Diagnosis of eccentric fixation using a calibrated ophthalmoscope: defining clinically significant limits

Visuscopy and other ophthalmoscopic methods are widely applied in the assessment of fixation behaviour in amblyopia, although the reliability and inter-examiner variability of this test has not been established. Typically eccentric fixation is diagnosed solely on the basis of retinal position, but this fails to address the accompanying sensorimotor adaptations. A double-blind (masked) trial of a paediatric population was undertaken (n = 30, age range 3 years 9 months to 11 years, mean 5.6 +/- 1.5 years), involving three examiners applying a detailed protocol. The criteria for eccentric fixation were established from the non-amblyopic eyes. The most reliable criterion for the diagnosis of fixation was established from the results of the study. No single parameter proved 100% reliable, and amplitude showed greatest inconsistencies. It is recommended that a consensus of at least three parameters from position, zero retinomotor point, principal visual direction and percent foveation is required to diagnose the fixation status reliably.