Use of Peli prisms to expand visual

field and prisms to support reading and

avoid diplopia (double vision)

Dr. Karthikeyan Baskaran, PhD.

Krister Inde

Prisms for Hemianopia

• Peli peripheral prism for field expansion.

• Yoked prism of 10∆ or more for reading.

• Prisms can be used to restore binocular single

vision in patients with diplopia after brain injury.

Peripheral Prism Horizontal Design

• Permanent prism segments on upper and lower parts of

the spectacle lens with 12mm inter-prism separation.

• Users always look through central prism-free area.

• No central diplopia and minimal peripheral diplopia.

• Two prism powers available 40∆ & 57∆ (monocular).

Prisms on left lens base out for left hemianopia

Visual Field Expansion

• Binocular visual fields – Left hemianopia

• Without peripheral prisms With 40∆ peripheral prism

• Upper & lower field expanded laterally by about 20°

Peripheral Prism Oblique Design

B

B

Horizontal

Prism

Oblique

Prism

• Only high power

available 57∆ and

expands field by 30°.

• The prism base is

rotated by 25°.

In-office training

• Demonstration of expansion effect– Binocular confrontation visual fields

• Head turning

– Fixate objects detected via prism image through the clear carrier

section

• Reach-and-touch exercise– Familiarization with shifted directions of objects

Home training instructions

• Wear prism glasses as much as possible

– Except driving and extended reading

• Practice to use it first in familiar environments

• Gradually expand range & complexity

– Always have a companion when expanding range first

• Practice reach and touch exercises

– Use head movement when not exercising

Yoked prisms for reading

• 10 ∆ or more yoked prism can be prescribed for reading

purposes.

• Especially useful for patients with right homonymous

hemianopia.

• A set of right bases can be used with right eye having

base out and the left eye having base in prisms.

• The image would be shifted to the left side of the field

where the patient can see.

Prisms for Diplopia

• Prism power depends on amount of diplopia

• Usually Fresnel stick on prisms are prescribed– Pros:

• Effective in temporary situations.

• Cost effective (lower cost than ground prisms)

• Useful when deviations vary from distance to near

• Can be applied on existing spectacles

– Cons:

• Degradation of visual acuity in distance

• Increased optical aberrations

• Loss of contrast and light scatter in larger Fresnel prism

• The grooves are not cosmetically appealing

• Can be made as ground in-prism as well.

References

• http://serinet.meei.harvard.edu/faculty/peli/index.html

• http://www.hemianopia.org/index_files/Hemianopicproductgui

de.htm

• http://www.chadwickoptical.com/index_files/otherhemianopic

products.htm