Cataract frequency and subtypes involved in workers assessed for their solar radiation exposure: a systematic review

Methodological quality of the review: Low confidence

Author: Modenese A, Gobba F

Region: Australia, India, China, Iran, France, Greece, Nigeria, Spain, South Korea, Sri Lanka, Myanmar and Pakistan.

Sector: Cataract

Sub-sector: Risk, Solar exposure

Type of cataract: Age-related cataract

Equity focus: None specified

Review type: Other review

Quantitative synthesis method: Narrative synthesis

Qualitative synthesis method: Not applicable

Background:

Cataract is currently the primary cause of blindness worldwide, and one of its main risk factors is solar ultraviolet radiation exposure. According to the localization of lens opacities, three main subtypes of cataract are recognized: nuclear, cortical and posterior subcapsular cataract. One of the main determinants of individual long-term solar radiation exposure is outdoor work.

Objectives:

To determine the risk of cataract in outdoor workers and on the specific subtypes involved, also investigating the methods applied to evaluate the occupational risk.

Main findings:

Authors included a total of 15 studies in the review, of which one was a longitudinal study, nine were cross-sectional/case-control prevalence studies and five were cross-sectional studies. Two studies each were conducted in Australia and India; and one study each was conducted in China, Iran, France, Greece, Nigeria, Spain, South Korea, Sri Lanka, Myanmar and Pakistan. Out of the 15 studies, 12 showed positive association. Authors reported that this included studies which confirmed the relationship between long-term occupational solar radiation exposure with cortical cataract and five new studies to support relationship with  nuclear cataract. However, authors note that no new substantial data were available to support the relation with the posterior subscapular type.

Authors noted that in most of the included studies, the exposure assessment was not adequate to support a representative evaluation of the ocular risk; however, outdoor work is clearly a relevant risk factor for cataract. Authors note that further research providing a better evaluation of the relation between solar radiation exposure levels and lens damage in workers is needed and aimed to establish adequate occupational exposure limits and better preventive measures, studying also their effectiveness.

Methodology: 

Authors conducted a search on Medline (through PubMed) and Scopus databases. Limiters were set to include scientific literature covering a period of 20 years, from 1 January 1997 to 1 January 2017.The reference listings of the selected papers were also checked to find other significant research articles.

Authors’ inclusion criteria consisted of original research articles with an available English abstract published in peer-reviewed journals. Type of study considered for this review were longitudinal and cross-sectional designs. Reviews, case reports, comments or letters were not considered. Authors only considered occupational solar radiation exposure related to outdoor work.

In the studies included in this review, solar radiation exposure was assessed using different methods: a) simple qualitative classification according to the general category of “outdoor” and “indoor” work, or according to the job performed, compared to the list of activities of the European Agency; b) more detailed evaluation of occupational solar radiation exposure based on questionnaire data or on measurements.

Two authors independently screened studies for inclusion, and data extraction was conducted by one reviewer and checked by a second author. Authors conducted a narrative synthesis of included studies.

Applicability/external validity:

Authors note that findings form their review is consistent with other studies and that there is a solid association between occupational solar radiation exposure in outdoor workers and cataract development.

Geographic focus:

Authors note that one study conducted in Australia found a significant adjusted relative risk in labourers, taking into account also leisure solar radiation exposure. In addition, five studies – one each conducted in China, Greece, Spain, South Korea and Australia – found positive adjusted Odds Ratios for cataract or at least for one subtype.

Summary of quality assessment:

Overall there is low confidence in the conclusions about the effects of this study. Authors did not conduct a thorough search of the literature to ensure that all relevant studies were identified and included in the review and restricted the search to published studies only. Therefore this study is prone to publication bias. In addition, authors restricted the search to studies published in English only. Although authors used appropriate methods to screen studies of inclusion, it is not clear if methods used to extract data of included studies were rigorous. Authors do not report assessing the methodological quality of included studies, therefore it is not clear which studies are subject to high or low risk of bias.