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Linda L. Cooper, MD; Ronald M. Hansen, PhD; Basil T. Darras, MD; Mark Korson, MD; Frances E. Dougherty, MD, PhD; John M. Shoffner, MD; Anne B. Fulton, MD

Arch Ophthalmol. 2002;120:1055-1062.

Objective  To test the hypothesis that function of the rod photoreceptors is abnormal in pediatric patients with mitochondrial disorders.

Methods  Patients (n = 22; median age, 5 years) with a deficiency of 1 or more of the mitochondrial enzyme complexes, or a mutation in mitochondrial DNA, were studied by means of scotopic, full-field electroretinography (ERG). The conditions of ERG testing allowed derivation of the parameters of the activation of rod phototransduction from the ERG a-wave, and postreceptoral function from b-wave and P₂ stimulus-response functions. The deactivation of phototransduction was studied in 5 patients. The patients' ERG responses were compared with those of healthy control subjects (n = 25).

Results  Responses from 19 patients were sufficient for analysis of rod photoreceptor and postreceptoral function. Saturated amplitudes of the rod photoresponse and b-wave sensitivity were significantly depressed in the patients. Saturated amplitudes of rod cell and P₂ responses were correlated. The kinetics of deactivation of phototransduction were slowed even if the kinetics of activation were normal.

Conclusions  In patients with mitochondrial disorders, some abnormalities of the scotopic ERG responses originate in the rod photoreceptors, but postreceptoral processes may also be abnormal. From a practical perspective, ERG testing can contribute to diagnosis of mitochondrial disorders.

From the Departments of Ophthalmology (Drs Cooper, Hansen, and Fulton) and Neurology (Dr Darras), Children's Hospital Boston and Harvard Medical School, Boston, Mass; Division of Metabolism, Department of Pediatrics, Floating Hospital for Children, Tufts New England Medical Center, Boston (Dr Korson); and Horizon Molecular Medicine, Norcross, Ga (Drs Dougherty and Shoffner). Dr Cooper is now with Ivey Institute of Ophthalmology, London, Ontario.

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