Congenital nystagmus is an involuntary, rhythmic, pendulum-like or beating-like oscillation of the eye that can manifest as a dominant, recessive, or dominant-implicit state, with the following clinical features: 1. Visual acuity Most patients with congenital nystagmus have poor visual acuity. Patients with perceptual deficit nystagmus have low vision due to the presence of organic eye lesions and the time of macular fixation affected by nystagmus to varying degrees. The degree of visual acuity varies depending on the ocular disease, ranging from no light perception to 0.1. The degree of visual acuity loss in patients with perceptual deficit nystagmus is often positively correlated with the frequency and amplitude of nystagmus, with the more pronounced the nystagmus, the worse the visual acuity. Most patients with motor deficit nystagmus have an intermediate band, and the nystagmus is often significantly reduced in the intermediate band. Congenital nystagmus reduces nystagmus when the eyes are assembled or turned inward, so that near vision is better than distance vision, and the resulting internal strabismus is called “nystagmus block syndrome. This syndrome usually occurs in infancy and early childhood and is similar to the clinical manifestation of abducens nerve palsy. The nystagmus is significantly increased when the eye is turned outward or in an orthogonal position; it is reduced or even disappears when the patient is assembled or internally oblique. Patients often adopt a compensatory head position, so that the gaze eye is in the inward turning position. However, when either eye is covered, the compensatory head position can disappear. 3. Intermediate band attenuation phenomenon When patients with congenital nystagmus gaze at a certain target, the nystagmus is enhanced, and when sleeping or distracted, the nystagmus is reduced; in different gazing directions, the frequency of nystagmus is different, showing fast phase and slow phase, and in the intermediate band direction the frequency and amplitude of nystagmus are significantly reduced. Patients produce different compensatory head positions to obtain the best visual acuity depending on the position of the middle band and the direction of binocular gaze. If the intermediate band is located on the left or right side, the patient’s face turns left or right; if the intermediate band is located above or below, the patient’s jaw is inward or upward; if the intermediate band is located in right or left rotation position, the patient’s head tilts to the left shoulder or right shoulder. 4. Nystagmus with strabismus Occult nystagmus is almost always combined with the occurrence of congenital internal strabismus, while the incidence of dominant nystagmus with internal strabismus is about 15%. In addition, other types of strabismus, such as exotropia, are often combined with dominant nystagmus. Surgery to correct compensatory head position may increase the degree of strabismus. Of course, if the compensatory head position is not taken into account before surgery and the strabismus is simply resolved, the compensatory head position may become more pronounced. 5.No vibration phantom vision Patients with congenital nystagmus do not have a sense of jumping in their visual objects, even though both eyes are under involuntary movement all the time, i.e. no vibration phantom vision. In normal people, the speed of movement of objects in the retina does not exceed 4°/second, and if this speed is exceeded, a jumping sensation will occur. In patients with congenital nystagmus, the speed of object movement across the retina exceeds this value, and in some cases even exceeds 100°/sec, but the appearance of phantom vision is still not felt. There may be multiple mechanisms involved in suppressing the phenomenon of tremor phantom vision, such as: the co-existence of visual afferent deficits may raise the threshold for the appearance of tremor phantom vision; the brain may apply an extraretinal message to delete the visual effects due to tremor; visual information may be transmitted to the center only during the stimulation of the central recess, while being suppressed at other times, etc. Doctor’s tip: In some cases nystagmus is caused by the presence of an abnormality in the eye, so early detection and diagnosis is especially important. When nystagmus is detected, it is important to go to the hospital to rule out organic eye diseases such as congenital cataract, congenital glaucoma, and treatable diseases such as pediatric hereditary fundus disease. Restoring clarity of visual pathways and promoting visual development in infants and children during the critical period of visual development (before age 2).