Troubleshooting Prism - Single Vision

When troubleshooting vision problems, prism is one of those topics that often makes doctors and opticians sweat. It’s the thing people suspect when “something just feels off” - but they can’t quite put their finger on it.

In this guide, we’ll break down common prism issues in single vision lenses, what questions to ask and how to solve them.

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Why Separate Single Vision from Bifocals?

It’s simple:

  • Single vision = single problem (usually)
  • Bifocals/Multifocals = multiple problems - distance and near, maybe intermediate, maybe prism differences at each zone

That’s why we handle them differently. Today, we’re focusing on single vision only.

Common Complaints & Red Flags

Most calls we get about single vision prism issues start the same way:

“The patient says their eye feels like it’s pulling.”
“They’re seeing double.”
“One eye feels ‘stronger’ than the other.”

To the patient, it’s simple - “You made me glasses. They should work, right?” To fix it, you need to look deeper.

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What Questions Should You Ask?

When a patient complains of prism-like symptoms in single vision glasses, here’s what to check:

1. Who made the glasses?

  • If Chadwick made them, we’ll pull the job file and double-check every detail.
  • If someone else made them, get as much info as possible: prescription, PD, OC heights, lens type, frame style.

2. Are the basics correct?

  • Pupillary Distance (PD): Does the optical center line up with where the patient’s eyes naturally look?
  • OC Height: Is the prescription sitting where it should vertically?
  • Lens Wrap: Is it a wrapped frame? If so, did someone add the compensating prism?
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How Wrap Frames Add Prism

Some people love the look of wrap frames, but they change the optical geometry. When you curve a flat lens around the face, the visual axis shifts outward. To fix that, the lab adds compensating prism to keep the prescription lined up with the eye’s natural sightline.

If that compensating prism is missing, the eyes feel like they’re “pulling” - a classic prism complaint.

Refraction Matters, Too

Sometimes the issue isn’t just the lens, it’s the refraction itself:
If the patient has anisometropia (big difference in power between eyes), tiny OC errors can create big prism imbalances

For similar powers (like +2.00 and +2.00), small OC shifts usually cancel out

For a big power difference (like +4.00 OD, plano OS), those same small OC shifts can cause big problems

What About Prism in One Eye Only?

If the doctor specifically prescribed prism in one eye, they likely had a good reason. But sometimes, splitting the prism between both lenses makes the glasses more balanced and comfortable. Always confirm if the split is okay before changing the doctor’s intent.

The Bottom Line

Prism issues in single vision lenses are often simple, but easy to overlook.

Always double-check:

  • PD and OC height
  • Lens design and wrap compensation
  • Refractive balance between the eyes