OBSTACLES TO BETTER IOL POWER CALCULATION
The percentage of cataract patients who are not within 0.5 dioptre of predicted outcome postoperatively ranges from 10 to 20%, and worse for difficult eyes. The second in a series of editorials commissioned by the JCRS to stimulate progress in this area looks at some of the remaining obstacles towards attaining the elusive goal of perfect IOL power calculation. Dr Warren Hill and colleagues note that for those willing to use all available resources in the best manner possible, outcomes have never been better. This would include more advanced vergence formulas and ray-tracing methods, along with approaches that involve hybridisation as well as other non-traditional methods such as artificial intelligence. They discuss the importance of factors such as measurement errors, validation criteria and the use of optimised lens constants.
W Hill et al., JCRS, “Pursuing perfection in IOL calculations. II. Measurement foibles: Measurement errors, validation criteria, IOL constants, and lane length”, Volume 43, Issue 7, 869–870.
POWER CALCULATION IN SHORT EYES
IOL power calculation is particularly challenging in short eyes. Accurate prediction of effective lens position is known to be more important in short eyes because of the high IOL powers and the relatively short distance between the IOL and the retina. Researchers in the US compared measurements from seven IOL calculation formulas in 86 eyes of 67 patients. The Hoffer Q and Holladay 2 formulas produced slightly myopic refractive prediction errors, and the Olsen formula produced hyperopic refractive prediction errors. When the mean numerical refractive prediction error was adjusted to zero, no statistically significant differences in the median absolute error were found between the seven formulas.
SE Gökce et al., JCRS, “Intraocular lens power calculations in short eyes using 7 formulas”, Volume 43, Issue 7, 892–897.
MANUAL CAPSULORHEXIS AND LENS TILT
The femtosecond laser can be used to create remarkably good capsulorhexes, but does this represent a step beyond what can be achieved with the manual approach? Researchers in Vienna conducted a prospective study in 255 eyes undergoing cataract surgery, looking at manual capsulorhexis size, shape and position on postoperative axial position, tilt, and centration of IOLs. Follow-up evaluations at one hour and three months postoperatively showed that modern IOL designs were not significantly influenced by a slightly imperfect capsulorhexis shape in terms of IOL tilt, IOL decentration, or ACD shift. Moreover, the postoperative change in the shape of the capsulorhexis was not different between a round capsulorhexis shape and an imperfect capsulorhexis shape.
O Findl et al., JCRS, “Effect of manual capsulorhexis size and position on intraocular lens tilt, centration, and axial position", Volume 43, Issue 7, 902–908.
