Hi @MyuuCree
Welcome to the Unreal Engine Developer Community!
This type of issue often occurs when dealing with custom head meshes, Mesh-to-MetaHuman, or custom eye implementations.
What you’re seeing is the outer cornea glass mesh (or eye refraction shell) being slightly out of alignment with the underlying iris/sclera mesh, or incorrect pivot placement/refraction settings when setting up your character.
Below are several details on what causes this issue, and methods in which you can fix it.
MetaHuman Eye Rig Structure & Pivots:
MetaHuman eyes are complex hierarchical assets, comprised of several layers of mesh (sclera, iris, outer cornea, and moisture layers).
If the custom head mesh alter the default MetaHuman bone structure or socket placement (eye_edge_ref_l/r or eye joints), the outer refractive shell can become decoupled with the visual eye center.
Refractions & Ray Tracing / Lumen Mismatch:
MetaHuman eye materials use a large amount of Screen Space Refraction (SSR) or Ray-Traced Refraction using the M_EyeRefraction shader.
If custom mesh scaling, normal map mismatch, or incorrect depth value on your eye’s material instance was used, the outer lens can appear offset from certain camera angles.
Mesh-to-MetaHuman Binding Issues:
When fitting in a custom mesh using the MetaHuman Identity tool, if the landmark tracking around your eyelids or eye sockets wasn’t fully tracked, your generated skeleton might have your eye sockets slightly outside the visual boundary of your custom mesh.
Step-by-Step Resolution Guide
Method 1: Re-aligning Eye Sockets via MetaHuman Identity Tool
If you’ve used the Mesh-to-MetaHuman workflow to import your custom mesh:
Open your MetaHuman Identity Asset in Unreal Engine, open the Component Editor tab and select your custom neutral mesh frame. Toggle on the Landmarks View (Ctrl + L). Check the eye markers - ensure that inner, outer and central eye ring are all perfectly flush against the geometry of your custom eye socket. Click Prepare for Performance and rerun MetaHuman DNA Generation. Export this new asset to Quixel Bridge / MetaHuman Creator and re-import into your project.
Method 2: Adjusting Material Refraction Parameters
If the mesh seems to be physically correct in DCC tools (Maya/Blender) but is “offset” inside Unreal Engine:
Find the Material Instance assigned to the eye asset (usually MI_Eye_L and MI_Eye_R can be found in Content/MetaHumans/[CharacterName]/Face/Materials/)
Open up this Material Instance, and check the Refraction and Cornea parameters:
IOR (Index of Refraction) should be around 1.335 - 1.338 (standard realistic water/cornea value)
Cornea Scale, Iris Concavity:
These values can be adjusted down slightly to reduce the amount of refractive bulge if it is going beyond the physical eye mesh.
If you’re using Ray Tracing, you must make sure that Refraction is enabled in your Post Process Volume:
Post Process Volume → Ray Tracing Features → Refraction: Enabled
Method 3: Checking Skeleton and Bone Transformations in Custom Meshes
If you imported a completely custom eye mesh in addition to your custom head:
Open your Skeletal Mesh that you’ve imported for your face (SK_Face), look at the bones FACIAL_C_Eye / FACIAL_L_Eye / FACIAL_R_Eye and ensure that the Pivot Point of your custom eye mesh matches the center of the sphere geometry in your 3D software (Maya/3ds Max/Blender) before you exported your meshes. Ensure that the mesh skinning weight for the outer shell matches up with 100% in comparison with the inner eye sphere, so the shell doesn’t lag or shift along with the main head mesh.
Epic Community Docs:
Using the MetaHuman Facial Rig
Videos:
Unreal Engine 5 Mesh to Metahuman Plugin Tutorial
Let me know if changing landmark points or material’s refraction values fixes anything!
If not, tell me what version of Unreal you’re using and post a screenshot of your SK_Face skeleton structure hierarchy.
