Abstract
Purpose: :
Perinatal injury to the visual cortex can be associated with ophthalmic signs such as tonic down gaze & optic nerve hypoplasia. Children born at term with injury to the cortex are described to have erratic or chaotic nystagmus while pre–term babies with predominant injury to the white matter have been described to have low amplitude, high frequency nystagmus with features of latent nystagmus (Brodsky et al. Ophthalmology 2002). However no eye movement recordings have been performed in these patients. Our aim was to characterise the nystagmus of patients with perinatal brain injury using eye movement recordings.
Methods: :
Six patients with low vision and nystagmus secondary to perinatal injury to the brain were examined. The visual acuities of these patients ranged from counting fingers to 6/12. Four of these patients had occipital infarcts on MRI scan while the fifth patient had a normal brain scan but his optic nerves were small in diameter. All patients had optic atrophy. The eye movements recordings were done using EyeLink pupil tracker (250 Hz), SMI GmbH, Berlin, Germany) while viewing stimuli projected on a rear projection screen (1.8x1.2m) using a video projector (Hitachi CP–X958). MRI scans were done to detect the brain/optic nerve lesion.
Results: :
Four of the six patients had horizontal jerk nystagmus with accelerating slow phase velocity when both eyes were open. The amplitude ranged from 3–4 degrees and the frequency ranged from 2–4 Hz. On covering one eye the amplitude increased to about 6–8 degrees indicating latent nystagmus. One patient had horizontal jerk nystagmus with decelerating slow phase (2–3 Hz) and the amplitude increased from 0.5 degrees to 3 degrees on covering one eye. One patient had horizontal pendular nystagmus (2Hz) and the amplitude increased from 0.5 degrees to 5 degrees on covering one eye, again corresponding to latent nystagmus.
Conclusions: :
Four patients with perinatal injury had horizontal jerk nystagmus with accelerating slow phase velocity similar to idiopathic congenital nystagmus. All the subjects had large amplitude latent nystagmus. This was documented for the first time with eye movement recordings. All our patients had optic disc pallor, which could be secondary to occipital lobe infarction (Jacobson et al. Arch Ophthalmol, 1997) or due to primary injury to the nerve itself. Perinatal occipital lobe injury can lead to optic atrophy and prominent latent nystagmus. This does not correspond to previous clinical observations (Brodsky et al. Ophthalmology 2002).
Keywords: nystagmus • visual cortex