In this app, we consider retinal degeneration and a rescue scheme by optogenetics means.
The compound eye of the fruit fly consists of 700-800 facets, called ommatidia. We model the retina here to have 721 ommatidia, positioned on a hemispherical surface. Such a structure is illustrated in 3 above.
Each ommatidium hosts 8 photoreceptors. For simplicity, we consider only one photoreceptor in each ommatidium. Each photoreceptor has a microvillar structure called rhabdomere, which is the functional equivalent of the rod and cone outer segment in vertebrate retina. The rhabdomere contains ~30000 microvilli where rhodopsin (light receptor) are hosted.
Below are detailed descriptions of each screen. Please click on the play button ▸ on the bottom playbar to start playing the results. You can double click on any of the screen to enlarge all 6 screens to fill the browser window.
We use a natural scene of foliage as the main scene. We emulate the movement of a fruit fly on this scene. The red circuit that will be shown on this scene indicates what one of the eye of the fruit fly can see.
The red circle in Screen 1 is mapped to the visual input of the fly (Screen 2).
From the visual input, the input to each photoreceptor (in photons/seocnd) can be calculated, and visualized (Screen 3).
This screen shows the responses of a healthy eye.
Retinal degeneration often results in reduced size of rhabdomere and partially or completely lacking of rhodopsin. Consequently, the diseased eye has low or no light sensitivity. This simulate a diseased eye by reducing the number of microvilli in each photoreceptor to 5% of the health photoreceptors. The responses of the diseased photoreceptor array are shown here.
Optogenetics is a technique to genetically modify neurons to express light-sensitive ion channels. We can express channelrhodopsin in each photoreceptor to partially restore sensitivity of diseased photoreceptor cells to light. The responses of the rescued photoreceptors are shown in Screen 6.