For FAQs regarding Coronavirus please click here

What Is A Prescription?

Mr Glenn Carp – “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 to the target.”

Prescriptions Explained Further…

To gain a prescription value Optometrists and Ophthalmologists measure the disorders of the eye, such as myopia, hyperopia, astigmatism, and presbyopia in units called dioptres. These show the amount of correction you need to see normally. One dioptre is the equivalent of a lens that can focus on an object one metre away. The more short-sighted, long-sighted, or astigmatic you are, the higher your prescription in dioptres. A typical prescription has three numbers such as -5.00 / -1.50 x 180.

The first number (-5.00) of a prescription identifies your degree of short-sightedness or long-sightedness. The minus sign in front of the number identifies you as short-sighted. A plus sign would show you were long-sighted.

The second number (-1.50) of a prescription identifies your degree of astigmatism. This is written with either a plus sign or a minus sign.

The third number (180) indicates the axis, the direction of your astigmatism. An axis of 180 degrees, for example, means the astigmatism is horizontal.

A prescription of -5.00 /-1.50 x 180 indicates 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-sightednessMyopia up to -3.00 dioptres
Low short-sightednessMyopia up to -3.25 to 6.00 dioptres
Moderate short-sightednessMyopia from -6.25 to -11.00 dioptres
Severe short-sightednessMyopia from -11.25 to -23.50 dioptres
Low long-sightednessHyperopia from +0.75 to +2.50 dioptres
Moderate long-sightednessHyperopia from +2.75 to +6.00 dioptres
Severe long-sightednessHyperopia from +6.25 to +12.00 dioptres

Knowledge Dispels Fear

Subscribe to our newsletter

Join over 5,000 people already receiving the very best advice on Laser Eye Surgery ...

Newsletter CTA
Your personal data is secure

Mr Glenn Carp provides an explanation of what prescriptions are.

You May Also Like:

Related questions:

(Please note: Some of the pages below may not yet be available but will be published soon.)

Related pages:

Ask us this question:

My prescription was relatively small pre-op so I wasn’t expecting a huge improvement. I’m definitely happy with the level of vision now and I’m very pleased with the level of comfort regarding dry eyes just 1 month post op.– James Chancellor

Go back

What Is A Prescription? [Video]

  1. Pingback: What is hyperopia (long-sightedness)?

  2. Pingback: London Vision Clinic | What is 20/20 or 6/6 normal vision?

  3. VIPIN CHAUHDARY 07/04/2017 at 11:59


    My left eye has no lens inside because of broken brown circle in my eye and also myopia in my right eye, so my left eye no. is +5 and my right eye no. is -5, kindly give me suggestion how i manage eye glasses because when i wear glasses the vision become dual. also suggest if left eye surgery possible.

    • Bethany Kingsley 07/04/2017 at 12:22

      Hi Vipin,
      Contact lenses may help with the difference between the eyes (anisometropia. We would need more information and any report on what has actually occurred before assessing whether it would be beneficial to have a consultation. If positive, refractive surgery could potentially help with the anisometropia.
      London Vision Clinic

  4. Rafael Axelsson 09/06/2017 at 09:21

    I have found the prescription part of the equation to be very confusing. Your article did a great job of explaining things.

Leave a Comment