The advent of optogenetics provides a new direction for the field of 
neuroscience and biotechnology, serving both as a refined investigative tool and 
as potential cure for many medical conditions via genetic manipulation. Although 
still in its infancy, recent advances in optogenetics has made it possible to 
remotely manipulate in vivo cellular functions using light. Coined Nature 
Methods' 'Method of the Year' in 2010, the optogenetic toolbox has the potential 
to control cell, tissue and even animal behaviour. This optogenetic toolbox 
consists of light-sensitive proteins that are able to modulate membrane 
potential in response to light. Channelrhodopsins (ChR) are light-gated 
microbial ion channels, which were first described in green algae. ChR2 (a 
subset of ChR) is a seven transmembrane α helix protein, which evokes membrane 
depolarization and mediates an action potential upon photostimulation with blue 
(470 nm) light. By contrast to other seven-transmembrane proteins that require 
second messengers to open ion channels, ChR2 form ion channels themselves, 
allowing ultrafast depolarization (within 50 milliseconds of illumination). It 
has been shown that integration of ChR2 into various tissues of mice can 
activate neural circuits, control heart muscle contractions, and even restore 
breathing after spinal cord injury. More compellingly, a plethora of evidence 
has indicated that artificial expression of ChR2 in retinal ganglion cells can 
reinstate visual perception in mice with retinal degeneration.