library(ltm)
data <- WIRS
two_pl <- ltm(data ~ z1)

Dffclt    Dscrmn
Item 1  3.4011395 0.1534064
Item 2 -0.9421221 0.3676923
Item 3  0.8093853 1.7179970
Item 4  1.3689278 1.0101043
Item 5  0.4762685 2.0324137
Item 6  1.6804632 1.3745785

(Intercept)        z1
Item 1  -0.5217566 0.1534064
Item 2   0.3464111 0.3676923
Item 3  -1.3905215 1.7179970
Item 4  -1.3827598 1.0101043
Item 5  -0.9679746 2.0324137
Item 6  -2.3099285 1.3745785

WIRStheta <- ltm::factor.scores(two_pl)