Visual Function Loss Through Opacified Media: Comparison Between Single- and Two-Photon Vision

The purpose of this study is to quantify the effect of monofocal intraocular lens (IOL) turbidity on visibility threshold and spatial pattern detection threshold with an infrared (IR)-two-photon (2P) approach, and visible light.

Three observers were tested with pulsed IR (1045 nm) and visible lights (522.5 nm) using visibility threshold and spatial pattern detection threshold methods on two clear control IOLs and 11 explanted opacified IOLs, using our 2P microperimetry setup. IOL power and straylight were measured. Data from the clear IOLs served as control.

Control IOLs (20 D) had a mean straylight of 0.57 ± 0.05 logs and opacified IOLs (18.9-21.8 D) had a mean straylight of 2.16 ± 0.37 logs. Most threshold measurements differed significantly between clear and opacified IOLs. For IR, slopes of linear regression of straylight vs. visibility threshold and spatial pattern detection threshold ratios were similar (0.78 vs. 0.93 logs-1; P = 0.8531). For visible light, the visibility threshold ratio slope was lower than the spatial pattern detection threshold ratio (2.97 vs. 4.53 logs-1; P = 0.0008). IR measurements showed significantly less dependence on straylight than visible light for both visibility threshold and spatial pattern detection threshold (P < 0.00001).

We found that 2P measurements yield lower variability and reduced straylight dependence compared with visible light with either the spatial pattern detection threshold or visibility threshold methods.

Regardless of spatial pattern detection threshold or visibility threshold methods, two-photon microperimetry is less affected by increased opacity and may yield consistent threshold ratio results.