Abstract
We provided a historical perspective of the Hirschberg test by reviewing the publications by Julius Hirschberg (1843-1925) and related articles on objective strabismometry. In 1885 and 1886, Hirschberg published three articles and proposed a new method for the objective measurement of ocular deviation using the location of a corneal light reflex. The deviation was defined with reference to the landmarks, i.e. the pupillary margin and corneal limbus, and its degree was classified into Stage I to V. Up to the present, the test which was later termed the Hirschberg test has been utilized worldwide without modification.
Hirschberg appeared to have noticed a numerical relationship between the reflex displacement and ocular deviation angle. Although he did not discuss this issue in detail in his articles, a value of 8 degrees /mm was used as the conversion factor, the Hirschberg ratio. In the literature up to the 1960’s, the conversion factor was estimated between 7 and 8 degrees/mm. However, the advanced theoretical and photographic image analyses after 1970 have proved the values between 7 and 8 degrees/mm incorrect and proposed a value of 12 degrees/mm for the Hirschberg ratio.
