The protocol of the study adhered to the provisions of the Declaration of Helsinki. After informed consent was obtained, blood samples were taken and molecular analysis on the
ABCA4 gene was performed as described by Maugeri et al.
14 The charts of patients with
ABCA4 mutations who originally had received diagnoses of isolated or autosomal recessive CRD were reviewed. All patients originated from the University Medical Centre Nijmegen (Nijmegen, The Netherlands) and the University of Heidelberg (Heidelberg, Germany). In this study the diagnosis of CRD was based on the following criteria: initial symptoms of blurred central vision without a history of night blindness, impairment of color vision, and fundoscopic evidence of maculopathy without or with mild peripheral retinopathy.
3 4 5 7 8 In patients with recordable ERGs a cone–rod pattern of degeneration had to be present (i.e., the photopic b-wave impairment had to be greater than or equal to the scotopic b-wave amplitude impairment). Patients 9250 and 13163, who had nonrecordable ERGs, were included because their histories and clinical features were similar to those of other patients with cone–rod degeneration and they were believed to represent advanced cases of CRD. In addition to an ophthalmic examination, Goldmann kinetic perimetry routinely was performed using III-4-e and I-4-e isopters. Color vision was tested with the Ishihara and Panel D15 tests, except in patients 9369, 9378, and 10125, who were tested under conditions described earlier.
18 Because these patients were examined in two different clinics and ERGs were recorded over a long period, the methods, instrumentation, and analysis techniques of the electroretinography varied. The ERGs in patients 9369, 9378, 10125, and 11872 were performed as described by Thijssen et al.
19 The ERG method used in patients 9370, 9553, 9633, and 13163 was described by Alexandridis and Krastel.
20 The ERGs of the remaining patients (9250, 9371, and 9650) are of a more recent date and were performed according to International Society for Clinical Electrophysiology of Vision (ISCEV) standards.
21 Fundus photographs were taken in most patients and some of the patients (9650, 9369, 9378, and 10125) also underwent fluorescein angiography.