What Are Prism Glasses? Purpose, Prescription and Fit
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Prism glasses are prescribed for some people with double vision or eye-alignment problems. Prism changes the direction of light reaching the eyes; whether it is appropriate depends on the cause of the symptoms and a clinical assessment.
Prism is a separate prescription detail
A prescription may include prism as well as sphere, cylinder and axis. The prism amount and base direction must stay together and with the correct eye. Base in, base out, base up and base down are not interchangeable.
Prism diopters are sometimes abbreviated in ways that can be confused with pupil measurements. Pupillary distance (PD) describes positioning in millimeters; it does not tell you how much prism to order. See the prescription field guide if the labels are unfamiliar.
Who decides whether prism is needed?
An eye-care professional needs to determine the reason for double vision and the appropriate correction. Do not use an online symptom description to choose a prism amount or add prism to a previous prescription. Sudden new double vision needs prompt medical assessment, particularly with other new symptoms.
The glasses still need to fit
The prescribed values are only one part of the order. Frame position, required measurements and lens availability also need review. A general frame label cannot confirm that a particular prism prescription can be made in it.
For a new online order, use the prism buying checklist. If you already have prism glasses and are experiencing difficulty, read what to check with your dispenser. Eyeisland can discuss an order, but an order discussion does not replace an assessment of new or changing symptoms.
