Decoding Prescription Terminology: ADD, PD, and Segment Height Explained

Prescription eyeglasses come with a unique set of terminologies that can leave you feeling perplexed. Terms like ADD, PD, and segment height may seem like foreign concepts, but they play a crucial role in ensuring optimal vision correction. In this blog post, we will demystify these prescription terminologies, shedding light on their significance. Let's dive in!

ADD (Addition):

The ADD value appears in prescriptions for individuals with presbyopia, an age-related condition that affects near vision. It indicates the additional power required for reading or close-up tasks. The ADD value, measured in diopters (D), allows the lens manufacturer to incorporate the necessary power for clear near vision.

Understanding the ADD value is crucial for individuals who need multifocal lenses, as it ensures that the lens provides adequate magnification for comfortable reading and other near activities. By including the ADD value in your prescription, your eyewear specialist can create lenses that address both your distance and near vision needs, allowing you to see clearly at various distances without constantly switching glasses.

PD (Pupillary Distance):

PD, or pupillary distance, refers to the measurement of the distance between the centers of your pupils. This measurement is essential for ensuring that your lenses are positioned correctly in relation to your eyes. It is typically measured in millimeters (mm) and can be a single number representing the total distance or separate values for each eye.

Accurate PD measurement ensures that the optical centers of your lenses align precisely with your pupils. Proper alignment is crucial for maximizing visual clarity and reducing eye strain. An incorrect PD measurement can result in discomfort, distorted vision, and reduced effectiveness of your prescription lenses. It's important to provide an accurate PD measurement when ordering eyeglasses to ensure optimal vision correction and comfort.

Segment Height:

Segment height is a relevant consideration for those who require bifocal or progressive lenses. The segment height refers to the vertical measurement from the bottom of the lens to the top of the segment for near or intermediate vision.

In bifocal or progressive lenses, the lower portion of the lens is dedicated to near or intermediate vision, while the upper portion corrects distance vision. The segment height ensures that the near or intermediate vision segment is positioned correctly, allowing you to access that portion of the lens effortlessly. Accurate segment height measurement is vital for ensuring that your lenses provide clear and seamless vision transitions between different focal points.

By understanding segment height, you can communicate effectively with your eyecare professional and ensure that the placement of the segment aligns with your specific needs. This will enhance your visual experience and provide a smooth transition between different viewing distances.

Understanding the prescription terminologies of ADD, PD, and segment height empowers you to make informed decisions about your vision correction needs. The ADD value ensures clear near vision for those with presbyopia, while an accurate PD measurement guarantees proper alignment of your lenses. Segment height plays a crucial role in ensuring seamless transitions between different focal points in bifocal or progressive lenses.

By familiarizing yourself with these terminologies, you can confidently communicate with your eyecare professional and ensure that your prescription eyeglasses are tailored to your specific vision requirements. Remember, your eyeglass prescription is a valuable guide that, when understood, can enhance your visual clarity and overall comfort.