Cystoid Macular Oedema (CM) is a condition that affects the macula, a crucial part of the eye responsible for sharp, central vision. The macula is located in the middle of the retina and so anything which affects the macular is likely to affect your central vision. In CMEO, fluid accumulates in the macula either below the layers of the retina or in between them, causing it to swell and form cyst-like spaces. This may cause distortion in your central vision or a general drop in vision.