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Comparative Study
. 2013 Mar 19;54(3):1998-2003.
doi: 10.1167/iovs.12-11054.

A quantitative study of fixation stability in amblyopia

Vidhya Subramanian  1 , Reed M Jost, Eileen E Birch
Affiliations
Comparative Study

A quantitative study of fixation stability in amblyopia

Vidhya Subramanian et al. Invest Ophthalmol Vis Sci. .

Abstract

Purpose: To determine whether fixation instability contributes to reduced visual acuity in amblyopia, we compared fixation instability, quantified by the Nidek MP-1 microperimeter, in amblyopic and nonamblyopic children.

Methods: Participants were 89 children (5-17 years old) with strabismus (n = 31), anisometropia (n = 29), or both conditions (n = 29). Fixation instability was measured using the Nidek MP-1 microperimeter, which calculated horizontal and vertical eye position at 25 Hz as the child attempted steady fixation for 30 seconds. Fixation instability was quantified as the 95% bivariate contour ellipse area (95% BCEA), the best-fit ellipse within which 95% of fixation occurred during the 30-second test. BCEA was normalized by log transformation.

Results: Children with amblyopia had significantly larger BCEAs for amblyopic eyes (mean = 0.56 log deg(2)) than fellow eyes (mean = 0.2 log deg(2), P < 0.01) and right eyes of normal controls (mean = 0.12 log deg(2), P ≤ 0.01). Fixation instability was significantly greater along the horizontal axis of the ellipse for amblyopic (mean = 3.53°) than fellow (mean = 1.98°, P = 0.008), and control (mean = 1.62°, P < 0.001) eyes.

Conclusions: Fixation instability in amblyopic eyes of children with strabismus and/or anisometropia, and the associated poor stereoacuity probably is the consequence of decorrelated binocular experience early in life. Longer duration of decorrelated visual experience is associated with increased fixation instability, poorer stereoacuity, and more severe amblyopia. Treatments that minimize the duration of decorrelated visual experience may improve stereoacuity and decrease fixation instability.

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Conflict of interest statement

Disclosure: V. Subramanian, None; R.M. Jost, None; E.E. Birch, None

Figures

Figure 1
Figure 1
Fixation patterns of a normal control and a child with amblyopia. The red circle is the fixation target. The 95% BCEA is indicated by the yellow ellipse. The 68% and 99% BCEAs are indicated by the inner blue ellipse and the outer turquoise ellipse, respectively. (A) Fixation pattern from the right eye of a 9-year-old normal control. Visual acuity 20/16, BCEA = 0.49 log deg, major axis diameter = 2.01°, minor axis diameter = 1.99°. (B) Fixation pattern from the right eye of a 7-year-old with esotropia, hyperopic anisometropia, and amblyopia. Visual acuity 20/250, BCEA = 1.3 log deg, major axis diameter = 8.67°, minor axis diameter = 2.95°.
Figure 2
Figure 2
Comparison of mean (± SEM) log10 95% BCEAs for amblyopic eyes (AE) and fellow eyes (FE) of amblyopic children, and right and left eyes (RE, LE) of nonamblyopic children and normal controls.
Figure 3
Figure 3
Correlation between BCEA and visual acuity for strabismic (solid triangle) and anisometropic (open square) amblyopic eyes. Best-fit line, y = 1.3214x − 0.0746.
Figure 4
Figure 4
Correlation between BCEA and stereoacuity for strabismic (solid triangle) and anisometropic (open square) amblyopic eyes. Nil stereoacuity has been assigned a value of 4.0 log arcsec. Best-fit line, y = 0.2028x − 0.1307.
See this image and copyright information in PMC

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