Accommodative performance of children with unilateral amblyopia

Abstract

Purpose: The purpose of this study was to compare the accommodative performance of the amblyopic eye of children with unilateral amblyopia to that of their nonamblyopic eye, and also to that of children without amblyopia, during both monocular and binocular viewing.

Methods: Modified Nott retinoscopy was used to measure accommodative performance of 38 subjects with unilateral amblyopia and 25 subjects with typical vision from 3 to 13 years of age during monocular and binocular viewing at target distances of 50, 33, and 25 cm. The relationship between accommodative demand and interocular difference (IOD) in accommodative error was assessed in each group.

Results: The mean IOD in monocular accommodative error for amblyopic subjects across all three viewing distances was 0.49 diopters (D) (95% confidence interval [CI], ±1.12 D) in the 180° meridian and 0.54 D (95% CI, ±1.27 D) in the 90° meridian, with the amblyopic eye exhibiting greater accommodative errors on average. Interocular difference in monocular accommodative error increased significantly with increasing accommodative demand; 5%, 47%, and 58% of amblyopic subjects had monocular errors in the amblyopic eye that fell outside the upper 95% confidence limit for the better eye of control subjects at viewing distances of 50, 33, and 25 cm, respectively.

Conclusions: When viewing monocularly, children with unilateral amblyopia had greater mean accommodative errors in their amblyopic eyes than in their nonamblyopic eyes, and when compared with control subjects. This could lead to unintended retinal image defocus during patching therapy for amblyopia.

Keywords: accommodation; amblyopia; children's vision.

Figure 1

The automated Nott retinoscopy system. The limits of the linear potentiometer were 0.68 D at the far distance and 4.69 D at the close distance. Thus, refractive states beyond these points could not be measured.

Figure 2

The relationship between amblyopic eye/worse eye logMAR visual acuity and stereoacuity (seconds of arc or ″) for amblyopic and control subjects. Amblyopic subjects are grouped by the associated amblyogenic factor: strabismus, anisometropia, or mixed (i.e., strabismus and anisometropia). No measurable stereopsis indicates stereoacuity worse than 800”, which is the coarsest stereoacuity level that can be assessed with the Randot Preschool Stereoacuity Test. The symbol groupings that represent the associated amblyogenic risk factors are shifted horizontally at stereoacuity levels of 800” and “no measurable stereopsis” to allow for ease of viewing.

Figure 3

Amblyopic/worse eye spherical equivalent cycloplegic refractive error plotted against nonamblyopic/better eye in amblyopic and control subjects.

Figure 4

Bland-Altman style plot of the difference between Nott retinoscopy measurements from two instruments, performed by the same examiner as a function of the average of the two measurements. Two examiners (AMC, VM) obtained these measurements from one pre-presbyopic, visually normal adult subject on different days. The mean intraexaminer, interinstrument, intersession repeatability was 0.03 (95% LOA: ±0.76 D).

Figure 5

Bland-Altman style plots, where the difference between the initial and repeated intrasubject and intrasession Nott retinoscopy measurements are plotted against the average of the two measurements. Each subject provided repeatability data from one eye in either monocular or binocular viewing at 2D, 3D, and 4D demands. (A) Intrasession repeatability measurements from 16 control subjects. Mean difference was −0.08 D (LOA: ±0.48 D). (B) Intrasession repeatability measurements from 15 amblyopic subjects. Mean difference was −0.06 D (95% LOA: ±0.80 D).

Figure 6

Graph of total accommodative response (measured accommodative response of the eye + residual uncorrected ametropia) as a function of total accommodative demand (target demand + residual uncorrected ametropia) for control and amblyopic subjects under binocular and monocular viewing as measured in the 90° meridian. The “out of range” points plotted above the graphs indicate the measured accommodative positions of >4.69 D and those plotted below the graphs indicate measured positions of <0.68 D. Closed circles, worse eye; open diamonds, better eye. Pale gray symbols, 2-D target position; gray symbols, 3-D target position; and black symbols, 4-D target position.

Figure 7

Graph of interocular difference in accommodative lag (better eye/nonamblyopic eye subtracted from worse eye/amblyopic eye) plotted against the average demand for the two eyes for control (A, B) and amblyopic (C, D) subjects in binocular and monocular viewing, as measured in the 90° meridian.

Figure 8

Graph of amblyopic eye monocular accommodative lag plotted against total accommodative demand at 2 D, 3 D, and 4 D for both 90° and 180° meridia. The upper limits of the 95% confidence interval for the better eyes of control subjects are plotted as horizontal lines.

Figure 9

Error in variables regression functions fit to the total accommodative response as a function of total accommodative demand. Functions for the better eye of control subjects and the nonamblyopic eye of amblyopes are shown for binocular viewing in the 90° (A) and 180° (B) meridia and for monocular viewing in 90° (C) and 180° (D) meridia.