An optical element (200; 300) for providing a variable refractive surface. The element comprises a chamber (215) defined by at least one side wall (270), with an optical axis (90) extending through the chamber (215). The chamber (215) contains a first fluid (220) and a second fluid (230) in contact over a meniscus (225) extending transverse the optical axis (90). The perimeter of the meniscus (225) is constrained by said side wall (270). The fluids (220, 230) are substantially immiscible and have different indices of refraction. A first electrowetting electrode (242; 243) is arranged to act on at least a portion of the meniscus perimeter constrained by said side wall (270). A second electrowetting electrode (280) extends through the meniscus (225).