This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cornea, Subject name: Ophthalmology
Aberrometer is used to measure: 
Select and explain. 
A. Endothelial count, B. Keratometry, C. Higher order abberation, D. Corneal stroma
C: Higher order abberation
Answer: C: Higher order abberation 
Explanation: Abberrometer is used to measure higher order abberations. Corneal investigations Specular: Endothelial Count. Aberrometer : Corneal higher order abberations. Aesthesiometer: Corneal Sensations. Placido disc: Keratometry(anterior surface of cornea). Pentacam & Orb scan: Both anterior & posterior surface of cornea. Pentacam: Investigative modality of choice to do any corneal topography, it may be keratoconus, ectasia, LASIK. Topography Corneal Topography Confocal microscopy: visualize stroma & used in diagnosis of stromal dystrophies & latent infections.