Hip-implant related chorio-retinal cobalt toxicity
A 39-year-old female with bilateral development dysplasia of the hips, for which she had undergone bilateral hip replacements (ASR™ Hip System, DePuy Orthopaedics , Warsaw, IN, USA) 2 and 5 years ago, presented with a 3-week history of a paracentral scotoma in her left eye and bilateral ocular discomfort. She also complained of occasional metallic taste in her mouth and early morning nausea. She denied taking any medication and was not aware of any occupational exposure to toxic substances. She had no other significant medical or ocular history. The family history was unremarkable. The type of implant present in this patient has recently been recalled owing to wear-related toxic cobalt and chromium release and hazardous metallosis.\nOn examination, the patient had good central visual acuity of 20/16 in both eyes. No relative afferent pupillary defect was noted. Intraocular pressures were within normal limits. Both anterior segments and fundi were unremarkable under slit lamp examination and indirect fundoscopy. Automated visual field testing (Humphrey 24-2) did not reveal any visual field defect. The patient proceeded to have a high-resolution optical coherence tomography (OCT) scan, which showed several circumscribed lesions of the outer retina at the level of the retinal pigment epithelium (RPE) and the photoreceptors []. These patchy lesions were hypofluorescent on indocyanine green (ICG) angiography [] but could not be demonstrated with fluorescein angiography. The thickness map showed diffuse mild thickening of the macula, predominantly perifoveal.\nElectrophysiology testing was also performed. Occipital pattern reversal visual evoked potentials were recorded for right and left eyes, monocularly using standard 35’ checks and also with the very small 9’ checks. The responses were well developed with normal latencies for both eyes. No significant interocular or interoccipital asymmetries were noted. Cutaneous electroretinograms were recorded using a Color Dome Ganzfeld stimulator and lower eyelid electrodes without pupil dilation. Dark adaptation was standard for 20 minutes. Electroretinograms were well developed for both eyes with responses for the left were generally of slightly lower amplitudes in comparison to the right. Pattern electroretinograms recorded using 140’ check reversal stimulation (4/s) showed equal and well developed responses for both eyes. The electro-oculograms were well developed with a well-defined dark trough and light peak. The light peak was higher for the right eye compared to the left. The Arden index was satisfactory for the right eye (2.9) whereas borderline normal for the left eye (1.9).\nLaboratory testing showed elevated serum cobalt and chromium levels, 757 nmol/L (0-20 nmol/L), and 595 nmol/L (10-200 nmol/L) respectively at the time of presentation. Physician assessment did not reveal any signs of other system involvement and electrocardiograph and thyroid function tests were within normal limits.\nThe diagnosis of toxic chorio-retinal degeneration presumably secondary to toxic serum levels of cobalt was made. The patient was advised to monitor her vision with the Amsler grid. No progression was noted on subsequent reviews, one and six months later. Thorough examinations by her orthopedic surgeon confirmed a good functional result of the implants. The serum cobalt and chromium levels remained stable. Given the lack of clinical progression, no intervention was considered necessary as yet. The patient continues to have regular follow-up with her family doctor, orthopedic surgeon, and ophthalmologist.