To assess the intraobserver and interobserver reliability of recording uniocular fields of fixation using a modified perimeter technique in healthy subjects and patients with Graves orbitopathy (GO). Patients with restrictive myopathies, particularly GO, require accurate measurement of monocular excursions. These ductions are recorded in 4 to 12 directions of gaze using a perimeter, producing a plot known as a uniocular field of fixation. While 4 direction plots give limited information on vertical muscles, recording 12 directions is time consuming and uncomfortable. This modified technique uses the 6 directions of gaze corresponding to the primary field of action of each muscle.
A single observer measured modified uniocular fields of fixation in 35 healthy subjects aged 20 to 60 years to establish normal and age-related ranges for all ductions. Fifteen subjects underwent measurement on 5 separate occasions by the same observer to establish intraobserver reproducibility. A second observer independently performed measurements in 10 of the subjects to determine interobserver reproducibility. Reliability was compared with that measured in 29 patients with GO.
The technique was reproducible to within 4° for healthy subjects undergoing assessment by a single observer. When results of 2 observers were compared, the coefficient of repeatability was 7.9°. For subjects with GO, however, maximal variability was 7.8°. For clinical purposes, only a change of 8° or more can be assumed to be significant.
This technique offers advantages for assessing any restrictive myopathy, including GO to within 8°. This level of accuracy is likely to be similar in other centers, and has implications for interpreting GO outcome measures, where 5° was previously taken to represent significant change.