Refractive Error: short-sightedness (myopia), long-sightedness (hyperopia) and astigmatism
These conditions cause distance blur. In myopia, the eye has a resting focus at a near distance so that people will be able to see objects clearly at some point close to them, whilst the distance is blurry. Hyperopia also causes distance blur but often does not become noticeable until the eye loses its ability to change focus, frequently in middle age. The loss of focus for near distance (presbyopia or “aged sight”) is also related to a decreased ability to change focus but only affects reading. Astigmatism causes an image to be blurry at all distances, but does not affect clarity of images unless it is severe. An optometrist or ophthalmologist can test for these conditions. Treatment is usually glasses or contact lenses which are only obtainable through an optometrist or dispensing optician. Laser surgery and other corrective surgical techniques can also be used to change the focus of the eye to give clarity of sight in suitable patients.
What do those numbers mean ?
6/12 - means that at 6 metres the patient can see letters the same size as a “normal” person can see at 12 metres
6/6 – “normal vision”
6/12 – drivers licence standard
6/24 – registerable as “Blind” with RNZFB
USA - 20/20, 20/40 (20 feet = 6 metres)
Why do I need glasses?
- Short Sighted/Myopic - can see close, but need glasses for distance.
- Long Sighted/Hypermetropic - need glasses for everything (especially reading).
- Astigmatism - the “shape of the eye” is more like the side of a rugby ball rather than a soccer ball.
- Presbyopia - inability to adjust the focus of the eye – need reading glasses.