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A Algaze, LE Leguire, GL Rogers, J Murakami, C Roberts; LDOPA and fMRI in Amblyopia . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4698.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:L-dopa has been shown to improve vision in amblyopia. The present study investigated the effects of L-dopa on visual acuity (va) and fMRI activation in normal and amblyopic subjects. Methods: Visual acuity was measured with ETDRS visual acuity charts utilizing a forced-choice method. BOLD-contrast fMRI was performed at 1.5T. Five amblyopes and seven normals were recruited. Monocular stimuli included 0.5 and 2 cpd gratings counterphased at 4Hz. Data were collected at baseline and 90 minutes following administration of L-dopa (2mg/kg body weight). FMRI Analysis was constrained to the occipital cortex posterior to the parieto-occipital sulcus. An absolute percent difference measure defined differences between responses in terms of total activated area, average level of activation and a pooled activation parameter. Results: At baseline, normals had a mean va of -0.19 LogMAR and amblyopes had mean va of -0.13 in the dominant eye and 0.82 in the amblyopic eye. Following L-dopa, va remained the same in normals (-0.21) and in the amblyopes' dominant eye (-0.16). Visual acuity significantly improved in the amblyopic eye to 0.74 (p=0.03). Due to artifacts, two amblyopes and one normal were excluded from the fMRI analysis. Following L-dopa, the fMRI pooled activation measure that combined total area and mean level of activation showed a marginally significant (p=0.069) population x drug interaction. Amblyopes showed a larger interocular activation difference following L-dopa administration. Normals showed no change. Further analysis revealed that the pooled activation from the amblyopic eye tended to decrease (p=0.07) after L-dopa. This trend was also observed with the total area measure (p=0.068). No trend was found for the dominant or normal eyes. Further, the L-dopa induced changes in the amblyopic eye were significantly higher than those observed for the normal eye with both the pooled activation and total area measures (p=0.037 and p=0.005). Conclusion: In agreement with previous studies L-dopa significantly improved va in the amblyopic eye. The present fMRI data suggest that L-dopa increased cerebral blood flow with stimulation of the amblyopic eye. Such changes in blood flow could increase the BOLD fMRI OFF-condition baseline. This effect would thus decrease the level of activation. Also, since less voxels are bound to pass the threshold that qualifies them as active, the area of activation could also be reduced. The present results suggest that a potential treatment of amblyopia may involve pharmacologic manipulation of cerebral blood flow.
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