Test-retest reliability and interchangeability are evaluated for three filter bars available to measure density of suppression: Sbisa bar, Bagolini filter (BF) bar and neutral density filter (NDF) bar. The study involved 10 strabismic adults. Testing conditions were altered and effects of this were evaluated. All filter bars showed changes in measurements on test-retest. From first to third test, a total reduction was found of five filters for Sbisa bar and NDF bar, and six filters for BF bar. This was significant for the BF bar. Measurements were taken with clinic lights on and off plus full or reduced intensity light source. Under normal lighting or darkness using full or reduced intensity light source, density of suppression was significantly denser with the NDF bar than BF or Sbisa bars. The authors conclude that BF and NDF bars possess relatively poorer test-retest reliability compared to the Sbisa bar. The greatest variation came from subjects subjectively reporting fixation swap or diplopia. Changes in testing conditions do not significantly affect test results as long as the same filter is used. The tests are not interchangeable. 

A pilot study examining density of suppression measurement in strabismus.
Piano M, Newsham D.
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Fiona Rowe (Prof)

Institute of Population Health, University of Liverpool, UK.

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