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A Fresnel lens ( / ˈfreɪnɛl, - nəl / FRAY-nel, -nəl; / ˈfrɛnɛl, - əl / FREN-el, -əl; or / freɪˈnɛl / fray-NEL [1]) is a type of composite compact lens which reduces the amount of material required compared to a conventional lens by dividing the lens into a set of concentric annular sections.
The Peli Lens is a mobility aid for people with homonymous hemianopia. It is also known as “EP” or Expansion Prism concept and was developed by Dr. Eli Peli of Schepens Eye Research Institute in 1999. It expands the visual field by 20 degrees.
Prisms or "field expanders" that bend light have been prescribed for decades in patients with hemianopsia. Higher power Fresnel ("stick-on") prisms are commonly employed because they are thin and lightweight, and can be cut and placed in different positions on a spectacle lens.
The provider may prescribe an eye patch to relieve the double vision. The patch can be removed after the nerve heals. Surgery or special glasses (prisms) may be advised if there is no recovery in 6 to 12 months. If diplopia turns out to be intractable, it can be managed as last resort by obscuring part of the patient's field of view.
Also, plastic prisms (Fresnel prisms) can be attached to eyeglasses of a diplopic patient, allowing for alignment of vision from both eyes in the affected direction, but are often problematic if the degree of muscle weakness, and therefore ocular misalignment, fluctuates frequently.
Symptom relief and/or binocular vision maintenance. This is most commonly achieved through the use of Fresnel prisms. These slim flexible plastic prisms can be attached to the patient's glasses, or to plano glasses if the patient has no refractive error, and serve to compensate for the inward misalignment of the affected eye.
- Double-slit experiment - Wikipediawikipedia.org
