Understanding Your Vision: What Is A Prescription?
If you’ve suddenly found yourself in need of glasses, or have recently discovered that your child requires visual aids, it can be a challenge to figure out what your prescription really means. With a range of numbers, abbreviations, and symbols, understanding prescriptions can be a challenge, to say the least.
But fear not – in this article, we’ll be breaking down everything you need to know about your prescription and how it is measured.
Breaking Down Your Prescription
Having an accurate prescription is integral to effective vision correction, whether you opt for glasses, contact lenses, or Laser Eye Surgery. Refractive errors such as myopia (short-sightedness), hyperopia (long-sightedness), astigmatism, and presbyopia are measured in units called ‘dioptres’.
These units are used to measure the amount of correction required to achieve clear vision. For example, one dioptre is the equivalent of a lens that can effectively focus your vision on objects one metre away. The number of dioptres appears after a plus (+) or minus (-) sign which signifies whether you are long- or short-sighted, respectively.
The more severe your refractive error, the higher the values in your prescription. In the video below, Dr Glenn Carp explains more about what prescriptions are and what the numbers mean.
As Mr Glenn Carp notes:
“A prescription is essentially the patient’s refractive error. When the light enters the eye through the cornea and through the lens to reach the retina, it needs to be focused on the retina.
“So any little refractive error in the pathway, whether it be in the lens or in the cornea in the front of the eye, will result in some de-focus in terms of the light reaching the retina.
“So your prescription essentially is just the correction factor to sharpen the light rays so that they do reach the target.”
Prescriptions Explained Further
Let’s take a closer look at a typical prescription: -5.00 / -1.50 x 180.
As you can see, this prescription features three values.
The first value (-5.00) of the prescription identifies the extent of long- or short-sightedness. In the example, the patient is short-sighted as indicated by the minus symbol.
The second value (-1.50) of the prescription identifies the degree of astigmatism. Similar to the first value, this is written as either a plus or minus value (usually minus in the UK). The number indicates the severity of the astigmatism.
Finally, the last value (180) of the prescription indicates the axis of the astigmatism. This is measured in degrees rather than dioptres. For example, an axis of 180 degrees indicates that the astigmatism is horizontal.
When all these values are put together, the example prescription shows us that the patient is moderately short-sighted, with a moderate degree of astigmatism in a horizontal direction.
The table below illustrates the ranges from mild to severe short-sightedness and mild to severe long-sightedness:
Mild short-sightedness | Myopia up to -3.00 dioptres |
Low short-sightedness | Myopia up to -3.25 to 6.00 dioptres |
Moderate short-sightedness | Myopia from -6.25 to -11.00 dioptres |
Severe short-sightedness | Myopia from -11.25 to -23.50 dioptres |
Low long-sightedness | Hyperopia from +0.75 to +2.50 dioptres |
Moderate long-sightedness | Hyperopia from +2.75 to +6.00 dioptres |
Severe long-sightedness | Hyperopia from +6.25 to +12.00 dioptres |
Every patient’s prescription is unique to them and their eyes. The values shown in your prescription will determine the lenses in your glasses and contact lenses and, importantly, your suitability for different Laser Eye Surgery procedures.
If you have any more questions regarding your prescription or you would like to learn more about your suitability for Laser Eye Surgery, get in touch with one of our friendly clinic coordinators or Book a Consultation today.