The non-surgical clinical treatment methods of binocular fusion abnormalities in optometry are mainly divided into two types: first, optical correction; Second, visual rehabilitation training guidance.

Optical Correction

Optical correction includes refractive correction, additional spherical lens and additional prism.

Additional prism

1. Mitigation prism

Alleviating the three prism is to keep the eyes on the hidden oblique position, and make the binocular image fusion through the refraction of the three prism, avoiding the tension fatigue caused by the fusion of the image set. The bottom direction of the relief prism is opposite to the direction of esotropia. For example, the bottom of the relief prism for recessive esotropia is outward, and the bottom of the relief prism for recessive exotropia is inward.

The quantitative methods to alleviate the prism include sheard criterion, Percival criterion and 1:1 criterion, commonly known as the three criteria.

(1) Sheard Criterion

It is required that the relative set should be at least twice the hidden skew value in order to achieve comfortable eye use. The positive relative set (PRC) should be at least twice the magnitude of implicit strabismus, and the negative relative set (NRC) should be at least twice the magnitude of implicit strabismus. If the relevant test results cannot meet the sheard criterion, prism mitigation shall be considered.

(2) Percival Criterion

Percival rule stipulates that the fusion image state in the eye environment must be within the fusion image range in order to feel more comfortable with the eye. This rule does not consider the hidden inclination. In the binocular visual pattern analysis method, one third of the area in the relative collection range and the area of adjusting stimulus 0 ~ 3D are determined as the comfort area. If the 6m and 33cm fixation points of both eyes are located in the comfort area, it meets the Percival criterion. If the Percival criterion is not met, the prism needs to be alleviated.

(3) Criterion 1:1

Criterion 1:1 is applicable to implicit strabismus. It is required that the recovery value of Bi should be greater than or equal to the detection value of implicit strabismus. If the inspection results do not meet the 1:1 criterion, the bottom-out prism can be considered to alleviate it.Because the human eye will adapt to the prism, although the prism alleviates the corresponding clinical symptoms, with the passage of time, the human eye adapts to the prism, and the prism gradually loses the remission effect. In order to continue to achieve the correction effect, the value of the prism must be increased. Therefore, when prescribing the prism in some cases, we must be careful and consider the adaptation of the prism. In other words, although the prism can alleviate the symptoms, it may aggravate the etiology, and even there may be the possibility that the remission of the prism will change cryptostrabismus into dominant strabismus. Therefore, sometimes when selecting the treatment method clinically, we first consider the visual rehabilitation training, or combine the visual rehabilitation training on the basis of the prescription of the remission of the prism, so as to relieve the symptoms and treat the etiology at the same time, We can also understand it as a process of "treating symptoms and root causes" or "treating both symptoms and root causes".

2. Training prism

The training prism is not used with the relief prism. The bottom direction of the training prism is the same as the hidden oblique direction. The hidden esotropia training prism has the bottom inward. The target light is refracted by the prism and biased towards the concave nasal side of the macular center. In order to overcome diplopia, the eye position is abducted to stimulate the divergence function of both eyes (as shown in figure 1); Similarly, recessive exotropia trains the bottom of the prism outward, and the target light is refracted by the prism and biased towards the temporal side of the macular fovea. In order to overcome diplopia, the eye position is retracted to stimulate the collection of both eyes (as shown in figure 2). If the value of trigonometry is gradually increased to 2 ~ 3 times of the value of esotropia, the patient can maintain binocular monocular state, which proves that the purpose of training has been achieved.

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