Possible Clues:

• Line of sight?
• Grid of fine lines in an eyepiece
• Scale lines in an eyepiece
• Grid of fine lines in an optical instrument's focus
• Heretic left to pen lines for reference
• Grid on an eyepiece
• Reference lines on an eyepiece; let rice (anagram)
• Cat not getting at cream runs back round attached network
• Optical reference grid
• Referring to habitual action, left European network