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Freshnel prism final
- 2. In 1822, AugustinFresnel, a French engineer, articulated the principle of Fresnel optics A prism's angle of refraction depends only upon the angle of the surfaces and the index of refraction of the material of which the prism is made. The angle of refraction is independent of the prism's thickness. Fresnel lens
- 3. Fresnel lens THE FRESNELPRISM PRINCIPLE A Fresnel prism, much thinner than a conventional ophthalmic prism of the same power, can be imagined to be a series of small plastic prisms lying adjacent to each other on a thin platform of plastic.
- 4. Fresnel Prism sheet,is a thin transparent plastic sheet, with one face consisting of a series of angular grooves. Figure 1 compares a conventional glass. Ophthalmic prism to a Fresnal prism sheet. This diagram demonstrates how the application of the Fresnel Prism provides a thin, light weight lens with the comparable power of a thicker conventional ophthalmic prism. Fresnel lens
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- 6. Compares a conventionalglass. Ophthalmic prism to a Fresnel Prism.
- 7. IndIcatIons for Useof fresneL Lens Ocular Motility Disorders Condition Function of 3M Press- On Prism PHORIAS Fusion disruption causes eyes to deviate. Hence promotes fusion & reduces deviation.
- 8. Ocular Motility Disorders ConditionFunction STRABISMUS Early onset Strabismus Mild Amblyopia Preoperative prism adaptation enhances surgical outcome or establishes fusion non-surgically. Applied over the preferred eye as a weak patch. IndIcatIons for Use of fresneL Lens
- 9. Ocular Motility Disorders ConditionFunction of 3M Press- On Prism Nystagmus Can allow the patient to assume a more normal head position to find the null point of the nystagmus. Prisms with the base away from the direction gaze preference can allow the eyes to rotate into position without a large head turn. Redirects the visual gaze toward the field of minimal tremor. IndIcatIons for Use of fresneL Lens
- 10. Ocular Motility Disorders ConditionFunction of 3M Press- On Prism Incomitant strabismus Applied over part of a lens to allow correction in specific gaze positions. For incomitant strabismus, which demands different prism power in certain fields of gaze, Prisms can be easily cut and placed on spectacles for correction where needed. IndIcatIons for Use of fresneL Lens
- 11. Ocular Motility Disorders ConditionFunction of 3M Press- On Prism 3rd, 4th, and 6th nerve palsies; resulting from recent-onset strabismus (e.g., Stroke, ocular muscle paresis, systemic disease). DIPLOPIA* Allows binocularity during recovery period. May be changed as muscle function returns which may recover with time IndIcatIons for Use of fresneL Lens
- 12. other MedIcaL IndIcatIons Condition Functionof 3M Press- On Prism Bed-ridden patients Cannot elevate head to read or watch television Base-down prisms on both lenses change image's angle
- 13. for Use InrehabILItatIon of head traUMa and stroke PatIents For Neglect Side: Fresnel prisms can be placed with the base towards the patient's neglect to make the patient more aware of the neglected side. Also for patients who tend to lean toward one side, placing the prism base in the direction of the inappropriate posture can help alleviate some postural deficits related to vestibular movements.
- 14. other Uses Bifocal wearerswith vertical anisometropia can read with comfort using this prism. For patients with hemianopsia or a large scotoma, apply a Fresnel prism several degrees off the central gaze with the base toward the non-seeing eye. To help low vision patients with high-prescription binocular adds.This approach helps avoid large decentration of the segments or other related problems, such as near point field of view limitation or the need for prism-controlled segments.
- 15. Lens Selection Before finalisingthe prescription try several powers at various angles. Better outcome is achieved if the prism is applied to only one lens. For correction of certain types of diplopia, you have the choice of applying different strength optics to each spectacle lens. In conditions such as nerve palsies, this adjustment is necessary to address down-gaze, up gaze or lateral gaze.
- 16. Fresnel Prism TrialSets 7 Rings per set TS 4000: 2^, 3^, 4^, 5^, 6^, 8^, 10^ or TS 5000: 12^, 15^, 20^, 25^, 30r^ 35^, 40^
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- 18. How to ApplyFRESNEl pRISMS Place the frsenel prism lens on the carrier lenses in the desired direction and cut the fresnel lens nearest to the size of the carrier lens. Then make careful cuttings on the fresnel lenses so as to match the carrier lens in the size. It is important to match the optical centre of the fresnel lenses with that of the carrier lenses in case of sphere fresnel lenses. The optical center is the smallest concentric ring. The base orientation of the optic is indicated with the word "base." The smooth surface should face the inside surface of the spectacles. Align the optical center with the mark on the spectacles. Gently shape to the desired location.
- 19. How to ApplyFRESNEl lENS With the Spectacle Lens Out of Frame : With scissors, cut the Fresnel prism as close as possible to the size of the carrier lens. With a razor blade held at the angle of the bevel, carefully trim optic flush with the beveled edge of the spectacle lens. It is now ready to be applied. Reinsert into frames.
- 20. With Spectacle LensIn Frame: With a felt-tip pen, trace the shape of the spectacle lens onto the Fresnel prism just inside the rim of the frame. Remove the Fresnel prism from the spectacle lens and carefully cut out the inner line. It is now ready to be applied. How to Apply FRESNEl lENS
- 21. Attachment of FresnelPrism sheet onto Spectacle Lens Wash both the spectacle lens and the Fresnel prism with a weak solution of liquid dish detergent (free of lotion) to remove grease and soil. Rinse thoroughly. Submerge the spectacles and Fresnel prism in a bowl of warm water or under a stream of running water. Wipe away any air bubbles clinging to either surface. Position the Fresnel prism with the smooth side toward the inside surface of the spectacle lens from the water, holding the Fresnel prism in place. Adjustments can be made by sliding the Fresnel prism Press dry.
- 22. Inspect the edgesof the Fresnel prism so no overlapping occurs on the spectacle frames. Remove and re-apply if dust particles or air bubbles Advise patients to handle spectacles gently for 24 hours following application. Faint, gray patches that may develop are temporary and usually disappear as drying is completed. Alcohol is not recommended for repeated application of the optics.
- 23. Cleaning proCedure forfreSnel lenS: Do not remove Fresnel prism from spectacle lenses for cleaning. Rinse spectacle lenses under a gentle stream of warm running water. If contaminants remain after rinsing, use a brush to clean grooves. Pat or blot dry with a soft, lint-free cloth. Follow any special cleaning procedures as instructed by your eye care specialist. For proper care of your Fresnel prism , use the above procedure often.
- 24. TAKE AWAY MESSAGE!! A simple, therapeutic, inexpensive way to correct several visual disorders. An immediate correction. A more comfortable, more cosmetically appealing treatment for strabismus than conventional prisms. An optic that adds no noticeable weight or thickness to the spectacle. Useful in treating temporary and/or variable visual problems without damage to the patients' spectacles. Easy maintainence.