Press-On Prisms Fresnel
Press-On Prisms are Fresnel optics that can
be applied to either part of or the entire carrier lens inner surface.
Ultra-thin Fresnel prisms, measuring only 1mm thick, can be cut to fit most
frame sizes and shapes and adhere to existing lenses with only water.
Press-On Prisms provide a simple therapeutic and
inexpensive way to correct several visual disorders. Press On Prism are useful
for bed-ridden patients, Diabetes mellitus, post cataract surgery, symptomatic
phorias, decompensated phorias and low vision. Also used as a fusion stimulus
in other muscle deficiencies.
Fresnel Press-On Prisms offer an immediate correction.
They are more comfortable and cosmetically appealing treatment for strabismus
than conventional prisms. Offering an optic that adds no noticeable weight or
thickness to the spectacle.
They are useful in treating
temporary and/or variable visual problems without damage to the patients'
These ultra-thin Fresnel
lenses are designed for pre- and post-operative trial fittings, inexpensive
vision therapy, during power changes, and for instant corrections on sports
goggles and sunglasses. The lenses, made of polyvinyl chloride, are available
in 1.00D to 40.00D prisms, plus powers to 16.00D, minus powers to 14.00D and
D-25 segs to +6.00D. 3M Press-On Optics, all only 1mm thick, are comfortably
lightweight for patients to wear and can be easily applied to any eyewear,
whether prescription or plano carrier lenses.
The observation that
prisms reduce visual acuity is brought here to attention: the visual acuity of
normal young individuals is reduced in all cases proportional to the strength
of the prism. The reduction in VA was found to be 2% per prism dioptre when
using conventional opthalmic or wafer-prisms and 3% in the case of
The least reduction of
VA is found when using conventional ophthalmic prisms; this reduction however
is not significantly different when using Wafer-prisms of lower strengths. A
significant difference is ascertained between conventional opthalmic and
Wafer-prisms of higher strength and between conventional opthalmic and
Wafer-prisms as opposed to Fresnel-prisms within the range of 5 to 30 prism
The advantage of using
Fresnel-prisms as opposed to Wafer- and conventional ophthalmic prisms is their
low weight, their simple adjustment and being able to change them without
ordering a new correction.
The disadvantage of
Fresnel-prisms as opposed to conventional ophthalmic prisms and Wafer-prisms of
low strength is their poorer optical quality. The visual acuity is reduced to
50% by using conventional ophthalmic wedge prisms of 30 prism dioptres and to
between 30% and 40% when using Fresnel-prisms. Fresnel-prisms are according to
our brief experience a useful optical aid especially in the application of