Jefferson and Eyeglasses
Even though Jefferson reported just months before his death that his eyesight was the faculty the least impaired by age, for many years he had used spectacles for reading. It was during his second presidential term that Jefferson placed an order with Philadelphia optician, John McAllister, which grew into a two year correspondence and resulted in spectacles designed by Jefferson to suit his specific visual needs.
Jefferson's November 1806 letter to McAllister begins, "You have 
heretofore furnished me with spectacles as reduced in their size as to give facility to the looking over their top without moving them. This is a great convenience; but the reduction has not been sufficient to do it compleatly, yet leave field enough for any purpose." The drawing which accompanied this letter diagramed frames of a narrow, elongated shape with each lens, or "eye glass", 7/8 inches long with a width of 3/8 inches, and gave the critical center to center measurement of each lens as 2 ½ inches.
The interpupillary measurement was Jefferson's one mistake, and placed McAllister in the position of informing the President that he feared the 2 ½ inches from center to center of the spectacle lenses too wide. McAllister wrote by return post, "Wishing to make them to please and recollecting the President has but a small head, I wish them examined again." He reminded Jefferson that when looking at a book or other object at about a 15 inch distance, the eyes will meet at a point and therefore the center of the "spects should be rather nearer than the eyes." Jefferson recognized his mistake of not reckoning the ". . .convergence of the two irises when directed to a book," as he had made his measurement looking directly into a mirror. He then instructed McAllister to correct the center to center measurement but proceed with his original design.
In addition to these newly designed reading spectacles, Jefferson wanted to try what would come to be known as bifocals. In the same 1806 letter to McAllister he wrote, "Those who are obliged to use spectacles know what a convenience it would be to have different magnifiers in the same frame. Dr. Franklin tried this by semicircular glasses joined horizontally, 
the upper & lower semicircles of different powers, which he told me answered perfectly. I wish to try it." Clearly, Jefferson had discussed with senior statesman Benjamin Franklin his spectacles of double lenses for both near and distance vision. Based upon Franklin's innovation, Jefferson included a second drawing of spectacles with two semicircular lenses set into small round frames and instructed that the lower lens was to be of greater magnifying power than the upper. For these frames he wished, "a compleat set of half glasses to be sent, from the magnifier adapted to the first use of spectacles, to that suiting the oldest eyes, all fitting exactly the frames." It was customary at the time to purchase a series of lenses along with the frames so that they could be changed as the eyes weakened with age.
McAllister completed Jefferson's order in less than two weeks but admitted that the double focus lenses had been extremely exacting due to, "the smallness of the eyes and the difficulty of getting so many pair to fit together in halves." Nevertheless he was able to comply with Jefferson's request in frame sizes and provided lenses in, ". . .12 pairs different focus for the double eye. . .and 6 different focuses for the other."
Jefferson's next request of McAllister presented an even greater challenge for the optician. Jefferson reported, "I am extremely satisfied with Dr. Franklin's method of joining the spectacles by composing each glass of two half glasses of different magnifying powers, and those you made for me answer positively except" that in the round frames the glass would shift until the seam between the two lenses was obstructing the line of vision. Jefferson's solution was to keep the convenience of the double lenses but put them in the very small oval frames from his previous order. He knew the size could be problematic but rationalized that, "Altho these glasses are very small and consequently the half glasses uncommonly so, I am not afraid but that they will present full space enough for reading, writing, etc."
McAllister's response began, "I am fearful I should not be able to put Dble glasses in such small frames," which he quickly contradicted with, "However I have put in two pairs and hope they will please." He had at least partially fulfilled Jefferson's request, but in case the new spectacles did not "please," McAllister included instructions for using a small amount of glue to prevent the glass from shifting in the round frames. One pair of the new lenses was of a 16 inch and 20 inch focus; the other of a 12 inch and a 16 inch focus. By combining a focal length for reading and a focal length for intermediate vision in a single frame so condensed in size that it did not interfere with distance viewing, Jefferson had essentially achieved the benefit of trifocals. His penchant for adapting and refining ideas had extended even to his spectacles.
Gaye Wilson, Monticello Research Department
Originally printed in the Monticello newsletter (Vol. 10, No. 2, Winter 1999)
Detail from Jefferson's letter to McAllister showing sketch of spectacles design.
Image of two pairs of Jefferson's eyeglasses; photo by Edward Owen.