Experimental and analytical quantification of light scattering from vacuoles in intraocular lenses.

PURPOSE: To develop an advanced test methodology for quantification of scattered light from intraocular lenses (IOLs) and to evaluate the correlation between IOL vacuole characteristics and measured scattered light. SETTING: U.S. Food and Drug Administration, Optical Therapeutics and Medical Nanophotonics Laboratory, Silver Spring, Maryland, USA. DESIGN: Experimental and analytical study. METHODS: Twenty-four IOLs containing vacuoles were evaluated using a digital microscopy approach for identifying and characterizing the vacuoles present. A scanning light scattering profiler (SLSP) was used to evaluate and quantify the amount of scattered light from each IOL and from a 25th control IOL without any vacuoles. A variety of IOLs and vacuoles were also modeled in a Zemax simulation of the SLSP, and the simulated scattered light was modeled. RESULTS: The scattered light as measured with SLSP was well correlated with vacuole characteristics, specifically density and size, as measured under the digital microscope for the 24 vacuole-containing IOLs. Additional correlations were found between vacuole sizes, orientations, and the angle at which light was scattered most severely. These correlations were also present in the Zemax model. CONCLUSIONS: Vacuole optical characteristics can be well correlated with measured scatter, demonstrating an ability to predict scattered light based solely on microscope evaluation. Furthermore, the quantitative amount of scatter predicted with Zemax simulations trended closely with the experimentally measured trends.

Quantitative Multiparameter Evaluation of Vacuoles in Intraocular Lenses Employing a High-Magnification Digital Microscopy Method.

As small imperfections with micrometric sizes, fluid-filled vacuoles, also referred to as glistenings, in intraocular lenses (IOLs) have been known to induce significant unwanted light scattering that in several cases presumably cause complaints and sometimes lead to IOL explantation and replacement. This unwanted scatter is of particular concern for patients viewing bright light in reduced-light conditions such as when driving at night, as the scattered light toward the retina can cause temporary blindness. In this study, we have developed and implemented an accurate test methodology based on a high-magnification digital microscopy approach for quantitative multiparameter evaluation and classification of IOL vacuoles depending on their critical optical characteristics including vacuole size, density, shape, and orientation within the IOL material. Using the multiparameter database developed by evaluating vacuole characteristics, we established a classification grading system that can be used to evaluate vacuole effects on light scattering.

Scanning Light Scattering Profiler (SLPS) Based Methodology to Quantitatively Evaluate Forward and Backward Light Scattering from Intraocular Lenses.

The scanning light scattering profiler (SLSP) methodology has been developed for the full-angle quantitative evaluation of forward and backward light scattering from intraocular lenses (IOLs) using goniophotometer principles. This protocol describes the SLSP platform and how it employs a 360° rotational photodetector sensor that is scanned around an IOL sample while recording the intensity and location of scattered light as it passes through the IOL medium. The SLSP platform can be used to predict, non-clinically, the propensity for current and novel IOL designs and materials to induce light scatter. Non-clinical evaluation of light scattering properties of IOLs can significantly reduce the number of patient complaints related to unwanted glare, glistening, optical defects, poor image quality, and other phenomena associated with the unintended light scattering. Future studies should be conducted to correlate SLSP data with clinical results to help identify which measured light scatter is most problematic for patients that have undergone cataract surgery subsequent to IOL implantation.

Evaluation of the Potential Optical Radiation Hazards with Led Lamps Intended for Home Use.

The authors evaluated the potential for ocular damage from optical radiation emitted by Light Emitting Diode (LED) based lamps used for general illumination. Ten LED lamps were randomly selected off the shelf from a local home improvement store. The LEDs were behind diffusers in half of these lamps, while in the other half, the LEDs were clearly visible. In addition, a battery powered LED lantern having a LED source behind a diffuser was measured. The optical radiation emissions from two common incandescent lamps were also measured to compare the relative hazards of LED and incandescent lamps. All lamp samples were evaluated in accordance with procedures specified in the American National Standards Institute/Illuminating Engineering Society of North America (ANSI/IESNA) Standard RP-27.3. For comparison purposes, the lantern and 100 W incandescent lamps were also evaluated according to ANSI RP-27.1. These measurements indicate that no lamp evaluated poses any photobiological hazard, and therefore, all lamps fall in the RP-27.3 category of Exempt Group. However, when evaluated in accordance with RP-27.1, the 100 W incandescent lamp would be classified in Risk Group 1 (low risk), while the LED lantern would be classified in Risk Group 2 (moderate risk).

Confocal laser method for quantitative evaluation of critical optical properties of toric intraocular lenses.

PURPOSE: To present a proof-of-concept study on the development and implementation of an innovative confocal laser method platform for precise quantitative evaluation of critical optical properties unique to toric intraocular lenses (IOLs). SETTING: U.S. Food and Drug Administration, Optical Therapeutics and Medical Nanophotonics Laboratory, Silver Spring, Maryland, USA. DESIGN: Experimental study. METHODS: The optical properties of hydrophobic toric IOLs were evaluated with a confocal laser method that was modified to isolate the 2 planes of focus that are observed with toric IOLs. RESULTS: The results show the confocal laser method has the potential to measure the orthogonally separated optical powers and then calculate them to the commonly referenced spherical equivalent and cylinder powers of toric IOLs with high accuracy (≤1 µm of focal length measurement). Furthermore, the proposed confocal laser method design includes a new component for precise differentiation of the 2 focal planes and isolation of the 2 focal points, and thus for accurate measurement of the anterior cylinder axis of toric IOLs. CONCLUSION: The modifications to the confocal laser method platform enabled the quantitative evaluation of optical properties attributed to toric IOLs. FINANCIAL DISCLOSURE: None of the authors has a financial or proprietary interest in any material or method mentioned.

