Aug
2008

Rimless and Wrap

Lenses, Designs, Materials and Compatibility

  • It is important to know the compatibility of lens materials when selling and ordering rimless eyewear. Here are some guidelines
  • Lens material – know the drillability
  • Manage prescriptions correctly
    • Standard curve frames (4, 6 base)
      • No Rx changes, order as other frames
      • Fit to PD and height as required
    • 8, 9 base frames
      • Since the lens is tilted around the vertical axis, the Rx must be compensated for the prism induced and this is required for plano and prescription powers
      • Even better compensate the Rx also
    • Plano wrap sunwear
      • Use prismatic planos

Be sure to know the material characteristics of the lenses used because they contribute to the overall effectiveness of materials as rimless options

  • Impact resistance – choose highly impact resistant materials, this is often a function of flexibility
  • Tensile strength – this is the stretch-ability of the material and affects the long term size of the drill hole
  • Flexural strength – allows for the daily stresses placed on the lens and frame combination
  • Compression stress and creep -  affects the surface shape changes of a material; for example, a too tight mounting on poly lenses will loosen faster if overly tightened
  • Notch sensitivity - is the resistance to cracking and splitting or the overall susceptibility to cracks after drilling; it is the formation of micro-cracks that can become star-cracks. Cracks in highly notch sensitive materials result in broken lenses, low notch sensitivity results in star cracks or slowly moving cracks

Star Cracks Are Caused by:

  • Lab processing if a dull drill or too fast drilling occurs, no chamfering of holes and leaving out any bushings or washers
  • Dispenser caused if using acetone or loctite
  • Consumer caused by household solvents or nail polish remover

Ordering Wrap Prescription Rimless Eyewear
Prescriptions change when tilted and some wrap frames tilt lenses more than 18-20°. This creates prism and a power change. Therefore, to make the glasses wearable, one must order with the lenses with a compensating prism and even better, order an Rx compensated for the tilt or wrap angle.

Steps

  • Order an 8 base lens in the lens design required. In single vision, consider SOLA Spazio or KbCo polarized lenses which have special surfaces for the requirements of wrap Rx’s. Consider softer design progressives like Varilux Physio or Carl Zeiss Vision SOLAOne.  Younger Image is available in a true 8 base and is spherical in design. Also consider the new Shamir Genesis or Piccolo with Attitude where the periphery of the progressive has been modified for extreme wrap angles 
  • Must - Compensate the prism (for powers -6 to +4 at an average wrap angle of 18-20 degrees)
  • For powers <±2.50D, order with 0.2 ∆BI in each eye
  • For powers >± 2.50D, order with 0.3 ∆BI in each eye
  • Better - Compensate the power
  • Download the Rx Compensator fro Opticampus.com at http://www.opticampus.com/tools/tilt.php
Check the Rx in the “as-worn” position and it should be the prescribed Rx.  Good luck.









 

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