An eyeglass prescription is a written order provided by an eyewear prescriber, typically an optometrist or ophthalmologist, that contains all the necessary information for constructing and dispensing corrective lenses for a patient. It specifies the parameters required to address the patient's refractive error and provide clear vision.

Well the phoropter is the instrument that the optometrist uses on every patient every single day. It contains all the lenses that are used to calculate what someone's prescription might be. This lens we use to control the nearsightedness and farsightedness that might be in the prescription.

This auxiliary dial is used to look for the astigmatism that might be in the prescription. And if we check for the coordination of the eyes and the muscle balances, and it will generally take about 10 minutes to do.

An eyeglass prescription typically includes the following information:

1. Sphere (SPH): This indicates the lens power needed to correct nearsightedness (indicated by a negative number), farsightedness (indicated by a positive number), or no refractive error (indicated by zero).

2. Cylinder (CYL): This denotes the lens power needed to correct astigmatism. It indicates the strength and direction of the astigmatism. If there is no astigmatism, this value will be zero.

3. Axis: This measurement is associated with the cylinder and denotes the orientation or angle of astigmatism in degrees.

4. Prism: If the patient requires prism correction, this indicates the amount and direction of the prism necessary.

5. Add or Near Vision (ADD): This value is used for bifocal or progressive lenses and indicates the additional lens power required for near vision in presbyopic individuals.

6. Pupillary Distance (PD): This measures the distance between the centers of the pupils, which is important for aligning the optical centers of the lenses correctly with the patient's eyes.

These are the primary parameters typically found in an eyeglass prescription. Additionally, the prescription may include other information or special instructions as needed. It is essential to have a valid and up-to-date eyeglass prescription to ensure the accurate production of eyeglasses that meet the patient's visual needs.