This photograph shows Single Vision lenses in the higher prescription range. With minus prescriptions, the lens edges are thicker than the centres, with plus corrections, the centres are thicker than the edges. With very high plus corrections, 'low-volume' masks are not advised, as the thicker lens centres can come into contact with the eyelashes. Again, the amount of aperture filled by the prescription lens is dependent on any individual's optical centres ( PD )

People frequently express concerns as to what prescription glazed, bifocal masks actually look like... worrying that there will be 'joins' across the middle of the lens, where two pieces of glass meet. Whilst this used to be the case, these days, nearly all bifocals are glazed using fused 28mm D-segment lenses. As you can see from the photograph below, of a Mares X-Vision mask, the bifocal segments are barely discernable and almost invisible to the camera.

 

We are also asked whether corrective lenses replace the masks original glass faceplates. The short answer is 'no they don't'. The reason is simple... The largest, flat-fronted lens blanks available for us to work with are 65mm in diameter, so there simply isn't enough glass to cut to the shape of the mask's lens apertures - especially as we are also governed by each customer's optical centres ( PD ).

Moreover, many masks do not have removable lenses. Some mask manufacturers do supply replacement lenses with correction, but these come in a limited range of prescriptions, with no correction for astigmatism and in half dioptre increments only.

All our prescription lenses are permanently, UV bonded to the inside surface of the mask's original, plain glass faceplates. This is the only way precise prescription glazing can be achieved.