Effect of a 7.0 mm intraocular lens optic on peripheral retinal illumination with implications for negative dysphotopsia.

PURPOSE

To use optical modeling to compare a 6.0 mm and 7.0 mm intraocular lens (IOL) optic diameters on peripheral retinal illumination with implications for negative dysphotopsia.

SETTING

Mayo Clinic, Rochester, Minnesota, and Simpson Optics LLC, Arlington, Texas.

DESIGN

Model eye.

METHODS

Ray-tracing software was used to simulate retinal illumination from an extended light source for a pseudophakic eye with in-the-bag biconvex IOLs (refractive index [n] = 1.46 and 1.55) and a 2.5 mm pupil. Ray-tracing diagrams and simulated retina illumination profiles were compared using the 6.0 mm and 7.0 mm optic diameter IOLs. Retinal locations were scaled to relative visual angles from 70 to 110 degrees horizontally.

RESULTS

A 7.0 mm optic (n = 1.46) expands the image field by 2.8 degrees compared with a 6.0 mm optic. High-angle input light misses 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 by 5.6 degrees. Consequently, a region of nonilluminated peripheral nasal retina is enlarged and shifted peripherally using a 7.0 mm optic (visual angle, 86.3 to 96.3 degrees) compared with a 6.0 mm optic (visual angle, 83.5 to 90.7 degrees). Similar illumination changes were seen modeling a 1.55 n IOL.

CONCLUSIONS

A narrow dark region in the nasal retina when using a 6.0 mm optic is changed to a broader, more peripheral dark region when using a 7.0 mm optic. An extended, more peripheral dark nasal region may make a temporal shadow less bothersome and explain lower negative dysphotopsia rates using a 7.0 mm optic.