Robert H. James

Handheld ophthalmoscopes for hazards analysis: an evaluation

The spectral irradiance was measured from twenty handheld ophthalmoscopes. The optical radiation emitted from each ophthalmoscope was compared to the threshold limit values (TLV(s)) for acute effects published by the American Conference of Governmental Industrial Hygienists. All ophthalmoscopes tested were found to emit unnecessary ultraviolet and infrared radiation in addition to visible light. The levels of optical radiation emitted from most of the ophthalmoscopes were below the applicable TLV(s). Nevertheless, suitable blocking filters can reduce the emission of ultraviolet and infrared radiation. Use of the ophthalmoscopes at the lowest possible power would further minimize patient exposure.

Noncontact common-path Fourier domain optical coherence tomography method for in vitro intraocular lens power measurement

We propose a novel common-path Fourier domain optical coherence tomography (CP-FD-OCT) method for noncontact, accurate, and objective in vitro measurement of the dioptric power of intraocular lenses (IOLs) implants. The CP-FD-OCT method principle of operation is based on simple two-dimensional scanning common-path Fourier domain optical coherence tomography. By reconstructing the anterior and posterior IOL surfaces, the radii of the two surfaces, and thus the IOL dioptric power are determined. The CP-FD-OCT design provides high accuracy of IOL surface reconstruction. The axial position detection accuracy is calibrated at 1.22 μm in balanced saline solution used for simulation of in situ conditions. The lateral sampling rate is controlled by the step size of linear scanning systems. IOL samples with labeled dioptric power in the low-power (5D), mid-power (20D and 22D), and high-power (36D) ranges under in situ conditions are tested. We obtained a mean power of 4.95/20.11/22.09/36.25 D with high levels of repeatability estimated by a standard deviation of 0.10/0.18/0.2/0.58 D and a relative error of 2/0.9/0.9/1.6%, based on five measurements for each IOL respectively. The new CP-FD-OCT method provides an independent source of IOL power measurement data as well as information for evaluating other optical properties of IOLs such as refractive index, central thickness, and aberrations.

Optical?thermal characterization of cutaneous transilluminators

In recent years, there has been an increase in the popularity of light-emitting diode (LED)-based, battery-powered transilluminators (BPTs) for facilitating transdermal vascular access in adults and neonates. BPTs are believed to have lower potential for inducing skin burns than prior devices based on high-power broadband lamps; however, the optical and thermal outputs of BPTs are not well documented and safety limits for these devices are not well established. In this study, we characterize and assess the optical and thermal outputs of six BPTs that incorporate red, orange and white LEDs. Optical measurements included spectral irradiance and peak local irradiance. Thermal measurements included transient temperature readings for an exposure time of 4 min in ambient air and ex vivo tissue pre-heated to physiological temperatures. The greatest mean temperature rise produced in tissue by a non-white-light diode BPT was 2.5 degrees C, whereas a mean temperature rise of 9.1 degrees C was measured in a BPT that incorporated white-light diodes with relatively high irradiance levels. The dominant cause of temperature rise was most likely heat generation within the devices. Thermal damage analyses based on temperature limits and the Arrhenius equation indicate that although some of the devices studied approach the threshold for damage, none appear to exceed it under normal operating conditions. The results demonstrated that ambient air measurements may be suitable for identifying worst-case BPT temperatures. This study highlights the potential risk of LED-based medical devices as well as the need for additional research on related issues such as neonatal thermal injury thresholds.

Quantification of glistenings in intraocular lenses using a ballistic-photon removing integrating-sphere method

An alternative method for quantification of glistenings in intraocular lenses (IOLs) using an integrating sphere with an adjustable back aperture to remove ballistic photons is presented. Glistenings in soft IOLs have been known for more than a decade; however, their severity and visual impact are still under investigation. A number of studies have been made to quantitatively describe glistenings in IOLs. Quantization and precise grading of IOLs will provide needed information to evaluate the severity and visual impact of glistenings in patients. We investigated the use of a simple modification of an integrating-sphere method to eliminate ballistic photons to quantitatively measure scattered light from glistenings in IOLs. The method described in this paper provides a simple and effective way to quantitatively characterize glistenings in vitro. It may be especially useful to quantify scattering associated with low-grade glistenings where the density of the scattering centers is low. Finally, the modified integrating-sphere method may also be generally applicable to quantitatively characterize scattering from other optical media.

