Exploring faster defocus curve measurements

Purpose: To investigate the effect of reducing the number of visual acuity (VA) measurements made in a defocus curve on the quality of data quantified. Setting: Midland Eye Institute, Solihull, UK. Methods: Defocus curves were constructed by measuring VA on a distance logMAR letter chart, randomising the letters between lens presentations. The lens powers evaluated ranged between +1.50 and -5.00 dioptres (D), in 0.50-D steps and were presented in a randomised order. Defocus curves were measured binocularly for 15 patients implanted with the Tecnis multifocal (mean age 61 ± 11 years), 15 patients implanted with the ReZoom multifocal (mean age 62 ± 8 years) and 15 patients implanted with the FineVision trifocal (mean age 65 ± 6 years) intraocular lens (IOL). Curves fitted using 0.50-D steps, 1.00-D steps, 1.50-D steps and a near addition specific profile (i.e. distance, half the near addition and the full near addition) were compared. Results: For the two bifocal IOL designs (Tecnis and ReZoom), all the methods showed close agreement. However, for the trifocal IOL design, the reduced-point-strategy curve profiles all differed significantly (p <0.01) from the 0.50-D step defocus curve. Conclusions: Faster methods of capturing defocus curves from bifocal IOL designs appear to be valid. Obtaining rapid defocus curves would be beneficial in reducing patient fatigue or for allowing additional defocus curve measurements to be performed in different luminance conditions or with low-contrast letters.