From the Grimoires: Fey Eyes
Many creatures with Fey ancestry from the Dwimmerwood or Dolemoor have the ability to see very well in dim light or darkness. This has contributed to the stereotype of “catlike” behavior when describing the Fey, as their eyes often gleam like a cat’s in the dark. But why do they have this trait?
Most native Fey creatures grow up in shaded environments, whether it’s the creeping shadows of the Balebark Woods in the Dolemoor or the Evensong Forest of the Dwimmerwood. There’s a great deal of light variance, requiring many to adapt to this setting. For many Fey, particularly Dolor, or Shadow, Fey, this manifests in an thin, translucent membrane that hoods over the eye, much like an eyelid. For most Fey, this gives them an exotic, almost mysterious look, as their eyes appear to lack an iris and only vaguely reflect the colors of the eye itself. This is why you will often see Faeries and Archfey depicted with glowing monochromatic eyes—most Feys’ eyes do have a gleam to them, but they are shaded by this membrane that often covers the eye in bright light. From most any distance, this just appears to be an iris-less eye; only upon extremely close inspection is the membrane visible.
Many also chalk the uncanny perceptive abilities of most Fey creatures to this trait, as it gets them used to investigating details with a mild obfuscation. Thus, when the membrane lifts, they are able to see with impeccable clarity.