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
Confirmatory investigation in retinitis pigmentosa is 
Select and explain. 
A. Optical coherence tomography, B. Pachymetry, C. Visual Acuity testing, D. Electroretinogram
D: Electroretinogram
Answer: D: Electroretinogram 
Explanation: Answer- D. ElectroretinogramAn accurate diagnosis of retinitis pigmentosa relies on the documentation of the progressive loss photoreceptor cell function, confirmed by a combination of visual field and visual acuity tests, fundus and optical coherence imagery, and electroretinography.