JCRS highlights chosen by Professor Thomas Kohnen, European editor, JCRS

  TORIC IOL CALCULATION CHALLENGES The influence of posterior corneal astigmatism on total corneal astigmatism is known to differ between eyes with with-the-rule astigmatism and eyes with against-the-rule astigmatism. No prospective long-term study has assessed the influence of preoperative corneal astigmatism axis on prediction error after toric intraocular lens (IOL) implantation. In particular, the influence of oblique astigmatism has not been well addressed. Japanese researchers now report a prospective study that assessed the one-year clinical outcomes of toric IOL implantation in 218 eyes, including the influence of the preoperative astigmatism axis orientation, postoperative contrast sensitivity, higher order aberrations (HOAs), and rotational stability of toric IOLs. Overall, the study found that the toric IOLs were rotationally stable and highly effective in correcting pre-existing corneal astigmatism. However, cases of against-the-rule and oblique astigmatism remained slightly under-corrected with the current toric calculation system based on anterior corneal curvature data alone. Ocular HOAs and contrast sensitivity were not significantly influenced by toric IOL implantation. Y Ninomiya et al, JCRS, “Toric intraocular lenses in eyes with with-the-rule, against-the-rule, and oblique astigmatism: One-year results”, Volume 42, Issue 10, 1431-1440. IMPROVING TORIC IOL OUTCOMES Recent research suggests that calculating the cylinder power for toric IOLs could become more accurate when allowing for the effect of posterior corneal astigmatism. Australian researchers compared the absolute value of the prediction error of the toric IOL cylinder power effect in consecutive eyes with preoperative anterior keratometric cylinder values of 1.0 dioptre or more with the absolute value of the prediction error in a historical control group. The anteriorly measured keratometric cylinder values were altered by two coefficients of adjustment, one for with-the-rule eyes and one for against-the-rule eyes, before calculation of the IOL cylinder power to be implanted. In the controls, unadjusted keratometric cylinder values were used. In this case series of 31 eyes of 29 patients and a control group of 65 eyes, the absolute error in prediction of the toric IOL cylinder power effect was reduced from a median of 0.45D (95% confidence interval [CI], 0.33-0.58) in the controls to a median of 0.23D (95% CI, 0.13-0.35) in the adjusted eyes (P = .004). Toric IOLs of 2.0D cylinder power or less were prone to an error in refractive astigmatic outcome due to the relationship between the anterior and posterior keratometric rule. The researchers conclude that adjustment of toric IOL cylinder power by application of a coefficient of adjustment to anteriorly measured keratometric cylinder values based on the keratometric rule of the eye led to a clinically and statistically significant improvement in refractive astigmatic outcome. 
M Goggin et al, JCRS, “Outcome of adjustment for posterior corneal curvature in toric intraocular lens calculation and selection”, Volume 42, Issue 10, 1441-1448.