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LB Szczotka, C Roberts, A Mahmoud, E Herderick; Soft Toric Fitting Nomogram Based on Topographic Corneal Shape Descriptors . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3077.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:Quantitative topographic descriptors previously generated as potential variables in predicting soft toric fitting success were incorporated into a new soft toric fitting nomogram. The nomogram was then prospectively evaluated for empirical fitting of soft toric contact lenses. Methods:Videokeratography was performed with the Humphrey Atlas (v. A6) instrument on 82 eyes of 41 patients. The raw data files were downloaded to the OSU Corneal Topography Tool and analyzed for specific quantitative descriptors of shape and astigmatism that were previously determined to predict success or failure of the manufacturer’s standard fitting nomograms. Up to 3 pairs of a back surface toric, prism ballasted, soft contact lens (tetrafilcon A, Preference Toric) were ordered and evaluated in a masked fashion for each patient which varied by the nomogram used to select lens base curve and power. The nomograms tested were: N1. original Preference Toric nomogram, N2. ToriTrack nomogram utilizing corneal HVID, and N3. topographic based nomogram. Results:75 eyes were available for analysis. Success rates with the first trial lens (for eyes that could be ultimately fitted) were N1: 42%, N2: 33%, N3: 60%. 67/75 (89%) eyes were ultimately successful after unsuccessful trial lenses were adjusted and reordered. N3 selected base curve appropriately in 51/67 (76%) eyes that were able to be fit into the Preference Toric lens compared to N1 and N2 which had success rates of 63% and 63%, respectively. N3 selected power appropriately in 53/67 (79%) eyes compared to N1 and N2 which had success rates of 66% and 58%, respectively (p<0.05). Conclusion:A new topographic based soft toric fitting algorithm improves the empirical selection of base curve and power compared to published nomograms which utilize keratometry data.
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