Glasses work by positioning a lens in front of
People with Hyperopia need lenses that have a 'positive' lens. This works in the opposite way, redirecting the image so objects viewed close to the eye are no longer blurry. Hyperopia is more commonly developed with age as the muscles which control the eye's lens become weaker.
All glasses lenses work by bending light. Lenses in spectacles are shaped specifically to bend light in a certain direction. They are like two prisms smashed together. Minus lenses have thick outer edges and thin middles. This makes light spread out, moving the focal point forward.
Plus lenses have thick middles, which is like the bases of the prisms put together, and thinner outer edges. This bends the light towards the middle, moving the focal point back. Most lenses are spherical lenses, this means the curve is smooth over the surface of the lens; the angle of the curve does not change. However, some lenses need to be specifically designed for people with astigmatisms.
It is not uncommon for two different lenses to be required.
The strength of a lens can vary dramatically and is primarily controlled by the angle of the curve. The deeper the curve, the more the light is bent. Opticians usually measure eye strength in units of 0.25 dioptres. The greater the dioptre (D number) the deeper the lens curve, so a -2.25 dioptre eye, would require a lens to combat short-sightedness. An eye strength reading of +2.25 D, would require a long-sighted lens. The material used can also greatly affect the strength of the lens, modern materials have seen the thickness of lenses greatly reduced from 'bottle-tops' in the early 1950s and 60s. Once a dioptre prescription has been received from an optician this is all that is require to purchase a pair of glasses, or spectacles.