<unk>  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<unk>  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.
Hypertropia
Quadrantanopia
Emmetropia
Cyclotropia
Heterotopia 
Ocular dysmetria
Exotropia
Nyctalopia