Jeff, what you're referring to isa clarifier that is commonly used in combination with a lens on competition sights. They can clear up the blurry pins giving you a clear view of your target and the pin. I would use one myself, but it doesn't bother me too much because I have good eye sight and the largest they come in is 1/8".

Check it out:

http://www.keystonecountrystore.com/Archery_Equipment_-_Supplies/Archery_Peep_Sights/Specialty_Archery_Super_Peep_Kit/Page_2/PEP2038903.html

http://www.keystonecountrystore.com/Archery_Equipment_-_Supplies/Archery_Peep_Sights/Specialty_Archery_Super_Peep_1_x_8_Aperature_-_Number_1_Lens/Page_3/PEP195102.html

http://www.keystonecountrystore.com/Archery_Equipment_-_Supplies/Archery_Peep_Sights/Specialty_Aperature_Super_Peep_Hunter_1_x_4/Page_3/PEP2270604.html

http://www.keystonecountrystore.com/Archery_Equipment_-_Supplies/Archery_Peep_Sights/Specialty_Aperature_Verifier_6_Apt_1_x_4/Page_3/PEP2270704.html

Added more links including one for a 1/4" hunting peep.