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Understanding prescriptions for glasses

Introduction

Almost everybody will need glasses at some time in their life, including people with learning disabilities. Six out of ten people with learning disabilities need to wear glasses and many will need support to get used to wearing them. People with learning disabilities are 10 times more likely to have serious eye conditions than other people, and many people are living with undiagnosed sight problems that could be corrected by wearing glasses.

It is recommended that carers and supporters always ask the optometrist (optician) or the 'dispensing optician' to explain in plain English why someone has been prescribed spectacles or glasses. Our form 'Feedback from the optometrist about my eye test' has a section within it for a prescription to be completed by the optometrist. This can then be saved with other useful eye care information.

Spectacles or glasses help some people to see far into the distance and other people to see near objects - such as food on a plate or pictures in books and magazines. 

Most people will start to need spectacles to see up-close for reading between the ages of 40 and 50.  The strength of spectacles can be described by a set of numbers. 

John’s prescription

John is aged 50, and needs glasses for both distance and for close up. He wears bifocals -spectacles with a small area at the bottom used for close work, and a larger area above for distance vision. His prescription could look like this: 

Superoptics,
Spex Street,
Anytown,
0195 660660

 

Name: John Smith

Address: 4 Any Road

Date of test: 04.04.07

Recommended date of next test: April 2008

 

  Sph Cyl axis Prism Base -
R +4.00 +0.50 75 - - D
Add +2.50 - - - - N
L +3.50 +0.75 80 - - D
Add+2.50 - - - - N
signed an Optometrist Date:4.4.07

His prescription could also be written: 

R +4.00/+0.50x75 

L +3.50/+0.75x80 Add +2.50


What this means

The positive or plus sign (+) beneath the 'SPH' (sphere) column means the eyes are long-sighted (hypermetropia).  Long-sighted means the person sees objects far away in the distance better than up-close for reading.  However, long-sighted people may still have difficulty seeing far away if they have a large prescription.

John is more long-sighted in his right eye with +4.00 units, than his left eye with +3.50 units.  The unit is called dioptres (D).

A negative or minus sign (-) would mean the eyes are short-sighted (myopia). Short-sighted means the person sees objects up-close better than far away in the distance.

The numbers beneath the 'CYL' (cylinder) and 'AXIS' columns mean the eyes have astigmatism.  Astigmatism means the surface of the eye is shaped like a rugby ball, as opposed to being shaped like a football.  The 'CYL' can be written with a plus (+) or minus (-) sign.  This will depend on how the individual optician decides to write the prescription.  When comparing subsequent spectacle prescriptions to see if there has been a change, it is important that each prescription has the same sign in front of the 'CYL', so that you are comparing like with like.

John has slightly less astigmatism in his right eye with +0.50 units, than his left eye with +0.75 units.  The orientation of the astigmatism is slightly different in the right eye at an axis of 75 degrees compared to an axis of 80 degrees in the left eye.

If John chooses bifocal spectacles the top part of the spectacles will be +4.00/+0.50x75 in his right eye, and the area used for reading - the reading segment - will be +2.50 stronger.

The numbers beneath the 'Add' mean the eyes require a different prescription to see objects clearly up-close for reading e.g. 33 cm away. John's ‘Add’ is +2.50.

If he wanted two separate pairs of glasses he would have the following prescription:

Distance R +4.00/+0.50x75 L +3.50/+0.75x80 Near +6.50/+0.50x75 +6.00/+0.75x80 

Lucy’s prescription

Lucy aged 23 is short-sighted (myopic) and wears her glasses all the time - we know that she is short-sighted, as there is a minus sign in front of her prescription.

She has more astigmatism than John - +3.00 in the right eye and +2.50 in the left, which will contribute to her blurred vision when she doesn't wear her spectacles.

Lucy's eyes need some help in working together properly too.  This is because she has a weakness in one of the muscles that move the eyes, and is why she has ‘2 base in’ written on her prescription.  This figure describes how much prism Lucy needs - this is how the lenses are specially shaped to help her eyes work together.

The words '2 base in' means the eyes need help to co-ordinate moving together.  Lucy requires two units of prism.  The unit is called dioptres (D).  The prism is orientated in front of the right eye with the base inwards towards the nose. 

Manfred Masters Optometrists, 
43 The High Street, 
Summertown, 
0395 686 939

Prescription for: 

Lucy Jones 

18 Stratford Grove

Summertown

Date of test:  04.04.07

Recommended date of next test:  09.06.2008

  Sph Cyl axis Prism Base -
R -5.00 +3.00x180 - - 2 D
- - - - - N
L -5.50 +2.50x175 80 - - D
Add+2.50 - - - - N
signed an Signed:    M.Masters        9.6.07

What it all means

Many people find it impossible to understand the series of abbreviations and numbers used by optometrists when writing a prescription.  Here are the explanations of some of the most commonly used terms.

  • R: right eye
  • L: left eye
  • sph or sphere: this is a number for how long-sighted (hyperopic) or short-sighted (myopic) you are

A plus/positive number means that you are long-sighted, (hyperopic). 

A negative/minus number shows that you are myopic, (short-sighted).

  • cyl or cylinder: this describes the shape of your eye.  It measures how oval your eye is, which is how much astigmatism you have.  Astigmatism is when your eye is oval or rugby ball shaped, rather than round.  Most people have a small amount of astigmatism, which they may not be aware of.  The cyl can be a plus or minus number depending on how the optometrist chooses to write it down.  The larger the number, the more astigmatism you have.
  • axis: this is always a number between 0 and 180, and describes the angle (in number of degrees) at which the astigmatism is, i.e. the plane of the astigmatism.  It is important for the person who is making up the spectacles to know the axis.  The degree sign (o) is left off so it is not mixed up with a zero.
  • prism: where the front and back surfaces of the spectacle lens are designed so that they are inclined at an angle to one another.  This provides help for both eyes to work together better in certain eye problems such as squints.
  • base: the direction in which the prism is effective - up, down, in or out.
  • distance: a prescription described as distance should be used for tasks such as watching TV or driving, or any activities taking place at a few metres distance.  Some people may wear this prescription all the time, and may not need a different prescription for other activities.
  • near: a prescription for near should be used for close work such as reading, craft work which may be carried out at a distance of 25-45 cm, (10-18 inches) depending on your individual needs.  It may also be useful to wear these spectacles when eating.
  • intermediate: this may describe a prescription for work at any distance from 40 cm to 1 m (16 to 40 inches), including woodwork and similar hobbies, or possibly for using a computer.
  • add or addition: this is the part of the prescription that is added on to the distance prescription to enable people who need reading glasses to focus on close work.  It is always written as a positive number, and is usually in the range +0.75 to +4.00.  Some people with poor vision may need a stronger add, this may mean that they need to hold their reading or craft work closer to their eyes to see it clearly in focus.

 

Did you know that the optometrist is obliged to give you a copy of your spectacle prescription immediately at the end of the eye test?  If you haven't been given your spectacle prescription, ask. You do not need to purchase spectacles or any other goods in order to obtain your spectacle prescription. 

Everyone’s spectacle prescription will look different.  If you don't understand yours you can ask your optician to explain it to you.  Alternatively you can call RNIB's Helpline on 08457 66 99 99 - but make sure you have your prescription in front of you when you call.


Note

A prescription almost never includes how well you see, it only tells you the lens power needed to achieve your best vision or most comfortable vision.

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