复视（英语：Diplopia）是把一个物体看成两个的视功能障碍。

当用两眼同时视物时，虽然在视网膜上形成的物象也只是二维空间的平面象，但由于两眼球的位置不同，左右稍为分开，看物体时的角度略有不同，因此物体投射到视网膜上的物象及其在视网膜上的位置也略有不同，物象的这种微细形态差别和位置差别称为视差。

两眼视网膜上具有视差的物象传到大脑视皮质中枢，经过综合后，就产生一个对周围环境有高、宽、深三维空间的立体象。这种视觉称为双眼视觉或双眼单视。双眼视觉仅存在于人类和高级脊椎动物，使其能更准确地判断周围环境中物体的位置、方向、距离、大小和形状。尤其在人类，它使眼和手的动作更为协调，更有利于劳动生产和工作学习。

Diplopia, commonly known as double vision, is the simultaneous **** of two images of a single object that may be displaced horizontally, vertically, diagonally (i.e., both vertically and horizontally), or rotationally in relation to each other. It is usually the result of impaired function of the extraocular muscles (EOMs), where both eyes are still functional but they cannot converge to target the desired object. Problems with EOMs may be due to mechanical problems, disorders of the neuromuscular junction, disorders of the cranial nerves (III, IV, and VI) that stimulate the muscles, and occasionally disorders involving the supranuclear oculomotor pathways or ingestion of toxins.