TEST TYPES ACCORDING TO THE GEOMETRICAL PROGRESSION OF DR. JOHN GREEN.

Abstract

In 1868, Dr. John Green, of St. Louis, wrote as follows: The letter proeven of Snellen are deservedly the acknowledged standard for determining the acuteness of vision. They are, however, somewhat imperfect both in plan and in the execution of the smaller letters. The defects in plan consist in the selection of letters which are not so uniform in size and character as is to be desired and still more in the fact that the gradations of size in the successive numbers of the series are not uniform. I have now to propose a new series-bearing the constant ratio of .795 and combining the advantage of regular geometric progression with the preservation of all the important numbers of Snellen. A series of such numbers in Gothic form was published in the transactions of the American Ophthalmological Society for 1868. Again, at the meeting of the Fourth International Ophthalmological Congress, held in