1993, 1998, 2004, all rights reserved, Lenstech
LLC
Copyright
1993, 1998, 2004, all rights reserved, Lenstech
LLC
5. 1 Impact Resistance Test: Impact resistance tests are to be performed in accordance with the Federal Regulation on Impact Resistant Lenses (21 CFR 801.410). The following is an abbreviated summary of the impact test:
A 5/8-inch diameter steel ball weighing approximately 0.56 ounces is dropped from a height of 50 inches upon the horizontal upper, convex surface of the lens. The ball shall strike within a 5/8-inch diameter circle located at the geometric center of the lens. The ball may be guided but not restricted in its fall by being dropped in a tube extending to within approximately 4 inches of the lens.
To pass this test, the lens must not fracture. A lens will be considered to have fractured if it cracks through its entire thickness, including a laminar layer, if any, and across a complete diameter into 2 or more pieces, or if any lens material visible to the naked eye becomes detached from the ocular surface. The test shall be conducted with the lens supported by a tube of the required material and dimensions, affixed to a base plate and attached fixtures of the required weight.
5.2 Flammability Test: Completed spectacles, or parts thereof, shall be placed in a preheated oven calibrated and set to 200 degrees C (+/-) 5 degrees C for 15 minutes (+/-) 1 minute. There shall be no evidence of ignition within the specified time period. Deformation or any other deterioration, other than ignition, of the spectacles, or parts thereof, is permitted.
5.3 Cosmetic Quality Test: The test method shall be capable of detecting defects which are visible under actual use conditions. A suggested method is to visibly inspect the lens against a dark background in the light from an open-shaded 40-watt incandescent clear lamp. The lens should be positioned approximately 305 mm (12 inches) from the light source.
5.4 Optical Quality Test
5.4.1 Test for Optical Aberrations: One method of visual inspection is to view a high-contrast grid pattern of alternate dark and white lines while scanning the lens area by area. The lens should be positioned 25 to 30 cm from the eye and the grid pattern should be approximately the same distance in front of the lens.
The image of the grid pattern should appear smoothly curved and gradually distorted with smoothly curved lines toward the lens periphery. In the case of aspheric lenses, there may not be any visible distortion. Sudden ripples or distortions are an indication of a possible optical aberration and should be marked for evaluation using a lensometer as described in 5.4.2.
5.4.2 Lensometer Test, Distortions: Areas that produce distortions using the test of 5.4.1, should be examined with a lensometer having a 5 to 6 mm aperture. Severe lensometer target element distortion or blur is not acceptable and shall be cause for rejection.
5.5 Refractive Properties, Method of Measuring Refractive, Astigmatic and Prismatic Powers: Any standard commonly used lens measuring instrument such as a lensometer or telescope with an aperture size of approximately 5 to 7 millimeters may be used. Individual lenses shall be measured at the geometric center. Mounted lenses or lenses of similar design intended for mounting in a frame shall be measured at the reference points.
5.6 Segment Location Test Method: Measurements should be made with a precision millimeter rule, grid, projection device or any instrument suitable for obtaining accurate measurements.
5.7 Ultraviolet Attenuating Test: The mean ultraviolet transmittances are to be calculated over the spectral ranges of 290 to 315 nanometers (Ultraviolet UVB or erythemal zone) and 315 to 380 nanometers (Ultraviolet UVA or near zone).
A recommended method of obtaining the measurements is to measure the spectral transmittances over the specified spectral ranges with a spectrophotometer. A resolution of not greater than 10 nanometers should be used in obtaining the measurements.
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