In vivo, as demonstrated for the Y99C and E155G GCAP1 mutations, the unabated cGMP synthesis results in abnormally high levels of cGMP and Ca2+ in rods, and the ensuing retinal degeneration can be significantly prevented by conditions that promote constitutive stimulation of PDE6 such as constant light exposure [23], [25], [26]. Here, GUCA1A is linked to retinal degeneration.