Implantation of Mouse Eyes with a Subretinal Microphotodiode Array

Abstract

Retinal prosthetics are designed to restore vision in patients with photoreceptor degenerative diseases, such as retinitis pigmentosa (RP) and macular degeneration. Subretinal microphotodiode arrays (MPAs), which response to incident light in a gradient fashion, have been designed to replace degenerating photoreceptors. Such devices have been implanted into rats (Ball et al., 2001), cats (Chow et al., 2001) and humans (Chow et al., 2004). These studies have revealed that implantation of a MPA device is capable of restoring some visual function in patients (Chow et al., 2004) and eliciting a superior colliculus response in normal and degenerating rats (DeMarco et al., 2007). Furthermore, the low level electrical stimulation produced by the MPA device has been shown to have neuroprotective properties (Pardue et al., 2005). When RCS rats are implanted with an MPA device at the beginning of the degenerative process, photoreceptor function and morphology are preserved (Pardue et al., 2005). Subretinal electrical stimulation may provide protection to the photoreceptors by stimulating the selective expression of FGF-2 in the RCS rat (Ciavatta et al., 2006). While these studies show promise for subretinal electrical stimulation as a treatment of RP, implantation of MPA devices in S334ter rats does not preserve photoreceptors (Walker et al., 2005). We hypothesize that this may be due to the underlying mutations between RCS and S334ter rats. RCS rats have a recessive mutation in a tyrosine kinase gene, Mertk, which results in failed phagocytosis of shed outer segments by the retinal pigment epithelium (Mullen et al., 1976; D’Cruz et al., 2000); while S334ter rats have a rhodopsin mutation which leads to photoreceptor death (Lee et al., 2003). Rat models with photoreceptor degeneration are few while there are numerous mouse models of RP that have been described (Chang et al., 2002; Dalke and Graw, 2005). Thus, to further elucidate whether the neuroprotective effect of subretinal electrical stimulation is generalized to all types of photoreceptor degeneration, implantation of mouse models of RP would be advantageous. This study describes the development of surgical techniques and the success of implanting a small mouse eye with a subretinal MPA device.