For the first time, Northwestern Medicine scientists have detailed how the semiannual clock changes impact a person's risk of developing retinal vascular disease, a group of disorders that affect blood vessels in the retina and can lead to vision loss. The findings were published last month in Scientific Reports, a Nature Portfolio journal.

The nationwide analysis of more than 18 million patients found an up to 30% higher risk of developing retinal vascular disease in the month following the transition to daylight saving time in the spring, and a 20% lower risk of disease in the month following the transition back to standard time in the fall.

"Our study suggests gaining an hour of sleep may be protective against disease risk," said study lead author Dr. Rukhsana Mirza, professor of ophthalmology and medical education at Northwestern University Feinberg School of Medicine. "Even one hour of change can impact a patient's health and perhaps patients who are reporting new symptoms in the period after a change in time, specifically in the spring, may warrant closer evaluation."

The findings come as the U.S. House of Representatives passed a measure this week to make daylight saving time permanent. The fate of the measure in the Senate is uncertain.

Seasonal clock changes have been shown to cause disruptions in circadian rhythm, the body's 24-hour internal clock that regulates the sleep-wake cycle, hormone production and body temperature, among other essential bodily functions. The retina - the innermost, light-sensitive layer of tissue in the eye - provides a "window to the body" and plays an important role in circadian rhythm, Mirza said.

Recent studies have shown an association between seasonal clock changes, which can result in disrupted sleep, and increased risk of acute cardiovascular events, including stroke.

"We have seen how daylight saving time transitions, particularly the spring transition when we lose an hour of sleep, are associated with increased rates of heart attack and stroke. This led us to ask if these similar effects would be happening in the retina, which is one of the most metabolically active tissues in the body and contains some of the body's most complex microvascular networks," Mirza said.

The findings

To understand how circadian disruption impacts eye health, Mirza's team analyzed health insurance claims data from more than 18 million patients aged 18 to 64 years who were newly diagnosed with retinal vascular disease. Patients were enrolled in the Merative MarketScan Commercial Database between 2012 and 2014.

The Northwestern scientists calculated the incidence of new diagnoses of four retinal vascular diseases in the month following the spring and fall clock changes and during two control periods in January and July. The conditions included retinal artery and vein occlusions, proliferative diabetic retinopathy and neovascular age-related macular degeneration.

The research team then compared disease risk during the week and month following each seasonal clock change.

They found that:

• The month following the spring transition to daylight saving time (when Americans lose an hour of sleep) was associated with a roughly 20-30% higher risk of proliferative diabetic retinopathy and neovascular age-related macular degeneration
• Patients had a roughly 20-40% lower risk of retinal artery occlusion, retinal vein occlusion, proliferative diabetic retinopathy and neovascular age-related macular degeneration in the month following the fall return to standard time

"I think that relationship was pretty interesting, and it makes a lot of sense. There's been literature showing that losing an hour's sleep and circadian misalignment can cause inflammatory responses and metabolic derangements, and there's also been some literature suggesting that getting an hour's sleep in the context of daylight saving might be protective," said Dr. Kyle Chan, a resident physician in the department of ophthalmology at Feinberg and co-first author of the study.

Chan also noted limitations of their study include having access to only three years' worth of patient data but that he hopes future work will replicate their findings using other larger databases.

"In the future, we'd love to see if other groups can replicate our findings in non-overlapping databases, for example those in the academic setting, or look at more years of data as well to see if these findings hold true," Chan said.

The investigators also hope the findings will prompt future studies to investigate the impact of daylight saving transitions and sleep disturbances on a more patient level. "I think this really opens up new opportunities of collaboration between ophthalmology, neurology, sleep medicine, cardiovascular medicine ... really exciting possibilities to understand the whole person," Mirza said.

This study is titled, "Daylight saving time transition and new-onset retinal vascular disease: a nationwide cohort study." It was supported by an unrestricted departmental grant from Research to Prevent Blindness and Merative MarketScan Dissertation Support Program by access to the MarketScan research database.

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