Title: Hip Implant Related Chorio-Retinal Cobalt Toxicity
A 39-year-old female with high levels of cobalt in her blood (a side-effect of her two hip implants) came to the doctors with complaints that her left eye had been blurry for three weeks. Eye imaging revealed that the light-sensitive portion of the patient’s retina (called the photoreceptor-RPE complex) was degenerating.
The authors believe this patient experienced damage to the choroid region of her retina due to cobalt poisoning from her hip implants; this is a condition called implant-related chorio-retinal cobalt toxicity.
Cobalt poisoning is rare, but it has become more common due to the high number of people opting for Metal-on-Metal hip replacement implants. These implants can increase levels of cobalt in the blood to toxic levels. Many health problems, including vision loss, have been associated with elevated cobalt levels in the blood. However, the doctors believe this is the first time a human’s retina has been damaged due to implant-caused cobalt poisoning.
The patient received the ASR™ Hip System implant in each of her hips. She replaced one hip 2 years prior to coming to the doctors and the other 5 years prior. She complained of having blurry vision in her left eye and discomfort in both of her eyes for 3 weeks. She also sometimes experienced a metallic taste in her mouth and nausea in the morning. She had a normal medical history. Her brand of implants had recently been recalled because of its high rate of failure.
The patient had 20/16 vision and normal fluid pressure inside both of her eyes. The front-most part of her eyes (called the anterior) appeared normal, as did the interior back wall of her eyes (called the fundi). However, an optical coherence tomography (OCT) scan revealed several lesions in the patient’s retina. The lesions were located in a portion of the retina called the RPE complex and the photoreceptors, which are the parts of the eye that are sensitive to light. Additionally, eye imaging showed the patient’s macula – an oval-shaped area near the center of the retina – was thicker than normal.
Multiple types of technology-aided eye exams, called electrophysiology tests, were performed on the patient. Almost all of the electrophysiology tests yielded normal results for both eyes.
However, while the Arden index for the right eye was normal at 2.9, the Arden index for the left eye was just borderline normal at 1.9. The Arden index measures the ratio of light and dark sensed by the eye. A score lower than 1.8 is indicative of an eye malfunction.
Lab tests showed high levels of cobalt and chromium in the patient’s blood. Normal cobalt levels are between 0 and 20 nmol/L, but the patient’s cobalt levels were at 757 nmol/L. Normal chromium levels are between 10 and 200 nmol/L, but the patient’s chromium levels were at 595 nmol/L.
The doctors diagnosed the patient with chorio-retinal degeneration, which occurs when the choroid region of the retina has been damaged. They attributed the cause to the toxic levels of cobalt in the patient’s blood, which were caused by her hip implants.
The patient was advised to monitor her eyesight, and she had two follow-up appointments where no new damage was noted. The patient’s orthopedic surgeon found that her implants were well-functioning, and her cobalt and chromium levels did not increase or decrease. Because the patient has not gotten worse, revision surgery has not yet been considered necessary.
The retina requires a large amount of oxygen in order to function. The choroid region of the retina is responsible for supplying most of the oxygen-filled blood to the retina. So a lack of blood in the choroid region will lead to a lack of oxygen in the retina, causing damage to the parts of the retina that are sensitive to light; these are called photoreceptors.
When there is an excess of cobalt in the bloodstream, it is as if the retina’s oxygen supply is diminished. Therefore, the authors believe high cobalt levels in humans damage the photoreceptors in the retina. This pattern has been observed in several animal studies.
OCT scans showed the patient’s photoreceptor-RPE complex was damaged. Additionally, another kind of eye imaging called ICG angiography suggested that the choroid region of the patient’s eye had a diminished blood supply. Examinations showed the photoreceptors in the left eye were more damaged and dysfunctional than those in the right eye.
Blood can pass through the choroids of different eyes at different rates, which may explain why the patient only experienced problems with her left eye. Cases where patients experience problems with only one eye have been observed in instances of lead poisoning.
The doctors believe this is the first case where an implant led to cobalt poisoning and caused damage to the retina.
Ng S. Ebneter A, Gilhotra J. “Hip-Implant Related Chorio-Retinal Cobalt Toxicity,” Indian J Ophthalmol. 2013 Jan: 61(1): 35–37.
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