If you’ve recently had an eye exam your optometrist may have given you a new glasses prescription. A typical glasses prescription includes various abbreviated terms. To get the most out of your new prescription it’s important to understand what all these different terms mean.
How to read your glasses prescription
Your optician will provide you with an eye prescription chart, including different numbers, letters, and symbols. To get to grips with these different terms, see the explanations below.
OS and OD
OD and OS refer to ‘oculus dexter’ and ‘oculus sinister’, these are latin terms that mean ‘right eye’ and ‘left eye’. You might also have noticed that your glasses prescription has a column that reads ‘OU’, these letters mean ‘oculus uterque’, or ‘both eyes’. Some optometrists use an updated version of these terms, and simply write ‘RE’ meaning right eye, or ‘LE’ meaning left eye.
Symbols ‘+’ and ‘-’
If your spectacle prescription shows the ‘+’ symbol this refers to ‘longsightedness’. If you see the ‘-’ symbol instead, this means ‘shortsightedness’.
If you’ve already had a look at your prescription chart you might be wondering what is cyl on an eye prescription? The CYL, or cylinder eye prescription, represents the astigmatism of lens power. If you do not see anything inside this column this means that you do not have astigmatism.
‘Cylinder’ means that the lens power used for astigmatism isn’t a spherical shape; alternatively, it’s designed so that one meridian does not have added curvature. You might notice that the cylinder number has a + sign, referring to long-sighted astigmatism, or a – sign, meaning short-sighted astigmatism.
Perhaps you’re looking at your glasses prescription and wondering about the optician sph meaning? The SPH number is used to show the lens power, this number is measured using dioptres. Dioptres are the units used to determine the light-bending (or refractive) power of your glasses’ lens. ‘Sphere’ means that the correction for both long sightedness and short-sightedness is equal across the eye, or ‘spherical’.
The axis refers to the lens which does not have cylinder power to support astigmatism. You’ll notice that the axis is represented using a number between 1 and 180. The number 90 refers to the vertical meridian, and 180 represents the horizontal meridian. If you have cylinder power as part of your spectacle prescription, the prescription also needs an axis value.
Back Vertex Distance
BVD means ‘back vertex distance’, it refers to the distance between your prescription glasses lens and the front of your eye. BVD is measured in millimetres, the distance has an impact on how strong the lens is. You’ll find that a BVD measurement is generally only provided for high-strength prescriptions.
PD Pupillary Distance
The PD refers to the distance between the centre of your two pupils. Most of the time, your optician won’t include this figure as part of your prescription. If you have a high-strength prescription it’s worth asking for this number. The PD can help you to ensure that your lenses are accurately centred.
The ‘Add’ section refers to any added magnifying power, sometimes magnifying power is added to multifocal lenses, to support presbyopia. The number shown in this section is a ‘plus’ power every time, (though it’s not always represented with a plus sign). This figure tends to be somewhere between +0.75 and +3.00D, it’s always the same number for each eye.
If you are over 40 years old you’re quite likely to have a number in the ‘Add’ section. The number refers to the extra correction you need, to observe close distances. If there’s a measurement this means that you need different prescriptions for reading and distance.
The prism value refers to the prismatic power, the number if measured in ‘p.d.’ which refers to prism dioptres. The prism is prescribed to correct any problems with eye alignment. Typically only a small number of glasses prescriptions include a prism value. The prism amount tends to be represented in fractional English or metric units. You’ll see that there are four different abbreviations that are used for prism direction:
- BO- this means base out (facing toward the person’s ear).
- BI- referring to base in, (facing toward the person’s ear).
- BU- meaning base up.
- BD- meaning base down.
How do eye prescription numbers work?
Perhaps you’re wondering how you determine reading glasses strength from prescription? The numbers that represent the strength are called diopters. It’s the diopters that describe how strong the magnification is. If your reading glasses have a lower number, this indicates less magnification. Higher numbers represent stronger magnification. Reading glasses tend to start around +1.00 diopters and increase to +4.00.
How to read a bifocal prescription
A bifocal prescription is a prescription for bifocal lenses, using the numbers on the prescription the lens designer can craft a pair of glasses that correct both farsightedness, and nearsightedness.
Bifocal prescriptions are rather similar to regular eyeglasses prescriptions. You’ll need to have the same understanding of the sphere, cylinder, axis, and so on. The ADD value is probably the most important part of a bifocal prescription, this is the figure that’s used to magnify the bottom of the lenses.
What are RX glasses?
If you need spectacles you might have also come across the term ‘RX glasses’, RX glasses is another way of saying ‘prescription sunglasses’. These glasses come in a range of different lens types. For example:
- Photochromic lens coating.
- Polycarbonate lenses.
- Polarized lens coating.
Extra eye prescription info
As well as the above information, your optometrist may add extra eye health info to your prescription card. Typically, the info will be about certain types of corrective lenses. A few examples include transition lenses, progressives, or multifocal lenses. Understanding how to read your eye prescription chart is an essential part of maintaining your eye health.
How often should you get your eyes tested?
Experts recommend that you should have your eyes tested at least every two years. Of course, if you notice any eye problems, you’ll need to contact your optometrist sooner. To learn more about glasses prescriptions, or book in an eye test, contact Belson Opticians today. Getting the right pair of prescription glasses is incredibly important for your eye health. If you’re still unsure about how to read your optical prescription, Belson Opticians can help.