Primidone can cause drowsiness, listlessness, ataxia, visual disturbances, nystagmus, headache, and dizziness. Glaucoma, nystagmus, scotoma, or strabismus may also occur. The characteristic ocular abnormalities are nystagmus and lateral rectus weakness. Symptoms include ataxia, nystagmus, and dysmetria. Individuals with incomplete achromatopsia have reduced visual acuity with or without nystagmus or photophobia. Symptoms often appear suddenly, and include head tilt, ataxia, nystagmus, and circling. Central nervous system effects, such as dizziness, nystagmus and ataxia, are also common. Some animals have neurologic signs, such as ataxia, nystagmus, and head pressing. Albinism is associated with a number of vision defects, such as photophobia, nystagmus, and amblyopia. Gaze-evoked nystagmus and other ocular signs of cerebellar dysfunction are common. Between attacks they have nystagmus and dysarthria. The nystagmus is commonly associated with vertigo spells. Accompanying symptoms include scanning speech, intention tremor, incontinence, and nystagmus. The most common side effects are dizziness, nausea, confusion, nystagmus and headache. The contralateral eye abducts, however with nystagmus.