Assessing a new technique for Intracranial pressure Recording Without Invasion or Needles

All subjects will need to have their pupils dilated using Tropicamide 1% 2 drops 5 min apart, so that we can view the retina and take the necessary video photographs. Dilation does blur the vision for 2 hours and so subjects will be advised not to drive for 2 hours after dilation. We then apply a contact lens on the eye after topical anaesthesia (Oxyprobucaine 2%) so that the retina can be viewed and intraocular pressure altered. Multiple video-recordings of the retina and retinal vessels are taken, which are later analysed. The contact lens is made of medical grade polymethyl methacrylate, lathed and polished to have zero optical power. A standard retinal camera is attached behind the contact lens and records video recordings of the central retinal vessels. The pupil dilation takes 20 minutes and the anaesthesia of the cornea takes one minute with the video recording taking 20 to 60 minutes. There is no follow-up required because all of the measurements needed are taken at the one sitting. So there is no need to monitor adherence. The only intervention is the dilation and the installation of the anaesthetic drops to allow contact lens imaging to take good quality video recordings of the retina. The new technique uses photoplethysmography, which is a system for measuring pulsation amplitudes in the retinal vessels. We have invented this technique and have published five papers, illustrating and validating the technique and demonstrating its accuracy in terms of predicting intracranial pressure. The system has been developed on a large benchtop optical set up. With this study, we have compressed the optical elements and camera into a small portable system which can be handheld. The underlying optical and analytical system with contact lens remains exactly the same, but the form factor has been reduced in size to allow an operator to hold the instrument in one hand.