Diagnosis and management of solar retinopathy

(Image credit: AdobeStock/Kevin Carden)

The April 8 total solar eclipse is a once-in-a-lifetime event for many people, and rare occurrences such as eclipse have enthralled humans since the dawn of time.

An estimated 44 million people live inside the 115-mile-wide path of totality when the solar eclipse passes over the United States. When it makes a path across North America, it could be prime time for eye damage known as solar retinopathy.

Viewing a total solar eclipse can be an awe-inspiring event as the moon crosses the path of the sun, blocking its light slowly until totality occurs. During the period of totality, the brief period of a total eclipse when the moon fully covers the sun (only a couple of minutes), the light of day gives way to a deep twilight sky.

During this period, the sun’s outer atmosphere, which is known as the solar corona, comes into view, appearing as a halo surrounding the moon. Stars may become visible and birds stop chirping.

While viewing the eclipse is a memorable event, looking directly at the sun can result in eye damage, and without proper eye protection, retinal damage can happen.

According to a study1 by Johns Hopkins retina specialists Fernando Arevalo, MD, Neil Bressler, MD, and research fellow Jun Kong, MD, viewing a solar eclipse without proper eye protection can burn the macula.

“When the moon completely blocks the sun at the minute of a total solar eclipse, dangerously, a person might look at the eclipse without protection and falsely believe that it is safe to view,” the researchers wrote. “However, within a few seconds, as the moon continues to move, bright sunlight suddenly might be focused on the unprotected macula.”

The trio noted in the study that even a few seconds of such viewing can temporarily or permanently burn the center of the retina.

“Once retina tissue is destroyed, like brain tissue, it cannot regenerate, resulting in permanent central vision loss,” they wrote.

NASA estimates that about 31.6 million people live in the path of totality this year, compared to 12 million in the path of the last eclipse in 2017. NASA also noted that totality in April's eclipse will also last longer than it did in 2017. During the last eclipse, the longest period of totality was near Carbondale, Illinois, at 2 minutes, 42 seconds. The maximum totality during the April event will last up to 4 minutes, 28 seconds, in an area about 25 minutes northwest of Torreón, Mexico.

NASA also noted that across the U.S., durations longer than 4 minutes will stretch from Texas as far north as Economy, Indiana. According to NASA, as the eclipse leaves the US and enters Canada, totality in the center of the path will last up to 3 minutes, 21 seconds.

Viewing a total solar eclipse can be an experience, but looking directly at the sun can seriously damage the retina. People who damage their eyes looking at the sun won’t know until it is too late. Looking at the sun without proper eye protection

Ophthalmologists could see an influx of patients exhibiting symptoms and signs of solar burns on the retina.¹

A diagnosis might be made on clinical evaluation or with diagnostic tests such as optical coherence tomography. Treatment is observation; sometimes there is partial recovery of vision.

Solar retinopathy

Solar retinopathy is caused by prolonged or high intensity exposure of the fovea centralis to light energy. Suspected cases of solar retinopathy may require urgent referral to an ophthalmologist for diagnosis, and to eliminate treatable causes for central visual disturbance.

Retinal phototoxicity is thought to be caused by the formation of free radicals and reactive oxygen species from incident ultraviolet energy (longer wavelength UV-A, shorter wavelengths of visible light, and near infrared wavelengths). The duration of exposure can be as short as a few seconds. It is not caused by direct thermal injury.

Phototoxicity leads to disruption of the retinal pigment epithelium (RPE; layer of cells underlying and supporting the retina), as well as damage to the choroid (blood vessels underlying the RPE) and vesiculation and fragmentation of photoreceptors. Resolution of these signs has been observed in animal models from 10 days after injury.

Diagnosis

A diagnosis of solar retinopathy typically is based on history, fundoscopic examination and ophthalmic imaging.

According to the American Academy of Ophthalmology, symptoms can include:

• Unilateral or bilateral blurred vision
• Headache
• A blind spot in your central vision in one or both eyes
• Increased sensitivity to light
• Distortion of shapes. For example, a straight line looks bent or a door jamb looks curved
• Changes in the way you see color

In addition to viewing an eclipse without protection, the symptoms can be the result of exposure to laser pointers, recent intraocular surgery and past ophthalmic history.

Patients may present with a reduction of visual acuity from the level of 6/7.5 to 6/36 or worse. Fundoscopy of both eyes with a hand-held ophthalmoscope should be attempted. Findings may range from no abnormalities in mild cases, to a yellow-white spot in the central macula, progressing to a reddish spot over days.

Management

Treating solar retinopathy is not exact, with no proven methods. Patients should be counselled to abstain from further sungazing or eclipse viewing.

The use of corticosteroids should be done with caution, and systemic steroids can present a risk for other macular diseases, and cataract formation and raised intraocular pressure.

While solar retinopathy shares some features of age-related macular degeneration, there is little evidence backed by studies in humans to show a benefit from anti-oxidants for solar retinopathy.

A surefire way to avoid eye injury is to use the method used by astronomers, projecting an image of the eclipse onto a screen. Eclipses may also be watched on televised broadcasts. The use of solar filers also can provide protection. These solar filters are used in eclipse glasses or hand-held solar viewers. They must meet a very specific worldwide standard known as ISO 12312-2.

References:

1. Arévalo JF, Kong J, Bressler NM. Safely Viewing Solar Eclipses. JAMA. 2017;318(11):1080. doi:https://doi.org/10.1001/jama.2017.9495