Contact Lens Fitting Tool

There are many hundred types of contact lens materials and designs available to the contact lens practitioner. Manufacturers of these lenses usually specify criteria for fitting their lenses based on the metrics of the patients' corneas, the prescription and various other factors. Most practitioners also develop their own criteria and preferences based on experience and clinical judgement.  With so many lens designs and fitting criteria, it is impossible to devise a generic algorithm that will calculate exact parameters for every patient and every lens type.

However, it is possible to provide a useful starting point in most cases.  The Contact Lens Tools originally formed part of the Optometric ToolBox and employ algorithms originally devised by David Campbell-Burns for Cantor and Nissel. These algorithms have been shown to provide a useful starting point for fitting most patients. However, practitioners are expected to exercise their clinical judgement and apply the specific criteria recommended by lens manufacturers before ordering lenses.

The Contact Lens Fitting calculator is shown by selecting Tools ...Contact Lens Fitting calculator from the menu on the Floating Control toolbar.

Spectacle Rx

Enter the patient's prescription by clicking on the various elements of the prescription then using the mouse-wheel to dial up a value. The program will automatically calculate the mean sphere in the plane of the spectacles (MS Specs) and the eye (MS Ocular), taking account of the Vertex Distance specified.

Keratometry

Enter the k readings for each eye in the same way. The program will then calculate the equivalent power along the principal meridians (F1 and F2) and the Corneal Astigmatism.

Rigid Gas Permeable

If RIGID GAS PERMEABLE is selected, the program will calculate a specification for a RGP lens including a Back Optic Zone Radius (BOZR), a Total Diameter (TD) and the power of the lens (Rx). This will provide a starting point for fitting a patient with RGP lenses. Practitioners are expected to refer to the fitting criteria specified by the manufacturer and apply their clinical judgement before ordering a lens.

Soft Spherical

If SOFT SPHERICAL is selected, the program will calculate a specification for a soft lens including a Back Optic Zone Radius (BOZR), a Total Diameter (TD) and the power of the lens (Rx). This will provide a starting point for fitting a patient with soft lenses. Practitioners are expected to refer to the fitting criteria specified by the manufacturer and apply their clinical judgement before ordering a lens.

Soft Toric

If SOFT TORIC is selected, the program will calculate a specification for a toric soft lens including a Back Optic Zone Radius (BOZR), a Total Diameter (TD) and the power of the lens (Rx). This will provide a starting point for fitting a patient with toric soft lenses. Practitioners are expected to refer to the fitting criteria specified by the manufacturer and apply their clinical judgement before ordering a lens.