Criteria
CSA is divided in 6 categories, Primary CSA, Cheyne–Stokes respiration, High-altitude periodic breathing, CSA due to a medical condition without CSB, Central sleep apnea due to a medication or substance and Treatment Emergent Central Apnea (also called Complex Sleep Apnea). The following symptoms are present in the Primary CSA: excessive daytime sleepiness, frequent arousals and awakenings during sleep or insomnia complaints, awakening short of breath, snoring, witness apneas. His polysomnography shows ≥5 central apneas and/or central hypopneas per hour of sleep, representing at least 50% of total respiratory events in the apnea-hypopnea index. CSA with Cheyne-Stokes breathing is characterized by at least one of the criteria of Primary CSA or the presence of atrial fibrillation/flutter, CHF, or a neurologic disorder. His polysomnography looks like the Primary CSA polysomnography with the addition of a ventilatory pattern compatible with CSB. High-Altitude Periodic Breathing requires that the patient has recently been at least 2500 meters. In the CSA due to a medication or substance, opioid or respiratory depressants must had been taken. For the CSA due to a medical condition without CSB, the criteria are the same as Primary CSA, but the symptoms are caused by a disease. In the Treatment Emergent Central Apnea, there was firstly some obstructive respiratory events but after their disappearance, the CSA has appeared.
Skew deviation is an unusual ocular deviation (strabismus), wherein the eyes move upward (hypertropia) in opposite directions. Skew deviation is caused by abnormal prenuclear vestibular input to the ocular motor nuclei, most commonly due to brainstem or cerebellar stroke. Other causes include multiple sclerosis and head trauma. Skew deviation is usually characterized by torticollis (head tilting) and binocular torsion. The exact pathophysiology of skew deviation remains incompletely understood. Skew deviation appears to be a perturbation of the ocular tilt reaction, which is itself is most likely a vestigial righting response used to keep fish and other lateral-eyed animals properly oriented.There are three types of skew deviations:Type 1: Upward deviation of both eyes; sound-induced vestibular symptoms; both eyes show counterclockwise rotary upward rotation
Type 2: Hypertropia in one eye; dorsolateral medullary infarctions; excyclotropia in the ipsilateral eye; hypertropia in the contralateral eye
Type 3: Simultaneous hypertropia one eye and hypotropia in the other eye; upper brainstem lesion

References
Further reading
Adams, Raymond D.; Victor, Maurice; Ropper, Allan H. (1997). Principles of Neurology (6 ed.). New York: McGraw Hill, Health Professions Division. ISBN 978-0-07-067439-4.