Love letter to Snellen Chart

The most iconic image associated with the undertaking of eye examinations is surely that of the Snellen visual acuity chart (figure 1). This deceptively simple black and white chart, consisting of capital letters of progressively decreasing size, is to be found in almost every setting where a measurement of visual performance is required. Even in the 21st century, it is hard to imagine the ocular world without this ubiquitous item. 

However, this was not always the case. In the 1800s, ophthalmology was emerging as a separate branch of medicine; it was the first sensory organ speciality. Yet practitioners diagnosing and treating eye disorders lacked an objective and repeatable method of measuring how well an eye could perform its basic function of seeing, namely vision if unaided, or visual acuity if optically corrected.