Authors: Zachary Snowdon Smith Forbes
Covid-19 infection is linked to eye conditions called retinal vascular occlusions—blockages of blood vessels in the eye that can cause vision loss—according to a study published Thursday by JAMA Ophthalmology that threw light on one of several little-understood long-term effects of the virus.
The first condition, called retinal artery occlusions, can cause sudden blurring or loss of vision in one eye, and was found to have increased 29.9% in the period two to 26 weeks after Covid-19 diagnosis compared to the period 26 to two weeks before diagnosis, researchers concluded.
The second condition, retinal vein occlusions, causes similar symptoms to retinal artery occlusions and was even more strongly associated with Covid-19, with a 47% increase in the period two to 26 weeks after Covid-19 diagnosis compared to the period 26 to two weeks before diagnosis, according to the study.
The strong association between Covid-19 and retinal vein occlusions seems to confirm previous research suggesting that Covid-19 generally affects veins more severely than arteries, researchers said—a finding that could help guide treatment approaches for Covid-19 patients.
Even following Covid-19 infection, retinal vascular occlusions remained rare, with retinal artery occlusions affecting about 1 in 333,333 patients and retinal vein occlusions affecting about 1 in 81,967 patients during the period two to 26 weeks after they were diagnosed.
Researchers did not find that Covid-19 patients who were hospitalized were more likely to experience retinal vascular occlusions than those who were not hospitalized.
The study included 432,515 patients without a history of retinal vascular occlusions more than six months prior to their Covid-19 diagnosis, and who were diagnosed with the virus between January 20, 2020 and May 31, 2021.
Retinal vascular occlusions are caused when blood clots or fat deposits block blood vessels in the retina, the part of the eye that receives light and transmits images to the brain. These occlusions may cause damage ranging from slight vision impairments to whole-eye vision loss. Retinal artery occlusion is linked to diabetes, high blood pressure, elevated levels of fat in blood and various disorders affecting the heart or the carotid artery, according to the National Library of Medicine’s MedlinePlus service. Retinal vein occlusion is linked to diabetes, high blood pressure, fatty buildup in the arteries and eye disorders like glaucoma. Outcomes are variable: while many patients regain a degree of vision, there are no reliable treatments for whole-eye vision loss due to a retinal vascular occlusion. These occlusions may indicate the presence of clots or fat deposits elsewhere in the body, warning of a risk of stroke, according to Johns Hopkins Medicine.
Though Covid-19’s immediate symptoms have been well documented, scientists have struggled to understand the longer-term effects of the virus. A study published Monday by JAMA Neurology determined that the long-term smell loss reported by some Covid-19 patients is tied to damage to the olfactory bulb, the part of the brain that processes smells. Covid-19 has also been associated with a range of vascular issues such as inflammation of the heart muscle or the sac containing the heart. Some researchers have concluded that much of the damage caused by the coronavirus is not directly inflicted by the virus itself, but by infection symptoms like inflammation, the New York Times reports. The authors of the JAMA Ophthalmology study suggested a similar interpretation, theorizing that the initial vascular damage caused by Covid-19 infection might make some people more vulnerable to a pre-existing risk of retinal vascular occlusions.
It’s possible that the JAMA Ophthalmology study underestimated the risk of retinal vascular occlusions among severely ill patients because those patients’ conditions may have prevented them from informing healthcare staff of vision changes, researchers said.
WHAT WE DON’T KNOW
Further research would be necessary to establish a cause-and-effect relationship between Covid-19 infection and retinal vascular occlusions, researchers said. The JAMA Ophthalmology study established only an association between the two conditions.