4 Facts About Glasses Prescriptions That You Didn't Know
Are you wondering what your glasses prescription really means?
After you have taken an eye test, you may start checking all the numbers and terms on the prescription that your eye doctor or optician has given you.
You probably want to know which glasses are right for you. You may also be wondering what kind of visual impairment your eyes have. There is nearsightedness, farsightedness, astigmatism and presbyopia, but which visual impairment actually applies to your eyes?
Read our guide, find out everything about glasses prescriptions in the United Kingdom and easily order your favourite glasses!
What do I need to know in advance?
First of all, you should know the most common visual impairments:
- Myopia – commonly referred to as nearsightedness, blurs vision in the distance
- Hyperopia – commonly referred to as farsightedness. Your vision becomes blurred when looking at near and distant objects, depending on the dioptres and the accommodation of your eye muscles
- Presbyopia – describes the loss of near-focus ability, that usually occurs with age
- Astigmatism – focuses light on more than one spot on the retina, blurring vision
These are all refractive errors, which means that your eyes have trouble focusing light correctly. Your prescription for these conditions is measured in units called dioptres. Dioptres represent the amount of correction you need to normalise your vision. The more nearsighted (or farsighted) you are the higher your prescription in diopters.
How do I read my glasses prescription?
Your glasses prescription may include the following terms: Sphere (SPH), Cylinder (CYL), Axis, Prism, Base, ADD, Distance Acuity and Near Aquity. These parameters represent:
- Right (OD) & Left (OS): Your prescription either contains the words „right“ and „left“ or the terms „OD“ and „OS“, which stand for „oculus dexter“ and „oculus sinister“. They indicate the difference in the parameters of your right and left eye.
- Sphere (SPH): The Sphere indicates the amount of lens power prescribed for nearsighted or farsighted vision. It is measured in dioptres and uses (+) for farsightedness (hyperopia) and (-) for nearsightedness (myopia). The term „sphere“ means that the correction for nearsightedness or farsightedness is „spherical“.
- Cylinder (CYL) & Axis: a Cylinder and Axis number (between 0 and 180 degrees) are required to correct Astigmatism. Both parameters are used together. If nothing appears in these columns, you have little or no astigmatism. A minus sign (for the correction of nearsighted astigmatism) or a plus sign (for farsighted astigmatism) may be placed in front of the number in the cylinder column.
- Prism & Base: Prism correction is used in glasses for people who suffer from strabism or double vision. The prism deflects the light so that it falls correctly on the retina in each eye. The brain then does its usual work by merging the two retinal images into a single, clear image. The direction of the prism is indicated by noting the relative position of its base (thickest edge).
- Reading Addition (ADD): Addition contains the necessary information in case a near vision correction is required. The additional magnifying power is applied to the lower part of multifocal lenses to correct presbyopia. The figure appearing in this section of the prescription is always a „plus“ magnification, even if not preceded by a plus sign. It is the same for both eyes. „D“ stands for the dominant eye and „N“ for the non-dominant eye.
- Distance & Near Acuity: During an eye exam, the number 6/6 is based on you standing a distance of 6 meters in front of a Snellen or Tumbling E eye chart during an eye test to check your visual acuity. This number is considered to be the standard vision with 100 % visus.
Note: Sphere power, cylinder power and add power always appear in diopters. They are in decimal form and generally written in quarter-diopter (-1,0 dpt) increments. Axis values are whole numbers from 1 to 180 and signify only a meridional location, not a power. When prism diopters are indicated in decimal form, typically only one digit appears after the period (e.g., 0.5).
What special features can glasses have?
Probably your prescription will look like the one described above. However, your ophthalmologist or optician can add a few special features to the list. These would be:
- Pupillary Distance (PD): In addition to the general parameters, glasses prescriptions may require a pupil distance (PD). Your PD is the distance between the centre of one pupil (the central black point of your eye) and the centre of the other pupil. It is measured in millimetres.
- Lens design: This indicates your eyesight requirement, detailing the lens design and function (single, bifocal, progressive,). Occasionally you will see a certain brand of progressive or single vision lenses inscribed. If you have any questions about your prescription, please feel free to contact our customer service on 0800 249 4219 or by e-mail at email@example.com.
- Anti-reflective coating: The AR coating increases clarity and concentration by allowing more light to enter and reducing reflection.
- UV protection: The UV protection in your lens prevents your eyes from being damaged by the sun's UV rays.
- Transition lenses: Transition lenses are equipped with a technology that adjusts the colour of your glasses to the light. In the sunshine your glasses become sunglasses!
- Blue light blocking glasses: These special lenses have a unique coating that protects your eyes from artificial light by reflecting blue light coming from digital devices.
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What are progressive, bifocal and single-vision lenses?
- Progressive lenses combine three prescriptions in one pair of glasses. That allows you to do close-up work (e.g. reading a book), middle-distance work (e.g. checking out a website on a computer), or distance viewing (e.g. driving), without the need to change your glasses. They're sometimes called multifocal lenses. Progressive lenses are an update to bifocal and trifocal lenses.
- Bifocal lenses are lenses with two distinct optical powers. Bifocals are commonly prescribed to people with presbyopia who also require a correction for myopia, hyperopia, and/or astigmatism.
- Single vision lenses are the most common prescription lenses. This lens type features a single field of vision, i.e. one prescription power throughout the entire lens, for correcting nearsightedness (myopia), farsightedness (hyperopia) or astigmatism. Single vision lenses are also used for reading glasses.