Reliability of fixation preference testing in diagnosing amblyopia
K. W. Wright, P. M. Edelman, F. Walonker and S. Yiu
We evaluated the sensitivity and specificity of standard fixation
preference testing and the 10-prism diopter (PD) fixation test in 427
patients. Standard fixation preference testing showed good sensitivity and
specificity for than 10 PD. Patients with small angle tropias, however, had
a high false-positive rate, with 40% of nonamblyopic patients
inappropriately responding with strong fixation preference. The 10-PD
fixation test reduced this high false-positive rate and showed only 1.5%
false-positive results. Unfortunately, this shift to equal fixation
preference was also seen in some patients with amblyopia, as five of 19
patients with three or more lines difference alternated fixation with the
10-PD fixation test. Retesting disclosed that, although these children
would briefly alternate to the amblyopic eye while viewing a stationary
target, they would not hold fixation with the amblyopic eye through smooth
pursuit. Our conclusion is that standard fixation preference testing can be
used to diagnose moderate to severe amblyopia in patients with tropias
greater than 10 PD. Patients with small angle deviations or straight eyes
should be examined with the 10-PD fixation test, with the criterion for
equal vision being the ability to hold fixation well with either eye
through smooth pursuit.
