Ībout 2000 BCE, the Egyptians believed that one was reincarnated in a decan star,* (* A decan star rose at the horizon just before sunrise at the beginning of a decade and thus the year had 36 groups of decan stars, 360 days. It will disregard stereoscopic acuity, Vernier hyperacuity, low-contrast optotypes, spatial frequencies or integrations, cortical visual functions and ultra-low vision. The most important improvements of these optotypes are discussed next, ignoring numerous later modifications of the first examples, ending with some recommendations and conclusions.
It will focus on early attempts to test VA, the emerging need for reliable vision tests in 19th century ophthalmology and the first optotypes around 1850. This paper will start with some notes on vision in ancient times followed by discussion on the minimum visual angle and VA. In clinical ophthalmology, optotypes are used in two ways: to aid in finding the optimal lens to correct a refractive error of an eye and to determine its VA. They could be printed with high or low contrast in different colors, pasted on a transparent screen with lighting behind, projected on a (computer) screen, or made of metal or other material shown to the test person. These aids gradually changed from printed texts, letters, numerals or figures, to a variety of forms. For the sake of clarity to the reader, I present here a working definition of optotype: An optotype is a visual aid to arrive at a dependable and standardized measure of visual acuity (VA) on arbitrary but commonly agreed grounds. Presumably, he composed a neo-Latin word from the Greek words οπτος (optos, visible) and τυπος (tupos, model to be imitated).
It is uncertain how he invented this word. It did not appear in the first edition of his “Lettertypen” but 13 years later, he introduced “Optotypi” in his international test type edition in Latin. The word “optotype” was described as originating from the German “Optotypus” but Herman Snellen from Utrecht, The Netherlands, was the first to coin this word in 1875. These definitions give limited guidance on what exactly an optotype is. The test types are subdivided into those of Jaeger, Landolt, and Snellen. The latter is explained as Printed letters of varying size, used in the testing of visual acuity see also under chart. In various dictionaries, “Optotype” is defined as: A type or letter of definite size used for testing acuteness of vision, a type by which to test the eyesight, or test type. Recent advances in aids and therapies for the blind and severely visually handicapped, necessitate further development of new and standardized VA tests. Multidisciplinary approaches between ophthalmology, linguistics, psychology and psychophysics improved optotypes and VA testing, which led to the more reliable LogMAR charts. However, 100 years later there was still no standard optotype to reliably test VA. Numerous variants emerged after the first edition of Snellen’s optotypes in 1862 in The Netherlands. In the early nineteenth century, the need for VA tests in ophthalmology resulted in German and English test charts. Around that time, texts were introduced by opticians in order to be able to prescribe more reliably. Around 300 BCE, Euclid formulated the existence of a visual cone with a minimal visual angle at its tip. After going into the etymology of the word “optotype”, this article covers some tasks in ancient times that required good visual acuity (VA).
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