A novel full-angle scanning light scattering profiler to quantitatively evaluate forward and backward light scattering from intraocular lenses.

Glare, glistenings, optical defects, dysphotopsia, and poor image quality are a few of the known deficiencies of intraocular lenses (IOLs). All of these optical phenomena are related to light scatter. However, the specific direction that light scatters makes a critical difference between debilitating glare and a slightly noticeable decrease in image quality. Consequently, quantifying the magnitude and direction of scattered light is essential to appropriately evaluate the safety and efficacy of IOLs. In this study, we introduce a full-angle scanning light scattering profiler (SLSP) as a novel approach capable of quantitatively evaluating the light scattering from IOLs with a nearly 360° view. The SLSP method can simulate in situ conditions by controlling the parameters of the light source including angle of incidence. This testing strategy will provide a more effective nonclinical approach for the evaluation of IOL light scatter.

Assessing the effect of laser beam width on quantitative evaluation of optical properties of intraocular lens implants.

The design and manufacture of intraocular lenses (IOLs) depend upon the identification and quantitative preclinical evaluation of key optical properties and environmental parameters. The confocal laser method (CLM) is a new technique for measuring IOL optical properties, such as dioptric power, optical quality, refractive index, and geometrical parameters. In comparison to competing systems, the CLM utilizes a fiber-optic confocal laser design that significantly improves the resolution, accuracy, and repeatability of optical measurements. Here, we investigate the impact of changing the beam diameter on the CLM platform for the evaluation of IOL dioptric powers. Due to the Gaussian intensity profile of the CLM laser beam, the changes in focal length and dioptric power associated with changes in beam diameter are well within the tolerances specified in the ISO IOL standard. These results demonstrate some of the advanced potentials of the CLM toward more effectively and quantitatively evaluating IOL optical properties.

Impact of environmental temperature on optical power properties of intraocular lenses.

Optical power properties of lenses and materials in general can be influenced by thermal changes of the material and surrounding medium. In the case of an intraocular lens (IOL) implant, the spherical power (SP), cylinder power, (CP), astigmatism, and spherical aberration are the critical fundamental properties that can significantly impact its efficacy. Directly evaluating how changes in temperature can affect these optical properties may show the importance of considering temperature when evaluating IOL optical characteristics. In this paper, we present a quantitative study on evaluating the impact of environmental temperature changes on IOL fundamental optical properties by testing IOL samples with different materials (e.g., hydrophobic and hydrophilic) and designs (e.g., monofocal and toric) to better encompass types of IOLs in conventional use today. The results from this study demonstrate that significant changes are observed as temperatures are changed from room temperature (20°C) to slightly above body temperature (40°C). Findings indicate that evaluating optical properties at arbitrary temperatures could significantly affect the characterization of IOLs that are already near the tolerance thresholds.

Nanophotonic ionization for ultratrace and single-cell analysis by mass spectrometry.

Recent mechanistic studies have indicated that at subwavelength post diameters and selected aspect ratios nanopost arrays (NAPA) exhibit ion yield resonances ( Walker , B. N. , Stolee , J. A. , Pickel , D. L. , Retterer , S. T. , and Vertes , A. J. Phys. Chem. C 2010 , 114 , 4835 - 4840 ). In this contribution we explore the analytical utility of these optimized structures as matrix-free platforms for laser desorption ionization mass spectrometry (LDI-MS). Using NAPA, we show that high ionization efficiencies enable the detection of ultratrace amounts of analytes (e.g., ∼800 zmol of verapamil) with a dynamic range spanning up to 4 orders of magnitude. Due to the clean nanofabrication process and the lack of matrix material, minimal background interferences are present in the low-mass range. We demonstrate that LDI from NAPA ionizes a broad class of small molecules including pharmaceuticals, natural products, metabolites, and explosives. Quantitation of resveratrol in red wine samples shows that the analysis of targeted analytes in complex mixtures is feasible with minimal sample preparation using NAPA-based LDI. We also describe how multiple metabolite species can be directly detected in single yeast cells deposited on the NAPA chip. Twenty-four metabolites, or 4% of the yeast metabolome, were identified in the single-cell spectra.

Laser-nanostructure interactions for ion production.

Interactions between pulsed laser radiation and nanostructured materials, with dimensions ranging from 1 nm to 500 nm, can result in enhanced desorption and ionization of organic and biomolecular adsorbates. When the critical dimensions of the nanostructures fall below the characteristic lengths for the involved transport processes, novel regimes of ion production are observed. Systems with dimensions commensurate with the wavelength of the laser radiation are the basis of photonic ion sources with unique properties, including polarization dependent ion yields and fragmentation. The main characteristics of these systems are often governed by altered modes of transport, e.g., ballistic vs. diffusive, energy confinement, plasmon resonances, and local field enhancements. Some structures offer control over the internal energy and the active fragmentation channels for the produced ions. Emerging applications of photonic ion sources in mass spectrometry benefit from ultrahigh sensitivity, a wide dynamic range for detection and quantitation, and a broad coverage of adsorbates ranging from small organic molecules to biopolymers, as well as to highly complex samples like single cells.

Nanophotonic ion production from silicon microcolumn arrays.

Nanoantennas for ions: Silicon microcolumn arrays harvest light from a laser pulse to produce ions. The system behaves like a quasi-periodic antenna array with ion yields that show profound dependence on the plane of polarization and the angle of incidence of the laser beam. Photonic ion sources promise to enable enhanced control of ion production on a micro- and nanometer scale and direct integration with miniaturized analytical devices.