From OMIM
Classic congenital or infantile nystagmus presents as conjugate, horizontal oscillations of the eyes, in primary or eccentric gaze, often with a preferred head turn or tilt. Other associated features may include mildly decreased visual acuity, strabismus, astigmatism, and occasionally head nodding. Eye movement recordings reveal that infantile nystagmus is predominantly a horizontal jerk waveform, with a diagnostic accelerating velocity slow phase. However, pendular and triangular waveforms may also be present. The nystagmus may rarely be vertical. As these patients often have normal visual acuity, it is presumed that the nystagmus represents a primary defect in the parts of the brain responsible for ocular motor control; thus the disorder has sometimes been termed 'congenital motor nystagmus' (Tarpey et al., 2006; Shiels et al., 2007). Congenital nystagmus may also be a feature of other ocular diseases, such as albinism (see, e.g., OCA1A, 203100), achromatopsia (see, e.g., ACHM3, 262300), and Leber congenital amaurosis (see, e.g., LCA1, 204000). Congenital nystagmus is associated with at least 3 X-linked disorders: Nettleship-Falls ocular albinism (OA1; 300500), which maps to Xp22.3; complete congenital stationary night blindness (CSNB1; 310500), which maps to Xp11.4; and blue-cone monochromatism (CBBM; 303700), which maps to Xq28. Genetic Heterogeneity of Congenital Nystagmus Two other X-linked forms of congenital nystagmus have been reported: NYS5 (300589), which maps to Xp11.4-p11.3, and NYS6 (300814), which is caused by mutation in the GPR143 gene (300808) on Xp22.3. Autosomal dominant forms have been mapped to chromosomes 6p12 (NYS2; 164100), 7p11 (NYS3; 608345), and 1q31-q32 (NYS7; 614826). An autosomal recessive form (NYS8; 257400) is caused by mutation in the ROBO1 gene (602430) on chromosome 3p12. A disorder formerly designated NYS4 has been reclassified; see 193003.  http://www.omim.org/entry/310700

From MedlinePlus Genetics
X-linked infantile nystagmus is a condition characterized by abnormal eye movements. Nystagmus is a term that refers to involuntary side-to-side, up-and-down, or circular movements of the eyes. In people with X-linked infantile nystagmus, the movements are typically side-to-side. In individuals with this condition, nystagmus is present at birth or develops within the first six months of life. 

The abnormal eye movements may worsen when an affected person is feeling anxious or tries to stare directly at an object. Some affected individuals will experience involuntary changes in the direction of their eye movements (periodic alternating nystagmus). The severity of nystagmus varies, even among affected individuals within the same family. Sometimes, affected individuals will turn or tilt their head to compensate for the irregular eye movements. Individuals with X-linked infantile nystagmus may have other eye abnormalities. For example, the region at the back of the eye responsible for sharp central vision may be underdeveloped (foveal hypoplasia).   https://medlineplus.gov/genetics/condition/x-linked-infantile-nystagmus