Entoptic phenomena, photopsias, phosphenes

Abstract

In medicine the term entoptic phenomena is used to describe perception of visual effects that are rendered by the eye’s own structures or visual system under suitable lighting conditions or stimulus. Customary such conditions are rarely met and hence do not produce an image. Entoptic phenomena produced or influenced by the native optical structures of one’s own eye result from either refractive or diffractive causes. What all have in common is that they are subjective and require direct attention and cooperation of the observer for their perception. They differ from optical illusions which do not have a physical substrate. Special form of visual disturbances are photopsias and phosphenes. Photopsias are visual symptoms or sensations of structured images such as geometric figures or other simple pictures often recurring in a repetitive pattern in the absence of external light stimuli. Phosphenes are a subgroup of photopsias that patients describe as either static or moving unstructured patterns of colourful lights, sparkles or zig-zag lines. Photopsias predominately suggest ocular causes, less commonly they may suggest neurologic or systemic causes and thus require a meticulous examination as they occur.