Indirect ophthalmoscopes: evaluation for potential hazard

The optical radiation emitted from eight indirect ophthalmoscopes was measured. The levels were compared with the threshold limit values (TLVs) published by the American Conference of Governmental Industrial Hygienists. Many tested instruments were found to emit unnecessarily high levels ofultraviolet and infrared radiation in addition to visible light. The levels of optical radiation emitted from most of the ophthalmoscopes were below the applicable TLVs. Nevertheless, suitable blocking filters can reduce the emission of ultraviolet and infrared radiation. Use of the ophthalmoscopes at the lowest possible power setting and the shortest possible exposure time would further minimize patient exposure.

Interlaboratory Evaluation of Ultraviolet Radiation Emissions from Compact Fluorescent Lamps

There have been many recent reports regarding the potential risks of UV emissions from compact fluorescent lamps (CFLs). In some of these reports, the robustness of the measurements was difficult to discern. We conducted round‐robin measurements, involving three lamp manufacturers and two government research laboratories to gather reliable data on the UV emissions from commercially available CFLs. The initial sample of lamps consisted of 71 spiral‐shaped CFLs purchased from local retailers. From the initial sample, 14 “high UV emitting” CFLs were chosen for further evaluation. We compared the UV emissions at a distance of 20 cm with the UV exposure limits (ELs) published by the International Commission on Non‐ionizing Radiation Protection (ICNIRP). We found that the allowable exposure time for measured lamps ranged from 21 to 415 h. This indicates that the emissions would not exceed the short‐term ELs that have been established by the ICNIRP for healthy individuals. We also evaluated the potential long‐term risk and found it to be insignificant. There was a large variation in the UV emissions found, even for lamps from a single package, indicating that it is impossible to predict the UV output of a CFL based on its physical appearance and model designation.

PHOTOAGING EFFECTS ON SPECTRAL TRANSMITTANCE OF PLASTIC FILTERS

Abstract— We examined the effects of ultraviolet (UV) radiation in combination with high levels of infrared (IR) radiation on the spectral transmittance of plastic filters. The biological action spectrum for damage to the human eye and skin changes dramatically in the 300–400 nm wavelength range. Cut‐off filters used in this region to shape the spectrum of exposure sources are thus critical to the design of experiments which use broadband light sources. The changes in transmittance of three types of plastic filters were observed over an exposure period of 1000 h. One set of three filters was exposed mainly to UV radiation, while the other set was exposed to UV radiation plus IR radiation. Filters exposed to both UV and IR radiation showed spectral changes in their transmittance, while the filters exposed to UV only showed no measurable changes.

Optical characterization of cutaneous transilluminators for eye safety

Cutaneous transilluminators are light-emitting devices used to localize blood vessels for various medical procedures. They are often used in populations that may be at increased risk for skin burns, such as neonates and the elderly. While there is a known potential for skin burns, little is known about the ophthalmic risk from the use of these devices. This paper will report on the laboratory evaluation of the potential ocular hazards from transilluminators (TIs). Our results indicate that transilluminators which incorporate white-light LEDs have emissions that have the potential for producing injury to the retina, especially in patients who may have a reduced aversion response.

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 &mgr;m 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.

Variables Associated With Ultraviolet Transmittance Measurements of Intraocular Lenses

We measured the spectral transmittance of 12 intraocular lenses with a spectroradiometer system that uses an integrating sphere input. We evaluated both low- and high-power lenses and varied the input aperture size between 1, 3, and 5 mm. These variations caused a significant difference in the transmittance characteristics of the intraocular lenses. Most significantly, the transmittance of the low-power model was two to six times greater than that of the high-power model in the cutoff region. The larger aperture resulted in, at most, a factor of two difference in transmittance. This effect was observed in intraocular lenses labeled both ultraviolet-absorbing and nonultraviolet-absorbing.