There is only one layer of pyramidal cells in the fovea of the human eye, which is the most sensitive area of vision. With the deviation from the fovea of the macula, the number of pyramidal cells gradually decreases and the visual acuity also gradually decreases. Relevant data showed that within 0.25 ° of macular fovea, the number of retinal pyramidal cells was 150000 / mm2 and the visual acuity was 1.0; Within 0.5 ° from the fovea, the number of pyramidal cells in the retina was 50000 / mm2 and the visual acuity was 0.5; The number of pyramidal cells in the retina is 150000 / mm2 within 10 ° from the macular fovea,? Visual acuity is greatly reduced. Therefore, the nature of fixation is different, the basis of vision is also different, and the difficulty of amblyopia treatment is also different. According to the fixation nature of children with amblyopia, amblyopia can be divided into central fixation amblyopia and eccentric fixation amblyopia. If the child takes the fovea as the fixation point, it is called central fixation, and the area outside the fovea is called eccentric fixation.

1. Central fixation amblyopia: it is generally seen in various causes of amblyopia. The fixation function of macula is well developed. Although monocular amblyopia has been found, its monocular fixation function is still normal. Although there is a deep dark spot in the center of the macula, if the amblyopia eye gaze, it can still restore some functions. In amblyopia training, if we cover the healthy eyes and carry out intensive training of amblyopia eyes, it is expected to improve vision.

2. Eccentric fixation amblyopia: the macula of the retina has two functions, one of which is used as the center of the fixation object to play the visual function, and the other is the positioning function as the monocular positioning center. For example, the development of macular function is inhibited for various reasons during the visual development period, or the macular function is actively inhibited for various reasons. In the early stage, although the visual acuity is significantly reduced, the positioning function may still be normal, so it can still be used as the center of monocular fixation. However, the inhibition will continue to deepen in the monocular. When the visual function of the macular is lower than that around the macula, the positioning center may be transferred to the peripheral area of the macula. At this time, even if the healthy eye is covered, it does not need to focus on the macular area, but instead focus on points outside the macular area, which is called eccentric gaze amblyopia. Covering the healthy eye can not improve vision, but may make the abnormal fixation point more stable. Eccentric fixation amblyopia is generally seen in those with severe amblyopia or obvious eye deviation.

Direct ophthalmoscope can be used to determine the nature of fixation. Examining the nature of fixation is of great significance to estimate the prognosis and guide treatment.

Methods: in the darkroom environment, the examinee takes a comfortable sitting position and raises his head slightly. The examinee adjusts the hand wheel of the adjustable diaphragm of the fundus mirror to the measuring diaphragm (Star target ring), and the compensation lens is adjusted to 0, so that the light is projected vertically from 30cm to the examinee's eye. Observe the pupil area of the examinee's eye from the peephole. After seeing the reflected light of the orange red retina, push the ophthalmoscope to the examinee's eye, try to be close to the examinee's eye, and gradually adjust the hand wheel of the compensation lens, Until clear fundus blood vessels and star target ring projection are seen.

Instruct the subject eye to look at the center point of the transmitted light, the examiner shall find the position of the reflective point of the macular fovea of the subject eye in the projection of the star target ring, and record the orientation of the macular fovea deviating from the gaze center.

Result analysis:

(1) The reflective point of macular fovea is located in the center of the star point, which is covered by the star point and cannot be seen. It is the central gaze (as shown in Figure 1 below).

⑵ The reflective point of macular fovea is located within the first target ring (3 °), which is paracentric gaze (as shown in Figure 2 below).

(3) The reflective point of macular fovea is located between the first target ring and the second target ring (3 ° ~ 5 °), which is paramacular fixation (as shown in Figure 3 below).

(4) The reflective point of macular fovea is located outside the second target ring and is peripheral gaze (as shown in Figure 4 below).

Figure 1 Central fixation 

Figure 2 Side center gaze

Figure 3 Paramacular gaze

Figure 4 Peripheral gaze

Clinical significance of fixation nature:

Central fixation amblyopia: central fixation amblyopia is due to various reasons, resulting in insufficient effective stimulation of the retina of amblyopia, and the function of macular region is inhibited. However, patients still take macular region as the center, so the focus of treatment is to eliminate the competitive inhibition of healthy eyes on amblyopia and restore the visual function of amblyopia. The traditional treatment includes covering treatment and depression treatment. The purpose is to improve the fixation ability of amblyopia.

Eccentric fixation amblyopia: eccentric fixation is a monocular phenomenon, which is the dysfunction of monocular positioning. Due to the deep inhibition of retinal macula, the part of retina beyond the macula at a limited distance is selected as the monocular fixation center. When both eyes are used together, although this eye may be accompanied by abnormal retinal correspondence, the fixation point of eccentric fixation is not the abnormal retinal correspondence point of non fixation eye. Eccentric fixation has low vision. For eccentric fixation amblyopia, its treatment method is different from central fixation amblyopia. The key to treatment is to first convert eccentric fixation into central fixation, and then train on this basis, so the treatment is more difficult.