Resistance of plastic ophthalmic lenses : The effect of base curve on different materials during static load testing

Resistance of plastic ophthalmic lenses : The effect of base curve on different materials during static load testing

This study was designated to evaluate, through a static load test, the influence of lens base curve on the fracture resistance of three common plastic materials. A JJ Lloyd load cell machine was used to test the fracture resistance of -4.00 D spherical lenses. The samples had a nominal center thickn...

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Bibliographic Details
Published in:Optometry and vision science Vol. 78; no. 7; pp. 518 - 524
Main Authors: MOHAMADOU LAMINE DIALLO, SIMONET, Pierre, FRENETTE, Benoit, SANSCHAGRIN, Bernard
Format: Journal Article
Language:English
Published: Hagerstown, MD Lippincott Williams & Wilkins 01-07-2001
Subjects:
Biological and medical sciences
Diseases of the eye
Eyeglasses - standards
Materials Testing - methods
Medical sciences
Optics and Photonics
Pressure
Prosthesis Design
Radiotherapy. Instrumental treatment. Physiotherapy. Reeducation. Rehabilitation, orthophony, crenotherapy. Diet therapy and various other treatments (general aspects)
Safety
Stress, Mechanical
Weight-Bearing
Human
Evaluation
Lentil
Instrumentation therapy
Fracture mechanics test
Spectacles
Plastic material
Mechanical properties
Spherical lens
Strength of materials
Static load
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Summary:This study was designated to evaluate, through a static load test, the influence of lens base curve on the fracture resistance of three common plastic materials. A JJ Lloyd load cell machine was used to test the fracture resistance of -4.00 D spherical lenses. The samples had a nominal center thickness of 2.0 mm and a base curve distributed in one of five groups (+0.50, +2.50, +4.50, +6.50, and +8.50 D). The lenses were manufactured in CR39, polycarbonate, and TL16, a high refractive index plastic (n = 1.599). The lens base curve influenced fracture resistance for all materials. For these materials, resistance increased as the base curve varied from +0.50 to +8.50 D. The resistance of CR39, TL16, and polycarbonate lenses was found to be linearly dependent on lens base curve. The effect is stronger for polycarbonate. Fracture resistance was higher for TL16 than for CR39, and polycarbonate was much more resistant to breakage than the two other materials. For a given power, the fracture resistance of an ophthalmic lens is reduced when its base curve has a low value. Consequently, the flattening of ophthalmic lenses for cosmetic purposes is not recommended as far as fracture resistance is concerned.
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ISSN:1040-5488
1538-9235
DOI:10.1097/00006324-200107000-00015