You cannot use the Link without the base artifact. Typically, you find the "Rusted Ocular Lens" in the Abandoned Astrolabe (Act 2, Floor 3). Do not skip this room—it is hidden behind a fake wall on the left side of the waterfall.
According to fragmented in-game texts (often found in the Sunken Library of Veridias): “The Eye sees what should not be. The Link walks where time has died. To sever the Link is to go blind; to blind the Eye is to become mortal again.” This explains why using the Eye Link slowly drains your health or sanity meter in some versions of the game. You are literally tearing the fabric of reality just to see the path forward. If you are currently stuck at a puzzle that requires "Establishing the Link," follow this generic troubleshooting guide. (Note: Key bindings may vary depending on the specific RPGremuz title or mod version.) rpgremuz the eye link
If you are currently staring at a dead end, a blank wall, or an unbeatable boss, remember: The Eye sees what should not be. Activate the Link. Look again. You cannot use the Link without the base artifact