Spontaneous reversal of nystagmus in the dark

Abstract

Aim: To report five children with horizontal jerk nystagmus in whom eye movement recordings in the dark revealed a spontaneous reversal in the direction of the nystagmus beat. Three patients were blind in one eye and were diagnosed as having a manifest latent nystagmus (MLN), and two patients had strabismus and congenital nystagmus (CN).

Methods: Eye movements were recorded using DC electro-oculography with simultaneous video recording, including infrared recording in total darkness.

Results: Four patients had decelerating velocity slow phase jerk nystagmus when recorded under natural lighting conditions; the fifth case had accelerating velocity and linear slow phase jerk nystagmus. Under absolute darkness, nystagmus reversed in direction of beat with a mixture of linear and decelerating velocity slow phase waveforms. One child with unilateral anophthalmos could wilfully reverse the beat direction of his nystagmus by trying to look with his blind eye in the light and dark.

Conclusions: These observations support the theory that LN/MLN beat direction is determined by the "presumed" viewing eye and may be consciously controlled. The spontaneous reversal of beat direction in the dark suggests eye dominance is predetermined. Eye movement recordings identified mixed nystagmus waveforms indicating that CN (accelerating velocity slow phases) and LN/MLN (linear/decelerating velocity slow phases) coexist in these subjects.

Figure 1

Horizontal eye movement wave forms recorded by bitemporal electro-oculography for cases 1-5. The manifest latent nystagmus in the light is left beating for cases 1 and 5 and right beating for cases 2, 3, and 4. In the dark this nystagmus can be seen to reverse in beat direction. Note that leftward eye movements are recorded as down and rightward eye movements as up.

Figure 2

Manifest latent nystagmus recorded in the light in case 5 who has a right ocular prosthesis as a result of anophthalmos. Under usual viewing conditions the nystagmus is left beating; however, when asked to try and look using his blind right eye (up arrow), the nystagmus characteristics change and the beat direction reverses and becomes right beating.