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WS Wilson, J Miller, CG Wilson, D Uttamchandani; In Vivo Detection Of Drugs In The Anterior Eye . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2316.
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Purpose: To design and test a corneal contact lens which effectively turns the anterior chamber of the eye into a cuvette, enabling absorption measurements to be undertaken. Methods: Placing the lens on the cornea enables a beam of light to be directed in, across and out of the anterior chamber. The light is guided to and from the contact lens via optical fibres. The output fibre is connected to a spectrograph, enabling real time, in situ spectroscopic measurements. Eye drops (30 µl) containing brimonidine (2% w/v) or fluorescein (2% w/v) were applied topically. The lens was placed in contact with the cornea of rabbit (sedated with fentanyl [1mg/kg] and fluanisone [3mg/kg] and locally anaesthetised with 2% lidocaine), or of man (with or without lidocaine) for a 5-25s period, once every 30min. Absorbance measurements were taken every 0.025s and summed over 0.5s. Drug concentration was measured/compared using peak height. Results: The light path within the anterior chamber is approx. 6mm long and the absorbance measured includes a corneal component. Spectra obtained following brimonidine or fluorescein had characteristic peaks at 320 and 490 nm respectively. Corneal absorption starts to rise rapidly at wavelengths shorter than 315nm. The time course of brimonidine levels in rabbit anterior eye showed a decline to 50% of peak value within 110mins. Absorbance measurements 25min following topical application of brimonidine (0.6, 1.2 or 1.8 mg ) showed dose-dependent kinetics. For fluorescein, the threshold of detection in vitro was 5nM and ex vivo was less than 50nM. The device was also successfully used in man to detect brimonidine after topical application. In man, corneal penetration of fluorescein was insufficient to permit detection by absorbance. Conclusion: This device will enable ocular pharmacologists to measure drug concentrations in the anterior eye by either absorption or fluorescence spectroscopy.
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