Some useful terms

Astigmatism

This is an irregular curvature of the front surface of the eye. The best analogy is where the curves are shaped more like a rugby ball than a football.

Cataracts: information page

Dispensing optician

Dispensing opticians are qualified to examine optometrist's prescriptions to determine lens specifications. They recommend frames, lens types and coatings after considering the prescription and the customer's occupation, habits, and facial features.

Glaucoma: information page

Long sightedness (hypermetropia)

Difficulty focusing on close objects eg. reading. Here the eyeball is too short to focus images on the back of the eye.

Macular degeneration: information page

Optometrist

Previously known as Ophthalmic Optician, this term was adopted in the UK to conform to the international standard.

Presbyopia ('ageing eye')

This is part of growing older, and usually occurs in the late forties. Whilst distance vision can remain good there is an inability in the eye's optical system to focus on near objects, requiring us to need reading glasses.

Short sightedness (myopia)

The inability to see clearly at longer distances, for example when driving. This is usually caused by the eyeball being too long to focus images clearly on the back of the eye.

Ultra Violet Light (UV)

Our eyes are able to perceive wavelengths of light in what we call the visible spectrum, from 380nm - 770nm. Each side of this visible spectrum there is invisible radiation which our eyes are not designed to detect, namely infra-red and ultra violet. Infra red radiation to the eyes should be avoided, however unlike ultra violet, there is a sensation of 'heat' which our natural instincts tell us to 'pull back' from, unlike UV, perceived by many as the most dangerous range as its prescence may not be felt or seen so readily. The front surface of our eye and the lens inside act as filters to the UV light but this can cause problems for those who spend a lot time outdoors in the sun.

UV light can be subdivided into:

UVC - (wavelengths below 280nm) which are effectively filtered out before they reach us by the ozone layer.

UVB - (wavelengths between 280nm and 315nm) these rays are responsible for sunburn and snow blindness. Reflective surfaces such as water or snow substantially increase the amount of UV entering our eyes.

UVA - (wavelengths between 315nm and 380nm) potentially the most damaging area because they can cause chronic eye damage, especially low exposure over a long period of time.

Some lens types such as photochromics are naturally UV absorbing, indeed untreated plastic lenses give protection up to 350nm. However special filters can be added to give full protection up to 400nm.