Chronic exposure to the ultraviolet radiation levels from arc welding does not result in obvious damage to the human corneal endothelium

Abstract

Occupational exposure of the cornea to ultraviolet radiation (UVR, e.g. in welding) is a well-known cause of ‘arc eye’ (photo-keratoconjunctivititis), but has also been considered to be a risk for the development of alterations in the size (polymegethism) and shape (pleomorphism) of the deeper-lying human corneal endothelial cells. Human data are however limited and so a further study was undertaken, with a control group. Non-contact specular micrographs of the central region of the corneal endothelium were obtained from 40 white males aged between 32 and 63 years; 20 were arc welders with an average of 25 ± 7 years job experience, while the others were office workers (n = 20). All the welders reported occupational exposure to UVR (i.e. welders ‘flashes’) and up to 3 times per year. None of the subjects had a history of contact lens wear, major eye disease or surgery. The endothelial image was scanned, projected onto an overlay and cell border marking carried out in a masked fashion. The overlay was independently analysed, by a customised semi-automated method, providing cell-border-adjusted data on cell areas and cell shape (sides) on 124 to 260 cells per image. The endothelial cell density (ECD) values were also calculated from individual cell area values. All corneas appeared to be healthy, and showed no fluorescein staining indicating damage to the surface epithelium. Central corneal thickness values were normal at 0.531 ± 0.031 (mean ± SD) and 0.527 ± 0.036 mm in the welders and non-welders respectively. All endothelia appeared healthy, with no evidence of cell oedema. The group-mean endothelial cell area was 393 ± 35 and 392 ± 21 µm², ECD values were 2855 ± 224 cells mm⁻² and 2852 ± 210 cells mm⁻², while the percentages of 6-sided cells were 60 ± 5.2 and 59 ± 4.1% respectively. Cell area distributions were statistically identical (p ≥ 0.8), and cell area-side relationships were marginally, but not statistically different. This study does not indicate that chronic ultraviolet radiation exposure, through occupational welding (mainly electrical arc), results in or is associated with endothelial cell polymegethism and pleomorphism. This may indicate that, despite the periodic flash welding exposures, the exposure levels are still below those needed to cause damage to the corneal endothelium. This study outcome can be taken to indicate that despite the occurrence of welders flash episodes, the eye protection habitually used by these workers was adequate to protect their corneal endothelium.