Assessment of spectral properties of positive dysphotopsia or glare caused by LED sources for different types of intraocular lenses.

Light emitting diodes (LEDs) have become a major source of lighting conditions. The increased prevalence of LED light sources introduces new concerns for the spectral effects of positive dysphotopsia (PD) or glare type photic phenomena for pseudo-phakic patients with intraocular lenses (IOLs). A significant amount of work has been published in the area of spectral discomfort and sensitivity of LEDs as well as automotive lighting. The wavelength dependence or spectral properties of PD due to LEDs for IOLs has not been reported. This study, to our knowledge, is the first one to assess the glare characteristics of four commercially available IOL models with different material types and design features using an optical bench and non-sequential ray trace simulations with LEDs of different wavelengths. A novel approach of representing the reflected and transmitted IOL glare utilizing Fresnel coefficients is found to be in close agreement with the measurements.

Evaluation of intraocular lens mechanical stability.

PURPOSE: To compare mechanical characteristics and stability of Clareon CNA0T0 intraocular lens (IOL) with 4 currently marketed monofocal IOLs and to evaluate axial displacement and simulated dioptric power shift using a range of compression diameters. SETTING: Alcon Laboratories, Inc., Fort Worth, Texas, USA. DESIGN: Experimental study. METHODS: Clareon CNA0T0, AcrySof SN60WF, enVista MX60, Tecnis ZCB00, and Vivinex iSert XY1 IOLs (10 per group) were assessed using standardized methods for axial displacement, optic decentration, and optic tilt per the International Organization for Standardization ISO11979-3. Axial displacement was also measured over a range of compression diameters (9.0 to 11.0 mm). RESULTS: At 10.0 mm compression, the mean axial displacement for the CNA0T0 IOL (0.02 mm ± 0.01 [SD]) was significantly lower than for the MX60, ZCB00, and XY1 IOLs (P < .005). At all compression diameters, the CNA0T0 and SN60WF IOLs had the lowest levels of axial displacement and corresponding simulated dioptric power shift at the corneal plane versus other IOL models. At 10.0 mm compression, the mean optic decentration was within ±0.06 mm for all models, and there were no significant differences between the CNA0T0 IOL and other IOLs. At 10.0 mm compression, the mean optic tilt was no greater than 1.2 degrees for all IOL models evaluated; however, the mean optic tilt for the CNA0T0 IOL was significantly lower than for the MX60 IOL (P < .005). CONCLUSION: The CNA0T0 and SN60WF IOLs showed the lowest levels of axial displacement and corresponding simulated dioptric power shift over all tested compression diameters, indicating they might provide the most consistent refractive outcomes.

In vitro and schematic model eye assessment of glare or positive dysphotopsia-type photic phenomena: Comparison of a new material IOL to other monofocal IOLs.

PURPOSE: To compare the glare-type photic phenomena for a new intraocular lens (IOL) to other monofocal IOLs, and to investigate how IOL design features might affect these phenomena. SETTING: Alcon Laboratories, Inc., Fort Worth, Texas; John A Moran Eye Center, University of Utah, Salt Lake City, USA. DESIGN: Schematic model eye evaluation and in vitro study. METHODS: Five monofocal IOL models (Clareon CNA0T0, Tecnis ZCB00, enVista MX60, Eternity W-60, and Vivinex XY1) were used to evaluate glare or positive dysphotopsia-type phenomena. Optical simulations of incoming light were generated using nonsequential ray-tracing software based on a collimated light source for various off-axis angles of illumination. The simulation analyses were verified using a laboratory in vitro bench-top glare measurement system. RESULTS: The Clareon and Vivinex IOLs produced focused off-axis images with negligible peripheral glare characteristics. The Tecnis and enVista IOLs produced dispersed images with additional glare characteristics at 45 degrees of off-axis illumination and higher. The Eternity IOL showed the highest edge-reflected glare characteristic, likely because of its straight optic edge geometry. The laboratory bench images and glare intensity profiles were consistent with the simulation data. CONCLUSIONS: In vitro and nonsequential ray-tracing evaluations showed that straight optic edges and peripheral nonimaging optic geometry might contribute to positive dysphotopsia. The IOL designs with optic edge curvature and full functional optics demonstrated the lowest level of glare-type photic phenomena. Only clinical studies can confirm whether the differences observed between the IOLs in vitro are clinically significant.

Effects of Intraocular Lens Opacification on Light Scatter, Stray Light, and Overall Optical Quality/Performance.

