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: Unknown
[{'content': 'In open angle glaucoma investigation least done is : \nSelect and explain. \nA. Indirect ophthalmoscopy, B. Tonometry, C. Direct ophthalmoscopy, D. Perimetry', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Investigations to be done in open angle glaucoma are :\nSlit lamp examination\nTonometry\nGonioscopy\nDirect ophthalmoscopy\nPerimetry', 'role': 'assistant'}]