Summary: The application presented here concerns the evaluation of a patient’s visual acuteness, using web-based medical advice. In order to achieve this one undergoes a certain number of tests during which letters of different sizes are presented to the patient. We propose an algorithmic treatment of the binary answers, based on the use of fuzzy set functions, in order to eliminate the different mistakes (voluntary or not) that can be incurred. This algorithm also makes it possible to evaluate the quality of the examination by measuring the uncertainty of the acuteness. This work enters the field of a survey on telemedicine, and more especially the feasibility of carrying out these tests without the physician’s actual presence.