Chameleon vision from the head, giving the lizard panoramic sight. An eyelid fused to the pupil protects the eyes, leaving only a small part exposed. With a negative (nearsighted or concave) lens and a positive (farsighted or convex) cornea, chameleons use a method of monocular focusing to judge distance called corneal accommodation. Each eye focuses independently, which is achieved by the chameleon eye’s unique anatomy of separated nodal and center points of the eye. Finally, “striated rather than smooth ciliary muscle in sauropsids” allows for rapid focusing. Chameleon eyes feature a negative lens, meaning that the lens is concave. This increases retinal
Lens clock clock can be used if a dial thickness gauge is not available. To do this, the contact lens is placed concave side up on a table or other hard surface. The lens clock is then brought down on it such that the center prong contacts the lens as close to its center as possible, and the outer prongs rest on the table. The thickness of the lens is then the sagitta formula_4 in the formula above, and can be calculated from the optical power reading, if the distance between the outer prongs is known. Lens clock A lens clock is