A contact lens prescription is a detailed document that specifies the parameters necessary to correct your vision using contact lenses. These prescriptions are typically provided by eye care professionals such as optometrists or ophthalmologists. Let’s delve into the critical elements of a contact lens prescription:

1. OD and OS (Oculus Dexter and Oculus Sinister)
   • • OD stands for “oculus dexter,” which is Latin for the “right eye.”
     • OS stands for “oculus sinister,” which is Latin for the “left eye.”
       
       

       These Latin terms are used to differentiate between your right and left eyes in your prescription. Your right eye is labeled OD, and your left eye is labeled OS. This distinction is crucial because your right and left eyes may have different vision needs, and your contact lenses will be customized accordingly.
       
       

2.  Sphere (SPH)
   • • Sphere value, denoted as SPH, is the core element of your prescription.
     • It represents the degree of your refractive error, which can be nearsightedness (myopia) or farsightedness (hyperopia).
     • Nearsightedness is indicated by a minus sign (-), e.g., -2.00.
     • Farsightedness is indicated by a plus sign (+), e.g., +2.00.
       
       

       The SPH value quantifies how strong the lens needs to be to correct your vision. A higher SPH number indicates a more significant vision correction requirement. For example, a prescription of -2.00 SPH means you are moderately nearsighted, while +2.00 SPH suggests moderate farsightedness.
       
       

3.  Cylinder (CYL)
   • • The cylinder value, labeled CYL, is relevant when you have astigmatism.
     • Astigmatism occurs when your eye’s cornea is not perfectly spherical but rather has an irregular shape.
     • The CYL value indicates the degree of astigmatism correction needed.
     • Astigmatism correction can also be either for nearsightedness or farsightedness, and it is denoted by a minus or plus sign, similar to SPH.
       
       

       For example, if your prescription includes -1.00 CYL, it means you have astigmatism that requires correction for nearsightedness, whereas +1.00 CYL would indicate astigmatism correction for farsightedness.
       
       

4.  Axis
   • • The axis is a number between 0 and 180 degrees.
     • It specifies the orientation or angle at which the cylinder correction should be placed on the lens to align with the astigmatism in your eye.
     • The axis value ensures that the cylindrical power is oriented correctly to provide the most effective astigmatism correction.
       
       

       For instance, an axis value of 90 degrees means that the astigmatism correction should be positioned vertically, while an axis of 180 degrees means it should be horizontal.
       
       

5. Addition (ADD)
   • • The addition value, noted as ADD, is typically present in multifocal contact lens prescriptions.
     • It represents the additional power required for reading and close-up vision, often associated with a condition called presbyopia.
     • Presbyopia is an age-related condition where the eye’s ability to focus on close objects diminishes.
       
       

       The ADD value is crucial for multifocal lenses as it allows you to have both distance and near vision correction in one lens. It is typically a positive value, such as +2.00, indicating the strength of the additional power required for reading.