Comparison of two laboratory-based systems for evaluation of halos in intraocular lenses

Abstract

Purpose: Multifocal intraocular lenses (IOLs) can be associated with unwanted visual phenomena, including halos. Predicting potential for halos is desirable when designing new multifocal IOLs. Halo images from 6 IOL models were compared using the Optikos modulation transfer function bench system and a new high dynamic range (HDR) system.

Materials and methods: One monofocal, 1 extended depth of focus, and 4 multifocal IOLs were evaluated. An off-the-shelf optical bench was used to simulate a distant (>50 m) car headlight and record images. A custom HDR system was constructed using an imaging photometer to simulate headlight images and to measure quantitative halo luminance data. A metric was developed to characterize halo luminance properties. Clinical relevance was investigated by correlating halo measurements to visual outcomes questionnaire data.

Results: The Optikos system produced halo images useful for visual comparisons; however, measurements were relative and not quantitative. The HDR halo system provided objective and quantitative measurements used to create a metric from the area under the curve (AUC) of the logarithmic normalized halo profile. This proposed metric differentiated between IOL models, and linear regression analysis found strong correlations between AUC and subjective clinical ratings of halos.

Conclusion: The HDR system produced quantitative, preclinical metrics that correlated to patients' subjective perception of halos.

Keywords: high dynamic range; multifocal IOL; quantitative metric; visual disturbance.

Figure 1

Schematic (A) and photograph (B) of halo bench components and layout. The optical layout of the Optikos system is similar to the halo bench system. Abbreviations: DI, deionized; IOL, intraocular lens.

Figure 2

Cross-section of halo images from the 2 systems. (A) Eight-bit images with saturated centers using the Optikos bench system. (B) Full-range halo intensity using the HDR system. Abbreviation: HDR, high dynamic range.

Figure 3

Optikos pinhole images: (A) IQ monofocal, (B) ReSTOR +2.5 D, (C) ReSTOR +3.0 D, and (D) ReSTOR +4.0 D.

Figure 4

Halo luminance profiles showing the average of 8 radii of the halo image for each IOL in (A) Log and (B) LogNorm. Abbreviation: IOL, intraocular lens.

Figure 5

Two-dimensional 16-bit HDR halo data with logarithmic scaling for IOL models: (A) IQ monofocal, (B) ReSTOR +2.5 D, (C) ReSTOR +3.0 D, (D) ReSTOR +4.0 D, (E) Symfony, and (F) Tecnis +2.75 D. Luminance values below 2 cd/m² were discarded to match with average road luminance at night. Abbreviations: HDR, high dynamic range; IOL, intraocular lens.

Figure 6

Linear regression of bench measurement plotted against clinical halo severity. For each IOL type, 1 value of laboratory-measured AUC was plotted against the 4 levels of halo severity reported clinically for that IOL. Halo severity was subjectively rated by patients as none, mild, moderate, or severe, giving 4 regression lines. The legend symbols are circle for IQ monofocal, square for ReSTOR +2.5 D, triangle for ReSTOR +3.0 D, and diamond for ReSTOR +4.0 D. Values for ReSTOR +3.0 D “mild” and “moderate” overlapped and did not appear as separate points. r is the Pearson’s correlation coefficient. Abbreviations: IOL, intraocular lens; AUC, area under the curve.