A glasses Rx is comprised of 3 numbers in order

Sphere 

• Reflects the degree of myopia / hyperopia

• Can be minus (myopia) or plus (hyperopia)

Cylinder Power 

• Reflects the degree of astigmatism

• At HEA it is always minus

Cylinder Axis 

• Reflects the axis of astigmatism

Add Power

• This is for a reading prescription for older patients only

• You will see this only in bifocal/trifocal or progressive glasses

Example

Note: You will see sph in the second place if there is no astigmatism

OD: -3.25 - 1.25 X 80

OS: -4.00 - sph

Single Vision

• These are for only one distance (distance, computer, or near)

• There are also over the counter (OTC) reading glasses (+2.50 is most common)

Bifocal

• Has 2 zones (DV at the top and NV (add) at the bottom)

• There is a distinct line separating the 2 zones

Trifocal

• Has 3 separated zones (distance, intermediate, and near)

Progressive or PAL (Progressive Addition Lens)

• Has distance, intermediate, and near blended together

• You can read the add power under the green light by the lensometer

Note

• Some glasses have prisms in them. If a person has double- vision due to an eye muscle imbalance, a prism can be put in the lens to realign the sight straight forward

• This makes reading the glasses difficult! If the lensometer keeps jumping around, likely there is a prism in the lens

Soft CTLs

• Majority of contact lens wearers use soft CTLs

• They are convenient and pre-made

• They are very comfortable and easy to get used to

• Must be constantly replaced though

Hard CTLs

• Can offer the best vision possible for high or unique prescriptions

• Need to be custom made for the patient

• Can be uncomfortable and take some time to get used to them

• Can last for years if taken care of properly

• Must be removed with a small plunger and use a special solution (Boston)

A CTL Rx will also have the following values for a proper fit

Base Curve (BC)

• This is a measurement of the back surface of the CTL needed to properly fit the shape of the cornea

Diameter

• The width of the CTL from edge to edge

Scleral Lenses

• These are mainly for Keratoconus patients because the cornea is so steep, regular ones will not fit right and will slip off!

• These are hard CTLs that rest on the rim of the Sclera and are filled with saline to fill the space in between the cornea and CTL

• They must be custom made and fit to the patient's eye and can last for years

• This measure the curvature of the cornea

• It is similar to astigmatism, mut more precise and helps validate the degree of astigmatism

• We get these from our auto refractor, but there are other machines that get them also (topographer/Pentacam)

• It is very important for CTL fittings!