Design and performance of a dark-field probe with confocal Raman spectroscopy for ophthalmic applications

A dark-field ophthalmic contact probe for analysis of aqueous humor (AH) was designed by ray tracing and constructed in quartz glass for experimental use as a prototype probe in a confocal Raman spectroscopic setup. The misalignment tolerance of this probe was theoretically evaluated, whereas the optical performance was experimentally evaluated by a concentration curve of the ocular drug phenylephrine HCl in an artificial eye model. The results indicated a ninefold improvement in misalignment tolerance and a 36-fold improvement in the signal-to-noise ratio at the phenylephrine HCl 1002 cm(-1) peak compared with a previous design. The prototype showed a good linear fit with the phenylephrine HCl concentration, with an R-2 of 0.996. Phenylephrine HCl concentration down to 0.1% is detectable.