Definition

Noun: 1. A line in an optical system: A straight line passing through the center of curvature of a lens or spherical mirror. Light traveling along this line is neither reflected nor refracted by the optical element. 2. The direction of clearest vision in the eye: In a normal human eye, this is the direction in which objects are seen most distinctly. 3. A direction in a crystal: In a doubly refracting (birefringent) crystal, it is the direction along which light propagates without splitting into two rays (i.e., no double refraction occurs). A crystal may have one or two such axes.

Examples of Usage

• In optics: "To minimize aberrations, the light source was carefully aligned with the optic axis of the lens."
• In physiology: "The optic axis of the eye does not perfectly align with the visual axis, which is the line of sight to the point of greatest acuity."
• In crystallography: "Calcite is a birefringent crystal with a single optic axis."

Advanced Usage

• Optic axis figure: In polarized light microscopy, an interference pattern observed when viewing a crystal along its optic axis, used to identify mineral properties.
• Optic axis direction (OA): A vector used in materials science to describe the orientation of anisotropic crystals in devices like liquid crystal displays.

Variants and Related Words

• Optical axis: A synonymous term, often used interchangeably with "optic axis."
• Principal axis: In geometric optics, a closely related concept for a lens or mirror; it is the line through the center of curvature and the focal point. For a symmetric lens, the principal axis and optic axis coincide.
• Visual axis: The line from the object of regard through the nodal points of the eye to the fovea. This is the physiological line of sight, distinct from the eye's anatomical optic axis.
• Birefringence: The optical property of a material having a refractive index that depends on the polarization and propagation direction of light, directly related to the presence of optic axes.

Synonyms

• Optical axis
• Principal axis (in specific, symmetric optical contexts)

Related Terms and Concepts

• Isotropic: Describing a material (like glass) with no optic axis, where the refractive index is the same in all directions.
• Uniaxial crystal: A crystal (e.g., quartz, calcite) with one optic axis.
• Biaxial crystal: A crystal (e.g., mica) with two optic axes.
• Wave normal: The direction perpendicular to the wavefront of light; in anisotropic crystals, this is generally different from the direction of the optic axis.

Noun

1. a line that passes through the center of curvature of a lens so that light is neither reflected nor refracted
   • in a normal eye the optic axis is the direction in which objects are seen most distinctly
2. in a doubly refracting crystal, the line in the direction of which no double refraction occurs
   • a crystal may have either one or two optic axes