In an example method of forming an optical film for an eyepiece, a curable material is dispensed into a space between a first and a second mold surface. A position of the first mold surface relative to the second mold surface is measured using a plurality of sensors. Each sensor measures a respective relative distance along a respective measurement axis between a respective point on a planar portion of the first mold surface and a respective point on a planar portion of the second mold surface. The measurement axes are parallel to each other, and the points define corresponding triangles on the first and second mold surfaces, respectively. The position of the first mold surface is adjusted relative to the second mold surface based on the measured position, and the curable material is cured to form the optical film.