ABSTRACT
Solar radiation causes acute foveal injury resulting in outer retinal defects. Symptoms often follow an event of unprotected gazing at a solar eclipse or directly viewing the sun. We encountered a series of cases during winter among habitants of high altitudes who complained of visual field scotomas. All of them had a typical history of prolonged sunbathing but denied gazing at the sun directly. Optical coherence tomography showed outer retinal defects involving the ellipsoid zone characteristic of solar retinopathy in all patients. In this case series, we would like to emphasize the role of geographical factors in the causation of solar retinopathy.
Introduction
Outer retinal defects are defects in the ellipsoid zone which predominantly involve the foveal cones. They often present with acute central scotoma following unprotected solar eclipse or sun viewing. These defects can also be caused by trauma, acute posterior vitreous detachment, and unprotected welding exposure.1 Eliciting a proper history can point towards the possible etiology and helps in formulating preventive measures. We encountered a series of patients with outer retinal defects who resided at high altitudes. They had no significant risk factors except for the history of prolonged sunbathing, which suggested solar retinopathy as a possible cause of the outer retinal defects.
Discussion
Outer retinal defects can be secondary to intrinsic ocular factors like acute posterior vitreous detachment (PVD), macular telangiectasia, Stargardt’s disease, and extrinsic factors like trauma, unprotected direct eclipse/sun-gazing, and welding arc exposure.1,2 Thorough history-taking is paramount to ascertain the etiology, since ultra-structural retinal changes due to all the above causes appear similar on OCT.
Solar retinopathy is an acute injury to foveal structures resulting from staring at the sun during a solar eclipse or during normal daylight hours. Patients often correlate the onset of symptoms with the event of sun-gazing or viewing a solar eclipse without protective glasses. Ultraviolet (UV) light from solar radiation is toxic to photoreceptors as well as the RPE. The major component of damage to the retina by UV radiation is through the photochemical pathway. It causes lipid and protein peroxidation in RPE cells, leading to loss of lysosomal integrity and cell death. Various morphological presentations have been described in OCT secondary to solar retinopathy, namely inner retinal layer hyperreflectivity, outer layer hyperreflectivity, full-thickness retinal hyperreflectivity, outer layer retinal defects, and foveal thinning in long-standing cases.3 In the present case series, all patients had outer retinal layer defects on OCT. None had predisposing factors or history of prolonged gazing at the sun. The common factor among them was repeated sunbathing for a few hours.
All of the patients resided in the Solan district of Himachal Pradesh, India. This area is at an altitude of approximately 1,300-1,500 m above sea level and often has snowfall in winters. It is well known that high altitudes above 1,350 m can cause deleterious health effects. The quantity of UV light increases with altitude at a rate of 4% for each 300 m ascent. A combination of high altitude and snow at 2,000 m results in twice the amount of UV light compared to sea level.4
UVB (280-340 nm) waves can cause a wide range of pathologies from snow blindness to skin cancer. UVB rays increase with high altitude, and high surface reflectivity (sand, watery snow, glass, metal) can increase the net solar irradiance.5 Yannuzzi et al.6 observed a similar series of cases with foveal pseudocyst presenting with an acute central scotoma. They had no history of prolonged sun gazing but had sunbathed and exercised under the sun for long hours. The author extensively analyzed the geophysical factors and attributed the occurrence of solar retinopathy to clear sky, exposure to solar noon, and possibly UVB radiation due to relatively lower ozone layers. Age-related lenticular changes reduce the transmission of radiant energy and protect the retina.7,8 In this series, all had a clear lens and were emmetropic, putting them at risk of damage by UV radiation.
The impact of altitude on the retina is secondary to a hypoxic environment. They present with engorged retinal vessels, retinal hemorrhages, and disc edema.9 The patients in this series were habitants of high altitudes. Though changes of altitudinal retinopathy were not seen, its deleterious effects might have added to the insult apart from sunbathing.
The other causes of outer retinal defects in this series were ruled out with good history taking and imaging. None of the patients’ OCT images showed PVD (except patient 1, Figure 1b) or gross vitreoretinal anomalies. The second patient exhibited ILM drape sign (Figure 1a) but the fundus had no parafoveal telangiectatic vessel or grey hue reflex suggestive of macular telangiectasia. No history of any intraocular procedure, topical or systemic medication, or previous hospitalization ruled out other causes of outer retinal defects.
To conclude, the present case series documents the occurrence of outer retinal defects as a presenting feature of solar retinopathy in individuals living at high altitudes who reported prolonged sunbathing under the direct sun to combat the cold climate but denied direct sun-gazing. This series adds additional evidence to the existing literature about the harmful effects of prolonged unprotected sun exposure at high altitudes.
