主题：[求助]这个表达式如何写？

取双眼视力差的绝对值，下面的表达式报错，请指点！

Dim dr As DataRow = e.DataRow
Dim dt As DataTable =DataTables("体检表")
If e.DataCol.Name = "班级" And dr.IsNull("班级") = False Then

    dr("视力_视力参差_轻度") = dt.Compute("Count(姓名)", "[班级_部门] = '" & dr("班级") & "' and (Math.Abs([视力_左眼] - [视力_右眼]) > 2 )")
End If