Use of Peli prisms to expand visual field and prisms to

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
• Only high power
available 57∆ and
expands field by 30°.
• The prism base is
rotated by 25°.
B
Horizontal
Prism
B
Oblique
Prism
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