Central or Peripheral Cone Dystrophy

The concept of regional cone dystrophy has been suggested by some clinicians [14], and these eyes were thought to have central or peripheral cone dystrophy. With central or peripheral cone dystrophy, the central or peripheral cone system is predominantly impaired and the rod system is completely preserved, even in the area where the cone system is impaired.

"Occult macular dystrophy" [5] is an example of a central cone dystrophy and is described later. We have reported that some patients with occult macular dystrophy show the pathophysiological properties of a central cone dystrophy, where only the macular cones are affected with preservation of the macular rods. These findings were detected by rod-cone sensitivity profiles in the macula area (see Section 2.19).

We have reported three patients from two pedigrees whose peripheral cone system was more affected than the central cone system and whose rod system was relatively normal [2,15]. The fundi of these patients with peripheral cone dystrophy are essentially normal except for mild temporal pallor of the optic disk in some of the patients (Fig. 2.100). The corrected visual acuity in the three patients ranged from 1.2 to 0.2, and the color vision was abnormal in two of the three. The full-field cone ERGs were significantly reduced, but the rod responses were normal, as in patients with typical cone dystrophy (Fig. 2.101).

However, the focal macular cone ERG were well preserved (Fig. 2.102), and the results of multifocal ERGs support the findings made by full-field and focal macular ERGs (Fig. 2.103). One of the patients (case 3) was examined 4 years after the initial examination using focal macular ERG because he had reported progressively increased blurring of his paracentral vision in the left eye. The responses clearly had become smaller during the 4 years (Fig. 2.101), suggesting that his retinopathy was progressive, even though his visual acuity was unchanged. Psychophysical rod-cone perime-try demonstrated that only the peripheral cone system was impaired, and the peripheral rod sensitivity was completely normal (Fig. 2.103).

Retinal Disease
Fig. 2.100. Fundus photographs (top) and fluorescein angiograms (bottom) of three patients with peripheral cone dystrophy. Cases 1 and 2 show slight temporal pallor of the optic disk, but otherwise their fundi appear normal. (From Kondo et al. [15], with permission)
Fig. 2.101. Full-field ERGs recorded from three patients with peripheral cone dystrophy. Cone-mediated ERGs are selectively impaired. (From Kondo et al. [15], with permission)

Fig. 2.102. Focal macular ERGs recorded with 5°, 10°, and 15° spots from the three patients with peripheral cone dystrophy shown in Fig. 2.101. Focal macular ERGs were recorded in 1993 and 1997 in case 3 (bottom) and show a progressive decrease in the responses. (From Kondo et al. [15], with permission)

Progressive Cone Dystrophy

Fig.2.104. Cone-rod perimetry (two-color perimetry) in the same three patients with peripheral cone dystrophy. Cone sensitivity profiles (upper trace) were determined with 31 red (600 nm) spots across a 60°horizontal meridian under a white background. For rod sensitivity (lower traces), two-color perimetry with blue-green (500- nm) and red (650- nm) stimuli being used after 45min of dark adaptation. Only the central cone was preserved. Rod sensitivity is normal over the entire retina. (From Kondo et al. [15], with permission)

Fig.2.104. Cone-rod perimetry (two-color perimetry) in the same three patients with peripheral cone dystrophy. Cone sensitivity profiles (upper trace) were determined with 31 red (600 nm) spots across a 60°horizontal meridian under a white background. For rod sensitivity (lower traces), two-color perimetry with blue-green (500- nm) and red (650- nm) stimuli being used after 45min of dark adaptation. Only the central cone was preserved. Rod sensitivity is normal over the entire retina. (From Kondo et al. [15], with permission)

Fig.2.103. 7op:Trace arrays of multifocal ERGs recorded from a normal subject and two patients with peripheral cone dystrophy (cases 1 and 2; see Figs. 2.100 and 2.101). Bottom:Three-dimensional (3D) topographic maps of the multi-focal ERGs shown in the trace arrays for the normal subject and the two patients with peripheral cone dystrophy. (From Kondo et al. [15])

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