Occupational Exposure to Solar Radiation and the Eye: A Call to Implement Health Surveillance of Outdoor Workers.

Globally, hundreds of millions of outdoor workers are exposed to solar radiation (SR) for the majority of their working life. Such occupational exposure is known to induce various adverse health effects to the eyes, mainly related to its ultraviolet (UV) component. The present work is a call-to-action aimed at raising the awareness on the need of health surveillance for the prevention of the chronic ocular diseases in outdoor workers. Photo-chemical chronic damage can induce pterygium at the outer layer of the eye and cataract in the lens. Considering carcinogenic effects, rare squamous-cells tumors of the cornea and/or of the conjunctiva and the ocular melanomas are associated with UV radiation exposure. Solar UV-related eye diseases should be considered as "occupational diseases" when there is sufficient exposure in workers, but they are often not recognized, and/or frequently not reported to the national compensation authorities. Therefore, to prevent the burden of these work-related eye pathologies, an adequate risk assessment with identification of appropriate preventive measures, and a provision of periodic health surveillance to the exposed workers, in particular considering those at higher risk of exposure or with individual susceptibility, should be urgently implemented.

WHO/ILO work-related burden of disease and injury: Protocol for systematic reviews of occupational exposure to solar ultraviolet radiation and of the effect of occupational exposure to solar ultraviolet radiation on cataract.

BACKGROUND: The World Health Organization (WHO) and the International Labour Organization (ILO) are developing a joint methodology for estimating the national and global work-related burden of disease and injury (WHO/ILO joint methodology), with contributions from a large network of experts. Here, we present the protocol for two systematic reviews of parameters for estimating the number of disability-adjusted life years of cataracts from occupational exposure to solar ultraviolet radiation, to inform the development of the WHO/ILO joint methodology. OBJECTIVES: We aim to systematically review studies on occupational exposure to solar ultraviolet radiation (Systematic Review 1) and systematically review and meta-analyse estimates of the effect of occupational exposure to solar ultraviolet radiation on the development of cataract (Systematic Review 2), applying the Navigation Guide systematic review methodology as an organizing framework and conducting both systematic reviews in tandem and in a harmonized way. DATA SOURCES: Separately for Systematic Reviews 1 and 2, we will search electronic academic databases for potentially relevant records from published and unpublished studies, including Ovid Medline, PubMed, EMBASE, and Web of Sciences. We will also search electronic grey literature databases, Internet search engines and organizational websites; hand search reference list of previous systematic reviews and included study records; and consult additional experts. STUDY ELIGIBILITY AND CRITERIA: We will include working-age (≥15 years) workers in WHO and/or ILO Member States, but exclude children (<15 years) and unpaid domestic workers. For Systematic Review 1, we will include quantitative studies on the prevalence of relevant levels of occupational exposure to solar ultraviolet radiation and of the total working time spent outdoors from 1960 to 2018, stratified by sex, age, country and industrial sector or occupation. For Systematic Review 2, we will include randomized controlled trials, cohort studies, case-control studies and other non-randomized intervention studies with an estimate of the effect of any occupational exposure to solar ultraviolet radiation (i.e. ≥30 Jm-2/day of occupational solar UV exposure at the surface of the eye) on the prevalence or incidence of cataract, compared with the theoretical minimum risk exposure level (i.e. <30 Jm-2/day of occupational solar UV exposure at the surface of the eye). STUDY APPRAISAL AND SYNTHESIS METHODS: At least two review authors will independently screen titles and abstracts against the eligibility criteria at a first stage and full texts of potentially eligible records at a second stage, followed by extraction of data from qualifying studies. At least two review authors will assess risk of bias and the quality of evidence, using the most suited tools currently available. For Systematic Review 2, if feasible, we will combine relative risks using meta-analysis. We will report results using the guidelines for accurate and transparent health estimates reporting (GATHER) for Systematic Review 1 and the preferred reporting items for systematic reviews and meta-analyses guidelines (PRISMA) for Systematic Review 2. PROSPERO registration: CRD42018098897.

When is protection from impact needed for the face as well as the eyes in occupational environments?

