The study of binocular vision can be carried out by different methods, among which the examination with a 4-point color test (test with a color device) is generally accepted.
The studied one observes 4 multicolored circles (2 green, white and red), glowing through optical filter glasses (with one red and one green glass). The color of the circles and lenses are selected in such a way that one circle is visible only with one eye, two circles - only with the second one, and one circle (white) is visible with both eyes.
Percent sits from a direct and strong light source at a distance of 5 m. Wears glasses-filters: the right eye is covered with red glass and the left eye is covered with green. Before the start of the diagnostic manipulations check the quality of the filters. To do this, one by one covers with a special eye shield, while the patient sees first two red eyes with his right eye and then three green circles with his left eye. The main examination is carried out with simultaneously open eyes.
There are three variants of examination results: binocular (normal), simultaneous and monocular vision.
Sokolov Method (1901)
The method consists in asking the patient to look into the tube with one eye (for example, a sheet facing the tube), and a palm is applied to its end from the side of the open eye. In the presence of binocular vision, an impression of “a hole in the palm of your hand” is created; through it, a picture is seen that can be seen through the tube. This results from the fact that the picture which is visible through an opening in a tube is superimposed on the image of a palm in the second eye.
With the simultaneous nature of the view, the “hole” does not coincide with the center of the palm, and with a monocular phenomenon, the “hole in the palm” does not appear.
The experience with two pencils (they can be replaced with ordinary chopsticks or felt-tip pens) is indicative. The patient should try to combine the tip of his pencil with the tip of the pencil in the doctor's hands so that a straight line is formed. A person with binocular vision easily performs tasks with two eyes open and misses when one eye is closed. In the absence of binocular vision, overshooting is noted.
Other, more complex methods (prism test, Bogolin striped glass test) are used by an ophthalmologist.
Strabismus by the method of Girshberg
The magnitude of the strabismus angle is simply and quickly determined by the Girshberg method: a beam of light is directed into the subject's eyes and the location of the light reflexes on the cornea is compared.
A reflex is fixed in the eye and is observed near the center of the pupil, or coincides with it, and in the eye that mows, it is determined at the place corresponding to the deviation of the visual line.
One millimeter of displacement on the cornea corresponds to the angle of strabismus at 7 degrees. The larger this angle, the farther from the center of the cornea the light reflex shifts. So, if the reflex is located on the edge of the pupil with its average width of 3-3.5 mm, then the squint angle is 15 degrees.
The wide pupil makes it difficult to accurately determine the distance between the light reflex and the center of the cornea. More precisely, the angle of strabismus is measured on the perimeter (the Golovin method), on the synoptophore, by a test with a cover of prisms.
Subjective method for determining binocular vision
To determine the level of light refraction in the eyes by a subjective method, a set of lenses, a test spectacle frame and a table for determining visual acuity are needed.
The subjective method for determining refraction consists of two stages:
- determination of visual acuity;
- attachment of optical lenses to the eye (first +0.5 D, and then -0.5 D).
With emmetropia, a positive glass degrades the Visus, and a negative glass degrades first, and then does not affect it, since accommodation is included. In case of hypermetropia, “+” glass improves Visus, and “-” glass deteriorates first, and then with a high voltage of accommodation is not displayed on Visus.
In young patients with visual acuity equal to one, two types of refraction can be assumed: emmetropia (Em) and mild hypermetropia (H) with accommodation.
In elderly patients with visual acuity “unit”, only one type of refraction can be assumed - accommodation is weakened due to age.
With visual acuity of less than one, two types of refraction can be assumed: hyperopia (high degree, accommodation cannot help) and myopia (M). In hypermetropia, a positive glass (+0.5 D) improves the Visus, and a negative glass (-0.5 D) worsens the Visus. In myopia, a positive glass affects visual acuity, and a negative glass improves.
Astigmatism (different types of refraction in different meridians of one eye) is corrected by cylindrical and spheroidal cylindrical lenses.
When determining the degree of ametropia, the glass changes for the better with the Vizus (1.0).
In this case, with hypermetropia, refraction determines the largest positive glass with which the patient sees better, and with myopia, less negative glass with which the patient sees better.
The different type or degree of refraction of both eyes is called anisometropia. Anisometropia up to 2.0-3.0 D in adults and up to 5.0 D in children is considered portable.
Objective methods for determining binocular vision
Skiascopy (shadow test), or retinoscopy - an objective method for determining the refraction of the eye. To carry out the method you need: a light source - a desk lamp; mirror ophthalmoscope or skiascope (concave or flat mirror with a hole in the middle); skiascopic rulers (this is a set of cleaning or diffusing lenses from 0.5 D-1.0 D in ascending order).
The study is conducted in a dark room, the light source is placed on the left and somewhat behind the patient. The doctor sits 1m away from him and directs the light reflected from the skiascope into the eye being examined. In the pupils while there is a light reflex.
By slightly rotating the glass knob, the reflected beam is moved up-down or left-right, and the movement of the skiascopic reflex in the pupils is observed through the opening of the skiascope.
Thus, skiascopy consists of 3 points: obtaining a red reflex; obtaining a shadow, the movement of which depends on the type of mirror, the distance from which it is examined, on the type and degree of refraction; Neutralization of shadow with skiascopic ruler.
There are 3 options skiascopic reflex (shadows against a red reflex):
- the skiascopic reflex moves in accordance with the movement of the mirror;
- it moves opposite to the movement of the mirror;
- the shadow on the background of the red reflex is absent.
In the case of a coincidence of the movement of the reflex and the mirror, we can talk about hypermetropic vision, emetropic or myopic to one diopter.
The second variant of moving the skiascopic reflex indicates myopia of more than one diopters.
Only with the third variant of the movement of the reflex do they conclude about myopia in one diopter and the measurements at this stop.
In the study of astigmatic eye skiascopy carried out in the two main meridians. Clinical refraction is calculated for each meridian separately.
In other words, binocular vision can be examined in different ways, everything directly depends on the brightness of the symptoms, on the patient's complaints and on the professionalism of the doctor. Remember, strabismus can be adjusted only in the early stages of development and this will take a long time.