• Add - This is an additional prescription added to the distance prescription to help patients read when they cannot accommodate/focus themselves. This is common in presbyopia (a condition that usually occurs in patients over the age of 40 who have troubles reading up close).
  • Anti-Reflective Coating (AR) - An additional coating placed on the spectacle lenses to decrease glare
  • Astigmatism - A refractive error where objects at all distances have a distorted appearance ("streaked" or stretched, with elongated shapes and unequally blurred borders). Symptoms of astigmatism include squinting, eye strain, headaches and reading problems.
  • Axis - Axis refers to where the astigmatism is oriented and lies between 1 and 180.
  • Base - This column in a prescription refers to the orientation of the Prism Power and is as follows: - BU: Base Up - BD: Base Down - BI: Base In - BO: Base Out
  • Bifocal - Lens with one segment for near vision and one segment for far vision. The term "bifocal" can apply to both eyeglass lenses and contact lenses.
  • Blue Light - Found in the light spectrum next to violet, which has the shortest wavelength of visible light. Also known as High Energy Visible (HEV) light, blue light has been linked to eye damage and diseases such as age-related macular degeneration.
  • CYL (Cylinder) - Cylinder refers to the amount of lens power required to correct for astigmatism (when eyes are not perfectly round like a basketball but oblong like a football). If this space is left blank, then the patient doesn’t have astigmatism
  • High-Index Plastic - A lens material which is extra thin to make higher spectacle lenses look thinner.
  • OD (Oculus Dexter) - A Latin term that translates to “Right Eye”
  • OS (Oculus Sinister) - A Latin term that translates to “Left Eye”
  • OU (Oculus Uterque) - A Latin term that translates to “Both Eyes”
  • PD (Pupillary Distance) - The distance between the pupils of the left and right eyes.
  • Polycarbonate - An impact-resistant lens material which also provides a natural UV filter
  • Prism - Prism is very rare and helps patients see a single image when they would otherwise see double. The amount of prism listed is also measured in diopters.
  • Progressive - refers to a no-line multifocal lens. It is technically a poly-focal lens, having focal points of all distances in the lens. 
  • Seg-height - The measurement used to place reading prescriptions as in bifocals, trifocals or progressives. 
  • SPH (Sphere) - Sphere represents the power of the lens and is measured in Diopters (D). A higher sphere usually correlates with a thicker lens to correct myopia (near-sightedness) or hyperopia (far-sightedness). A (+) prior to the number indicates a correction for hyperopia while a (-) indicates a correction for myopia.
  • Trifocal - A lens with 3 segments of prescription. There is distance, intermediate and near segment corrected for. The intermediate prescription usually corresponds to a typical computer distance.