The switch from daylight saving time to standard time—and vice versa—affects not only the time of day but apparently also the human body. A new study by researchers at Northwestern Medicine shows that the time change may be linked to an altered risk of certain retinal vascular diseases. In particular, the switch to daylight saving time in the spring—which results in the loss of one hour of sleep—appears to play a role. The researchers found that the risk of certain retinal vascular diseases could be up to 30 percent higher in the month following the change. The results were published in the journal Scientific Reports.

One Hour Less Sleep—Effects on the Eye?

The study was led by Dr. Rukhsana Mirza, a professor of ophthalmology at Northwestern University. The study suggests that even a relatively small change in the daily rhythm can affect sensitive biological processes.

“Our study suggests that an extra hour of sleep could protect against the risk of disease,” explained Mirza. People who notice new vision problems or other eye symptoms after the time change, in particular, could benefit from a more thorough examination. The human body has a natural 24-hour clock—the so-called circadian rhythm. This influences numerous processes:

• the sleep-wake cycle,
• hormone production,
• body temperature,
• metabolism,
• and the activity of various organs.

The time change can temporarily throw this internal clock out of balance. The spring time change, in particular, is stressful for many people because the body loses an hour of sleep. The researchers suspect that this disruption could have similar effects to other situations involving sleep deprivation: inflammatory processes may be exacerbated, metabolism may change, and the strain on the cardiovascular system may increase.

Why the Retina Is Particularly Sensitive

The retina is the light-sensitive layer at the back of the eye. It converts light signals into nerve impulses, thereby enabling vision. At the same time, the retina is one of the body’s most metabolically active tissues. It requires a particularly good supply of oxygen and nutrients and possesses one of the most complex networks of tiny blood vessels. For this reason, the retina is also considered a kind of “window into the body.” Changes in its blood vessels can provide clues about general health processes. The retina’s particular sensitivity is primarily related to its high energy requirements. The light-processing sensory cells of the retina—especially the so-called photoreceptors (rods and cones)—work constantly and require large amounts of oxygen. Even minor changes in blood supply can therefore impair the function of these cells.

The tiny blood vessels of the retina are highly sensitive to changes in the entire vascular system. Conditions such as diabetes, high blood pressure, or inflammatory processes can therefore often manifest early in the retinal vessels. For this reason, ophthalmologists use retinal examinations not only to assess visual acuity but also as an indicator of potential changes throughout the body. The smallest blood vessels in particular—known as microvessels—play a crucial role in this process. They supply the retina with oxygen and nutrients while simultaneously regulating blood flow with great precision. Disruptions in this sensitive system can lead to vascular occlusions, circulatory problems, or damage to nerve tissue.

The connection between the retina and the body’s internal clock is also particularly interesting: The retina contains special light-sensitive cells that are not only responsible for vision but also transmit information about light and darkness to the brain. These signals help control the body’s internal clock and adjust the sleep-wake cycle. This creates a direct link between light perception, sleep regulation, and biological processes in the body. A disruption of this system—for example, due to changes in light conditions or sleep patterns—could therefore also affect the health of the retina.

For the study, the team analyzed health data from more than 18 million people aged 18 to 64. The data came from the U.S. health insurance database Merative MarketScan Commercial Database and covered the period from 2012 to 2014. The researchers examined newly diagnosed cases of various retinal vascular diseases:

• retinal artery occlusion (RAO),
• retinal vein occlusion (RVO),
• proliferative diabetic retinopathy (PDR),
• neovascular age-related macular degeneration (nvAMD).

They then compared the incidence rates following the time change with control periods in summer and winter.

Spring and Fall Show Different Effects

The results revealed a different pattern between the spring and fall time changes. After the switch to daylight saving time in the spring—which results in the loss of one hour of sleep—the risk of certain retinal diseases increased:

• The risk of a new diagnosis of certain diseases rose by up to 30 percent.
• Proliferative diabetic retinopathy and neovascular age-related macular degeneration were particularly affected.

After the switch to standard time in the fall, however, the opposite effect was observed:

• The risk of certain retinal vascular diseases was about 20 percent lower in the month following the change.

The researchers suspect that the extra sleep gained from the extra hour could play a protective role.

Possible Explanation: Sleep, Inflammation, and Metabolism

Why the time change might affect the retina is not yet fully understood. One possible explanation lies in the effects of a disrupted sleep rhythm. Previous studies have already shown that sleep deprivation and changes in the body’s internal clock can be linked to various health problems, including:

• inflammatory responses,
• metabolic changes,
• and an increased risk of cardiovascular disease.

Links between the summer time change and an increased risk of heart attacks or strokes have also been examined in earlier studies. This new research now extends these findings to the field of ophthalmology.

What Does this Mean for Those Affected?

The researchers emphasize that further studies are necessary. The current study is based on insurance data from a limited time period and can only demonstrate an association. For example, it was not possible to account for all individual factors such as:

• sleep habits,
• diet,
• physical activity,
• genetic risks,
• and personal circumstances.

Future studies will examine whether the results can be confirmed in other population groups and over longer periods of time. The findings do not mean that the time change automatically causes an eye disease. For most people, the time change remains a temporary strain to which the body adapts within a few days. Nevertheless, certain groups of people may be particularly sensitive to changes in sleep—such as those with existing medical conditions, sleep problems, or an increased risk of vascular disease. If symptoms occur suddenly, an eye exam should always be scheduled promptly. These symptoms include:

• loss of vision,
• blurred vision,
• dark spots in the field of vision,
• new vision problems

Conclusion: The Body’s Internal Clock May also Influence Eye Health

The new study shows that the effects of the time change may extend further than previously assumed. A single hour of time shift could influence biological processes related to inflammation, metabolism, and vascular health. Of particular interest is the possible connection between sleep, the body’s internal clock, and retinal health. The findings provide a new approach to research and demonstrate how closely interconnected various systems of the human body are.

The study makes it clear that the eyes cannot be viewed in isolation but work closely with other bodily processes. The retina not only responds to light stimuli but is also connected to the biological clock, which controls numerous functions throughout the body. Although the time change alone does not cause eye disease, changes in sleep and disruptions to the natural rhythm could place an additional strain on certain individuals. It may be particularly important for people with existing vascular risks, diabetes, or other chronic conditions to monitor changes in their health and vision.

Further research will need to determine exactly which biological mechanisms are involved and whether this could lead to new possibilities for the prevention or treatment of retinal vascular diseases in the future. The findings serve as a reminder that adequate sleep and a daily rhythm that is as stable as possible are important components of overall health—and may also contribute to protecting eye health.