It's trying to look at an open visio document and see if a layer (in this case Option02) is visible.

Done!

I was using the wrong property for the layers, but had no idea which to use. I finally managed to find it.

The final code is as follows:

Sub UpdateOptions()

    Dim VisioApp As Object
    Dim vsoPage As Visio.Page
    Dim vsoLayer As Visio.Layers
    
    Set VisioApp = GetObject(, "Visio.Application")

    Set vsoPage = VisioApp.ActiveDocument.Pages("Model")
       
    If vsoPage.Layers("Option02").CellsC(visLayerVisible) = "1" Then
        Range("E8").Value = "Yes"
    End If
    

End Sub
Thanks for all the help Norie!