refrativa

Refrativa is an adjective used in optics and vision science to describe aspects related to refraction, the change in direction of a wave that occurs as it passes between media with different optical densities. The term is derived from Latin refractus, meaning broken back.

In physics, refraction is governed by Snell's law: n1 sin θ1 = n2 sin θ2, where n is refractive index. The refractive index n = c/v, with c the vacuum speed of light and v the phase speed in the medium.

Refractive elements include lenses and prisms, which bend light to form images or disperse light; optical fibers use refractive index contrasts to guide light by total internal reflection and refraction. Refractive telescopes use lenses (refractors) rather than mirrors.

In human vision, the eye's cornea and lens refract light to focus images on the retina. When refractive power and eye length are mismatched, refractive errors such as myopia, hyperopia, astigmatism, or presbyopia occur. Treatments range from corrective glasses and contact lenses to refractive surgery (LASIK, PRK, SMILE) that alter corneal curvature or lens power.

Other notable examples include atmospheric refraction affecting celestial positions near the horizon and chromatic dispersion causing color separation. The term 'refrativa' is sometimes used broadly to contrast refractive methods with reflective systems, as in refracting versus reflecting telescopes.