Strabismus or squinting is a disorder of the position of eyes and visual function, at which it is not possible to direct both visual lines towards a fixed point.
Normally, when an object is observed, images of both eyes fall simultaneously into the point of central vision of the eye. However, if both eyes are not balanced in their movements, as with strabismus, phenomena such as double vision and confusion occur. Any deviation from the parallel position of both eyes is called strabismus.
The main feature of vision in humans is binocularity, and that is the ability of two images of one subject, each formed in its eye, to unite into one image. Two eyes in binocular vision, therefore, function as one organ. Even if these two images slightly differ, with their merging only one image appears. All of this works well if the eyes are properly located, and the whole process develops before the eighth year of life.
When it comes to strabismus, each eye sees a different image; at the same time different things are viewed, and that is called visual confusion. That is – visual mess. Furthermore, the image in the healthy eye falls into the center of the retina (a part of the eye responsible for creating images), and the image from the squinted eye falls on the periphery of the retina, therefore, two images appear.
Normal vision requires a sharp image that falls onto proper places in the eye, proper function of all external eye muscles, and the brain to be capable of creating the accurate image from received stimuli. Causes of strabismus can be divided into several groups:
Sensory causes lead to strabismus if both eyes create images that are too different to be able to unite. Any eye disease can cause strabismus, for example, corneal opacification, congenital cataract, retinal diseases and deterioration of the optic nerve. If the disease occurs at an early age, it is mostly convergent and in adults it is divergent strabismus. At the early appearance of strabismus blinking of the eyeballs (nystagmus) and mostly amblyopia occur. Also, optical factors are important: hyperopia and myopia in one eye.
Anatomic causes include narrowing of the bones around the eye (craniosynostosis), too great a distance between the eyes (hypertelorism), changes in the muscles – their insertions of development, their length and strength.
Innervation causes (disorders of the nervous tissue) can be disturbances of accommodation and divergence, weak merging of two images or central disturbances in the brain. Hyperopic eye accommodates too intensely, which can lead to so called accommodative strabismus. It occurs at moderate hyperopia (2-6 diopters), at lower hyperopia hidden strabismus occurs, and at larger hyperopia fallacies aren’t corrected with accommodation. When it comes to myopic people, there is a tendency towards divergent strabismus in moderate and low myopic people because they do not have to put objects very close to their eyes in order to see sharply. In high myopia convergent strabismus occurs because such people have to put everything close to their eyes in order to see clearly. Strabismus can be found at children who had suffered brain inflammation (encephalitis).
Psychosomatic strabismus may occur after psychological trauma or too weak or too strong brain excitability. With squinting, then, very often occur also stutter and difficulty while reading or writing.
Types of strabismus according to the position of the eye:
In squinting, according to position of the eye, it is distinguished between convergent strabismus (esotropia) in which one eye is deflected inwards, and between divergent strabismus (exotropia) with deflection turned outwards. Deflection of the eye can also be vertical, which is called hypertropia, and it can be alone or combined with convergent and divergent strabismus.
Strabismus therapy can be surgical and conservative, which includes the closure of the eye with patches, glasses, prisms and exercises. Only if the conservative treatment fails, a surgical one can be considered. How much time would be necessary depends on each child. In treating strabismus, firstly, normal vision in both eyes needs to be achieved, then it is needed to correct strabismus with eyeglasses or surgery, which is a precondition for achieveing normal binocular vision.
Firstly, glasses with optical correction that provides the best visual acuity are determined. Glasses are determined based on testing that is conducted every year because with small children it is hard to get the most accurate results at the first examination. When the child is accustomed to the glasses, atropinization and occlusion of the leading eye are starting to be implemented with pleoptic exercises if they are possible.
– Atropinization is the instillation of atropine into the eye, which is used for expanding the pupil.
– Occlusion is covering of the eye. Direct occlusion is covering of the leading eye, and the inverse one is covering of the amblyopic squinted eye.
– Exercises are carried out using special equipment: pleoptofor, centrofor and separator, eutiskop.
Contact lenses are used at high farsightedness, nearsightedness and astigmatism. Prisms are used to divert light rays into the desired direction and to encourage the development of binocular vision. Treatment with prisms takes months or even a year or two.
Surgical procedure is carried out in order to improve the function, to enable binocular vision and to improve aesthetics of eyes.
Surgery is undertaken in the following cases:
– If the combined conservative treatment fails
– At large deflection angle
– Unaccommodative strabismus
– Partial accommodative strabismus at which glasses and occlusion do not solve the problem
– Early strabismus
– A large number of cases of paralytic strabismus
Surgical intervention is not carried out in:
– Accommodative strabismus
– Strabismus with a small deflection
– With fresh paralysis / paresis of muscles
– Each of strabismus in which conservative treatment can achieve success
After the surgery these might occur:
– Puncturing of the sclera
– Puncturing of the retina
– Uplifting of the retina
– Adhesion and proliferation of connective tissue in the eye, which limits the movement of muscles and often requires re-operation
– Incorrect estimation can lead to excessive or too weak correction, which might lead to re-operation
– Surgery on wrong muscles because of switching them