Inspirational Research Has Re-opened My Eyes

In the midst of my day-to-day research — generally transferring small amounts of colorless liquid from tube to tube — it is all too easy to become bogged down by the practical details and lose sight of what originally excited me about science. But an article detailing a triumph of biomedical research recently rekindled my "new scientist" excitement.

The article in The Times reported European approval for the medical use of an artificial eye,¹ the first to successfully negotiate trials and reach the clinic. The system, called Argus II, can restore useful vision to patients who have lost their sight through retinal degeneration, which involves abnormalities and eventual loss of function in the light receptors at the back of the eye. This new medical technology roused my inner neuroscientist, but no sooner had this dormant creature rubbed its eyes and found its feet than it was promptly bowled over in amazement. A functional artificial eye is a technically astounding achievement, involving no end of physiological and technical challenges.

Normal retinal function is incredibly complex. Photoreceptors, the cells that detect light and respond to it, first transform light into electrical signals, which propagate to neurons in the eye. These signals pass first through bipolar cells, then through ganglion cells. Bipolar cells are arranged into a complex network that combines and crudely processes information from several photoreceptors. As for the ganglion cells, there are several different types, each with a different function, and combined they total over one million. These different levels of cells, the intricate connectivity between them, and their selective sensitivities show the difficulties involved in artificially recreating a human eye.

Argus II uses live images from a camera mounted on eyeglasses and converts them into 6 x 10 pixel grids. This information is sent to an electrode array implanted in the patient's eye, each pixel represented by one electrode. The electrodes stimulate ganglion cells directly, which are usually still functional despite photoreceptor deterioration. Direct excitation of ganglion cells generates an electrical signal passed directly to the brain. This signal is interpreted as light falling on the retina, from which the brain forms an image. The concept is simple; the technicalities not so.

It is difficult to stimulate ganglion cells such that they give an accurate spatial signal, since they are closely packed and their position on the retina does not always correspond to the spatial information that they relay.² In addition, each patient's retinal network structure differs, and the impact of disease may also vary. As if this were not enough, eye movement poses an extra challenge, since this causes the electrode array to move while the camera remains still, completely changing the spatial relationship between them. Compensational head movements are required for the artificial spatial information to correspond to reality.

Argus II has overcome many of these challenges. Users are able to see light, movement, and color and identify the position of simple shapes on a screen. Some individuals can even read large text.^3,4

Of course, there is still a long way to go before artificial eyes are commonplace and easy to use. Argus II requires calibration for each patient, and the vision it provides is extremely limited. But in comparison to years of almost nothing, even limited vision must be life-changing. What's more, with long-term use, the brain will likely make better use of the input it receives. Indeed, this thought reminded me of what first enticed me into a science lab.

The nervous system is the ultimate example of how simplicity in nature combines to produce immense complexity. Neurons work by simply receiving electrical signals and passing them on. It is the sheer number of cells and the intricacy of their connections that give the nervous system its power and flexibility. Argus II is a perfect example of how this can be exploited; we do not need to understand the entire visual system, but can provide a minimal input and allow the brain to do the rest. I'm sure the process of achieving this has been long and hard, and those who have done it have toiled over difficulties, failures, and experimental cul-de-sacs. But these scientists must feel the most extraordinary satisfaction in knowing that their work will change the lives of many who had lost hope. In the midst of my own research struggles, their work has re-opened my eyes to the amazing possibilities of science.

Image Credits: IKO (via iStock), Second Sight Medical Products

References:

1. Henderson, M. Bionic eye implant wins safety approval. The Times 30 May 2011
2. Cohen, E.D. Prosthetic interfaces with the visual system: biological issues. J Neural Eng 4: R14-R31 (2007)
   
3. Ahuja et al. Blind subjects implanted with the Argus II retinal prosthesis are able to improve performance in a spatial-motor task. Br J Ophthalmol 95: 539-543 (2011)
   
4. Second Sight announces significant results from the Argus II Retinal Prosthesis trial at the ARVO 2011 Annual Meeting. Press release from Second Sight website.