By Kai Rands, ABOC, NCLEC

An optician’s customer reports experiencing symptoms of asthenopia. Suspecting digital eye strain, the optician asks about screen use. Based on the customer’s answers, the optician estimates that the customer may spend about 7 hours viewing screens per day. The customer is also exposed to prolonged direct sunlight as an avid hiker on the weekends. Both sunlight and digital screens emit high-energy-visible (HEV) light–the blue light between wavelengths of approximately 380 and 450 nm (NIH). The optician knows that digital devices contribute a small proportion of HEV light as compared to sunlight. In fact, an individual outdoors on a sunny day is exposed to 100 to 500 times as intense HEV light as when viewing digital devices, as Jackie O’Keefe Lincoln reminded attendees of the September of 2023 continuing education series hosted by SECO/ NAO. Because the customer is exposed to both sunlight and digital screens, the optician recommends blue-light protection. As the optician enters the order, the optician wonders how HEV light contributes to asthenopia symptoms, such as sore eyes.

A research team led by Nan Gao investigated the role of the cornea in asthenopic-like responses in mice exposed to blue light. One group of mice spent 12 hours in a blue-light lit room. A second group was exposed to white-light instead of blue-light. The intensity of the light for both groups was 320 lux, the approximate intensity of light in an office setting. Both groups spent the next 12 hours in darkness. The mice exposed to blue light wiped their eyes more often than those exposed to white-light. Analgesic eye drops greatly reduced how often the blue-light exposed mice wiped their eyes, a sign that blue light exposure contributes to ocular pain responses.

The cornea has more sensory nerve endings per square millimeter than any other part of the body. If blue-light exposure relates to ocular pain responses, we might wonder whether there are also changes to the sensory nerve endings in the cornea. Gao and colleagues found that the blue-light exposed mice showed several differences compared to the white-light exposed mice. The nerve fibers in the corneal stroma of the blue light exposed mice branched more often. These nerve fibers had more bends and had more beaded structures. Not only did blue-light exposure lead to asthenopic-like symptoms and increased pain responses among the mice, these changes were associated with neural structural changes in the cornea.

Other articles, such as a review by Sunali Goyal and Pedram Hamrah in 2016, have noted associations between ocular pain and nerve fiber differences among humans. For example, patients with ocular pain related to diabetes also show more corneal nerve branching and neural bead-like structures. While recent research has focused on blue-light induced damage to the retina, Gao’s research team’s investigation shows that blue-light also appears to affect the cornea and leads to nerve fiber changes. The aforementioned optician’s recommendation for blue-light protection may not only reduce asthenopia and ocular pain but also prevent neural structural changes in the corneal stroma.

Gao, N., Lee, P. S., Zhang, J., & Fu-Shin, X. Y. (2023). Ocular nociception and neuropathic pain initiated by blue light stress in C57BL/6J mice. Pain, 164(7), 1616-1626.

Goyal, S., Hamrah, P. (2016). Understanding neuropathic corneal pain–gaps and current therapeutic approaches. Seminars in Ophthalmology, 31,1-2, 59-70.

O’Keefe, J. (September, 2023). The chronicles of digital devices and their relationship to CVS and DES. Session presented at the SECO/ NAO continuing education series.