Which type of lens is thicker in the middle and thinner at the edges?

The type of lens that is thicker in the middle and thinner at the edges is the biconvex lens. This lens has two outwardly curved surfaces, which means that light rays passing through it are converged to a point. The central thickness allows for this convergence of light, making it effective for conditions that require the correction of hyperopia (farsightedness). The shape of a biconvex lens enables it to increase the manifesting light on the retina, thereby enhancing the viewer's ability to focus on objects that are both near and far.

In contrast, biconcave lenses, plano-concave lenses, and meniscus lenses either curve inward or have varied shapes that do not produce the same optical effect as a biconvex lens. Biconcave lenses are thinner in the middle and thicker at the edges, typically used for myopia correction. Plano-concave lenses have one flat side and one concave side, also serving to diverge light. Meniscus lenses, which can be either convex or concave, have one side that is more curved than the other but do not necessarily fit the description of being thicker in the middle and thinner at the edges like a biconvex lens.