Major article
Functional magnetic resonance imaging as a tool for investigating amblyopia in the human visual cortex: A pilot study*,**

Presented at the 27th Annual Meeting of the American Association for Pediatric Ophthalmology and Strabismus, Orlando, Florida, March 21-25, 2001.
https://doi.org/10.1067/mpa.2002.124902Get rights and content

Abstract

Purpose: This study investigates interocular differences in the level and extent of cortical activation in amblyopic and normal subjects. Subjects and Methods: Blood oxygenation level dependent functional magnetic resonance imaging (FMRI) was performed at 1.5 T. A total of 5 subjects with amblyopia and 6 control subjectswere recruited. Visual stimuli included a homogeneous field flickering at 8 Hz and vertical sinusoidal gratings with spatial frequencies of 0.5, 1, and 2 cycles per degree of visual angle (counterphased at 8 Hz). Baseline images were taken in darkness. Stimuli were presented monocularly and binocularly. Data analysis was constrained to the occipital cortex, including striate and extrastriate areas. An absolute percent difference measure defined interocular differences in terms of total area, average level of activation, and a pooled activation parameter. Results: Subjects with amblyopia exhibited a significantly larger (P <.05) interocular activation difference compared to controls. The level of activation driven by monocular stimulation of the amblyopic eye was reduced by 8.25% ± 1.3% relative to the dominant eye. Controls showed an interocular difference in level of activation of 4.82% ± 0.74%. The total area of activation driven by the amblyopic eye was reduced by 34.86% ± 6.25% relative to the dominant eye. Controls showed an interocular difference in total area of activation of 20.80% ± 3.67%. Subjects with amblyopia also manifested significantly greater (P <.05) cortical area and level of activation differences between the binocular and monocular states; the dominant eye response differed less from the binocular response than did the amblyopic eye response. Conclusion: FMRI is sensitive to amblyopia-related deficits in the human occipital cortex and, therefore, has potential as a tool for basic amblyopia research. (J AAPOS 2002;6:300-8)

Section snippets

Subjects

Subjects included 5 patients with amblyopia (15-56 yrs. old) and 6 controls (25-48 yrs. old). Control subjects had no history of amblyogenic factors and had normal logMAR VA in each eye (mean VA, OD and OS, −0.17 (20/13.5)). Control subjects had a mean stereoacuity of 30 sec of arc based on the Randot stereoacuity test (Stereo Optical Co, Chicago, Ill) and normal contrast sensitivity functions in each eye based on the VCTS 6500 (Vistech Consultants Inc, Dayton, Ohio). Subjects with amblyopia

Monocular data

A statistically significant difference was found in the interocular cortical activation discrepancy of subjects with amblyopia versus that of the control group. The mean for the APD measure is reported in Table 1 along with the SE for the mean, as calculated for the 3 response measures (average signal change, area, and sum).

The population main effect was found to be statistically significant for all 3 response measures, as shown in Figure 3, where corresponding P values are reported.

. Evidence of

Discussion

The results suggest that BOLD-contrast FMRI can detect amblyopia-related interocular cortical activation differences. Stimulation of the amblyopic eye elicits less total area and mean level of activation in the occipital cortex than stimulation of the dominant eye. An example of this effect is illustrated in Figure 6, which shows the occipital cortex activation patterns recorded for a subject with amblyopia under monocular stimulation of the dominant and amblyopic eyes with a 1 cpd stimulus.

.

Acknowledgements

The authors would like to thank Edward Herderick, BS, Jim Ibinson, BS (Biomedical Engineering Center, The Ohio State University), Jim Murakami, MD, and Mark Smith, MS (Department of Radiology, Columbus Children's Hospital).

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    *

    This project has been supported by the Ohio Lions Eye Research Foundation. This study was conducted at The Ohio State University and Children's Hospital, Columbus, Ohio.

    **

    Reprint requests: Cynthia Roberts, PhD, 270 Bevis Hall, 1080 Carmack Rd, Columbus, OH 43210; e-mail, [email protected].

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