What is it to be short sighted?
Myopia (or short-sightedness) is on the rise. What is myopia, and how can we fix it?
We’ve all heard the term ‘short-sighted’ before. Also known by the equally familiar term ‘near sighted’, and the likely lesser-known ‘myopic’, all describe the inability of the eye to focus on objects in the distance.
We still don’t know what causes myopia, but we do know that it is on the rise and predicted to reach epidemic proportions with half the world affected by 2050 1 We do not yet have any proven methods of completely preventing myopia. We can however do something to fix the poor vision associated with it.
What causes short sightedness to blur vision in the distance?
The eye in its most simplified form can be thought of as a camera with two powerful lenses designed to focus light. The most powerful lens is the cornea and in a normal eye has a fixed power of around 40 Dioptres. The second lens is within the eye and accounts for around 20 Dioptres of power. This lens however has variable power which allows you to focus on objects at various distances. Images must be focused precisely onto the light-sensitive cells at the back of the eye (the macula) in order to generate a clear image. Errors of this focussing ability cause blur.
In myopia, the system of lenses in the eye is too powerful, meaning that light is focussed in front of the macula. We can readjust this focus by wearing glasses or contact lenses, or by making a change to this system of lenses. One way to achieve this is with laser eye surgery, in which the laser is used to reshape the cornea, making it less powerful. If your glasses for example have a prescription of -3.00 (diopters), then the laser will make the cornea 3 dioptres less powerful.
If you are extremely short-sighted however, sometimes the laser cannot accomplish the task. As you might have guessed, the more short-sighted you are, the more of the cornea that has to be reshaped and there are safety limits on how much cornea can be removed. Luckily there are alternatives. In ICL surgery, a permanent implantable lens takes the place of glasses and contact lens prescriptions. ICLs can correct prescriptions up to -18, but fortunately only very few people are this short sighted. Where ICL surgery is not appropriate however, the lens within the eye can be swapped for one with a different power to produce the same effect.
More information on laser, ICL and RLE surgery, including prices can be found here.
- Holden BA, Fricke TR, Wilson DA, Jong M, Naidoo KS, Sankaridurg P, Wong TY, Naduvilath TJ, Resnikoff S, Global Prevalence of Myopia and High Myopia and Temporal Trends from 2000 through 2050, Ophthalmology, May 2016 Volume 123, Issue 5, Pages 1036–1042.
About the Author
In addition to working with Dan, Marcello is the lead optometrist of the Keratoconus service at Moorfields Eye Hospital. He is responsible for development of protocols on keratoconus monitoring and progression criteria and is actively involved in research in corneal tomography, and the effectiveness of both new and existing treatments for the condition.