Soft toric lens power accuracy and reproducibility

Lens power accuracy is the most frequently cited requirement for reproducible soft toric lens performance. Power accuracy is even more critical with planned replacement soft toric lenses because of the increased rate at which lenses are replaced. However, no reproducible methodology exists for making such an evaluation. We developed a power measurement method from which measurement error was eliminated. Geometric optical calculation was used to calculate the resulting optical error. The relationship between visual acuity loss and optical errors was used to predict the effect on visual acuity. This method was applied to a sample of 457 Focus Toric soft contact lenses. We found that 83.5 +/- 1.7% of the lenses were accurate enough to deliver one line or less of loss in visual acuity. Our estimate of the clinical problem rate associated with power reproducibility was 3.3 +/- 0.9% of lens pairs. If lenses were replaced on a monthly basis, this would amount to one problem pair every 30 months.