Rubens Peale's spectacles: an optical illusion?

The painting Rubens Peale with a Geranium (1801), by Rembrandt Peale, has earned a reputation as a masterpiece of early American portraiture. In recent years the painting has also been the source of controversy, because Rubens was depicted with two pairs of eyeglasses at a time when most people would not have been portrayed with spectacles at all. Scholars of American art history and ophthalmology have studied the painting and have promoted various theories for this peculiarity. A combined study of the painting, historical documentation, and optical effects in the painting, however, sheds new light on the answer to this mystery.