  Proliferative sickle cell retinopathy (PSCR) is the most important ocular
manifestation of sickle cell disease (SCD), but understanding of its
pathophysiology remains incomplete. Red blood cell (RBC) deformability has been
identified as a critical factor in SCD and is intrinsically related with cell
sphericity index (SI). The aim of this study was to develop an algorithm that
automatically analyzes defocusing microscopy (DM) images, providing
biomechanical parameters of individual RBCs, including cellular SI.
Furthermore, association of RBC SI with severity of PSCR in individuals with
HbSC-SCD was also investigated. We determined the SI of 255 RBCs from 17
individuals using DM. Nine individuals (53%) were healthy and eight (47%) had
HbSC-SCD. Mean SI was significantly lower in SCD than in control group (0.69
versus 0.73), and also in severe than in mild PSCR (0.67 versus 0.70). Lower SI
was also associated with more severe retinopathy (ROC AUC = 0.85) and the
proportion of participants with SI <= 0.69 was significantly greater in severe
than in mild PSCR (100% versus 25%). In conclusion, lower RBC SI determined by
DM was associated not only with the presence of SCD, but also with more severe
PSCR, possibly being a surrogate biomarker of disease severity.
