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Paralytic strabismus
Last reviewed: 07.07.2025
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[ Symptoms of paralytic strabismus
It is characterized primarily by limited or no mobility of the squinting eye in the direction of the paralyzed muscle. Looking in this direction causes double vision, or diplopia. If in concomitant strabismus double vision is eliminated by functional scotoma, then in paralytic strabismus another adaptation mechanism occurs: the patient turns his head in the direction of the affected muscle, which compensates for its functional insufficiency. Thus, the third symptom characteristic of paralytic strabismus occurs - a forced turn of the head. Thus, in case of paralysis of the abducens nerve (dysfunction of the external rectus muscle), for example, of the right eye, the head will be turned to the right. A forced turn of the head and tilt to the right or left shoulder in cyclotropia (shifting of the eye to the right or left from the vertical meridian) is called torticollis. Ocular torticollis should be differentiated from neurogenic, orthopedic (torticollis), labyrinthine (in otogenic pathology). The forced rotation of the head allows the image of the object of fixation to be passively transferred to the central fovea of the retina, which eliminates double vision and provides binocular vision, although not entirely perfect.
With early onset and long-term existence of paralytic strabismus, the image in the squinting eye may be suppressed and diplopia may disappear.
A sign of paralytic strabismus is also the inequality of the primary angle of strabismus (of the squinting eye) to the secondary angle of deviation (of the healthy eye). If you ask the patient to fix a point (for example, to look at the center of the ophthalmoscope) with the squinting eye, the healthy eye will deviate to a significantly greater angle.
Diagnosis of paralytic strabismus
In paralytic strabismus, it is necessary to determine the affected oculomotor muscles. In preschool children, this is judged by the degree of eye mobility in different directions (definition of the field of view). At an older age, special methods are used - coordinatemetry and induced diplopia.
A simplified method for determining the field of view is as follows. The patient sits opposite the doctor at a distance of 50-60 cm, the doctor fixes the patient's head with his left hand and asks him to follow with each eye in turn (the second eye is covered at this time) the movement of an object (pencil, hand ophthalmoscope, etc.) in 8 directions. Muscle insufficiency is judged by the limitation of eye mobility in one direction or another. Special tables are used for this. With the help of this method, only pronounced limitations of eye mobility can be detected.
In case of visible vertical deviation of one eye, a simple adduction-abduction method can be used to identify the paretic muscle. The patient is asked to look at some object, it is moved to the right and left, and it is observed whether the vertical deviation increases or decreases at the extreme gaze deflections. The affected muscle is also determined by this method using special tables.
Chess coordinatemetry is based on the separation of the visual fields of the right and left eyes using red and green filters.
To conduct the study, a coordinate-metric set is used, which includes a grid screen, red and green flashlights, and red-green glasses. The study is carried out in a semi-dark room, on one of the walls of which a screen is fixed, divided into small squares. The side of each square is equal to three angular degrees. In the central part of the screen, nine marks are allocated, placed in the form of a square, the position of which corresponds to the isolated physiological action of the oculomotor muscles.
The patient in red-green glasses sits 1 m from the screen. To examine the right eye, he is given a red flashlight (red glass in front of the right eye). The researcher holds a green flashlight, the beam of light from which he alternately directs to all nine points and asks the patient to match the green light spot with the light spot from the red flashlight. When trying to match both light spots, the patient usually makes a mistake by some amount. The doctor records the position of the fixed green and aligned red spot on a diagram (sheet of graph paper), which is a reduced copy of the screen. During the examination, the patient's head must be motionless.
Based on the results of a coordinatemetric study of one eye, it is impossible to judge the state of the oculomotor apparatus; it is necessary to compare the results of coordinatemetry of both eyes.
The field of view in the diagram drawn up based on the results of the study is shortened in the direction of action of the weakened muscle, while at the same time a compensatory increase in the field of view in the healthy eye is observed in the direction of action of the synergist of the affected muscle of the squinting eye.
The Haab-Lancaster method of examining the oculomotor apparatus under conditions of induced diplopia is based on assessing the spatial position of images belonging to the fixing and deviated eye. Diplopia is induced by placing a red glass against the squinting eye, which allows one to simultaneously determine which of the double images belongs to the right eye and which to the left eye.
The nine-point examination scheme is similar to that used in coordinometrics, but there is only one (not two). The examination is conducted in a semi-dark room. A light source is located 1-2 m from the patient. The patient's head should be motionless.
As with coordinometrics, the distance between the red and white images is recorded in nine positions of the gaze. When interpreting the results, it is necessary to use the rule according to which the distance between the double images increases when looking in the direction of the affected muscle. If the field of view is recorded in coordinometrics (it decreases with paresis), then with "provoked diplopia" - the distance between the double images, which decreases with paresis.
Treatment of paralytic strabismus
Treatment for paralytic strabismus is primarily performed by a neurologist and pediatrician. An ophthalmologist specifies the diagnosis, determines refraction, prescribes glasses for ametropia, and performs occlusion. Orthoptic exercises are useful for mild paresis. Glasses with prisms are used to eliminate double vision. Medicinal resorption and stimulating therapy is prescribed. Electrical stimulation of the affected muscle and exercises aimed at developing eye mobility are performed. In case of persistent paralysis and paresis, surgical treatment is indicated. The operation is performed no earlier than 6-12 months after active treatment and in agreement with the neurologist.
Surgical treatment is the main type of treatment for paralytic strabismus.
Plastic surgery is often indicated. Thus, in case of paralysis of the abducens nerve and absence of outward movements of the eyeball, fibers of the upper and lower rectus muscles (1/3-1/2 of the muscle width) can be sutured to the external rectus muscle.
Surgical approaches to the oblique muscles, especially the superior oblique, are more complex due to the complexity of its anatomical course. Various types of interventions have been proposed for these, as well as for the vertical rectus muscles (upper and lower rectus). The latter can also be recessed (weakened) or resected (strengthened).
When performing surgery on the extraocular muscles, they must be handled with care, without violating the natural direction of the muscle plane, especially if this is not clinically justified. Special operations performed for complex types of strabismus can change not only the strength, but also the direction of muscle action, but before they are performed, a thorough diagnostic examination must be carried out.
One of the methods of treating paralytic strabismus is prismatic correction. It is most often helpful in treating recently developed paresis and paralysis of the oculomotor muscles in adults, for example after craniocerebral trauma.
Prismatic glasses combine double images, preventing the development of diplopia and forced head rotation in the patient. Paralytic strabismus can also be treated with medication and physiotherapy.