Nystagmus with slow phases that show an increasing exponential time course are typical of congenital nystagmus and may arise due to instability of smooth-pursuit gaze-holding mechanisms. 

Congenital nystagmus usually is:

• Primarily horizontal, and remains horizontal in all gaze angles¹
• Accentuated by attempted fixation
• Characterized by the presence of a null point (a gaze position where the nystagmus is absent or minimal)
• Diminished by convergence or active eyelid closure
• Associated with a head turn
• Sometimes accompanied by reversed smooth pursuit (as seen when testing optokinetic nystagmus, quick phases are in the same direction as the motion of the OKN drum)¹

Latent nystagmus is a type of congenital nystagmus that is only present on monocular viewing and beats toward the viewing eye².