fixation

Fixation is a term used across disciplines to describe the act of making something stable, fixed, or preserved, or the process by which a thing becomes anchored to a particular state, object, or position. The precise meaning depends on the field.

In psychology and psychoanalysis, fixation refers to a persistent focus on a particular developmental stage or unresolved conflict, which can shape behavior in adulthood. Classic Freudian theory links fixation to stages such as oral or anal, where energy remains invested in related activities or needs.

In ophthalmology, fixation describes the act of maintaining steady gaze on a target. Tests of visual acuity or ocular motility rely on patient fixation to obtain accurate measurements; dysfunction can indicate neurological or ocular problems.

In biology and medicine, fixation is the process of preserving tissue, cells, or specimens for observation. Chemical fixatives such as formaldehyde or glutaraldehyde crosslink proteins and halt biological processes, allowing tissues to be sliced into thin sections for microscopy while maintaining structure and composition.

In chemistry and related sciences, fixation refers to incorporating atoms into chemical compounds. Nitrogen fixation converts atmospheric N2 into ammonia or related molecules, making nitrogen available to living organisms; industrial processes such as the Haber-Bosch method supply fixed nitrogen for fertilizers. Carbon fixation, by contrast, denotes the conversion of inorganic carbon dioxide into organic molecules, a central process in photosynthesis.