Tracking Drug Release

Monitoring drug release in the human eye / measuring the viscosity of the vitreous

With the growth of age related eye disorders it is of increasing importance to be able to treat ocular diseases effectively, especially age related macular degeneration, which is the second largest cause of blindness in the developed world today. Some drugs are now available to treat certain aspects of the disease, but the treatment involves unpleasant and potentially dangerous injections into the eye. A "drug implant" would be a much preferred treatment. However, little is known about the release and delivery of drugs in the human eye.

To gain more knowledge about the movement of drugs in the aqueous and vitreous chamber of the eye, the group is working in collaboration with Lein Applied Diagnostics (http://www.lein-ad.com/), Allergan (http://www.allergan.com/) and Professor Clive Wilson from the Strathclyde Institute of Pharmacy and Biomedical Sciences (http://spider.science.strath.ac.uk/sipbs/staff/staffDetails.php?u=cgwilson ) to develop a new instrument which will be able to monitor drugs efficiently (Ref 1). This instrument will use a spectrometer to monitor absorption or fluorescence introduced by specific drugs in the aqueous and vitreous chamber. From the recorded spectrum, the concentration of the drug can be determined. This project forms the core of Kim Buttenschoen's PhD.

The instrument is based upon a confocal imaging system which records "depth profiles" through the eye. The initial results are being taken concentrating on the cornea to observe changing in thickness with a resolution of around a micron. This potentially has applications in studying the tear film, corneal "plumping" due to drugs and also the relationship between the corneal thickness and measured Intra Ocular Pressure (a consequence and sign of Glaucoma)

Outline of the confocal instrument with the inset showing the laboratory version

Dissection of a Bovine Eye

In previous work with Prof. Clive Wilson at Strathclyde we have used multiphoton microscopy to track drug movement through the sclera (Ref 2) and folic acid using Surfaced Enhanced Raman Scattering (SERS, Ref 3). The project above describes how we aim to monitor the drug in the eye but we also need to have a better understanding of the internal properties of the vitreous.

One method being explored in collaboration with the Institute of Photonics (www.photonics.ac.uk ) is the use of optical tweezers. Optical trapping or laser tweezers is a technique whereby micron sized particles can be trapped and manipulated using a laser beam with minimal or no damage to the trapped particle. Most trapping systems are built around a conventional microscope providing the imaging capabilities required to view the trapped particles. The key element to a successful trapping system is a high numerical aperture microscope objective lens, typically oil immersion objectives are used with numerical apertures around 1.3. The optical force exerted by the laser beam on the trapped particle is of the order of picoNewtons. Optical trapping has a widespread application across the life science field and has been used to gain further understanding of several fundamental physics questions. We have previously used the method to investigate fundamental physics properties in air born water droplets, create arrangements of cells and monitor optical angular momentum (Ref 4,5,6).

The diffusion rates of drugs delivered to the eye are highly dependant on the viscosity of the vitreous of the eye. The viscosity is affected by many factors including the age of the eye and the serum content in the eye and is know to change in different regions of the vitreous. Laser tweezers provide the perfect tool for determining the local viscosity of the vitreous. The work is now looking to undertake this in a perfused bovine eye with a window created to enable the interior to act a as a chamber for optical tweezing.

So called Miyake-Apple prepared bovine eye injected with fluorescent beads.

References

1.  "Development of a low-cost confocal instrument to measure the axial dimensions of components in the anterior section of the eye" K K Buttenschoen, J M Girkin, D Daly Clinical Optometry, 2, 67-72, (2010)
2. "SERS as a sensitive and selective technique for the detection of folic acid in water and human serum" Robert J. Stokes, Eileen McBride, Clive G. Wilson, John M. Girkin, W. Ewen Smith and Duncan Graham, Applied Spectroscopy, 62,  371-376, (2008)
3.  "Two-photon fluorescence excitation microscopy to assess transscleral diffusional pathways in an isolated perfused bovine eye model" Kek W K, Foulds W S, McConnell G, Wright A J, Girkin J M, Wilson C G Invest Ophthalmol Vis Sci  51, 5182-9, (2010)
4. "Creating Permanent 3D Arrangements of Isolated Cells using Holographic Optical Tweezers", Pamela Jordan, Miles Padgett, Paul Blackburn, Neil Issacs , Mattias Goksör, Dag Hanstorp, Amanda Wright, John Girkin and Jonathan Cooper; Lab on a Chip  5 (11)1224-1228 (2005)
5. "Transfer of orbital angular momentum from a super-continuum, white-light beam" Amanda J Wright, John M Girkin, Graham M Gibson, Jonathan Leach and Miles J Padgett Opt Exp 16, 9495, (2008)
6. "Parametric Resonance of Optically Trapped Aerosols" R. Di Leonardo,_ G. Ruocco, J. Leach, M. J. Padgett,A. J. Wright, J. M. Girkin, D. R. Burnham, and D. McGloin Physical Review Letters 99  010601 (2007)