# Clinical, Cognitive and Behavioural Assessment in Children with Cerebellar Disorder
## 2 Clinical Assessment
To this aim, different mechanisms are needed, such as saccadic and smooth pursuit control, the vestibulo-ocular and the optokinetic reflex [10]. In cerebellar disorders, the mechanisms underneath eye movements control can be disrupted with the onset of peculiar ocular signs. Accuracy, velocity trajectory and latency of the saccades can be impaired in cerebellar disorders. Hypermetric saccades are usually observed in cerebellar diseases, while hypometric saccades are mostly seen in brainstem lesions or neurodegenerative diseases [11]. Ocular dysmertia can be disconjugate, with the saccade impairment being bilateral but asymmetric [12]. One possible ocular manifestation of cerebellar involvement is nystagmus, a condition with involuntary rhythmic eye movements that may impair vision. Nystagmus can be classified in three categories: physiological, infantile and acquired, the three groups presenting differences in amplitude, frequency, direction and other features. In some neurological conditions with cerebellar involvement, nystagmus could appear very early in life and present features hardly discernible from more benign types [13]. A sign of cerebellar or brainstem involvement is fixation nystagmus, which can be observed in primary position and does not disappear but increases during fixation [11]. Gaze evoked nystagmus consists of the impossibility to maintain an eccentric position because of repetitive corrective saccades that reposition the gaze to the primary position. This type of nystagmus is frequent in patients with midline cerebellar lesions [14]. Ocular motor apraxia is been defined as the failure in voluntarily start a horizontal saccade, while vertical ocular movements and smooth ocular pursuit are generally still possible [15; 16]. Patients with ocular motor apraxia often try to compensate by turning the head in the target direction [17]; as a result, the head reaches the target before the eyesdo. In 1952, [PERSON] described this phenomenon in four children and called it \"congenital ocular motor apraxia\" [18]. Since then, ocular motor apraxia has been described in many other conditions. Most of the children with ocular motor apraxia show other neurological signs, such as hypotonia, ataxia and developmental delay [15; 19], which has been kept open the debate between considering congenital ocular motor apraxia as a neurological sign rather than an independent condition [19]. In [PERSON] syndrome, a congenital brain development disorder which involves the cerebellum and the brainstem, ocular motor apraxia is the most frequent ocular manifestation [17]. Oculomotor apraxia is also a critical sign of a group of autosomal recessive cerebellar ataxias such as ataxia telangectasia and ataxia oculomotor apraxia type 1 and 2 [20]. It is also well known (confirmed by studies on adult patients with acquired lesions, but also on children with congenital lesions) that the cerebellum plays an important part in the acquisition of certain cognitive and emotional-relational functions, such as planning and visuospatial organisation, language, memory, attention, and affectivity [2; 21]. The neocerebellar system (which is of particular interest with regards to the connections with the prefrontal area) is a common site of structural or functional anomalies in neurodevelopmental disorders (autism, evolutional dyslexia, attention deficit hyperactivity syndrome, metabolic-degenerative diseases, and genetic syndromes) [22].