Indolent Postoperative Endophthalmitis With Vitreous Metagenomic Detection of Enterobacter hormaechei in an Eye With Central Retinal Vein Occlusion: A Case Report
This case report describes a rare instance of indolent postoperative endophthalmitis caused by multidrug-resistant *Enterobacter hormaechei* in a patient with central retinal vein occlusion, highlighting the diagnostic utility of metagenomic next-generation sequencing for identifying low-abundance pathogens and the necessity of pars plana vitrectomy when intravitreal antibiotics fail to resolve persistent vitreous opacity.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
The human eye is a delicate, self-contained world where clarity is everything. When the lens inside the eye becomes cloudy, surgeons can replace it with a clear artificial one, a routine procedure that restores sight for millions. However, the eye is also a place where infection can take hold, sometimes quietly and sometimes with violent speed. When bacteria invade the fluid-filled center of the eye, a condition called endophthalmitis occurs. This is a serious complication that can destroy vision if not treated immediately. While some bacteria are well-known troublemakers, others are rare and difficult to identify, especially when they hide in the eye's deep, dark fluids. In recent years, doctors have gained a powerful new tool to find these hidden invaders: a method that reads the genetic code of every tiny organism in a sample, looking for matches in a massive library of known life. This technology allows them to see pathogens that traditional tests might miss, but it also brings a new challenge: distinguishing between a true infection and a faint, misleading signal in the data.
This story begins with a sixty-eight-year-old woman who had undergone cataract surgery in her left eye. Before the surgery, she had a blockage in a major vein at the back of her eye, a condition that had already caused some damage to her retina. The surgery itself went smoothly, and the new lens was placed perfectly. But about a month after the operation, once her eye drops were stopped, she began to feel discomfort. At first, doctors thought it was a simple surface infection, like conjunctivitis, and treated her with antibiotic drops. She did not return for regular checkups, and by the time she came back four months later, her vision in that eye had faded significantly. When she arrived at the hospital, her eye looked surprisingly calm on the outside. There was no redness, no pain, and the front part of the eye showed no signs of inflammation. Yet, when the doctors looked deeper, they saw a thick cloudiness in the fluid behind the lens, obscuring the view of the retina.
The medical team faced a puzzle. The patient had a history of vein blockage, which could explain some vision loss, but the cloudiness suggested an active problem inside the eye. They needed to know if an infection was hiding there. Instead of relying on standard cultures, which grow bacteria in a dish and can take days or fail to grow at all, they took a tiny sample of the fluid from inside the eye and sent it for a genetic search. This test, known as metagenomic sequencing, scans the sample for the DNA of any bacteria, viruses, or fungi present. The result came back with a specific name: a bacterium called Enterobacter hormaechei. This organism is known to be a tough, multi-drug-resistant germ that usually causes severe, aggressive infections. However, the test did not find a huge amount of this bacteria; it found a small number of genetic signals, which the laboratory flagged as a low-priority finding rather than a definitive confirmation.
Because the genetic test suggested a bacterial cause, the doctors tried to treat the eye with strong antibiotics injected directly into the fluid. They used two different types of medication, hoping to kill the suspected germ. A week passed, but the cloudiness in the eye did not clear, and the patient's vision did not improve. The lack of response to the antibiotics, combined with the persistent cloudiness, led the team to a different conclusion. They decided to perform a vitrectomy, a surgery where the cloudy fluid is carefully removed and replaced with a clear silicone oil to hold the eye in place. During this procedure, they did not find a massive infection, but the removal of the fluid allowed the eye to settle. The inflammation was brought under control, and the retina remained attached.
Two months after the surgery, the patient's vision had improved slightly, though it remained limited. This limitation was not entirely due to the infection; the original vein blockage and the scarring from previous laser treatments had already damaged the retina, and the silicone oil used to fill the eye also affected how light focused on the back of the eye. The key takeaway from this case is that an infection inside the eye can sometimes be very quiet, showing no redness or pain on the surface, yet still cause significant vision loss. The genetic test helped identify a rare bacterium that might have been the culprit, but because the amount of bacteria found was small and could not be confirmed by other methods, the doctors treated the result as a strong clue rather than absolute proof. The success of the surgery suggests that when antibiotics fail to clear a cloudy eye, removing the fluid can be a necessary step to stop the infection and save what vision remains. This case highlights how modern genetic tools can reveal hidden threats, but also how doctors must still use careful judgment to decide what those clues mean for a patient's health.
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