November 21, 2018
It’s no question that having good eyesight is important for the safety of all motorists and road users. You need to be able to judge distances, read road signs and traffic lights and respond to changes in your environment quickly and efficiently.
Clear vision means safer drivers and safer driving on our roads and it’s important that you have you eyes tested on a regular basis. There are a number of eye conditions that cause vision problems among drivers; however, the most common reason for drivers and learner drivers failing the vision-screening test is due to uncorrected refractive errors.
What is a refractive error?
A refractive error is defined as an imperfection in the focusing power of the eye, in which light rays are not brought into sharp focus on the retina. This results in blurred vision that can usually be corrected easily with spectacles or contact lenses. A refractive error is not a disease, merely an error.
There four types of refractive errors namely
- myopia (short-sightedness),
- hyperopia (farsightedness),
- Myopia (short-sightedness)
Myopia occurs when light rays come to a point of focus in front of the retina instead of precisely on it.
People with hyperopia tend to have more symptoms at near than at distance. They often complain of headaches, eyestrain, and tired eyes. They usually manage well enough during the day but find that they have difficulty seeing when driving at night. The vision problem occurs when the light rays come to a point of focus behind the retina instead of on it.
Astigmatism often accompanies either short-sightedness or farsightedness. It is usually caused by an irregularly shaped cornea. The shape of an astigmatic cornea is often compared to that of a rugby ball, which has one shorter (steeper) curve and one longer curve. A normally spherical cornea is described as being shaped like a soccer ball. Due to the distorted surface, there are two points of focus are formed instead of one, resulting in blurred vision.
Presbyopia is an age-related change that occurs in the eyes focussing ability at near only. It usually affects people over the age of 40 but does not affect your vision for driving.
If a vision problem is detected during the vision screening test it is important for you to have a comprehensive eye examination done. This is because some eye problems can result in permanent loss of if not detected and treated in time.
A Comprehensive eye examination should consist of the following tests:
Case History – You should be asked several questions relating to your general health, your family’s health and the problems that you are experiencing with your vision. It is important to report medical illness, surgery, injuries and any medication that you may be taking.
Visual acuity test – This test measures what you are able to focus on and see clearly at various distances, with each eye individually and with both eyes together. This is vitally important for quick identification of road signs and obstacles on the road eg animals.
Binocular vision (extra-ocular muscle alignment test) – These tests determine how your eyes work together. It is important in diagnosing squints, focusing problems etc.
Depth Perception – This tests your ability to judge space and the relative distance between objects eg, between an object and a vehicle.
Visual field test – These tests check your “side vision” or peripheral vision. This is the ability to see and be aware of a wider field or area of vision around you while looking or focusing straight ahead. This is important in that it allows one to be aware of pedestrians, animals and cyclists on the sides of the road.
Subjective Refraction – This is the process of determining the power of the lenses required to improve your vision.
Slit-lamp exam – This instrument allows a magnified view of the eye.
Tonometry – This is the measurement of your eye pressure.
Ophthalmoscopy – This is an internal examination of the eye. It can be done through undilated pupils or more thoroughly, through dilated pupils
Take care to remember that a quick or even free eye exam may not include all of the above and may be at the expense of losing your vision if vision-threatening conditions are not diagnosed.
Source: Arrive Alive