Two siblings with late-onset cone–rod dystrophy and no visible macular degeneration
Case 1 was an 82-year-old man who first noticed a decrease in his vision and color vision in both eyes in his early seventies. His decimal best-corrected visual acuity (BCVA) at our initial examination was 0.3 oculus dexter (OD) with +3.25 diopters (D) and 0.2 oculus sinister (OS) with +3.25 D. His pupillary light reflexes and intraocular pressures were normal in both eyes. There was no history of the use of retinotoxic drugs. His cataracts were removed in both eyes at age 75; however, his vision was not improved.\nOphthalmoscopy showed that the fundus was normal in both eyes, and FA showed small hyperfluorescent spots at the parafoveal region of the left eye (). Goldmann kinetic perimetry showed a central scotoma in both eyes (), and Farnsworth D-15 test showed a tritan axis error. Goldmann–Weekers dark adaptometry revealed a slight elevation of the threshold in both eyes (). The full-field scotopic ERGs elicited by both low- and high-intensity stimuli were slightly reduced. The scotopic b-wave elicited by a high-intensity stimulus was smaller than the a-wave, resulting in a negative-type ERG (). On the other hand, photopic single-flash and 30 Hz flicker ERGs were severely attenuated in both eyes (). The mfERGs were nonrecordable in the central area, but small responses were recorded in the midperiphery (). The photoreceptor inner segment/outer segment junction line was indistinct in the OCT images (). The thickness of the outer nuclear layer was 76 μm OD and 65 μm OS (normal mean 172 ± 17 μm) at the fovea, 65 μm OD and 43 μm OS (normal mean 128 ± 19 μm) at 0.5 mm superior to the fovea, and 65 μm OD and 54 μm OS (normal mean 135 ± 23 μm) at 0.5 mm inferior to the fovea. At 2 mm superior to the fovea, the thickness of the outer nuclear layer was 65 μm OD and 43 μm OS (normal mean 97 ± 13 μm), and at 2 mm inferior to the fovea it was 43 μm OD and 54 μm OS (normal mean 88 ± 18 μm). Thus, the outer nuclear layer was thin, especially in the parafoveal region in both eyes (). The thickness of the middle and inner layers of the retina were within normal limits.