Introduction

When we have to operate on an adult for strabismus, it will be necessary to know the possibility of postoperative diplopia. Not all adults can be told that they are worried about the aesthetic problem, that it has no solution and that it should stay that way for life, with this striking situation and a source of psychological complexes.

There is a problem when exploring these patients, and that is that there is no test that places the eyes of this patient in the same situation that the surgery will leave them, and therefore we cannot know with certainty, no matter how many tests we do, if in the postoperative, there will or will not be diplopia.

There are some situations that, although not in a very safe way, do give us an orientation of the possibilities of postoperative diplopia:

1. Strabismus since childhood, in adulthood. Horizontal or vertical strabismus that at some point accuses or triggers diplopia in any gaze position, torticollis or other discomfort.

2. Decompensation of a childhood strabismus in adulthood. For example, intermittent divergent strabismus.

3. Strabismus or diplopia appearing at age Secondary convergent or divergent strabismus.

This and other factors such as the current age of the patient, amblyopia, angle of deviation, CRA, preoperative orthoptic treatments and psychological factors of the patient, allow us, together with different explorations, to have a fairly firm criterion about the possibilities of intervening without fear or have to regret it. This will also be taken into account so as not to excessively delay the age of operation.

With the surgery, what we do is take the image of the deviated eye out of the suppression scotoma. A diplopia occurs; in children it usually lasts a few days or even months in an exceptional way, but it is usually adapted with a new retinal correspondence or deletions in this area. The angle of anomaly will depend on the new sensory-motor situation. If the angle of anomaly is equal to 00, you may have bifoveal vision. This evolution of the angle of anomaly is possible due to the brain plasticity of the child, which is greater, the younger the age.

In adolescents and adults, brain plasticity is much lower. The suppression scotoma at the level of the deviated eye may be limited to the 00 point. It does not spread, as often happens in children, it reaches the foveal region. It will be smaller or limited if the squint is constant. Diplopia appears as the angle of deviation decreases.

Factors that favor the appearance of diplopia

1. Unilateral amblyopia.

This assumes the existence of a unilateral dominance and the absence of alternation. The suppression always falls on the same eye. This is the reverse of what happens in alternating strabismus in which the suppression is constantly changing eyes, and where there is almost never binocular vision in simultaneous vision.

This concept is contrary to the classic one that an eye that sees badly will not give problems of diplopia. In practice we have found an adult patient who saw only light with one of his eyes and after the operation he noticed that a spot was put in front of the objects that he looked at with the other eye. One cannot think that if one eye does not see or sees very little, we will forget about diplopia, from what has been said above, the scotoma is more localized because it is always in this eye.

2. The deflection angle is large.

The suppression scotoma is constant and tends to be limited around the retinal area of ​​the 0 point or its subjective angle. By taking the image of this area because we modify the deviation of the eye with the surgery, the image is projected in an area that is not suppressing, an area near the fovea or in the fovea. For this patient, it was not his point 0, but rather an area that corresponds to the nasal visual field, if the strabismus is convergent and his fovea is therefore in the temporal area or vice versa in divergent strabismus.

Intermittent convergent strabismus, such as far near incomitances or intermittent or variable divergent strabismus, conversely, have broad retinal area deletions and no diplopia is seen.

3. Anomalous retinal correspondence.

It is a very predisposing factor for postoperative diplopia. The retinal area on which the image is formed after surgery has an abnormal spatial value.

4. Orthoptic treatments.

Orthoptic and anti-suppression treatments performed preoperatively favor the appearance of diplopia. These treatments should not be done after 12 years. It has been confirmed that the diplopia appeared by strabismus surgery in adults were in many cases caused by orthoptic exercises performed indiscriminately.

5. Psychological factors.

Suppression is a cerebral phenomenon, and the lack of acceptance of diplopia can influence its persistence. Many patients recognize that they see double when they look or pay attention, but that it does not bother them and they forget their diplopia. On the contrary, neurotic patients do nothing more than observe themselves and test themselves on how separate images are, more or less marked and what color they are, in what position they join or separate. The fact is that this diplopia does not accept it and does not let them live.

6. Surgical overcorrection or excess surgical correction.

Both lead to diplopia because the image falls into an area that it has never suppressed. Strabismus with an incomitant angle of deviation may be overcorrected due to a specific situation, due to poor surgical indication. Sometimes overcorrection only occurs in lateral gaze and in PPM there is hypocorrection.

Conduct to follow before operating

1. Study of suppression scotomas.

We do the study of suppression by passing the “Bagolini filter bar in front of the deviated eye. If density No. 5 or higher must be passed to cause diplopia, the risk is small.

2. The study of the suppression scotoma with the synoptophore.

If the angle is small and the diplopia area is wide, we will be cautious or reserved in surgery. If the scotomas are broad and the abnormal retinal correspondence is not rooted, there is little chance of diplopia.

If the suppression scotoma, in addition to being large, affects the area of ​​the target angle, we will be more certain that there will be no problems. If there is no suppression at the target angle and it is far from it, the suppression scotoma that only exists in the 0-motor situation, the possibility of diplopia is great.

3. Placement of prisms in sensory orthophoria.

We will put prisms, which compensate for the horizontal deviation. When the entire deviation can be compensated, without diplopia, there is no operative risk.

If diplopia appears, we will leave the prisms in place for several hours or up to 15 days to see if this diplopia disappears or even if it persists, if it is not annoying. We can also consider the prognosis favorable.

If diplopia bothers, the prismatic power should be lowered. The accepted prismatic power without diplopia gives the amount of deviation that we can correct with surgery. The appearance of a diplopia with the prisms does not mean that there will surely be postoperative diplopia and therefore we will have to assess the patient's reactions or her psychological behavior. The patient should not be scared with the problem of possible diplopia, especially in cases where the study of the removal and placement of the prisms is favorable and if the patient is determined to undergo surgery, they will be told that after a few training days will ignore diplopia.

4. Passive duction and straightening of the deviated eye.

We will carry out this test after the other studies and it is one more demonstration of the existence or not of diplopia when straightening the eyes.

We repeatedly instill anesthetic eye drops every minute or half a minute, ten or twelve times. With an atraumatic forceps we grasp the bulbar conjunctiva near the limbus.

In convergent strabismus in the temporal area of ​​the deviated eye, and we pull out. In divergent strabismus it is pulled inward. The eye is placed in parallelism with the other, evaluating the test by means of corneal reflexes.

Setting a light point at 5 meters, we ask the patient whether or not there is diplopia.

In case of existence of diplopia, we give in the traction or push of the eyeball, assessing in which deviation we must operate to avoid diplopia.

Sometimes in fixation at 5 meters, diplopia is less evident with real objects than with bright spots or vice versa.

Care will be taken in adults not to over-correct the deviation and surgery in these cases can be performed using adjustable sutures. The next day they will allow us to modify the result, especially in the case of hypercorrection.

Conduct to follow in the postoperative period

1. Do not perform orthoptics unless there is normal retinal correspondence.

2. If there is diplopia, reassure the patient and wait in case it gives way or gets used to it after a few days ... don't give it too much importance.

3. If there is annoying diplopia we can:

- Divert the image to the suppression scotoma with a prism, nasal base if esotropia was operated.

- Blur the image of the non-dominant eye, with optical hypercorrection, filters or lacquer.

- If it is very annoying, you can put a black contact lens.

4. When diplopia persists and is very annoying or we have gone through surgery.

If there is diplopia in a lateral gaze position, and esotropia in PPM, it can be re-intervened by retro-inserting the lateral rectus, without danger of increasing esotropia in PPM.