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G. Bowler, P. Chapman, A. Tarn, W. Ayliffe; Composition Analysis of Deep Corneal Plaques Secondary to High Phosphate Drops. Invest. Ophthalmol. Vis. Sci. 2009;50(13):907.
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To analyse plaques from patients previously intensively treated with high PO4 drops in the presence of persistent epithelial defects.
Patients presenting acutely with ulcerated plaques were seen, and consented for plaque removal under sterile conditions. Plaques were mounted on dry glass slides, packaged in an airtight plastic box and sent for Fourier transform infrared spectrophotometry (Nicolet and JASCO).
9 patients with deep calcific deposition have been reviewed regularly. On 4 occasions a total of 3 patients presented with ulceration and pain necessitating therapeutic plaque removal. These 4 plaques were subsequently sent for analysis. A further 7 cases of non-ulcerating deep corneal plaques have been left in situ and will be analysed as and when removal is therapeutically expedient.Plaque 1, patient treated with 25 days of timolol 0.5% PF bd (MSD) and prednisolone phosphate PF (Chauvin) qds, was found to contain >95% Ca2PO4.Plaque 2, patient treated with prednisolone 0.5% PF drops bd (Chauvin), timolol 0.5% PF (MSD) bd, ofloxacin 0.3% (Allergan) qds, and cefuroxime 5% (Moorfield’s) qds, was found to contain 78% Ca2PO4.Plaques 3 and 4, insufficient quantity received for FTIR analysis.
High levels of Ca2PO4 were found in these analysed plaques. None of these patients had plaques prior to developing an epithelial defect and being exposed to high PO4 drops. PO4 ions are present in eye drops as a buffer, and in the cases of certain medications (e.g. prednisolone and dexamethasone PO4) as a salt. Whilst it would seem sensible to treat patients with persistent epithelial defects with preservative free drops, it may be more important in the initial stages to reduce inflammation using non PO4 containing drops, (e.g. prednisolone acetate) until corneal reepithelialisation. None of the preservative free products described above declare the PO4 buffer content on the packaging in a manner that would alert Pharmacists or Clinicians to the risk of corneal calcification in high risk patients. Furthermore, these products do not contain information on the primary dose form. Corneal calcification is underreported in the literature and the causes are usually not identified. New formulations are required. The Manufacturers and the MHRA have been advised.
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