Glossary of technical terms
No two single eyes are the same. Which is why Brille24 prepares each lens individually. To do this we need the details of your prescription. And because optical prescriptions aren't easy to read, here's an explanation of the terms used.
If after reading this you still have questions, feel free to contact our customer service.
Sphere
Sphere - "SPH" - is the unit of measurement for the refraction power of lenses. Spheres specified to what degree lenses make things appear bigger or smaller. The SPH number on your prescription - which can be positive or negative - tells us how strong your lenses need to be.
The number also relates to the point on which your eyes focus when looking into the distance. If you don't need glasses, your eyes can focus comfortably on the horizon or even the stars - in fact on a point infinitely distant. If you're shortsighted and have a value of, say, -10.0 spheres, the point of focus is only 10 centimetres away.
- Your SPH value is always found on the left side of your prescription. It will be indicated in positive or negative numbers.
Cylinder
The cylinder is a value for correction of a corneal irregularity, also called corneal curvature or astigmatism. This value is listed under "CYL" in your prescription.
A corneal irregularity is present if there is an uneven curvature of the cornea. Essentially, this means that lenses for cylinder correction vary in thickness at the edges, as they are adjusted to the surface of the eye.
- The second position on your prescription indicates your CYL. This will also be indicated in positive or negative numbers.
Axis
The axis determines the angle of the lens in your glasses - ie. in which direction the lens will be fitted into the frame and where the thick and thin parts of the lens should be. The axis is indicated with a number between 0° and 180°. The value is listed under "A" on your prescription.
- The Axis is between 0 and 180 degrees. There is a value for both your right and left eye.
Pupil-Distance
Pupil-Distance (PD) measures the distance between your pupils and the bridge of the nose when you're looking straight ahead. This value doesn't necessarily have to be the same for both eyes. Your prescription will contain values measured in millimetres for left and right, marked L and R.
- The PD is often listed in the lower right hand corner of your prescription and is denoted in millimeters (mm). The value can consist of a right and left PD or of a total value (31/32 = 63mm).
Accomodation
As we get older, we become less flexible. This includes our eyes, which expand and contract as we focus on things nearer and further away. Old eyes have more of a problem "accommodating" a change of focus. Depending on your eyes you may find that you need glasses just for driving or just for reading. Deterioration of vision caused by aging is called "presbyopia".
Addition
Addition is used to describe the cumulated power of bifocal or varifocal lenses. These glasses are good for seeing close-up and into the distance. At present, Brille24 doesn't offer bifocals or varifocals. For additional information on varifocal lenses please click here.
Prism
There is a box on your prescription marked "prism" - which is probably not been ticked by your optician or ophthalmologist. If it has, however, it means that you have binocularity defect - or to be less politically correct, a bit of a squint. This can be corrected with the aid of the right glasses, but they need to be individually made, and at present Brille24 doesn't offer glasses that correct binocularity.