Abstract: An apparatus includes a sensing region. A flexible membrane positioned in the sensing region defines a plane, a radial center, and a central axis extending perpendicularly relative to the plane at the radial center. The membrane deforms along the central axis and along a lateral dimension using at least a property of fluid (e.g., pressure or density) in the sensing region. The lateral dimension is transverse to the central axis. An optical feature changes a visual state in response to deformation of the membrane along the lateral dimension. A camera is positioned to view the optical feature and capture images of the optical feature.