Rod and Rod-Driven Function in Achromatopsia and Blue Cone Monochromatism

Abstract

Purpose To evaluate rod photoreceptor and postreceptor retinal function in pediatric patients with achromatopsia (ACHR) and blue cone monochromatism (BCM) using contemporary electroretinographic (ERG) procedures. Methods Fifteen patients (age 1 to 20 years) with ACHR and six patients (age 4 to 22 years) with BCM were studied. ERG responses to full-field stimuli were obtained in scotopic and photopic conditions. Rod photoreceptor (Srod, Rrod) and rod-driven postreceptor (log σ, Vmax) response parameters were calculated from the a-wave and b-wave. The ERG records were digitally filtered to demonstrate the oscillatory potentials (OPs); a sensitivity parameter, log SOPA1/2, and an amplitude parameter, SOPAmax, were used to characterize the OP response. Response parameters were compared to those of 12 normal control subjects. Results As expected, photopic responses were non-detectable in patients with ACHR and BCM. In addition, mean scotopic photoreceptor (Rrod) and postreceptor (Vmax and SOPAmax) amplitude parameters were significantly reduced compared to those in normal controls. The flash intensity required to evoke a half maximum b-wave amplitude (log σ) was significantly increased. Conclusions The results of this study provide evidence that deficits in rod and rod mediated function occur in the primary cone dysfunction syndromes, achromatopsia and blue cone monochromatism.

Genetics and Disease Expression in the CNGA3 Form of Achromatopsia

“…Less anticipated was the finding that a considerable percentage of patients had mild to moderate abnormalities of rod-mediated ERG, even though the genetic defect is cone specific. This has been previously reported in CNGA3 ACHM 10,37 and in other genetic forms of ACHM 38,39 and could reflect a reduced number of rods, dysfunction of rods, or abnormal connectivity of rods to postreceptoral neurons. 39,40 Our cross-sectional retinal imaging studies (based on a limited number of patients) showed no evidence of a reduced number of rod nuclei, but unexpectedly there was mild shortening of the ROS length within the central retina similar to recent findings in another Figure 5.…”

An extended 15 Hz ERG protocol (2): data of normal subjects and patients with achromatopsia, CSNB1, and CSNB2

“…Therefore, we argue that there is no difference between the 15 Hz ERGs of an achromat and normal subjects for low flash strengths and that the primary and secondary rod pathways function normally. In the literature, the functioning of the rods in achromatic patients is generally described as normal [32][33][34][35][36], although recently, abnormalities in rod driven ERGs have also been reported [37,38]. Therefore, it would be interesting to measure 15 Hz ERGs in more patients with achromatopsia.…”

Achromatopsia: On the Doorstep of a Possible Therapy

“…In few cases, a partial function loss has been reported, resulting in milder forms like incomplete ACHM, oligocone trichromacy, and cone dystrophy [25,26,27]. …”

“…Electroretinographic examinations typically show absent or markedly reduced cone responses, while rod responses are reported to remain normal or nearly normal [1,2,25]. However, deficits in rod and rod-mediated function have also been demonstrated by Moskowitz et al [26]. …”