UP A LENS?
A lens is made up of three components:
Design (or surface) - The lens is designed to the wearer’s prescription needs, whether that’s for distance, intermediate or near vision. Design options include single vision, reading, bifocal, trifocal, progressive and computer lenses.
Material - The look, weight and resistance of your spectacles will depend on whether the lens is made from plastic, polycarbonate, high-index plastic or glass.
Lens technology - This is applied on either or both sides of the lens to enhance the features of the design and material. It can extend the longevity of spectacles and improve clarity of vision. Options include photochromic, polarised, anti-reflective, anti-scratch and anti-smudge, and coatings that repel dust or water and combat fog.
Normally, light rays bend (refract) evenly onto a small area of the retina to give a clear image. For people with refractive errors like myopia, hyperopia and astigmatism - the light is unable to focus on this area of the retina. Corrective lenses bend the light that passes through to the retina, adjusting its focus and enabling the wearer to see clearly again.
MATCHING LENSES TO
Different lenses are required for different eye conditions
Short-sightedness - Light rays fall short and focus in front of the retina, causing distant objects to blur. The lens to correct this issue is a ‘minus’ lens. This is concave (thicker at the edge, thinner in the middle) to bend rays outwards, allowing light to focus on the right spot to correct the vision.
Long-sightedness - Light rays focus behind the retina, causing objects at all distances, especially close up, to blur. In this case, a ‘plus’ lens is needed. This is convex (thicker in the middle, thinner at the edge) to bend rays inwards, allowing light to focus on the right spot to correct the vision.
Astigmatism - The cornea of the eye is oval, rather than round, so light is unable to find a single focus on the right part of the retina, giving a blurred image. Astigmatism could lead to short-sightedness, long-sightedness or both. To fix the vision, a cylindrical lenses is the most common way to correct astigmatism. This may also be minus or plus, depending on the type of astigmatism.