Prescription Terms and Information

To help you understand your prescription, here is a list of common optical terms often found in most eyeglass prescriptions

DV - Distance vision. Usually part of the prescription designed to improve far vision. For bifocals, this usually the prescription for the top half of the lens.

NV - Near vision. This may represent a single-vision lens prescription to improve near object view, or the reading portion of a bifocal lens. Some prescription forms use ADD in place of NV with a single box to indicate the additional refractive power to be added to the spherical of each eye.

OD - Oculus dexter, Latin for right eye.  Sometime prescriptions use RE (right eye), LE (left eye), BE (both eyes).  

OS - Oculus sinister, Latin for left eye. 

OU - Both eyes.

SPH - SPHERE: The amount of long or short sightedness. This value specifies the optical power of a lens in diopters. It always has a plus (+) or a minus (-) sign in front or above it. The lens power for the distance correction will be minus while the correction for near distance and reading will be plus power. There will always be a value for sphere, even if it is just zero (written as 0.00, Plano or PL). If the vision in one eye is very poor, the word 'balance' or 'bal' may be written.

CYL - CYLINDER: This is the measure for astigmatism. Again, there is always a plus (+) or minus (-) sign present. There may not be a value of cylinder in your prescription.

AXIS - This is a number anywhere between 0 and 180 degrees. It reveals the orientation of the astigmatism. It is not enough to specify how much astigmatism there is; you have to know where the difference in curvature is taking place. If an eyeglass prescription includes cylinder power, it also must include an axis value, which follows the cyl power and is preceded by an "x" when written freehand.

PRISM -This is the amount of prismatic power, measured in prism diopters, prescribed to compensate for eye alignment issues. Only a small percentage of eyeglass prescriptions include prism.

AXIS - This is a number anywhere between 0 and 180 degrees. It reveals the orientation of the astigmatism. It is not enough to specify how much astigmatism there is; you have to know where the difference in curvature is taking place. If an eyeglass prescription includes cylinder power, it also must include an axis value, which follows the cyl power and is preceded by an "x" when written freehand.

PRISM -This is the amount of prismatic power, measured in prism diopters, prescribed to compensate for eye alignment issues. Only a small percentage of eyeglass prescriptions include prism.

BASE - Rotation of the prism that is simply specified as 'base in' (where 'in' means towards the nose)or 'base out' or 'base up' or 'base down'. Only these four positions exist, however, orientations between these four positions can be specified by using combinations of horizontal and vertical prisms in the same lens.

READING PORTION (PROGRESSIVE, BIFOCAL, TRIFOCAL)

ADD, ADD POWER, SEG POWER - For near vision or reading, it is the additional power in the lower portion of a multifocal lens (progressive, bifocal, or trifocal).

SEGMENT HEIGHT (Seg Ht) - The distance from the lowest portion of the lens to the top horizontal line of the Segment or change in power (Your pupil height from the bottom of the frame). There are average segment heights for each frame, but it can be important to have an accurate segment height for your eyes with a particular frame. Depending on the sunglasses, you might need to take the frame to an optician for him to measure the Segment Height for that frame to work properly for your particular face.  We recommend that when ordering progressives, you use same or similar frame to get your prescription.

  

Examples: 

 

 

Measuring Pupil Distance and Frame Sizing

Pupillary Distance or PD is the distance between pupil centers of your eyes in millimeters.  Also known as Binocular PD. Monocular PD is needed if your eyes are not equal distance from your nose. Right eye (OD PD) and left eye (OS PD) are measured from the center of your nose to each pupil.  

PD is needed to accurately center the lens in the frame you select

For bifocals or progressive lenses, some people will need a Distant Vision PD (DV PD) and a Near Vision PD (NV PD).  This is because some peoples eyes converge when looking at near objects.   PD measurements are essential for all spectacle dispensings, monocular PDs being essential in progressive lenses and for those with high prescription. PDs can be measured using a pupilometer or by using a ruler. 

- Normal PD for adults range from 58 to 70mm.

 

Frame Sizing:

Measurements For Glasses ( eye, bridge, temple, vertical )

(Often the measurements do not include Vertical height)


Using your existing glasses to get your current sizing: 

Most name brand glasses have sizing information printed on the inside of the frame or bridge.  Sometimes this is the first part to wear away.