PURPOSE: To evaluate light scatter and stray light in intraocular lenses (IOLs) explanted because of postoperative opacification (13 calcified hydrophilic acrylic, 1 calcified silicone, and 4 polymethylmethacrylate [PMMA] lenses with snowflake degeneration), as well as effect of opacification on other optical quality/performance indicators, in comparison with controls. METHODS: The Complete Angle Scatter Instrument (CASI) scatterometer was used to measure the forward light scattering (FLS) of the IOLs, and the stray light values at various angles were calculated from the measured FLS. Modulation transfer function (MTF) was obtained with an optical bench, and a Badal optometer was used to obtain letter chart images through the lenses. Back light scatter and light transmittance were also measured. RESULTS: Average stray light values (Log (s)) at a scattered angle of 10° were 1.79 ± 0.37 for hydrophilic acrylic IOLs (controls 0.36 ± 0.05), 1.53 for the silicone lens (control 0.41), and 1.62 ± 0.46 for PMMA IOLs (control 0.25). Stray light was significantly higher for explanted opacified lenses (N = 18) in comparison with controls (N = 7; two-tail P < 0.001 at 10°). Modulation transfer function and Badal image contrast were drastically reduced in lenses with calcification and snowflake degeneration. CONCLUSIONS: Different studies described the impact of stray light in human vision, with serious hindrance above 1.47 Log (s). Lenses explanted from patients because of clinically significant opacification are associated with a considerable increase in light scatter and stray light, as well as with a decline of other optical quality/performance indicators.

Light scattering, straylight, and optical quality in hydrophobic acrylic intraocular lenses with subsurface nanoglistenings.

PURPOSE: To evaluate forward light scattering and straylight in single-piece hydrophobic acrylic intraocular lenses (IOLs) (Acrysof) removed from cadaver eyes and design- and power-matched controls, as well as the effect of subsurface nanoglistenings on other optical quality and performance indicators. SETTING: John A. Moran Eye Center, University of Utah, Salt Lake City, Utah, USA. DESIGN: Experimental study. METHODS: Seventeen single-piece IOLs (11 blue light-filtering; 6 without blue-light filter) with subsurface nanoglistenings were removed from cadaver eyes. The Complete Angle Scatter Instrument scatterometer was used to measure the forward-scattered light; straylight values at various angles were calculated. The modulation transfer function (MTF) and Badal images were also obtained. Backscatter was measured with a Scheimpflug camera (EAS-1000) and light transmittance with a spectrophotometer (Lambda 35 UV-VIS) to confirm findings in previous studies. RESULTS: The mean straylight values at a scattered angle of 10 degrees were 1.06 ± 0.23 log(s) for blue light-filtering IOLs, 0.97 ± 0.28 log(s) for IOLs without a blue-light filter, and 0.22 ± 0.22 log(s) for controls. The MTF and Badal image contrast of IOLs removed from cadaver eyes were similar to control values (no subsurface nanoglistenings). Backscatter was significantly higher in IOLs from cadaver eyes, although light transmittance was similar to that of controls. CONCLUSION: Straylight in hydrophobic IOLs resulting from subsurface nanoglistenings was well below the value of straylight hindrance and would not cause noticeable visual impairments. FINANCIAL DISCLOSURE: Dr. Das is an employee of Alcon Laboratories, Inc. The Complete Angle Instrument scatterometer was developed by Dr. Stover at the Scatterworks, Inc. Neither of the other authors has a financial or proprietary interest in any method or material mentioned.

Technique for measuring forward light scatter in intraocular lenses.

PURPOSE: To develop a technique for measuring the forward light scattering of intraocular lenses (IOLs). SETTING: The Scatter Works, Tucson, Arizona, USA. DESIGN: Evaluation of diagnostic technique. METHODS: A scatterometer with laser sources of 488 nm and 633 nm was used to directly measure the forward-scattered light of IOLs. These sources illuminated balanced salt solution-immersed IOLs within a cylindrical wet cell. The wet cell was placed at the center of rotation of a goniometer arm. On the end of the arm was a detector that measured the amount of laser light scattered from the IOL as a function of incident-beam angle. The measurements provided a profile of the scatter distribution for regions outside the directly transmitted beam. Forward and back light scatter was measured in new and artificially aged IOLs. RESULTS: Forward light scatter was increased in artificially aged IOLs compared with that in new unaged IOLs. The artificially aged IOLs developed sub-wavelength-diameter water nanoglistenings in the bulk material just below the surface. The measured scatter profiles were consistent with these subsurface droplets, suggesting Rayleigh-type scatter in the aged IOLs. The amount of light scatter from nanoglistenings does not appear to be sufficient to impair vision. Although the severely aged IOLs showed increased scatter, the level of increase was within 1 standard deviation of what is found in the normal population. CONCLUSION: A technique was developed enabling quantification of forward-scattered and back-scattered light from IOLs.