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Br J Ophthalmol 2005;89:1147-1151 doi:10.1136/bjo.2004.060780
  • Clinical science
    • Extended reports

Minimally invasive, direct, real time measurement of drug concentration in the anterior eye

  1. J Miller1,
  2. W S Wilson3,
  3. C G Wilson2,
  4. D Uttamchandani1
  1. 1Department of Electronic and Electrical Engineering, University of Strathclyde, Glasgow, UK
  2. 2Pharmaceutical Sciences, Institute for Biomedical Sciences, University of Strathclyde, Glasgow, UK
  3. 3Ocular Pharmacology Laboratory, Institute of Biomedical and Life Sciences, Glasgow University, UK
  1. Correspondence to: Dr Joseph Miller Department of Physiology and Pharmacology, Lions Eye Institute at the University of Western Australia, 2 Verdun Street, Nedlands 6009, Western Australia, Australia; joecyllene.uwa.edu.au
  • Accepted 24 January 2005

Abstract

Aims: To evaluate a corneal contact lens which effectively turns the anterior chamber of the eye into a cuvette, enabling the concentration of a drug to be measured using absorption spectroscopy.

Methods: A hand held contact lens incorporating optical fibres connected to a spectrograph enabled a beam of light to be directed in, across, and out of the anterior chamber. The device was used to follow the time course of drug concentration in the anterior chamber of rabbit (sedated) and humans, using topical brimonidine or fluorescein (with or without local anaesthesia). Absorbance measurements were taken for a 5–25 second period, repeated every 30 minutes. Drug concentrations were compared using absorbance peak height.

Results: Corneal absorption starts to rise rapidly at wavelengths shorter than 315 nm. The light path within the anterior chamber is 6.9 mm (rabbit) and 5.8 mm (human), the absorbance measured also includes a corneal component. Application of fluorescein (three drops of 2% solution) in rabbit allowed detection, 60 minutes later, of a large absorbance peak at 490 nm. In the human eye, the device could not measure fluorescein (applied as in rabbit), but clearly detected brimonidine for 3 hours following topical application of 0.6 mg. Modification of the device to measure fluorescence resulted in the detection of 5.3 nM fluorescein in the ex vivo rabbit eye, an increase in sensitivity of two orders of magnitude over the absorption measurements.

Conclusion: This device has the potential to allow repeated measurements of drug concentrations in the anterior eye provided the drug has suitable absorption or fluorescence characteristics.

Footnotes

  • This project was funded by a grant from the Engineering and Physical Sciences Research Council of the UK.

  • Competing interests: none declared

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