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Contact Lens Design and Calculation System

The Idea

The idea on which CALCO is based is the tight integration between corneal topography and contact lens fitting. The purpose is to obtain the maximum advantage from the information of the corneal topographic map to design and optimize the geometry of rigid contact lenses, considering not only the central corneal curve, but also the overall shape of the cornea. The development of existent topographers can nowadays provide complete computerized information to optimize the design of contact lenses.

Expert contact lens fitters are aware of the fact that aspherical geometries may conspicuously improve the comfort and general performance of rigid (gas permeable) contact lenses.

CL fitters who work with aspherical geometries also know that it is impossible to design these kinds of surfaces without other details besides the center curve, and that these details can only be acquired through a topographer or with multiple trials. They are also aware of the fact that it is very difficult to correlate corneal data to the parameters of an aspherical surface, and which eccentricity to select for a bi-conic contact lens for each particular cornea. The rules are very empirical and there is no general guideline.

We believe that the natural evolution of this situation is a computerized system combining the data from the computerized corneal topography and the generation of geometrically optimized lenses for each specific cornea. At the same time, we do not wish to replace the work of contact lens practitioners; rather, we would like to provide the ability to design aspheric contact lenses in terms of fitting parameters instead of having to calculate complex geometries or of empirical trials.

The CALCO system was developed for this purpose.

The CALCO contact lens is the first to have been designed to favor the shape factor, and therefore it is not made of spherical caps. Rather, of an irregular aspherical surface similar to the irregular shape of the cornea under study. This means that the radii of curvature of the base differ from each other. The radius of curvature that results identifies the contact lens and refers only to the central point. Based on the changing eccentricity, the periphery may have very different radii, as is typical of keratoconus. Needless to say, there is no comparison between a Calco contact lens and a traditional one as far as fitting is concerned, and it is not possible to manufacture the Calco CL with traditional lathes, which can only produce regular surfaces.

Calco CLs can only be manufactured with CNC lathes with nanometric resolution run by a dedicated software, which can create a geometry defined by superior mathematics.

In this scenario, the first step in designing a contact lens is deciding the shape of the tear layer (or clearance). This is the means through which fitters can operate on the lens design, instead of having to calculate the geometric parameters (radius or curvature). More specifically, with CALCO the back surface of the lens is an optimized approximation of the shape of the cornea to which the tear layer clearance has been added.

The lens design is therefore controlled thanks to the luminescence of the tear film between the shape of the cornea and that of the contact lens, and not between the corneal radius of curvature and the geometrical parameters of the contact lens. The fitting concept is therefore reversed: fitters choose the best support of the contact lens and the system transforms the selected support into complex parameters that define the final shape of the contact lens.

It is worth observing that this method allows the complete control of the design of the contact lens, and at the same time the best support, or relation with the corneal surface, in other words, of the tear film. This criterion is closer to the fitting philosophy compared to other geometrical parameters (radii of curvature and so on), also in terms of precision. Moreover, working with luminescence (clearance) frees fitters from problems linked to using complex geometric parameters.

It is therefore clear that CALCO is commited to the complete design of distinctively optimized contact lenses, since each lens is based on the special shape of the cornea provided by the link of the corneal topography. Each lens is designed and manufactured for the eye on which it will be fitted.

The corneal map is the first source of information used to shape the lens, and therefore the quality of this map will influence the outcome of the fitting. Keratron and Eyetop topographers have proven to be able to create very accurate maps for optimal fitting results.

To summarize, the design of a CALCO lens includes:

Ensuing advantages: