This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Ophthalmology
Ex-Press glaucoma implant is made up of? 
Select and explain. 
A. Silicone, B. Titanium, C. Gold, D. Stainless steel
D: Stainless steel
Answer: D: Stainless steel 
Explanation: Ans. d. Stainless steelIt is made of made of surgical-grade stainless steel, nonvalved filtration device designed to shunt aqueous humor from the anterior chamber to a subconjunctival filtration bleb.The EX-PRESS Glaucoma Filtration Device is intended to reduce IOP in glaucoma patients when medication and conventional surgical treatments have failed.The device channels aqueous humor through a secure lumen (of either 50 mm or 200 mm) to a half-thickness scleral flap, creating a subconjunctival filtration bleb.It is a minimally invasive glaucoma surgery (MIGS) to increase aqueous drainage.It has lower complications of ocular hypotony.The commonly used devices are as follows: Shunts using episcleral explants:* Ahmed glaucoma valve: Silicone* Molteno implant: Polypropelene plate and silicone plate* Baerveldt implant: Silicone Mini-shunts:* Ex-Press(tm) Mini-Shunt: Stainless steel * iStent(r): Titanium