Prism Glasses

Prism glasses contain special lenses that bend light, shifting the image seen by one eye to align with the other. They're used to treat double vision from various causes.

How Prisms Work

• Light is bent toward the prism's base
• The image shifts in the opposite direction
• Both eyes see images in the same location
• Brain fuses images into single vision

Types of Prisms

Ground-In (Permanent) Prisms

• Prism incorporated into lens
• Best optical quality
• For stable, long-term deviations
• Look like regular glasses

Fresnel (Stick-On) Prisms

• Thin plastic sheet adhered to lens
• Can be changed easily
• Useful for temporary or changing deviations
• Slight reduction in clarity
• Good for trials before permanent prisms

Common Uses

• Cranial nerve palsies (third, fourth, sixth)
• Post-stroke double vision
• Thyroid eye disease
• Decompensating childhood strabismus
• Visual field defects (in some cases)

Limitations

• Only work for certain amounts of misalignment
• Large deviations may need surgery
• Prisms can be thick and heavy
• May not help if deviation changes with gaze direction
• Not suitable for all causes of double vision

What to Expect

Fitting

• Based on prism and cover test measurements
• Trial with Fresnel prism often done first
• Adjustment period may be needed

Adaptation

• May feel strange initially
• Brain adapts over days to weeks
• Report any concerns to doctor

Follow-Up

• Check if still working
• Adjust if deviation changes
• May eventually need surgery