JCRS Highlights

THOMAS KOHNEN European Editor of JCRS

DYSPHOTOPSIA AND IOL DESIGN

A new IOL design with a 7.0 mm optic and plate haptics appears to produce less positive and negative dysphotopsia while providing good visual outcomes. A prospective randomised patient-masked comparative clinical study including 120 eyes of 86 patients compared the 7.0 mm and plate-haptics (ASPIRA-aXA, HumanOptics) with the 6.0 mm and C-loop haptics (ASPIRA-aA, HumanOptics). Both are single-piece, aspheric IOLs manufactured from the same hydrophilic acrylic material with a refractive index of 1.46. The study found a statistically significant difference between both groups in positive dysphotopsia at 1 month postoperatively—31.6% in the 7.0 mm IOL group versus 52.4% in the 6.0 mm group. The number of cases progressively decreased in both groups throughout the clinical follow-up, and the difference was no longer statistically significant at months 3 and 12. There was also a statistically significant difference in the incidence of negative dysphotopsia at 1 month postoperatively, with a lower incidence in the 7.0 group (5.4%) versus 20.6% in the 6.0 mm group. The new design also provided good visual performance in terms of stable visual acuity and refraction, contrast sensitivity, mesopic vision, and glare sensitivity. The study also suggested that longer axial length and greater pupil dynamics might serve as predictive risk factors for positive dysphotopsia. MK Bonsemeyer et al., “Dysphotopsia and functional quality of vision after implantation of an intraocular lens with a 7.0 mm optic and plate haptic design”, 48(1): 75–82, January 2022.

7.0 MM IOL NEGATIVE DYSPHOTOPSIA LABORATORY STUDY

In a related laboratory study, investigators used optical modelling to compare 6.0 mm and 7.0 mm intraocular lens (IOL) optic diameters on peripheral retinal illumination with implications for negative dysphotopsia. They used ray-tracing software to simulate retinal illumination from an extended light source for pseudophakic eyes with different IOLs to verify their effect on negative dysphotopsia. The simulations involved biconvex IOLs with optic diameters of 6.0 mm and 7.0 mm, refractive indices of 1.46 and 1.55, and a 2.5 mm pupil. For the lower refractive index (1.46), the 6.0 mm IOL was modelled with a 5.5 mm optic surrounded by a 0.25 mm rim. The 7.0 mm IOL was modelled with a 6.0 mm optic surrounded by a 0.5 mm rim. The team found similar results for IOLs with both refractive indices. The 7.0 mm optic expanded the image field. Furthermore, high-angle input light was found to miss a 7.0 mm optic at a larger visual angle than a 6.0 mm optic, shifting illumination of the peripheral retina by this light anteriorly. Consequently, investigators created an extended and more peripheral dark nasal region. The narrow retinal shadow using a 6.0 mm optic is converted to a broader, more peripheral shadow when using a 7.0 mm optic. This could explain the lower negative dysphotopsia rates associated with a larger 7.0 mm optic, the authors note. JC Erie et al., “Effect of a 7.0 mm intraocular lens optic on peripheral retinal illumination with implications for negative dysphotopsia”, 48(1): 95–99, January 2022.