Hertel exophthalmometry without orbital rim contact.

BACKGROUND: The Hertel exophthalmometer is the most widely used instrument for the measurement of globe malposition, but an absent or damaged lateral orbital rim will preclude its application. To circumvent this shortcoming, the authors have developed a fixation adapter that attaches to a standard Hertel instrument and transfers fixation to the forehead and nasion from the lateral orbit.
METHODS: The adapter design is presented and discussed, along with illustrative clinical cases. A study of 30 healthy patients was performed to assess the validity of the adapter with respect to the Hertel standard. The agreement was then evaluated by comparing the Hertel adapter measurements from each patient with that of the adapter. A Wilcoxon statistic was performed to assess differences in the paired values from each patient for both techniques.
RESULTS: Analysis on a sample (n = 30) of a healthy adult population does not show a statistical difference between the Hertel adapter and the adapter data (P > 0.05). In addition, more than 90% of the differences fall within +/- 1 mm (standard deviation = 1.02 mm) of the means for both eyes, which is within the accepted variance for the Hertel instrument.
CONCLUSION: The new fixation adapter promises to become useful in assessing trauma and surgical cases where the lateral orbital rim has been violated and will expand the application of Hertel exophthalmometry to these situations.