Exotropia is a disorder in which both eyes are looking at the target and the line of sight of one eye is deviated from the target and skewed outward. Intermittent exotropia is a disorder in which the eyes are partly orthotropic and partly exotropic, and is a disorder in which the eyes are separated. Intermittent exotropia is a type of strabismus that is intermediate between exotropia and common exotropia. As the disease progresses, the number and duration of intermittent exotropia increases, and eventually exotropia can occur when looking close. Eventually, the exotropia develops into a constant exotropia and does not maintain an orthotropic position.
Clinical manifestations
(1) The strabismus of intermittent exotropia often occurs when one is tired, ill, drowsy, or inattentive. This leads to the perception of absent-mindedness and loss of decorum in social situations.
(2) The gaze is usually alternate and there is usually no amblyopia. Most patients have equal or no more than one line difference in corrected visual acuity between the two eyes.
(3) The patient is generally photophobic. Unlike normal people who partially close both eyes in bright light, patients with interstitial exotropia often habitually close the nondominant eye completely in bright light.
(4) Blurred vision: Looking away to maintain orthophoria and over-regulating, resulting in blurred vision, with normal vision when looking monocularly or strabismus. However, there is significant under-regulation when exotropia is present.
(5) Due to the loss of stereopsis, the patient may develop abnormal spatial orientation.
(6) It may be combined with A-V sign and other vertical strabismus, such as separated superior strabismus.
Examination
(1) Examination of oblique perspective: When looking at the oblique perspective at a distance, it is better to make the patient look at the target at a distance of 6m in order to fully examine the degree of exotropia and determine the type of exotropia. Because different types of intermittent exotropia have different treatment timing and treatment methods. The refractive error should be corrected when measuring the strabismic angle to control its adjustment.
(2) Examination of the sharpness of stereopsis: the patient must also measure his stereopsis during the occultation period. If the stereopsis is not normal, it means that the stereopsis caused by the intermittent episodic strabismus decreases, and if the stereopsis continues to decrease within a few months, it is a strong indication for surgery to correct the intermittent strabismus.
Treatment
(1) Refractive correction: Refractive examinations for ciliary muscle paralysis (dilated pupils) should be performed if necessary, especially in infants and children. Patients with significant refractive error, especially astigmatism and refractive aberration, should be fully corrected to ensure a clear retinal image; those with myopia in surgery should be fully corrected; those with hyperopia in emmetropia, correction of hyperopia will reduce the regulatory collection and increase emmetropia, whether full or partial correction is needed depends entirely on the degree of hyperopia, the patient’s age and the AC/A ratio, usually less than +2.00D infants and children, can not be corrected. In older patients, correction of hyperopia is usually necessary to avoid refractive fatigue. Older patients with emmetropia with presbyopia and weakened accommodation, such as hyperopia, need correction and can be given a minimum degree to facilitate near vision.
(2) Negative spherical lens add-on: correction of intermittent exotropia with negative lens can be a temporary measure. For the separation of too strong type wearing the upper half of the additional lenses of bifocal lenses; for the collection of insufficient can wear the lower half of the additional bifocal lenses, to stimulate its regulatory collection, control exotropia. This method of treatment should not be advocated, as it often causes visual fatigue in children treated in this way. This method is often used for young children with inadequate accommodation.
(3) Trigonometry: Bottom inward trigemetry can enhance the central recess stimulation of both eyes. The prescription can be made to compensate for the partial deviation with a bottom-facing 1/2 to 1/3 prism, and the stimulus fusion is corrected. Alternatively, an inward-facing prism may be prescribed to completely neutralize the entire deviation in an attempt to obtain more permanent binocular perceptual fusion. However, partial trigeminal correction is more commonly given.
4.Surgical treatment
(1) Timing of surgery: The most appropriate age for intermittent exotropia surgery is still debated. Some people advocate that the earlier the surgery, the better, otherwise it will become a constant exotropia.
The indications for surgery are determined by the fusion control, the normal stereopsis, the size of the strabismus and the age of the patient. Surgery should be performed as soon as possible if there is no intermittent exotropia soon after birth. 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. The best time for surgery is to eliminate exotropia surgically before it develops into inhibition and abnormal retinal correspondence.
(2) Surgical approach: The surgical plan can be designed according to the size of the emmetropia in its distance viewing and near viewing, and the amount of surgery can be determined according to each physician’s test and method.
(3) Overcorrection and undercorrection The prevalence of overcorrection after exotropia has been reported to range from 6% to 20%. If the postoperative overcorrection is 10-15△, it can disappear completely. If the postoperative undercorrection is greater than 15-20△, two surgeries can be performed within 6-8 weeks after the first surgery. For patients with mild undercorrection, the residual obliquity is less than 15～18△, the disinhibition and fusion set training can be used to make them reach the state of occlusion.
5.Visual training.
Visual training after surgery is very important and is an important step in restoring binocular abnormalities caused by strabismus, curing interstitial exotropia and avoiding recurrence. It includes extending fused aggregation amplitude and agility, eliminating inhibition and improving accommodation.