NYSTAGMUS

Nystagmus, i.e. rhythmic oscillation of one or both eyes, is physiological in newborns due to immature visual fixation or during certain stimuli, i.e. ear irrigation.

Etiology: Pathological nystagmus may be congenital or acquired, due to—(a) defective visual perception in ocular or visual pathway disorders, (b) defective neurological control of extraocular movements, e.g.

Clinical evaluation of nystagmus requires recording the: (a) frequency, (b) amplitude, and (c) direction of oscillations as well as effect of gaze-direction on them.

Two most important types of pathological nystagmus are pendular nystagmus, i.e. equal velocity movements on both directions and jerky nystagmus, i.e. slow movement in one direction and rapid movement in other direction.

TABLE 26.16: Common causes of nystagmus

Physiological

• Newborns

• Physiological stimuli: Optokinetic, caloric test

Pathological

• Congenital nystagmus

• Ocular (sensory): Cataract, retinal disease

• Vestibular: Labrynthitis, drugs

• Neurological disease

- Cerebellar lesions: Cerebellitis, tumors, drugs

- Brain-stem lesions: Arnold-Chiari syndrome

- Lesions of optic chiasma, e.g. tumors

- Others: Spasmus nutans

Important diagnostic features of nystagmus are as follows:

• Physiological nystagmus is slow, low-amplitude with not more than 3-4 oscillations at a time.

• Horizontal jerky nystagmus is usually vestibular in origin, with quick component away from lesion and tends to disappear after gaze fixation.

• Sensory or ocular nystagmus is usually asymmetrical (mono-ocular) and latent, manifesting only when the better eye is covered.

• See-saw nystagmus (one eye rises and other falls) is usually seen in Lesions of optic chiasma.

• Horizontal nystagmus in a particular gaze-direction indicates vestibular or brain-stem lesion, while Horizontal nystagmus irrespective of gaze-direction (gaze-paretic) indicates cerebellar disease.

• Vertical nystagmus almost always indicates cerebellar or brain stem lesions.

A detailed ophthalmic and neurological evaluation is essential in all cases of pathological nystagmus, to exclude serious neuro-ocular disease.

Other important variants of oculomotor disorders include:

Opsoclonus, i.e. spontaneous, non-rhythmic, multi­directional, chaotic movements of eyes (agitated eye) may be seen in encephalitis and neuroblastoma.

Ocular dysmetria is akin to limb dysmetria, i.e. over­shooting or under-shooting of visual fixation on rapid gaze changes with corrective oscillations, seen in cerebellar disease.

Ocular bobbing, i.e. up and down jerky movements of eyes indicates pontine disease.

BIBLIOGRAPHY

1. Shenoi et al. Ophthalmia neonatorum standard treatment guidelines. Indian Academy of Pediatrics. 2022.

2. Indian Academy of Pediatrics: Allergic conjunctivitis. Standard treatment guidelines. 2022.

3. Upadhyaya A. Retinopathy of prematurity. Standard treat­ment guidelines. Indian Academy of Pediatrics. 2022.