The insert sits very close to your eyes but works well. The issue I have is the perscription does not seem to be the same as the new eye glasses I had made up using the same perscription.
Sports sunglasses with this type of Rx adapter are rare. A viable option if cost is an issue, or you want to switch out the tinted main lens, or have a need for a progressive/bifocal prescription. These fit the Defender well- they are quite a low profile (a concern when I ordered), and the Defender's nose bridge can be adjusted outward so they fit without eyelashes brushing the Rx lens, it however will push the glasses themselves a couple of mm further out. Still the fit is excellent. Rimless means that peripheral transitions fade to nothing.
The one concern I found is that I did need the help of a computer repair scribe to nudge the adapter into place.
First pair of prescription shooting glasses and these are great. Perfect fit and finish. Prescription requirements were perfect.