Drill-mount frames are still popular with patients. And with many styles of lenses to choose from, we receive many questions about what would be best for the patient.
The advent of digital progressives and single vision lenses has dramatically helped provide solutions for lenses that were not previously available for drill mount applications. For example, you could not find a Trivex, polarized progressives only a few years ago. Now, there are several optional designs with different features that are perfect for this type of frame.
Based on our experience and the release of several new materials, we would like to offer the following guidelines for producing the best possible product using the latest technology:
Trivex 1.53 Index
This material combines the best attributes of polycarbonate and CR39. Trivex is lighter than polycarbonate and offers superior optics with great strength! With an abbe value of 43, it is far better than polycarbonate with only a 29. It can be ordered in a 1.0mm center thickness for non-antireflection coated prescriptions or 1.3mm with coating. It soaks up tint and has a strong hard-coat to reduce scratches. It is great for drilling and polishes to a beautiful “jewel-like” luster. Trivex is very heat resistant and maintains its original shape in a variety of conditions and comes with UV. Meeting ANSI Z87.1, this material has the strongest impact resistance and is great for children. Unaffected by common household chemicals (including acetone), this material will become the standard. Since it is a 1.53 index, we recommend it in prescriptions up to +/- 4 for most drill mounts.
With proper care, our drill mount service comes with a 1 year warranty when prescribed in any of the recommended materials, except poly.
1.70 High Index
1.70 is highest index material that can be used successfully in drill-mounts. These are super thin in design, usually a 1.2 centers on minus.
1.67 High Index
There are many single vision and multi-focal lenses available in 1.67 index. However, only products using MR10 resin should be considered. This monomer is strong enough for drill mounts and has the tensile strength to withstand normal pressure. It is available in both clear and Transitions in many different types.
Polycarbonate (1.59 Index)
This is a good choice but there are some tradeoffs. Optically, polycarbonate has very low abbe value (27) and some patients experience problems adjusting to the “birefringence” or distortion. It is lightweight, relatively inexpensive, and can be ordered with a 1.0mm center thickness. However, polycarbonate tends to stretch, causing the screws to loosen with wear. It is also very sensitive to some chemicals and will react poorly over time. We have seen some Rx’s returned with small cracks and crazing around the drill holes. This should be the least preferred material.