The advantages of this classification method according to the pathogenesis can guide the clinical practice, such as the posterior migration of the external rectus muscle in both eyes for the true separation overstrength type, and the tendon amputation of the internal rectus muscle in both eyes for the collection understrength type, and postoperative collection training to strengthen the central collection. The exotropia type has a developmental trend, so do not delay treatment.
Treatment of common exotropia
1. The distance strabismus angle is greater than the near strabismus angle, at least greater than 15°, and the AC/A ratio is high. This type is fast developing and basically stable, so surgical treatment should be considered for the posterior migration of the external rectus muscle bilaterally.
2. The basic external oblique type has a distant oblique angle equal to the near oblique angle, with a difference of no more than 10° and a normal AC/A ratio. This type of external oblique has a development trend. Surgery is considered for posterior external rectus with internal rectus tendon osteotomy.
3.The angle of near oblique is greater than the angle of far oblique, and the AC/A ratio is low. The muscle strength is normal during internal rotation. It is characterized by fast development, intermittent, and soon becomes constant, and the fusion function disappears, so it should be closely observed and operated in time, and the chance of obtaining binocular monocularity is still large after the operation.
4, similar to the separation of the strong type initially examined to see the far oblique angle is greater than the near oblique angle, after special examination found to see the near oblique angle far oblique angle, or see the near oblique angle equal to see the far oblique angle, so it is not a true separation of the strong type, surgery only to do the external rectus muscle effect is not good, should be done at the same time the internal rectus muscle cut tendon surgery.
Treatment of intermittent external strabismus
The most appropriate age for surgery for intermittent exotropia is still debated. Some people advocate that the earlier the surgery, the better, otherwise the strabismus will become permanent. Since most intermittent exotropia has good fusion and binocular vision, the results of surgery after 2 to 3 years of age or 10 years of age are almost identical and can be observed for several years. For infants and children with immature vision, in order to avoid overcorrection of surgery, it is recommended to delay surgery, strengthen fusion with negative spherical lenses, and prevent suppression by alternate masking, and consider surgery if the fusion function deteriorates rapidly or if the oblique angle is stable.
The indications for surgery are determined by the fusion control, the size of the oblique angle and the age of the patient. Those with exotropia soon after birth without intermittent exotropia should be operated as soon as possible; those with strabismus greater than 20° measured by masking at the time of heliodynia; and those with significant dominant strabismus component and visual loss of compensation. In terms of the effect of surgery on retinal correspondence, intermittent exotropia can occur with abnormal retinal correspondence and inhibition in order to eliminate the interference of diplopia and confusion, and the best time for surgery is to surgically eliminate exotropia before it develops into inhibition and abnormal retinal correspondence.
The results of Yu Gang’s follow-up of 77 cases of intermittent exotropia showed that the younger the age, the higher the chance of restoring normal binocular vision after surgery, while most adults could not restore normal binocular vision after surgery even if the eye position was corrected. It is not easy to master the best timing of surgery clinically. If the age is too young, the examination is not cooperative and the amount of surgery is not easy to master, which increases the rate of reoperation. It is believed that children with intermittent exotropia who are around 4.5 years old and have normal intelligence can cooperate with general eye position examination after repeated training, and this is the appropriate time for surgery. Conclusion: The earlier and more frequent the surgery, the higher the reoperation rate and the greater the risk of amblyopia and fusion loss.
We believe that for children with progressive intermittent exotropia, those with a deviation greater than 20°, and those with a period of apparent obliquity of more than 50% of the time, the surgical plan can be designed according to the size of their deviation and the masking test. If, after 30-45 minutes of masking, their deviation, looking at the ingot is greater than looking at the near by at least 15°, they can do bilateral posterior migration of the external rectus muscle, and the amount of surgery can be determined according to each physician’s test and method. If the oblique angle of looking at the near is greater than the oblique angle of looking at the far by at least 15° and less than 55°, the posterior migration of the external rectus muscle can be done bilaterally or the posterior migration of the non-dominant eye can be done – tendon amputation surgery. If the exotropia is greater than 55°, three muscles can be done, posterior migration of the external rectus muscle in the primary eye and posterior migration-truncated tendon surgery in the non-primary eye. If the external obliquity is greater than 70°, a bilateral posterior migration-tendon amputation is done.
If the strabismus is at least 20% smaller than the first eye position when the patient gazes to the left and right, there is a significant risk of overcorrection, especially for patients with immature vision.
