Sir, Syrimi and Ali wrote on the need for stereopsis in dentists (Br Dent J 2015,218: 597–598). The paper is an interesting one, but I believe their conclusion to be stronger than that represented in the few papers that were available for review. All the articles used the TNO test which uses 3-D pictograms to decide whether a student could see stereoscopically. The point in dentistry however is not whether one can see stereoscopically, but rather the ability to place an instrument close to, or on, a tooth. This is stereo perception and is important in avoiding erroneously placing a bur and causing damage. Subjects with poor stereo perception are considerably aided by visual clues such as objects lying in front or behind other objects.

Miller commented on this paper by saying 'that if one uses a mirror to view the operative field then one is using monocular vision....' I am surprised by this remark as stereoscopic binocular vision is most certainly used for example when shaving or putting on make-up with a mirror. Indeed, Wheatstone invented the earliest (mirror) stereoscope in 18381 and similar mirror stereoscopes were used to view and measure stereopair photographs in surveying and photogrametry until the recent advent of digital methods.