Three Level Visual Function

Three level visual function refers to the essential characteristics of two eyes. Two eyes can see an object at the same time, integrate what they see together, and are three-dimensional senses. Therefore, it is simultaneous perception, fusion vision and stereoacuity
Binocular Simultaneous Perception
Both eyes can gaze at the same image with macular fovea at the same time. This is the most basic condition for the formation of normal binocular vision. That is, the corresponding points outside the macular fovea and macula of both eyes are required to have normal retinal correspondence, and both eyes have a common visual direction without visual inhibition.

During the inspection of Worth 4-Dot Flashlight, the right eye wears a red filter lens and the left eye wears a green filter lens. Due to the effect of spectral antagonism, the visual channel of green light in the right eye and the visual channel of red light in the left eye are closed, resulting in local binocular division. The right eye can only see the lower circular visual acuity and the upper circular visual acuity, and the left eye can only see the lower circular visual acuity and the left circular visual acuity.

Steps:
1.The diopter is normal or wear the universal trial frame with corresponding diopter lens inserted to complete diopter correction.
2.Add a red filter to the right eye and a green filter to the left eye.Ask the examinee to look at the Worth 4-Dot vision chart.
3.Ask and record the patterns and number seen by the patient.

Diagnostic Results：            
Result 1            
If the patient sees four lights, it indicates that he has normal  simultaneous perception and fusion vision.(Fig. 1)
Result 2           
If the patient sees only the upper and lower red lights and cannot see the green light, it indicates that the left eye is suppressed (Fig. 2)
Result 3            
If the patient sees only the left, right and lower green lights, and can not see the red light, it indicates that the right eye is inhibited (Fig. 3)
Result 4            
If the patient sees five lights, the upper and lower red lights, the left, right and lower green lights, or the circular visual markers below are oval, indicating diplopia, which is the manifestation of binocular fusion dysfunction (Fig. 4)
Result 5           
If the red light is on the right side of the green light, it is ipsilateral diplopia, indicating that the patient has esophoria. (Figure 5)           
Result 6           
If the red light is on the left side of the green light, it is crossed diplopia, indicating that the patient has exophoria. (Figure 6)

Attention Points:
1. The red and green lenses must completely cover the corresponding visual indicators, otherwise the inspection effect is invalid
2. Most monocular macular suppressors have formed amblyopia due to the long-term neglect of one eye vision in the visual center. Therefore, the visual function of the examinee needs to be pre examined before the examination.
3. If there is inhibition of looking far and there is no inhibition of looking near, it indicates that the examined eye has a central inhibition dark spot. 

Fig. 1

Fig. 2

Fig. 3

Fig. 4

Fig. 5

Fig. 6