STRABISMUS AND AMBLYOPIA (SQUINT)
STRABISMUS (squint) is anomaly of parallel position of the eyes, visual axis deviation in a certain gaze, temporary or constantly present, with the binocular vision impaired. It is a motor and a sensory anomaly.
Practically, it means a misalignment or inability of both eyes to focus simultaneously in order to form a unique image.
Ortophoria is called the normal, parallel position of eyes while looking in a distance target.
Phoria (eso, exo, hyper, cyclo): latent visual axis deviation, discovered by certain tests, and compensated by fusion. Reason for this lost of fusion may be Blurred vision due to opacity of optic media (cornea, lens), uncorrected refractive error, defect in accommodation and convergence, or muscular problem.Tropia is the manifest visual axis deviation of one or both eyes, constantly or intermittently present.
There are several types of the strabismus: congenital, acquired, convergent (in-deviation-esotropia), divergent (out deviation, exotropia), vertical deviation, in one or both eyes or alternating. etc.
Strabismus is quite common (4-6 percent of the population), mostly in preschool children, followed by the amblyopia in almost 50 percent. With the most frequent range between the ages up to 3 years old.
Amblyopia is a “developmental defect of spatial visual processing that occurs in the central visual pathways of the brain”. It presents most dramatically as loss of visual acuity in one or, rarely both eyes .Certain forms of amblyopia presents as diminished contrast sensitivity and spatial localization of objects.
It is inability to obtain a clear, sharp image regardless the adequate correction of refractive error. These defects may be explained by the mechanism of lack of use of an eye because of media opacity or extreme refractive errors that cause a chronically blurred image to form on the fovea.
The main reason could be lack of adequate correction of refractive error or impossibilities in spectacles or contact lens correction of high anisometropic refractive problems (large dioptric difference in both eyes).
The full refractive error correction is imperative in early childhood , and patching of the better eye, in certain regime, in order to develop as much of visual function, as possible. In the case of contact lens intolerance or incompliance to spectacles, refractive surgery should be recommended for fully correction and achieving isometropia.
Certainly, neither the laser nor any other procedure can ‘construct’ the vision, but only give the chance for better development of visual function and binocular vision and stereopsis. If we make condition for sharp vision, from early childhood, it will help the amblyopia to reduce.
Amblyopia and strabismus present a problem for the whole society and the person, itself, giving a limiting choice of possible professions.
For normal visual function and binocular vision development, it is necessary to have parallel position of the eyes, and sharp image created on the corresponding points on the retina of both eyes. The most important period for developing the binocular vision is from the age of three months to 3-4- Th years of age and 7-8th, respectively. After that period, the chances to get more on visual acuity are low.
To develop normal visual function, normal anatomy of eyes is mandatory, meaning: normal shape and alignment of eyes, no refractive error, or corrected properly on time, normal anatomy and functions of ocular muscular system and innervations for achieving regular eye movements, and healthy central nervous system with visual centre for receiving the visual stimuli from both eyes and analyzing them, having a unique, sharp image.
If there is impairment in the early childhood at any of these levels, the binocular functional vision is impaired. An eye that is not able to fix ‘escapes’. If there is an obstacle in both eyes, nistagmus (fast, uncontrolled eye movements) could be expected with a severe amblyopia.
This obstacle can be the a cataract, glaucoma with optic nerve damage, or ptosis with a covered pupil, and long-term pleoptic treatment with prolonged occlusion of one eye, every possible reason for disturbing the light get into the eye or make blurred or different images on both eye’s retina, aniseiconia (non corresponding) as in high anisometropia.
Strabismus can appear later in the life ,in all long-lasting disturbances such as uncorrected refractive error, corneal opacities, cataract, retinal or optic nerve damages, central nervous system damages (cerebro-vascular insult with cranial nerve palsy), trauma, psychological traumas without an organic cause, etc.
Convergent strabismus (crossed eyes, eso-deviation) is more common among children and the divergent strabismus (out- exo deviation) among adults.
Prevention of strabismus and amblyopia can be achieved by early detection and correction of refractive errors (far-sightedness, astigmatism, near-sightedness), in a proper way, and specific exercises and controlled patching of the better eye or alternatively, to train the ‘lazy eye’ to look. Soon after these steps, a strabismus surgery is mandatory for eliminate the residual misalignment of visual axis on both eyes. If the reason for amblyopia and strabismus is cataract, or ptosis, than of course first these obstruction should be removed and strabismus surgery thereafter.
Amblyopia treatment is strongly recommended after that.
An early cataract surgery with intraocular lens implantation for fully correction of refractive error, performed in the first months or years of life, is one of the most important conditions to reduce or eliminate amblyopia and strabismus.
Primarily PC IOL implantation in children during cataract surgery is of great impact for better visual acuity and binocular vision development than standard aphakia correction with glasses or contact lenses, and can reduce amblyopia significantly. Of course, patching of better eye, in certain regime, according to the age of child, and possibilities for amblyopia development, is obligatory.
Further axial length and consecutive refractive changing should be regularly monitored.
If the progression in axial length growth is discovered, scleroplasty is recommended, in order to cease further elongation of the bulbus.
With the early onset of strabismus, by the first 6 months of life, an early surgery is planned, by the second year of age.
With later onset from2 year up to 6, a good refractive error correction is mandatory and strabismus surgery thereafter, when necessary.
With sustained problem, in older age, amblyopia is fixed and strabismus or refractive surgery has only esthetic, not functional purpose. The binocular vision has already been lost.
In the case of the paralytic strabismus, the eyes are put into aligned position that prevents double images.
Strabismus surgery has to align the position of the eyes, by adjusting the ocular-muscular attachments. It is done under the general anesthesia, in one day conditions, with leaving the hospital few hours later.
In the Special Hospital SVETI VID, the famous experts in the field of refractive and cataract surgery, and strabismus approach this problem carefully and complex.
In one place there are possibilities to solve not only the problem with misalignment of eye position, but to exclude many of the causes of It., as well.