Thursday, 23 January 2014

Contact lens as a diagnostic tool

Advances in mini and microcomputers are turning science fiction into reality. A couple of months ago, we had a visitor from MIT to our lab who was wearing a strange kind of spectacles. When I asked him about it, he said it was actually a wearable computer called Google Glasses, made by Google. And of course we now know of a wrist watch computer made by Samsung. Last week Google announced the introduction of a wearable contact lens which would monitor the sugar levels in your tears and let you know if you are a diabetic or not. With this, you no longer need to ‘invade’ or prick your finger to draw blood and wet it on a litmus-type paper to read your sugar levels. And we all thought that a contact lens is worn to correct your eye sight to normal.
Contact lens can be used to diagnose glaucoma, blood pressure and diabetes. Photo: R. Ragu
So, with the Google contact lens, there is literally more than what meets the eye! We have come a long way since 1508 when the great Italian Leonardo da Vinci thought up the idea of slipping a glass piece over the eye to correct vision, and 1823 when the British physicist John Herschel thought up a practical design.
Fifty years later, such a glass was made, though it covered the entire eye. With the advent of plastics, the first lightweight contact lens was made in the year I was born, 1939, and was made to cover not the whole eye but the corneal surface.
But it was Drs. Otto Wichterle and Drahoslav Lim in 1959 who introduced the hydrophilic ‘soft’ contact lens. Currently we have contact lenses that you can wear and sleep, lenses that are disposable after each use, and those meant for fashionistas.
A typical contact lens is lighter than feather, has a diameter of about 14 mm, curvature of about 8.7 mm, fitting smug over the cornea and held in place thanks to the surface tension of the tear fluid that wets it.
And it is this tear fluid that holds the key for the diagnostics. Produced by the tear glands on the outer surface of the eye, it contains hundreds of proteins and metabolite molecules, and thus an indicator of the health of the body.
And since one does not have to pierce the body to collect blood but simply collect it or study it as it is held between the cornea and the contact lens, it becomes an attractive diagnostic fluid.
All that one needs to do is to fit the contact lens with an appropriate sensor which measures chosen properties or levels of any component in it.
This last sentence is easier said than done; and it is here that innovation has played a role. Early enough, in the 1990s and 2000s, Drs Matteo Leonardi and Rene Goedkoop from Switzerland, supported by ‘Sensimed’, used the contact lens to measure the pressure within the eyeball, also called the intraocular pressure (IOP), which is an indication of the pressure that the optic nerve feels.
If the IOP becomes higher than normal, the optic nerve can become inefficient over time, thanks to this higher than normal pressure and can eventually lose its activity, leading to loss of vision. This condition is termed glaucoma, a silent stealer of vision.
What the duo did was to put together a circular strain gauge on the edges of the contact lens in order to measure the changes in the circumference of the outer surface of the eye due to IOP, and read out as electrical signals. This was an alternative to the conventional method of using a pressure sensor (tonometer) with which the eye doctor would contact and slightly press the curved corneal surface (applanation) and measure the intraocular pressure.
Any change beyond the accepted ‘normal’ range of IOP would be diagnosed as possible glaucoma.
The Leonardi-Goedkoop machine, termed Triggerfish, does this in a more convenient way. Likewise, Drs Stodtmeister and Jonas Jost of Germany devised a method to measure the systolic and diastolic pressures of the ophthalmic artery, and have used it as a method to make blood pressure measurements.
And in all this the main function of the contact lens (to correct the refractive ‘power’) was not affected so that it does double duty.
What Drs Brian Otis and Babak Parviz of Google have done is to put in a sensor on the edges of the contact lens, which measures the level of glucose in the tear fluid which bathes the contact lens, and thus monitors diabetic status in a continuous manner.
Currently it has been tried out on a series of subjects, and awaits FDA clearance for marketing and widespread use. Dr Parviz, who was earlier at the University of Washington, Seattle, had already used the contact lens as a GPS device to let the wearer know where he/she is going. This was done by putting in a tiny integrated circuit, powered by a cell phone in the pocket, and which contains a GPS set up and can voice- announce directions.
This bionic lens has wireless communication system, rf power, and transmission capability. The use of this to the visually handicapped is obvious. Such use of the contact lens as a multifunctional device would certainly have pleased da Vinci.
Shailesh shukla

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