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Recently, indocyanine green (ICG) has been used to stain and visualise the internal limiting membrane (ILM) during vitrectomy.1 Some case series showed that visual field defects on the nasal side can occur after the surgery through unknown cause.2,3 Here, we report a case in which nasal visual field defects occurred after ICG assisted ILM peeling for epiretinal membrane (ERM). Detailed examination revealed that the superior and inferior retinal nerve fibre is severely damaged in this case.
A 60 year old woman who received ICG assisted ILM peeling for ERM in her right eye was referred to our hospital. The preoperative best corrected visual acuity (BCVA) was 20/60 in the right eye. According to the referring ophthalmologist, 25 mg of ICG (Diagnogreen; Daiichi Pharmaceuticals) was dissolved in 10 ml of distilled water, which was further diluted by a viscoelastic material (Healon; Pharmacia) to give 0.16% ICG solution. To stain ILM, ICG was injected into an air filled eye and the dye was washed 2 minutes later. An air infusion cannula was placed at the temporal side. There was no complication during the surgery. Seventeen days after the operation, she noticed nasal visual field loss, which got worse 22 days after the surgery. Sixty days after the surgery, she was referred to our hospital. At the initial visit, the BCVA was 20/25 in the right eye. Goldmann perimetry revealed a nasal visual field defect (fig 1A). In the right eye, a relative afferent pupillary defect was found. Ophthalmoscopic examination and fluorescein angiography showed no abnormalities. The optic disc rim appeared to have lost colour without being associated any cup or rim changes typically seen in glaucoma (fig 1B). Residual ICG was evident at the optic disc and along the nerve fibre (fig 1C). The nerve fibre staining was most evident in the superior and inferior quadrants. ICG angiography revealed ICG staining of the optic disc and superior and inferior nerve fibres, but no other abnormalities. Full field electroretinogram (ERG) and multifocal ERG (VERIS science ver3.8, EDI) revealed no abnormalities. The results of visual evoked potential testing were also non-remarkable.
During our 8 month follow up period, there was no significant change in the visual field defect and the distribution of the residual ICG. Scanning laser polarimetric analysis (GDx VCC, Laser Diagnostic Technologies, Inc, San Diego, CA, USA) performed 8 months after the surgery showed profound nerve fibre loss around the disc, especially evident at superior and inferior quadrants (fig 2).
In this case, an air infusion cannula was placed at the temporal side and Goldmann perimetry showed nasal visual field defects. Thus, the dehydration injury to the retina during air-fluid exchange, which is observed at the opposite side of the cannula, is unlikely to be the cause of this visual field defects.2–4 Optic neuropathy unrelated to the use of ICG may be considered as a differential diagnosis. However, this visual field damage is not typically seen in optic neuropathy and may be rather associated with ICG, based on recent clinical findings.2,3 Retinal damage was not evident by morphological, angiographic, and functional analysis. However, it was evident that the nerve fibres are damaged in this patient. Although the direct causal relation cannot be proved, it is highly likely that the damage to the nerve fibre was caused by the ICG because of the remarkable correspondence of the distribution pattern of ICG and the nerve fibre defects. This is also supported by our experimental findings that ICG showed neurotoxicity at concentrations lower than clinically employed.5 To our knowledge, this is the first report of ICG induced retinal nerve fibre damage assessed by scanning laser polarimetry.
Competing interest: none.