Intraocular lens far peripheral vision: image detail and negative dysphotopsia.

PURPOSE

To evaluate negative dysphotopsia in the far periphery of the pseudophakic eye by generating simulated images of text charts.

SETTING

Consultancy.

DESIGN

Laboratory study.

METHODS

Simulated images of a peripheral text chart were created using a ray-trace model of a pseudophakic eye. The point spread function varies strongly with a radial location. Retinal angles subtended at the second nodal point were used to linearly scale retinal locations to a polar plot in object space, weighting rays by the object luminance, the total transmittance, and a cosine normalization for pupil effects. Improved scaling using a phakic 70-year-old eye was also explored.

RESULTS

Images demonstrate a distinct shadow with a 2.5 mm pupil between the upper limit of the text image formed by the intraocular lens (IOL) and a second larger image due to light missing the IOL. The shadow is rapidly softened by a small increase in pupil diameter.

CONCLUSIONS

The images verified characteristics that previously were only inferred indirectly: (1) With a 2.5 mm pupil, there is a prominent dark shadow. (2) Light missing the IOL experiences lower power and forms a larger image and also comes from a lower visual angle. (3) A small increase in pupil diameter causes the shadow to fade. The calculations showed that imaging in the far periphery is very different for the pseudophakic eye in comparison with the phakic eye. The limit of the focused image is probably the primary cause of the shadow, yet relatively few patients find this to be bothersome.