A typical symptom of squint is a disorder when cooperation between both eyes is disrupted. In the majority of cases, one eye looks straight whereas the other eye turns inwards, or less often outwards, upwards or downwards. Another symptom that may occur is a partially closed eye or tilted head. Sometimes squint appears only while looking at short distances, while looking at long distances both eyes are in the normal position. In some patients, squint might occur only in the evening or when tired.
Squint (strabismus) occurs approximately in one out of every 30 children and it is very often hereditary. The exact causes are unknown but the main presumed ones are dioptric defects, movement defects of the eye muscles or their nerve supply. It is more common in children with brain diseases (e.g. cerebral palsy, brain tumors, Down’s syndrome etc.). However, it can also be caused by cataract, eye injury, or other eye diseases. However, detecting the cause is not possible in the majority of cases.
To diagnose squint a doctor uses two simple tests. The first is a ‘cover test.’ The doctor will ask you to focus both of your eyes on one of his. Then he covers your left eye, quickly uncovers it, and covers the right one. While doing this he observes whether your left eye had to move in order to look straight. If the eye has to move (‘adjust its position’) after being uncovered, it is a sign of latent strabismus (squint).
The second test is a ‘focus test.’ A doctor holds an object, usually pen or pencil, in the center of your gaze at a distance of about 50 cm from your eyes. He asks you to follow the object with your eyes without moving your head. To make sure you really keep your head still he can hold your chin slightly. Then he moves the object in front of your eyes from side to side and up and down. He asks you to tell him if you see the object double. Meanwhile the doctor assesses if both eyes move in full extent, continuously and simultaneously.
Glasses with an occlusor
Non-surgical treatment of squint is focused on comparing the position of both eyes, preserving/regenerating the patient’s vision and regenerating the deep visual field. Squint caused by dioptric defects is firstly treated only by wearing glasses. So as not to develop lazy eye blindness (squint eye vision worsening), it is necessary to cover the healthy eye with an occlusor, a non-transparent patch which forces the squinting eye to adjust to the correct vision. The occlusor exists in the form of a plaster that adheres to the patient’s face and covers the healthy eye completely. This plaster is usually in the form of a special suction cup attached to the glasses or in the form of a cloth (also attached to the glasses). Also available is an occlusive contact lens, which is dark and non-transparent and used according to the doctor’s recommendations. An occlusion is prescribed for children in the age of 2 – 3. It loses its effectiveness as the child gets older. If accommodative squint develops, it is essential to use bifocal glasses, where the upper lens part is for long distances and the lower one for short distances.
Orthoptic and pleoptic exercises
In treating squint, orthoptic and pleoptic training helps. Orthoptics generally deals with the training aimed at achieving the best visual acuity possible. It involves induction of simple binocular vision in hereditary and acquired disorders (squint, lazy eye, double vision etc.). Pleoptics, on the other hand, deals with lazy eye training. It can be in an active form when the child exercises at home e.g. bead stringing, picture retracing, target focusing etc., or when using orthoptic devices in the doctor’s office. A passive form includes exercises with prisms, visual stimulators etc.
The main task in the surgical treatment of squint, suitable mainly for adolescent patients and adults, is to achieve equal eye position and improve conditions for binocular functions. Surgery is usually done in both eyes. It begins with a small cut in the lens through which a doctor is able to adjust the straight and transverse eye muscles. In adjusting their length or repositioning them, the eye will reach its ideal, natural position. There are various types of eye surgery procedures that both weaken the eye muscles (e.g. eye elongation) and strengthen them (e.g. eye resection). A new method, which is called the technique of adjustable sutures, allows eye muscles to be tied or released within several hours of the completion of the operation, depending on the functional eye position. The operation is done on an outpatient basis using only local anesthesia. The whole procedure lasts about 30 – 40 minutes.
This device is used for binocular (dual eye) vision diagnosis and treatment by means of optic methods. It serves for eye coordination assessment in squint, for angle and fusion width measurement etc. It enables binocular function training in strabismus as well as in lazy eye.