| |
sphere |
cylinder |
axis |
|
OD: |
-2.75 |
-1.25 |
x15 |
|
OS: |
pl
|
-0.75 |
x85 |
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.
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:
1) Add the sphere and cylinder powers together; this becomes
the new sphere power.
2) Change the sign of the cylinder power, from minus (–) to plus
(+) or from plus (+) to minus (–).
3) 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 |
|
style="border-left-style: solid" bordercolor="#C0C0C0"
|
sphere |
cylinder |
axis |
|
|
OD: |
-2.75 |
-1.25 |
x15 |
|
|
OD: |
-4.00 |
+1.25 |
x105 |
|
OS: |
pl
|
-0.75 |
x85 |
|
|
OS: |
-0.75
|
+0.75 |
x175 |
|
minus cylinder form |
|
|
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:
1) Divide the cylinder power by 2.
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
|
Table of Eye Prescription Terms
|
|
OD |
|
Right Eye |
|
OS |
|
Left Eye |
|
BC |
|
Inside curve of
your contact lens (8.0, 8.1, 8.2, etc.) |
|
Diameter |
|
Size of your contact
lens (13.8, 14.0, 14.2, etc.) |
|
Power |
|
[Pow] Strength
of your corrective lens (-1.00, -2.75, +2.25, etc.) |
|
Cylinder |
|
[Cyl] Strength
of your astigmatism (-0.75, -1.00, -1.25, etc.) |
|
Axis |
|
Orientation of
your astigmatism in degrees (170, 160, 090, etc.) |
|
Plano |
|
No refractive error |
|
Pl |
|
No refractive error |
|
Add |
|
Bifocal plus power
for near distance (+1.00, +2.00, etc) |
If you are ready to choose a doctor to be evaluated for conventional
or custom
wavefront
Lasik,
All-Laser Lasik,
PRK,
LASEK,
Epi-Lasik,
NearVision CK,
RLE, or any
refractive surgery procedure, we highly recommend you consider
a doctor who has been evaluated and certified by the USAEyes
nonprofit organization. Locate a USAEyes Evaluated &
Certified
Lasik Laser Eye Surgery Doctor.
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