Ocular protection in congenital erythropoietic porphyria: A potential role for gaming glasses.

Abstract

Congenital erythropoietic porphyria (CEP) or Günthers disease is a rare hematological porphyria, which occurs due to an inherited reduction in activity of the uroporphyrinogen III synthase enzyme (UROS). This results in the accumulation of water soluble, type I isomer porphyrins in the skin.1 Exposure to violet light in the Soret waveband (roughly 400– 410 nm) leads to the development of blisters on exposed skin, scar formation and subsequent disfigurement. Uroporphyrins are also deposited in other body tissues including the eye. Exposure of the ocular surface to violet light leads to vesicle formation, scarring, and symblephara. Scleral damage includes both acute scleritis and slowly progressive scleral necrosis, and may be accompanied by corneal thinning, perforation, visual loss and significant morbidity.2,3 Early education regarding the importance of photoprotection for patients with CEP is vital to limit the development of irreversible ocular damage. Many sunglasses offer a high level of protection against UVA and UVB helping to prevent against chronic UV exposurerelated cataract and pterygium formation. However, the protection afforded by standard sunglasses is only guaranteed up to 380 nm in Europe (BS EN ISO 123121:2013) and thus offers patients with CEP little or no protection against ocular damage caused by porphyrinrelated, short wavelength, visible light.4 Despite this, patients with CEP rely on standard sunglasses or, in some instances, nothing at all, given that the orangetinted lenses that provide protection against short wavelength visible light are often considered cosmetically unacceptable. Such behavior puts patients at risk of exposure to potentially damaging levels of visible light. In recent years, there has been increasing public awareness of the negative impact of exposure to artificial blue light on sleep.5,6 This has led to the manufacture and marketing of blue light protecting glasses to protect the eyes against blue light from computer and mobile device screens (gaming glasses). In view of these potentially useful properties for patients with porphyria, we undertook a small study to assess the wavelength of light blocked by these lenses to determine whether the protection might be sufficient to recommend their use in CEP. Seven different pairs of gaming spectacles were randomly selected and purchased online via Amazon UK marketplace (Table 1). The optical transmission characteristics of all lenses were measured using a DMC150 Bentham spectroradiometer (Bentham Instruments) in a radiation beam from an Abet 2000 Solar Simulator (Abet Technologies, Inc) in the ultraviolet and near visible region from 250 to 500 nm. Comparison of the transmitted spectrum of each lens with that of the unfiltered monochromator was used to derive the lens transmission.7 Of the seven spectacles (G1– G7) tested, five reduced transmission within the CEP spectral band (400– 415 nm) by more than 94% and six by more than 87%. Two pairs of glasses, G2 and G3 attenuated all incident UV and near visible radiation from the solar simulator between 250 and 410 nm, with G2 extending to around 415 nm (Figure 1). The G6 pair also exhibited a unique transmission characteristic with reduced transmission at all wavelengths tested. Since no safe minimum threshold for light within the 400– 410 nm region (peak wavelength absorbed in CEP) has been established for these patients the ideal protective eyewear should completely block any incident radiation within this spectral band. Our study identified two lenses, the CGID (G2) and the LifeArt (G3) which satisfied this requirement with both lenses completely attenuating incident UV and near visible radiation (see Table 1). We also determined the UV protection afforded by all the gaming glasses tested. All but one pair of glasses completely attenuated incident UV radiation. The remaining pair (G7) was found to have a total UVB and UVA transmission between 280– 315 nm and 315– 380 nm of approximately 17% and 26%, exceeding BS EN ISO 123121 recommendation of 0.5% maximum transmittance4 (Figure 1). Were gaming glasses not to provide UV protection, the reduction in intensity of light reaching the eye could lessen the eye's protective forced closure and pupillary contraction and could lead to an increase in UV light reaching ocular surfaces and deeper ophthalmic tissues of these patients. Reassuringly, our results have demonstrated that most gaming glasses assessed did provide adequate UV protection; however, the protection provided by one pair proved inadequate to both UV and blue light despite advertising to the contrary. Therefore, we would advise confirming the range of protection provided by any pair of glasses purchased by an individual before recommending their use. If gaming glasses are to be recommended for use both indoors and outside by patients with CEP, frames and lenses need to be considered cosmetically acceptable. A variety of frames were observed amongst the glasses tested, with a larger range of frames available online; from fine frames that simulate those of prescription glasses, to close fitting, wraparound styles that provide peripheral coverage from scattered and reflected light that might otherwise reach the eye.7 Such choice should enable the purchase of a cosmetically