Balance in the Strabismic Patient Undergoing Strabismus Surgery

It is a useful test to assess some characteristics of strabismus. It is always performed for both distance (6 m) and near (33 cm). The cover/uncover test is performed by occluding one of the two eyes with a screen for a few seconds and then uncovering it again allowing binocular vision, then performing the same maneuver on the other eye. Next, the alternating cover test is performed, which consists of covering first one eye and then the other with a screen, without allowing both eyes to see at the same time.

The test allows measurement of the angle of strabismus and is performed by sliding a slat of Berens prisms in front of either eye. The cover-test is repeated by sliding the prism bar and observing the amount of movement the deviated eye makes to take fixation. They will decrease, increasing the power of the prism, until they are cancelled. The prism that cancels the movement corresponds to the magnitude, in prism diopters, of the deviation angle.

The test consists of placing an externally based prism of 4 prism diopters in front of one eye. If there is convergence movement due to the disparity of image presentation to the two eyes, there is fusion movement, and if such movements are present for near (33 cm) and far (6 m and beyond), there is normal binocular vision. Otherwise, fusional motion will be absent.

The method generally employed for this measurement is the screen test (cover test) in conjunction with a vertical or horizontal prism bar. Ocular deviation should be assessed in the following positions of gaze:

• primary position, with head erect and looking straight ahead;
• 4 secondary positions, are straight down, straight up, horizontally right and left;
• 4 tertiary positions, are the oblique positions (up right and left, down right and left) Evaluation of these nine positions of gaze, referred to as diagnostic positions, provides a complete picture of alterations in the function of various muscles.

Streaked glasses are flat lenses with thin streaks along a meridian. On each glass is a mark called the striated glass axis, which indicates the orientation of the light streak seen by the patient. The test is performed for near (33 cm) and far (6 m). It can identify:

a normal retinal match if there is no bulb deviation or an abnormal retinal match if tropic motion is detected in the cover-uncover test.

Complete suppression of the deviated eye. This is a condition prevalent in wide-angle strabismus.

suppression scotoma.

• diplopia disparity of fixation.

This test consists of four lights, 2 green, 1 red and 1 white. It can be performed for both distance and near; the patient being tested must stare at the four lights while wearing a pair of anaglyphic glasses (red-green lenses). Since the lights are complementary to the filters placed in front of the patient's eyes, he will see red light through the red filter and green light through the green filter. The patient can see:

• four lights (one red, two green and a fourth red or green depending on ocular dominance), indicating normal retinal matching or abnormal retinal matching;
• three green lights or two red lights in case of suppression;
• five lights (two red and three green) in case of diplopia.

Lang's test consists of the presentation of a card in which there are random stimuli printed with a panographic system, that is, with small cylinders oriented so that each is perceived by only one eye. The disparities proposed in Lang's first test range from 600 to 1200 arc seconds, specifically the star and the car have a disparity of 600 arc seconds, while the cat has a disparity of 1200 arc seconds.

TNO test This test splits images with a red and green complementary color glasses. The parts of the images displayed stimulate the eyes separately: the red parts of the images are seen only by the eye with the red glass; the green parts only by the eye with the green glass. In binocular combination, parts of these images stimulate different retinal areas and are seen in relief. This test provides images with gradations of up to 15 arc seconds.

A red glass is placed in front of one of the eyes and a bright vision is presented to the patient, which is arranged in the various positions of gaze. If there is a deficit, the patient sees two lights, one white and one red, indicative of diplopia. The test is based on finding the direction of gaze in which diplopia is greatest. First, it must be ascertained whether diplopia is also present in primary gaze; then it is assessed whether it is greater in the right or left version and finally whether it is such, or increases, in upward or downward gaze. Another important finding is whether diplopia is horizontal and/or vertical. Once the direction of gaze in which the two fixation view images are furthest apart is established, the diagnosis will have been limited to only two muscles (one in each eye). Keeping in mind that the image of the eye with the muscle deficit is always the one farthest from the patient, it will be easy to arrive at an exact determination of the deficit muscle.

The PAT aims to assess whether the phenomenon of prism compensation (abnormal fusion movements) occurs. Prisms that best neutralize the deviation are placed in front of the eyeglass; after a longer or shorter observation period, three possibilities may occur:

1. the angle does not change, the patient does not compensate for the prisms;
2. As the angle of deviation increases, the patient compensates for the prisms; we are probably in the presence of abnormal fusion movements. These may be: poorly rooted, very rooted, apparent;
3. the angle of deviation decreases (rare occurrence).

The PPT is used to evaluate, in cases of prism compensation, the radication of MFAs. Prisms of magnitude greater than the deflection angle are placed in front of them and it is observed whether they are compensated or not.

This examination involves evaluating areas of diplopia and single vision within the visual field. It is useful for tracking the progress of paralysis or the effect of surgery. It is performed with Goldmann's perimeter in binocular vision. It is done by placing the subject seated in front of the perimeter, a light sight is presented that moves over the various meridians, the patient is asked to follow it with his or her eyes, and an assessment is made of where the subject sees double the light projected by the perimeter and where there may be areas of single vision. Areas of diplopia and single binocular vision are mapped in the appropriate perimetry diagrams.

The SI is an objective test conducted through a robotic platform that can identify the risk of falling. It consists of seven domains: (i) static balance, (ii) dynamic balance, (iii) reactive balance, (iv) sensory integration, (v) stability limits, (vi) sit-to-stand, and (vii) gait speed.

The platform returns a fall risk ranging from 0% to 100%: higher values indicate higher fall risk