Query About Keratoconus. By slit lamp?

Doctor, I'm Having Double Vision (Monocular) in Both Eye And Blurry Vision For Almost 1.7 Years. I Was Consulted A Doc (Who is Also A Vitreo-Retina Specialist) Before 1.5 Years Ago And Then He Diagnosed Me With BE Myopic Astigmatism. However, He Prescribed Me Eyeglasses. His Prescribed Eyeglass Cannot Eliminate My Double Vision Fully But With Glasses, My Vision Was 6/6 And It is Still 6/6. However,I Have Consulted The Same Doc After 1 Years From First Consult And Then He Changed My Glass Power. There Was No Big Changes in My Eye Power. 2nd Time, His Prescribed Glass Cannot Fully Eliminate The Double Vision. From Doubting,I Went To An Another Doc And He Also Diagnosed Me With The Same BE Myopic Astigmatism.Both Of The Doc Checked Me Eye Totally 3 Times With Slit-Lamp.After Hearing The Double Vision Complaint From Me, The 2nd Doctor Told That The Remnant Double Vision (Which Amount Of Double Vision is Normal. Now, Why Doctor Told This?And If I Have KC,Would It Must Detected by Slit Lamp?