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Hypertropia is a condition of misalignment of the eyes (strabismus), whereby the visual axis of one eye is higher than the fellow fixating eye. Hypotropia is the similar condition, focus being on the eye with the visual axis lower than the fellow fixating eye. Dissociated Vertical Deviation is a special type of hypertropia leading to slow upward drift of one or rarely both eyes, usually when the patient is inattentive. ==Causes== Hypertropia may be either congenital or acquired, and misalignment is due to imbalance in extraocular muscle function. The superior rectus, inferior rectus, superior oblique, and inferior oblique muscles affect the vertical movement of the eyes. These muscles may be either paretic, restrictive (fibrosis) or overactive effect of the muscles. Congenital cases may have developmental abnormality due to abnormal muscle structure, usually muscle atrophy / hypertrophy or rarely, absence of the muscle and incorrect placement. Specific & common causes include: * Superior oblique Palsy / Congenital fourth nerve palsy * Inferior oblique overaction * Brown's syndrome * Duane's retraction syndrome * Double elevator palsy * Fibrosis of rectus muscle in Graves Disease (most commonly inferior rectus is involved) * Surgical trauma to the vertical muscles (e.g. during scleral buckling surgery or cataract surgery causing iatrogenic trauma to the vertical muscles). Sudden onset hypertropia in a middle aged or elderly adult may be due to compression of the trochlear nerve and mass effect from a tumor, requiring urgent brain imaging using MRI to localise any space occupying lesion. It could also be due to infarction of blood vessels supplying the nerve, due to diabetes and atherosclerosis. In other instances it may be due to an abnormality of neuromuscular transmission, i.e., Myasthenia Gravis. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「hypertropia」の詳細全文を読む スポンサード リンク
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