MULTIFOCAL IOL BIOMETRY
Varying designs and differing near additions among available multifocal intraocular lenses (IOLs) complicate preoperative prediction of individual patients outcomes. To seek clarity on this issue an international collaborative group conducted an experimental study to calculate the near focal distance of different multifocal IOLs, as a function of the two parameters that are measured before cataract surgery: axial length and refractive corneal power (keratometry [K]). Investigators calculated the IOL power for emmetropia in an eye model with the axial lengths ranging from 20 to 30mm and K from 38 to 48 dioptres. They then calculated the predicted myopic refraction for any given IOL add power (from +1.5 to +4.0D). From this value the near focal distance was obtained. Calculations were also performed for the average eye (K = 43.81D; AL = 23.65mm). This revealed that the near focal distance increased with increasing values of keratometry and axial length for each near power add. Longer eyes with steeper corneas showed the longest near focal distance and could experience more difficulties in focusing near objects after surgery. The opposite was true for short hyperopic eyes. Since the effective lens position is predicted from the preoperative keratometry and axial length, the surgeon can use these parameters preoperatively to estimate the near focal distance, the study concludes. G Savini et al, JCRS, “Influence of the effective lens position, as predicted by axial length and keratometry, on the near add power of multifocal intraocular lenses”, Volume 42, Issue 1, 44-49.
Nearly one half of eyes having cataract surgery are believed to have corneal astigmatism greater than 1.0 dioptre, with more than 10 per cent having greater than 2.0D of cylinder. Intrastromal astigmatic keratotomy (AK) provides a safe and effective approach to astigmatic correction during cataract surgery, without additional cost, report researchers from Moorfields Eye Hospital, UK. The study included 196 eyes of 133 patients undergoing laser cataract surgery with concurrent astigmatism management by intrastromal AK. All eyes had greater than 0.7 corneal dioptre cylinder. The mean correction index was 0.63 ± 0.32 (range 0.00 to 1.93), indicating that the mean astigmatism correction was 63 per cent. Fourteen eyes (7.1 per cent) and seven eyes (3.6 per cent) had an astigmatism correction of greater than 100 per cent and greater than 120 per cent, respectively. Overall, 0 per cent, 48.5 per cent, and 51.5 per cent of eyes had 0.50D or less, 1.0D or less, or greater than 1.0D, respectively, preoperatively compared with 32.1 per cent, 85.7 per cent, and 14.3 per cent, postoperatively. There were no cases of corneal endothelial perforation or inadvertent placement within the visual axis. Further understanding of the factors influencing femtosecond laser intrastromal AK efficacy are required to optimise outcomes, the researchers note. A Day et al, JCRS, “Nonpenetrating femtosecond laser intrastromal astigmatic keratotomy in eyes having cataract surgery”, Volume 42, Issue 1, 102-109.