial adjustment period, most kids adapt well and the patch just becomes part of their daily routine, like brushing their teeth. If glasses and/or patching or atropine drops do not achieve the proper alignment, eye muscle surgery may be recommended. Surgery involves loosening or tightening the muscles that cause the eye to wander. The social aspect to strabismus also should not be overlooked. Properly aligned eyes are important for a healthy self-image and good interpersonal relationships in kids and adults. Fortunately, when strabismus is recognized and treated effectively, it can be cured and permanent vision loss prevented.