Poor correlation between "fix-follow-maintain" monocular/binocular fixation pattern evaluation and presence of functional amblyopia

Purpose: To assess the reliability of visual screening with fix-follow-maintain (FFM) method in early detection of amblyopia in children who are not able to cooperate in testing with Allen Figures or Snellen E-chart. Methods: Followup records of 89 patients that were examined in our pediatric ophthalmology department between May 1996 and May 1999 were evaluated retrospectively. The visual acuities that were measured with FFM method at the first visit were compared with the visual acuity levels that were measured with the Snellen E-chart at later followup visits. Functional amblyopia was defined as a difference of 2 or more Snellen lines between the two eyes. Results: Amblyopia was later defintively diagnosed on the E-chart in only 17 (32.6%) of the 52 eyes that were estimated to have a significantly lower visual acuity than the fellow eye with the FFM method. Sensitivity of the FFM method in diagnosing amblyopia was found to be 53.1% and the specificity was 38.5%. Conclusions: The use of the FFM monocular/binocular fixation pattern to determine visual acuity and the possible presence of amblyopia is so insensitive, and so unspecific, that its reliability is very low and the results of such testing are therefore virtually useless, if not medically hazardous. There is, therefore, a need to make more universally available more sophisticated tests of vision (preferential looking, VEP); where they are not available, further emphasis should be placed on Snellen equivalent vision testing as with Allen Cards, Tumbling E, HOTV Test, Lea Figures etc. so as to obtain an accurate direct visual acuity at as young an age as possible. Amblyopia treatment should not be initiated solely on the basis of FFM testing.