In group C , the speed of sound of the treated corneas was 1717.97 18.92 ms ( -1 ) anteriorly and 1616.62 17.58 ms ( -1 ) posteriorly , while it was 1628.69 9.37 ms ( -1 ) anteriorly and 1597.68 11.97 ms ( -1 ) posteriorly in the controls .