Freeform Software
Crossbows can provide freeform software for the production of finished
progressive lenses from semi-finished spheres where the progressive surface
is machined on the concave side and incorporates the patient's prescription.
This software can produce two designs Custom 14 and Custom 18 in 1.00
to 3.00 additions and 1.498, 1.56, 1.60 and 1.67 indices. Details of the
designs are shown below. File outputs can be generated for a range of
freeform equipment including machinery from Schneider, Optotech, Satis-LOH,
Gerber Coburn, DAC and VCA standard output.
Benefits of Back Surface Progressives:
- Premium products at reduced costs - only requires a stock of semi-finished
spheres in each material. Not restricted to purchasing semi-finished
spheres from Crossbows.
- Progressive on the back surface to maximize fields of view in the
corridor and reading areas
- Patients distance correction is incorporated into the progressive
design to improve accuracy of prescription
- Two corridor lengths available (14 and 18mm) to suit a wide variety
of frame sizes. Corridor lengths are measured from fit point to centre
or reading reference circle i.e. to 100% of full add power, unlike some
of our competitors
- Wide cylinder free distance and reading areas
- Ability to be integrated with VCA compliant Lab Management Systems.
- Technical support available at no extra charge.
Crossbows Freeform Designs:
Crossbows can offer two different progressive designs.
You can choose to use these brand names or if you wish you may market
the lenses under your own name. Details of the designs are shown below.
Crossbows Freeform Custom 14
Custom 14 Features of design
- Short corridor (14mm to full addition power)
- Minimum fitting height of 15mm
- Low distortion soft, aspheric design
- Individual designs for left and right eyes
- Moulds in 1.498, 1.56, 1.60 and 1.67 indices
The Custom 14 progressive is designed specifically for frames with small
eye sizes. This is achieved in a soft design without compromising the distance,
corridor and reading areas.
Design Marking Details for Custom 14 Lenses
Note: The decentration on these lenses is variable.
Crossbows Freeform Custom 18
Custom 18 Features of design
- Low distortion soft design
- 18mm corridor length to full addition power
- Minimum fitting height of 19mm
- Wide usable corridor
- Individual designs for left and right eyes
- Moulds in 1.498, 1.56 and 1.60 indices
The Custom 18 design with its low rates of change and levels of astigmatism
provides good dynamic vision combined with generous intermediate and reading
areas. Maximum astigmatism is located on the nasal side where most of
it will be edged away.
Design Marking Details for Custom 18 Lenses
Note: The decentration on these lenses is variable.
Software Features
The Crossbows freeform software is simple to use and can be run in two
different modes. It can act as a standalone program which can provide
a simple interface for entering freeform prescriptions and will produce
output files for the machines mentioned above. It can also be run as a
server program and this can be integrated with a suitable Laboratory Management
System to function automatically. The software is compliant with latest
VCA freeform standards.
- Optimisation of centre and edge thicknesses can be carried out in
a number of ways depending on the information available: No Frame Information
- where the prescription is calculated for a circular or elliptical
blank of specified dimensions.
- Frame Box Dimensions - where the user enters the frame box dimensions,
fitting dimensions and blank dimensions. The centre and edge thicknesses
are then optimised using this data.
- Frame Digitized Data - where the frame tracing information is available
in a file. In this case the user only has to enter the file name and
fitting information. The centre thickness, edge thickness at the frame
shape, edge thickness at the crib shape and the crib dimensions are
then optimised using this data.
Examples of the data input screens are shown below. Click on the pictures
for a larger image.
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