How to Test Ophthalmic Lenses for Abrasion Resistance Transparency and Clarity
This article will discuss some of the standard physical tests performed and the test instruments used to control the quality of ophthalmic lenses. Testing of abrasion and impact resistance, refractive index, UV filtering, light transmission, clarity, haze, and gloss is all utilized in quality control for ophthalmologic lenses. Various physical test instruments ensure these lenses meet stringent optical performance, durability, and safety standards. Here are some key types of test instruments used for these tests.
Scratch Abrasion Testers:
Taber Oscillating Abrasion Tester Model 6160 (ASTM F735, ASTM F903)
The most common abrasion test for ophthalmologic lenses is the Bayer Test or Oscillating Sand Test. The Bayer Test uses a custom specimen holder; you then fill the tray to a uniform depth (e.g., 12.5mm) with a standardized abrasive media such as sand. The sand is moved back and forth across the specimen's surface, creating abrasion. Then, evaluate the surface for haze and scratches by measuring the increase in abrasion of the specimen compared to a reference material, resulting in a Bayer Ratio. The Bayer Ratio measures a material's relative resistance or susceptibility to surface abrasion and scratching. Then, the haze and clarity can be evaluated with the haze-guard i (See Transparency and Haze meter below).
Taber Rotary Abraser Model 1700/1750 (ASTM D1044):
Taber Abraser Model 1700 or 1750 is ideal for assessing the wear resistance of lens coatings by subjecting them to controlled abrasive actions. This ensures that the lenses can withstand daily wear and tear. For ophthalmic lenses, ASTM D1044 is typically the standard used to evaluate surface abrasion resistance using a Taber Abraser.
The test is conducted by mounting the lens in a holder and then abrading it with a rotating abrasive wheel under specified load, speed, and abrasion cycles. Then, the abraded lens is examined for haze and scratches and evaluated for the extent of wear. This abrasion test helps measure abrasion or the abrasion resistance of ophthalmic lenses.
Pendulum Hardness Tester (Modified for Lenses)
While typically used for materials testing, a modified version can be used for lenses. The impact tester tests the lenses' impact resistance by swinging a pendulum with a specific weight to hit the lens at a controlled force. The tester then measures the energy absorbed by the lens before it breaks, providing data on the lens's resistance to impact, which is essential for safety eyewear.
It is important to note that these tests do not simulate all potential sources of abrasion that a lens may encounter in use. Nevertheless, the abrasion tests mentioned are still a viable way to compare the abrasion resistance of different lenses and screen for abrasion-related problems.
Gardner Falling Sand Abrasion Tester (ASTM D968):
The Gardner Falling Sand Abrasion Tester is a viable method for testing abrasion resistance of ophthalmic lenses. This test uses a jet of sand or dust particles to simulate abrasive conditions and evaluate the lens coating's resistance to abrasive particles.
Transparency and Clarity Testing Instruments
Transparency and clarity testing of ophthalmic lenses ensure they provide the intended visual correction and user safety, meet industrial standards, and maintain high quality. These tests help manufacturers to deliver reliable, effective, and durable lenses that enhance vision and the overall experience.
Transparency and Haze Meter:
The haze-gard i haze meter is a valuable tool for measuring the transparency of ophthalmic lenses, making it well-suited for quality control applications in the lens industry. The haze-gard i can also be used to measure the haze of other transparent materials, such as windows and plastics.
In conclusion, abrasion or Bayer testing is a useful way to measure the abrasion resistance of ophthalmic lenses. The haze-gard i, is a valuable tool for measuring the transparency of these lenses. By using both methods, we can more accurately assess the quality of ophthalmic lenses.
If you have any questions about abrasion testing or the haze-gard i, please contact us. We would be happy to assist you.
Spectrophotometer:
A Spectrophotometer analyzes and measures the transmittance and absorbance of light through the lens at various wavelengths. This information is essential for testing UV protection and light filtering properties and ensuring the lens meets clarity and light transmission standards, including UV protection.