BACKGROUND: The most commonly identified reason for requiring or using occupational eye and face protection is for protection against flying objects. Standards vary on what risk may require protection of the eyes alone and what requires protection for the whole face. Information on the minimum energy transfer for face damage to occur is not well-established. METHODS: The heads of pigs were used as the common model for human skin. A 6 mm steel ball projected at velocities between 45 and 135 m/s was directed at the face area. Examples of impacts were filmed with a high-speed camera and the resulting damage was rated visually on a scale from 1 (no visible damage) to 5 (penetrated the skin and embedded in the flesh). RESULTS: The results for the cheek area indicate that 85 m/s is the velocity above which damage is more likely to occur unless the skin near the lip is included. For damage to the lip area to be avoided, the velocity needs to be 60 m/s or less. CONCLUSION: The present data support a maximum impact velocity of 85 m/s, provided the thinner and more vulnerable skin of the lids and orbital adnexa is protected. If the coverage area does not extend to the orbital adnexa, then the absolute upper limit for the velocity is 60 m/s. At this stage, eye-only protection, as represented by the lowest level of impact test in the standards in the form of a drop ball test, is not in question.

Effect of Ultraviolet Exposure on Impact Resistance of Ophthalmic Lenses.

PURPOSE: To investigate the effect of ultraviolet radiation (UVR) on the impact resistance of organic ophthalmic lens materials. METHODS: Plano power CR39, Phoenix, Trilogy, and polycarbonate lenses with various scratch-resistant (SR) and/or antireflection (AR) coatings were obtained in batches of 40 units. All lenses had a nominal thickness of 2 mm. Half of each batch was conditioned following the European Standard EN 168 protocol for the test of resistance to UVR (exposed group). The remaining lenses comprised an unexposed group for that combination of lens substrate and coating treatment. Each group was subjected to ballistic impact with 6-mm steel balls following the ZEST protocol to determine its mean breakage velocity. The difference in mean breakage velocity between exposed and unexposed groups of each combination of lens substrate and coating was assessed for statistical significance. RESULTS: Exposed uncoated CR39 showed a reduction in fracture velocity of 10.3 m/s whereas CR39 with ultra hard coat had a reduction of 3.5 m/s and CR39 with AR and SR coating had a reduction of 4.1 m/s. Scratch-resistant coated Phoenix had a reduction of 4.8 m/s whereas AR-coated Phoenix had a reduction of 3.7 m/s. The corresponding reductions for Trilogy were 3.9 and 17.8 m/s. All differences were significant at the p level of less than 0.05. Although we were unable to break unexposed SR-coated polycarbonate lenses with our test apparatus, exposed SR-coated polycarbonate had a mean breakage velocity of 142 m/s. CONCLUSIONS: Our data suggest that extended UVR exposure causes a significant reduction in the impact resistance of the ophthalmic lens substrates commonly used for occupational eye protectors. Protective lenses that have been exposed to high levels of UVR for extended periods should be replaced regularly to maintain optimal impact protection, even if they do not show visible damage owing to wear and tear.

Forward light scatter and visual acuity through scratched protective eyewear.

BACKGROUND: Scratches and other surface abrasions on protective eyewear can shorten their life cycle by scattering light from the image, which will compromise visual performance. Although scratch and abrasion resistance testing is well developed, there is little information available regarding visual acuity through lenses scratched in an actual work environment. METHODS: We collected protective eyewear from mine and smelting operations that had been returned because vision through the lenses was unacceptable due to scratches and abrasions. Forward scattered light was measured on both cleaned and partially cleaned lenses using both haze and light diffusion measurements. Visual acuity through a selection of lenses was determined for both high and low contrast letters under photopic light levels. RESULTS: Lenses with scratches in the central region had haze values ranging from one to 30 per cent. The highest haze values were measured on lenses that were both scratched and covered with dirt, whereas haze values less than 10 per cent were measured on lenses that had the dirt removed and just had scratches in the central region. Light diffusion values were highly correlated with haze. Visual acuity for high and low contrast letters became worse as the percentage haze increased but the linear correlation was only moderate. CONCLUSION: The appearance of the scratches on the lens surfaces strongly suggests that they were a result of improper lens cleaning. The findings also suggest that haze values less than two per cent or a luminance reduction factor less than 3.0 cd/(m(2) lx) are unlikely to affect high and low contrast acuity.

Ballistic impact resistance of selected organic ophthalmic lenses.

PURPOSE: The aim was to assess the impact resistance of coated and uncoated mid-index spectacle lens materials using the ballistic impact test. METHODS: Nominally plano lenses of each material in three thicknesses were obtained. The lenses were flat edged to a 50 mm diameter. Each lens was impacted by a 6.35 mm steel ball. Impact velocities were selected using the Zippy Estimation by Sequential Testing protocol to determine the threshold fracture impact velocity. RESULTS: Threshold fracture impact velocity generally increased with thickness; however, there was a wide variation in performance among the various lens materials at each thickness. In all but two instances, the differences in impact velocity at each thickness of lens material were significant. Comparison of the data for CR39 and Hoya Phoenix with the results of earlier studies showed that the lens mounting is a significant factor. The fracture velocities found in the present study were significantly lower than the fracture velocities found when the lens edge is restrained in the mounting. A scratch resistant coating reduced the impact resistance of CR39. The effect of the antireflection coating on the fracture velocity depended on the nature of the base scratch-resistant coating. CONCLUSIONS: Mid-index lens materials of the same thickness show widely varying levels of impact resistance under the ballistic test. Impact resistance increases non-linearly with centre thickness. The lens mounting might affect the results of the ballistic impact test. The presence of 'cushion coatings' might enhance impact resistance.

