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Knowing your eyeglass or contact lens prescription is an important part of knowing if Lasik is right for you. |
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Reading your eyeglass or contact lens prescription is often the first step to understanding if conventional or custom wavefront Lasik, Bladeless Lasik, PRK, LASEK, Epi-Lasik, RLE, or any refractive surgery procedure is appropriate for you. You should understand your glasses and contact lens prescription even before you select a Lasik Surgeon.
Bending Light
Refractive error, or the degree from which you do not have normal vision, is commonly measured in diopters and indicates the amount light bends within your eye to be focused on the retina and be "seen". A diopter is often represented by a capital "D" in a prescription. No refractive error is referred to as "plano", often represented as "pl". The greater the refractive error, the larger the number for both sphere, representing the amount of myopia or hyperopia, and and cylinder, representing astigmatism. This known as a spherocylinder or spherocylindrical prescription.
Spherocylindrical Prescription
A typical spherocylindrical prescription would look like:
|
sphere |
cylinder |
axis |
OD: |
-2.75 |
-1.25 |
x15 |
OS: |
pl |
-0.75 |
x85 |
OD is an abbreviation for the Latin oculus dexter, meaning right eye. OS is an abbreviation for the Latin oculus sinister, meaning left eye. The first number after the determination of which eye is the sphere. A negative number indicates myopia. A positive number indicates hyperopia. The second number in this prescription is the cylinder (astigmatism), and the third number is the axis of the cylinder component. The axis of the astigmatism does not relate to the amount of cylinder, just the location of the irregularity. If the patient has no cylinder, then the last two columns may remain blank, or "DS" for "diopter sphere" may be used.
This prescription shows that the patient has 2.75 diopters of myopia with 1.25 diopters of astigmatism at an angle of 15 degrees in the right eye, and the left eye is plano with 0.75 diopters of astigmatism at an angle of 85 degrees.
|
sphere |
cylinder |
axis |
OD: |
-2.75 |
-1.25 |
x15 |
OS: |
pl |
-0.75 |
x85 |
The above prescription shows that the patient has 2.75 diopters of myopia with 1.25 diopters of astigmatism at an angle of 15 degrees in the right eye, and the left eye is plano with 0.75 diopters of astigmatism at an angle of 85 degrees.
Minus Cylinder or Plus Cylinder
Spectacle prescriptions can be written in two value sets, minus cylinder or plus cylinder, which are mutually exclusive of each other but provide the same information. As a rule, ophthalmologists write scripts in minus cylinder whereas optometrists write scripts in plus cylinder. Why these two professions cannot get together and decide on a common method of reporting refractive error is impossible to explain, but if you have ever had competing siblings in your family, you may get an idea why this has not yet occurred.
To convert a minus cylinder form prescription into plus cylinder, or to convert the plus cylinder form into minus cylinder, do the following:
- Add the sphere and cylinder powers together; this becomes the new sphere power.
- Change the sign of the cylinder power, from minus (–) to plus (+) or from plus (+) to minus (–).
- Change the axis value by 90?, remembering that the axis must be a number from 1 to 180.
The following lens prescriptions, therefore, are equivalent and interchangeable:
These two prescriptions are exactly the same
presented in both minus cylinder and plus cylinder form. |
|
sphere |
cylinder |
axis |
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sphere |
cylinder |
axis |
OD: |
-2.75 |
-1.25 |
x15 |
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OD: |
-4.00 |
+1.25 |
x105 |
OS: |
pl |
-0.75 |
x85 |
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OS: |
-0.75 |
+0.75 |
x175 |
minus cylinder form |
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plus cylinder form |
Spherical Equivalent
The spherical equivalent power of a lens prescription is the average of the dioptric powers in all meridians of a lens. To obtain this value, add half of the cylinder power to the sphere power. In other words, do the following:
- Divide the cylinder power by 2.
- Add this value to the sphere power; the result is the equivalent sphere power of the lens.
For the glasses prescription...
|
sphere |
cylinder |
axis |
OD: |
-2.75 |
-1.25 |
x15 |
OS: |
pl |
-0.75 |
x85 |
minus cylinder form |
...the equivalent sphere powers of each lens would be calculated as follows:
OD: –2.75 D + (–1.25 D ÷2) = 2.75 D + 0.625 D = –3.375 D
OS: 0.00 D + (–0.75 D ÷2) = 0.00 D + 0.375 D = –0.375 D
Eye Prescription Terms
Table of Eye Prescription Terms |
OD
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Right Eye |
OS
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Left Eye |
BC
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Inside curve of your contact lens (8.0, 8.1, 8.2, etc.) |
Diameter
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Size of your contact lens (13.8, 14.0, 14.2, etc.) |
Power
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[Pow] Strength of your corrective lens (-1.00, -2.75, +2.25, etc.) |
Cylinder
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[Cyl] Strength of your astigmatism (-0.75, -1.00, -1.25, etc.) |
Axis
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Orientation of your astigmatism in degrees (170, 160, 090, etc.) |
Plano
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No refractive error |
Pl
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No refractive error |
Add
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Bifocal plus power for near distance (+1.00, +2.00, etc) |
Looking For Best Lasik Surgeon?
If you are ready to choose a doctor to be evaluated for conventional or custom wavefront Lasik, Bladeless Lasik, PRK, or any refractive surgery procedure, we recommend you consider a doctor who has been evaluated and certified by the USAEyes nonprofit organization. Locate a USAEyes Evaluated & Certified Lasik Doctor.
Personalized Answers
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