For children with immature vision, undercorrection should be advocated, because a mild overcorrection to an internal oblique state is more likely to result in monocular gaze syndrome than a mild undercorrection to an external oblique state, and may result in the formation of an inhibitory dark spot, leading to developmental amblyopia. Conversely, a mild overcorrection of 10 to 20° is ideal if the patient’s vision is developmentally mature, and it will eventually produce stable results. Overcorrection at 25° should be avoided even in visually mature patients, as such overcorrection can create a blind spot syndrome and prevent postoperative fusion.
If the patient has an A or V sign, caused by an overactive superior or inferior oblique muscle, an intramuscular reduction of the overactive muscle can be done at the same time as the horizontal strabismus surgery.
The prevalence of overcorrection in external strabismus has been reported to range from 6% to 20%. If a large degree of overcorrection occurs immediately after external oblique surgery, the patient should be reoperated within 24 hours because there is a risk of muscle loss or slippage, and the external rectus muscle is less likely to be lost than the internal rectus muscle. If there is an excessive amount of tendon truncation of the internal rectus muscle by mechanical factors, significant overcorrection can also occur, but the amount of overcorrection is not as great as the former.
The internal oblique is common and can wait for observation, and can disappear completely when the internal oblique is 10 to 15° after surgery. The small amount of overcorrection after exotropia also depends on the age of the patient. Children with immature vision who have a small amount of overcorrection should be carefully monitored for the development of inhibited dark spot and developmental amblyopia. If the patient does not have a tendency to gaze, alternate masking is feasible, and if there is a moderate tendency to gaze, masking therapy is feasible. In addition, further optometry should be performed, and full correction should be applied if there is hyperopia, and treatment with pupil reduction agents or bifocal lenses should be applied if there is a large near skew. After the above treatment for 4 months, vision has not done more than a small amount, to treat a new patient, can not simply restore the previous exotropia surgery.
It is ideal to overcorrect 20° for a patient with mature vision. 6 weeks after surgery there is still 20° of internal obliquity, 2 surgeries are feasible, and the surgery should be performed 6 months after the first surgery. It is important to do a traction test before surgery. If traction is found, the muscles, conjunctiva and fascial sac should be appropriately posteriorly displaced.
Precautions before surgery
1. Refractive status should be checked before surgery for external strabismus. If there is refractive error, appropriate glasses should be worn, and if strabismus is still present after wearing glasses, surgery is required. Check the vision of both eyes. Children with amblyopia should first be treated for amblyopia and then undergo strabismus surgery.
2.If the operated child is small, the operation needs to be performed under general anesthesia, and the operation should be performed on an empty stomach from 22:00 pm onwards the night before the operation, and water should be prohibited to avoid choking on vomit into the trachea and causing asphyxia during the operation.
3.Patients with external strabismus surgery should avoid menstruation if they are female.
4.In order to obtain a functional cure for children with exotropia, preoperative visual function training can be performed to achieve a certain range of fusion and stereo vision function, if available.
5.In order to do a good job of external strabismus surgery and avoid undesirable accidents, after the scheduled surgery, both eyes need to be dotted with antimicrobial eye drops until the day of surgery. A full set of examination should also be performed before surgery, such as blood, urine routine, blood sugar, ECG, vital signs, etc.
6. For patients undergoing local anesthesia, if they eat breakfast or lunch, intraoperative muscle pulling may cause nausea and vomiting during or after surgery. The way to prevent this is to eat less or lighter food before surgery, and not to eat greasy food.
Precautions after surgery
1. Avoid systemic infection.
2. Teach the patient and family members the correct way to order eye drops. First of all, the family or patient should wash their hands clean, then the patient should take a supine position and ask their eyes to look upward, the family or patient should separate the upper and lower lids with their left thumb and index finger, pull the lower lid lightly with the thumb downward, hold the eye medicine bottle in the right hand, put the eye medicine on the lower fornix, ask them to turn their eyes lightly and close their eyes for 1-2 minutes, and wipe off the outflow of medicine with absorbent paper. Do not touch the eyelashes. If you order more than two kinds of drugs at the same time, interval 3-5 minutes between each drug and order 1-2 drops each time.
3. Pay attention to eye hygiene, don’t overuse your eyes, don’t rub your eyes, avoid excessive eye fatigue, and ensure sufficient sleep.
4. Pay attention to balanced nutritional intake, avoid smoking, alcohol and spicy stimulating food.
5. For patients with refractive error, timely prescription treatment is required after surgery. For children with partially adjusted internal strabismus, they should bring the original corrective glasses after surgery and try not to use near vision to avoid adjustment to the recurrence of internal strabismus. If there is amblyopia, amblyopia training should be carried out under the guidance of doctors.
6. Regular review.