Prescription compliance in ophthalmic lenses.

PURPOSE: Tolerances required for ophthalmic lenses are set down in national and international standards. It appears that the compliance of manufactured lenses has not been reported previously. Assembling a statistical quantity of lenses of a single prescription is usually an expensive process. It was, secondary to a lens impact study, possible to assemble a large number of plano lenses. In the assessment of the fracture velocity of lenses approximately 20 plano lenses of each material and thickness are required. Prior to using lenses for the impact study, they were checked for prescription. The results of the prescription measurements are reported here and the results of the impact study are reported in a separate paper. METHODS: Using an automated focimeter, 679 plano lenses in stock thickness, typical occupational eye protector thickness and up to 3.5 mm thick were measured. There were 21 combinations of material/thickness/coating from seven suppliers. The power was evaluated against Australian Standard 2228.1-1992, as the lenses were supplied in Australia. The permitted tolerances are ±0.09 D sphere and ±0.06 D cylinder. RESULTS: When assessed for material/thickness/coating combination, failure rates varied from <0.0001 per cent to 77.5 per cent (with a further 17.3 per cent classified as borderline, because they were within the uncertainty of measurement of the required limit). Grouped by supplier, the failure rates ranged from <0.0001 per cent to 7.6 per cent (with a further 12.3 per cent borderline). To improve understanding of the result, it may be easier to quote the figures without considering uncertainties. When assessed by supplier, the failure rate varies from <0.0001 per cent to 12.6 per cent. CONCLUSIONS: Compliance of plano lenses should be among the easiest of tasks for a laboratory. While we know of no defined or required acceptance rates for prescription lenses, a failure rate for a laboratory of 12.6 per cent, which includes a failure rate of 88 per cent in 2.8 mm thick refractive index = 1.53 hard coated lenses (n = 20) cannot be considered satisfactory and is a strong indication of a failure to check lenses before they leave the laboratory.

Effects of 400 nm, 420 nm, and 435.8 nm radiations on cultured human retinal pigment epithelial cells.

The present study demonstrates narrowband short-wavelengths radiation- (400, 420, and 435.8 nm) induced cellular damage of cultured human retinal pigment epithelial cells using in vitro biological assays to determine wavelengths that are responsible for photochemical lesions of the retina. This work involved the exposure of retinal pigment epithelial (RPE) cells (ARPE-19) to narrowband light of three different wavelengths (400, 420, and 435.8 nm) using a xenon arc lamp and interference filters. Cellular viability, mitochondrial distribution, and nucleic acid (both DNA and RNA) damage were quantified after various energy levels of exposure, using the Alamar blue assay, and confocal laser scanning microscopy with two fluorescent stains (Rhodamine 123 and Acridine Orange). The results clearly show that 400 nm light radiation can cause significant dose-dependent decreases in RPE cell viability as well as degradations of DNA/RNA and mitochondria in RPE cells, while 420 and 435.8 nm light radiation cause no cellular damage. While further evaluations may be needed to assess specificity and confounding factors of these assessment tools, the results may be a matter for consideration in future IOL design efforts.

Effect of multiple antireflection coatings on impact resistance of Hoya Phoenix spectacle lenses.

PURPOSE: To investigate how the impact resistance of Hoya Phoenix spectacle lenses is affected by centre thickness and the application of a multilayer antireflection (MAR) coating. METHODS: Four groups of plano lenses were tested: dress thickness with scratch resistant (SR) coating on both surfaces, dress thickness with SR and MAR, industrial thickness with SR and industrial thickness with SR and MAR. Lenses were edged to a clear circular aperture of 50 mm with a 0.5 mm hidden bevel and mounted in a specially-designed lens support. A pneumatic gun was used to propel a 6.35 mm steel ball at the centre of each lens. Impact speed was varied using the ZEST protocol to determine the threshold breakage speed. RESULTS: The threshold breakage speeds of the dress and industrial thickness SR lenses were 55.1 and 63.2 m/s, respectively and the corresponding threshold breakage speeds for SR-MAR lenses were 50.1 and 54.7 m/s. All comparisons were statistically significant using Student's t-test with a rejection level of p < 0.005. Unlike polycarbonate lenses, dress thickness Phoenix lenses do not display 'oilcanning' deformation on high energy impact and therefore are less likely to be dislodged from their mountings. CONCLUSIONS: We found that the mean impact resistance of the Phoenix lenses was greater than the level required of eye protector lenses by the standards AS/NZS 1337:1992, ANSI Z87.1-2003 and CSA Z94.3-02. Similar to CR39 and polycarbonate, the application of MAR to Phoenix lenses reduces their impact resistance, however, they provide an acceptable level of impact protection in industrial settings, where there is little danger of exposure to pointed or sharp-edged high-speed missiles.

