Ferdinand Monoyer was a French ophthalmologist born on May 9, 1836. He is best known for developing the Monoyer scale, a method for measuring visual acuity. This scale uses letters of varying sizes to help assess how well a person can see, which is crucial in eye examinations. In addition to his work on visual acuity, Monoyer also contributed to the field of optometry and made advancements in understanding the anatomy of the eye. He published numerous scientific papers and was recognized for his contributions to eye care, making a lasting impact on the field of ophthalmology.