Non-invasive monitoring of commonly used intraocular drugs against endophthalmitis by Raman spectroscopy

Purpose: To develop a non-contact and non-invasive method for quantification of the local concentration of certain antibiotic and antifungal drugs in the eye. Study Design/Materials and Methods: An integrated CCD-based Raman spectroscopic system designed specifically for ophthalmic applications was used to non-invasively detect the presence of ceftazidime and amphotericin B in ocular media. Specific Raman signatures of the above named drugs were determined for various concentrations that were injected through a needle in the aqueous humor of rabbit eyes in vivo. Raman spectra were subsequently acquired by focusing an argon laser beam within the anterior chamber of the eye. Results: Compared to ocular tissue, unique spectral features of ceftazidime appeared near 1,028, 1,506, 1,586, and 1,641 cm^-1. Amphotericin B exhibited its characteristic peaks at 1,156.5 and 1,556 cm^-1. The amplitude of the spectral peak corresponding to these drugs (acquired by 1 second exposure time and 25 mW of laser power) were determined to be linearly dependent on their local concentration in the anterior chamber of the eye. Conclusions: Raman spectroscopy may offer an effective tool to non-invasively assess the local concentration of the delivered drugs within the ocular media. This technique potentially could be used to investigate the pharmacokinetics of intraocular drugs in vivo either from a releasing implant or a direct injection.