cataract, film over the eye
瞖 centers on an eye condition that clouds vision: a cataract or a film over the eye, causing opacity and impaired sight.
瞖 combines 殹 (a phonetic component with a sense of covering or obscuring) and 目 (eye), together expressing a film or cataract that covers the eye. The exact historical development of 殹 is uncertain.
The top part 殹 looks like a covering or obstruction, and the bottom 目 is the eye. Imagine a cloudy film settling over the eye, like a cataract dimming the light.
For エイ, picture an eye with a cataract that makes everything look hazy, like a faded 'A' on an eye chart: 'A' -> エイ, and the eye struggles to see it clearly.