The effect of multiple antireflective coatings and center thickness on resistance of polycarbonate spectacle lenses to penetration by pointed missiles.

PURPOSE: Previous work has shown that the impact resistance to blunt missiles is affected by coatings applied to either CR-39 or polycarbonate lenses. We investigated the effects of multiple antireflection (minimum angle of resolution [MAR]) coatings on the resistance of polycarbonate lenses to puncture on impact by sharp, high-speed missiles. METHODS: Four groups of surfaced plano polycarbonate lenses were investigated. Two groups had a scratch-resistant (SR) coating applied to both surfaces. One of these groups had a 2-mm center thickness and the other had a 3-mm center thickness. The other two groups of 2-mm and 3-mm thick lenses had a MAR coating applied over the SR coating. The lenses were impacted by a missile consisting of an industrial sewing machine needle mounted in a cylindrical aluminum carrier. RESULTS: The sharp missiles were able to pierce the lenses at speeds between 29.6 m/s and 46.2 m/s. Impact resistance was lowest for the thinner lenses and lenses with a MAR coating. The effect of the MAR and lens thickness was subadditive. CONCLUSIONS: We have confirmed previous observations that polycarbonate lenses are more susceptible to penetration by sharp, high-speed missiles than blunt missiles. We have also found that reducing lens center thickness and applying a MAR coating further reduces the penetration resistance. Therefore, the use of 2-mm center thickness and MAR-coated polycarbonate lenses should be discouraged for industrial eye protectors where sharp missile hazards are possible.

Durability of coated CR-39 industrial lenses.

PURPOSE: To study the effect of coatings on the resistance of CR-39 industrial plano lenses to ballistic impacts and abrasion from fine particles. METHODS: Twelve groups of CR-39 lenses with various scratch-resistant (SR) or combinations of scratch-resistant and antireflective (SR-AR) coatings were mounted in metal industrial spectacle frames. The ZEST protocol was used to determine the mean impact speed for breakage of each lens group using the Canadian Standards Association ballistic test protocol. One pair of lenses from each group was tested for abrasion resistance using the falling sand method. Abrasion resistance was ranked by the degree of haze observed by three independent observers. RESULTS: Uncoated lenses had the best impact resistance and worst abrasion resistance. SR-coated lenses showed mild to moderate reductions in impact resistance, with no correlation between impact and abrasion resistance. SR-AR-coated lenses had very good abrasion resistance, but severely reduced impact resistance. CONCLUSIONS: Most SR-coated CR-39 lenses have a high probability of meeting the high-velocity impact resistance requirement of industrial lenses, whereas CR-39 lenses with SR-AR coats are too fragile to be used in industrial spectacles. As a group, the SR-AR coating tended to be more resistant to abrasion by fine particles and less resistant to ballistic impacts, but the abrasion resistance of the SR-coated lenses was more variable, and, thus, overall there was no significant correlation between impact resistance and abrasion resistance.

Evaluation of a porcine lens and fluorescence assay approach for in vitro ocular toxicological investigations.

Cell biology, as monitored with the fluorescent indicator dyes Alamar Blue and 5-carboxyfluorescein diacetate acetoxymethyl ester (CFDA-AM), and lens optical quality, as measured with an in vitro scanning laser system, have been used to evaluate in vitro the condition of porcine lenses after being placed in a culture medium. The measurements, beginning from week one of culture, were compared statistically. Optical quality and cellular viability, as measured with either dye, were unchanged in lenses that had been maintained for 6 weeks in modified M199 medium. Some lenses were treated with 0.152J/cm(2) UVB radiation, and a decline was observed after 48 hours in both optical and metabolic capabilities, as indicated by a decreased capacity of the lenses to reduce Alamar Blue. The measurements with CFDA-AM did not show complete concordance with the other indicators of lens health after UV treatment, making this dye less reliable as applied currently to lens cultures. Overall, the findings suggest that porcine lenses can be maintained for weeks in culture, and that their condition can be evaluated quantitatively by assays that probe cellular functions and optical properties. Such a system should prove valuable for in vitro ocular pharmacotoxicological research.