A modified method for measuring uniocular fields of fixation: reliability in healthy subjects and in patients with Graves orbitopathy.

Objective: 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.

Methods: 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.

Results: The technique was reproducible to within 4 degrees for healthy subjects undergoing assessment by a single observer. When results of 2 observers were compared, the coefficient of repeatability was 7.9 degrees . For subjects with GO, however, maximal variability was 7.8 degrees . For clinical purposes, only a change of 8 degrees or more can be assumed to be significant.

Conclusions: This technique offers advantages for assessing any restrictive myopathy, including GO to within 8 degrees . This level of accuracy is likely to be similar in other centers, and has implications for interpreting GO outcome measures, where 5 degrees was previously taken to represent significant change.