aHUS and Vision
Atypical hemolytic uremic syndrome (aHUS) primarily affects the kidneys. But it can also damage other organs, including the eyes.
Vision problems such as eye pain, blurry vision, and, in severe cases, vision loss have been reported in patients, although they are not considered to be common.
How does vision work?
The sense of vision is complex and involves the passage of light through various structures in the eye.
Light first enters the cornea, its clear and curved front layer. The cornea bends the light to help with focus. The light then passes through the pupil, a circular window surrounded by the iris or colored portion of the eye. The pupil can adjust in size to let more or less light in.
Light that makes it through the pupil gets focused by the lens, before passing through a clear liquid called the vitreous humor and striking the retina at the back of the eye. This activates special cells in the retina called photoreceptors, which include rods and cones. These photoreceptors send signals that travel along the optic nerve until they reach the visual cortex of the brain, which interprets them as images.
How might aHUS cause vision problems?
In aHUS, the complement system, a cascade of proteins, plays a role in the immune system turning hyperactive and causing inflammation. Uncontrolled activation of the complement system is the primary cause of organ damage related to aHUS.
Here, the immune system mistakenly attacks the lining of small blood vessels, causing blood clots to form in capillaries. This is called thrombotic microangiopathy (TMA). Red blood cells can rupture as they try to squeeze past partial blockages in the capillaries.
Moreover, platelets are involved in the formation of these abnormal clots, so that fewer are available in circulating blood to carry out their normal functions. This can cause unusual bleeding and bruising.
The formation of clots (TMAs) and related bleeding lead to the symptoms of aHUS.
A number of small blood vessels run through the retina of the eye, and TMAs in them can affect a patient’s vision.
Eye problems in aHUS patients
In a 2016 survey of 233 aHUS patients and their caregivers in 23 countries, 50 respondents (over 20%) indicated that problems with vision were “a serious or frequent enough issue” to bring them to a doctor’s attention. Still, such problems in aHUS patients are rarely studied by researchers, with most reported as case studies.
One 2007 case study described a child with aHUS who experienced pain in the eyes and blurred vision resulting from bleeding into the vitreous humor, and a lack of blood (ischemia) to parts of the retina, with an increase of pressure inside the eye.
A 2015 case study described a woman with aHUS with blood vessel blockage in both eyes, internal eye bleeding, and vision loss. Another study reported on an aHUS patient who experienced retinal detachment in both eyes.
Finally, a case report from Taiwan detailed a man with aHUS who arrived at a hospital with bleeding inside the eyes and retinal detachment.
How do doctors treat vision problems in aHUS?
Doctors typically first treat aHUS-related symptoms with plasma exchange (PEX) therapy. During PEX therapy, a machine filters and separates the patient’s blood into its clear portion (plasma) and cellular components. These components are then mixed with a plasma substitute and infused back to the patient. The aim is to decrease the number of antibodies floating in the blood and causing disease symptoms.
In some of the case studies, problems with patients’ vision and other aHUS symptoms were eased by treatment with Soliris (eculizumab).
In the case study from Taiwan, the man’s aHUS was treated with PEX and Ultomiris (ravulizumab), and doctors injected ranibizumab into his eyes after the bleeding was evident. Its use, however, was not beneficial and vision worsened, with retinal detachment occurring. Surgery done to reattach the retina also did not improve his vision. Doctors suspected damage to the optic nerve due to inadequate blood supply (ischemic optic neuropathy).
Last updated: Oct. 19, 2020
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