Article Date: 8/1/2002

contact lens case reports
Computer-assisted Toric Soft Lens Fitting, Part 1
BY PATRICK J. CAROLINE, FCLSA, FAAO, & MARK P. ANDRÉ, FCLSA, FAAO

Figure 1. The ToriTrack vertexes the spectacle Rx and calculates the effective K.

Throughout the years, significant controversy has surrounded the correct calculations required for toric soft lenses. Only recently have new algorithms been developed to calculate the complex cross-cylinder effects often associated with these lenses. One such program is CooperVision's new ToriTrack system.

ToriTrack features a traditional menu for vertexing the spectacle Rx to the corneal plane as well as a new system for calculating cross-cylinder effects. This new system utilizes data from the manifest refraction, the lens on the eye and the sphero-cylinder over-refraction to determine the direction and amount of lens rotation. The final lens powers are calculated from this data. The program also assists with lens design and ordering and stores patient data to simplify the task of adjusting the lens on follow-up visits. In our next two case histories, we will share with you some of the ToriTrack features we have found useful in our practice.

Patient DP

In past columns we've described how corneal diameter influences overall sagittal height of the cornea. One case illustrating this was DP, referred to us due to multiple failures with soft contact lenses. Despite a K reading of 40.00 diopters, DP's excessively large 13.0mm cornea ultimately required an extremely steep soft lens with an 8.3mm base curve and a 15.0mm diameter.

Figure 2. The ToriTrack lists the lens parameters of the recommended CooperVision toric soft lens.

When we enter DP's data into the ToriTrack program, it automatically adjusts the spectacle prescription to the corneal plane. Additionally, the ToriTrack combines the patient's central keratometric reading and corneal diameter measurements to calculate an effective K value (estimation of sagittal height), in this case equivalent to 46.00 diopters (Figure 1). When you select the "next" icon, a list of available CooperVision lenses, which match the patient's HVID, estimated sagittal height and Rx, is displayed (Figure 2). You can place the empirical lens order online directly from the screen on the desktop version of ToriTrack.

ToriTrack is available on CD-ROM or for the Palm Pilot at www.coopervision.com. In Part 2 we will describe the calculator's unique system for identifying axis rotation and calculating cross-cylinder effects. 

Patrick Caroline is an associate professor of optometry at Pacific University and an assistant professor of ophthalmology at the Oregon Health Sciences University. Mark André is director of contact lens services at the Oregon Health Sciences University.

 


Contact Lens Spectrum, Issue: August 2002