Parallax-free exophthalmometry: a comprehensive review of the literature on clinical exophthalmometry and the introduction of the first parallax-free exophthalmometer.

Purpose: To present the first parallax-free exophthalmometer design.

Background: Exophthalmometry is an important clinical tool. We provide a historic overview of clinical exophthalmometer designs, and we review current problems encountered in exophthalmometry.

Methods: We present a new and parallax-free exophthalmometer design that we have evaluated in 49 patients visiting our orbital clinic.

Results: The mean age of the patients was 49.8 years and 72% were female. The Pearson interobserver variation was 0.97, and 94% of the Hertel values measured by the two observers were within the limits (1.6 mm) of agreement.

Conclusion: This meter appears to be a reliable instrument for exophthalmometry. It is the first instrument that allows for a complete parallax-free measurement.