It is sometimes advisable to increase the edge thickness of plus lenses to glaze rimless frames. If the optician expressly specifies that the order is for a Supra or rimless frame with screw connections, ZEISS will automatically produce a minimum edge thickness of 1.5 mm.
A marked difference between the dioptric powers of the right and left eyes may result in a major difference in lens thickness. For patients with pronounced anisometropia, it is possible to match the front curvature and/or the center or edge thickness of the lens with the lower power to that with the higher power.
Tips for eye care professionals:
If this is required, a comment to this effect should be made on the lens order. If, however, the thickness matching is to be exactly calculated, ZEISS requires the following data:
The same principle used to calculate OPTIMA
For the correction of aniseikonia (different images between right and left eye), ZEISS produces special lenses with an increased curvature and center thickness. In this way it is possible to achieve the required shape factor (effective magnification) and hence improved binocular vision.
Tip for eye care professionals:
"Iseikonic lenses" should be indicated on the lens order.
Single vision lenses without an aspheric front curve can be produced with non-standard curvatures. Lenses with a flatter or greater curvature are usually ordered for cosmetic or fashion reasons. Flatter curvatures can sometimes result in poorer visual quality.
For diving goggles, ZEISS produces special glass plano-convex and plano-concave lenses which are cemented onto the inside of the diving goggles. The range of products available includes both single vision and bifocal lenses for diving goggles.
Tips for eye care professionals:
The goggles should be sent to ZEISS Aalen, Germany, for glazing and include the patient’s centration data and back vertex distance.
For plus lenses, it is often advisable to order a diameter which deviates from the standard diameters given in the price list. In this way, a thinner lens can be produced than with the next highest standard diameter.
Remember: the smaller the diameter, the thinner a plus lens becomes. For single vision lenses, optimized diameters as small as 38 mm are possible. The size of the optimized diameter is selected by the optician so that the lens is as large as required yet as small as possible.
Chemical toughening increases the resistance of glass lenses to breakage (exceptions: ZEISS Single Vision Sph Mineral 1.7, ZEISS Single Vision Sph Mineral 1.8 and ZEISS Single Vision Sph Mineral 1.9). An ion exchange process on the lens surface causes compressive strain which increases the resistance of the lens to breakage. Subsequent coating (AR coating) leads to a reduction in the breaking strength achieved in this process.
ZEISS limits this toughening process to edged lenses in order ensure that a subsequent grinding process does not negatively influence the breaking strength achieved by chemical hardening.
In some countries, the use of thermally toughened glass is more common and it is recommended that safety glasses be purchased as a complete appliance in order to guarantee the effectiveness of the device.
To cover an eye which a patient does not want to be visible for cosmetic or other reasons, all lenses in the ZEISS product range can be frosted on their front surface.
If an eye is to be excluded from vision for medical reasons, this can be achieved with an occluded lens. As the front surface is only roughened, the outline of the eye can still be seen from the outside - unlike frosted lenses.
In some countries, plastic executive or Franklin split lenses are often used to reduce accommodation in children. Executive or Franklin split lenses are special bifocals without image jump which provide a very wide zone for near vision. They are produced by cementing together two lens halves, one the distance portion and one the near portion.
Prismatic lenses are produced "true to prescription" by ZEISS. This means that, during wear, the user experiences exactly the prescribed power in the major reference point of the lens. Due to the different ray path present during measurement in the focimeter, a different value is measured than that ordered. To allow accurate checking with the focimeter, the measured value is printed on the lens packet.
For additions over 6.00 D, magnifying bifocals are preferable to standard lenses.
Further information about: Low Vision Devices
Prismatic effects in the Distance and Near Portions
All bifocal and progressive lenses by ZEISS can be produced with prism by surface tilting. This results in the same prismatic effects for the distance and near portions.
If different prisms are required for distance and near, a prism segment can be cemented onto a Punktal base.
For presbyopic eyeglass wearers whose eyes do not converge in near vision, customized progressive lenses from ZEISS - ZEISS Progressive Individual 2 - can be ordered without an inset. The progressive lenses are then specially computed for this situation. The distance and near reference points then lie directly beneath each other in the vertical axis.
Note for eye care professionals:
These customized progressive lenses are ordered by specifying "Inset 0".