This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Primary Open-Angle Glaucoma and Related Conditions, Subject name: Ophthalmology
A patient of glaucoma with bronchial asthma presents to the emergency with status asthamaticus, causative agent might have been) 
Select and explain. 
A. Pilocarpine eye drop, B. Timolol eye drop, C. Betaxolol eye drop, D. Levobunolol eye drop
B: Timolol eye drop
Answer: B: Timolol eye drop 
Explanation: Ans. is 'b' i.e. Timolol eye drops Timolol maleate is the most widely used drug for open angle glaucoma.It is non-selective B blocker (Blocks both B1 and B2B2 is responsible for bronchodilation, therefore blocking B2 would aggravate asthma.Instead of Timolol, Betaxolol can be used because it is a selective B1 blocker and causes less respiratory side effects.