Rod and rod mediated function in patients with beta-thalassemia major

An electroretinographic (ERG) study was undertaken to test the hypothesis t hat scotopic retinal function is altered in transfused thalassemics on chro nic Deferoxamine (DFO). ERG a- and b-wave responses and dark adapted visual thresholds were obtained from 11 patients with beta-thalassemia major, age s 7 to 38 (median 17) years. A quantitative model of the activation of phot otransduction was fitted to the a-waves to estimate the gain of the transdu ction processes and the saturated amplitude of the rod photoresponse. From b-wave stimulus/response functions, the saturated b-wave amplitude and an i ndex of b-wave sensitivity (log sigma) were calculated. The patients' data were compared to those of normal subjects. The relations of the ERG paramet ers to age, average ferritin level, and duration of transfusion without DFO as well as other clinical parameters were examined. Longitudinal measures of b-wave responses and dark adapted visual thresholds, available for nine of the patients, were examined for significant changeover time. For all pat ients both the gain and saturated amplitude of the rod response are normal. In two patients log a is below the 99% prediction interval for normal. One has low scotopic visual sensitivity. The duration of transfusion therapy u nprotected by DFO chelation therapy was correlated with log a. These result s suggest iron accumulation rather than DFO toxicity underlies scotopic dys function in older thalassemics, some of whom may have had extended periods of transfusion without the protection of chelation. Thus, monitoring of ret inal function is recommended in such patients.