Does the retina encode visual information like a Bitmap or an SVG? I heard recently that a scientist has developed a retina prosthesis. So I think this is a question that has an answer.

Does the retina encode information like a Bitmap image or an SVG image?

(A Bitmap is a grid of pixels. An SVG image is vector based, so that it defines a shape and says 'in this region, it's green, in that it's red', so to speak.)
Short answer
The retinal image corresponds more to a bitmap, than a vector-based image

Background
The retina contains a layer of about 100 million photoreceptors that are topographically organized. In other words, each photoreceptor codes one specific pixel in the field of view. In turn, the nerve fibers running from the eye to the brain are also topographically organized in the same way the retina is (retinotopy is maintained up until the higher brain centers and is lost only in the inferotemporal cortex). Hence, yes, basically, but grossly oversimplified I agree with @Krysta that the retinal image more closely corresponds to a bitmap than a vector-based image. Nonetheless, colors, contrasts and edges are coded in the retina. 

Here is a picture on retinotopy. Basically a 1:1 topographic representation of the retina can be found in the primary visual visual cortex:

source: University of Leeds and Sydney

Retinal implants are devices that replace the lost photoreceptors in the retina in patients with retinitis pigmentosa or other retinal degenerative diseases. Retinal implants typically consist of a grid of electrodes (60 - about 1500 in commercially available systems) that are placed on (Argus II) or below the retina (alpha-IMS). 

Here's a fundus photo of an Argus II implant:



The electrodes directly stimulate the surviving neruonal cells in the retina. Retinal implants make use of the retinotopy. An electrode in the center of the retina will elicit a spot of light (a phosphene) in the central fielfd of view, whereas a more peripherally situated electrode will generate phosphenes more eccentrically. Hence, camera images (in the Argus II device) are simply downsampled and projected onto the electrode grid as intensity-coded stimuli. In the alpha-IMS system the intra-ocular part consists of a grid of photosensitive diodes coupled to small amplifiers. Hence, in this device it is, quite literally, a photosensitive chip thrown on the retina. In both approaches, brighter areas in the image receive higher electric currents and result in brighter and/or larger percepts.  

Reference
Stronks et al. Exp Rev Med Dev;11:23-30