The reflection of light by the eyes is considered by many painters to be an important detail that can make or break the whole painting in terms of making it look lifelike, and such reflection has been depicted by various painters over the years in many shapes and locations on the pupil and iris of the eyes of the individuals they painted. Below is a sampler that I have put together from my collection of photographs.
Painting of Russian Princess Anna Alexandrovna Galitzin by Elisabeth Louise Vigee Le Brun (c. 1797). Baltimore Arts Museum, Baltimore, U.S.A.
Painting of Eunice Brown Fitch, wife of American businessman Timothy Fitch, by Joseph Blackburn (1760). Peabody Essex Museum in Salem, Massachusetts, U.S.A.
Painting of Archduchess Maria Karoline of Austria when she was Princess-Abbess of the Theresian Royal and Imperial Ladies Chapter of the Castle of Prague from 1844 to 1852 (painter unknown). Rosenberg Palace, Prague Castle, Prague, Czech Republic.
Painting of American art collector and Amateur photographer Sarah Lawrence Brooks by John Singer Sargent (1890). The Peabody Essex Museum in Salem, Massachusetts. U.S.A.
But the importance of depicting the reflection of light by the eyes goes beyond art. For some living things it can be a matter of life and death. Many butterflies, moths, and caterpillars have evolved eye spots on their wings or bodies that imitate eyes to deter predators, and these eye patterns also have spots that mimic that twinkle in the eyes!
Butterfly image from pikist is free for use under a public domain license. All other photographs are property of the author and can only be used with permission.