Dear Friend,
You have diposited 13×15= 195 days (say) as medical leave. But PhD in regular course within such time? How it can possible? Besides this, Your Medical leave will be granted by the submission/production of a Medical Certificate. How would you be able to do your PhD on submission of a medical certificate?
You may do it if you applied for EOL ( Extra ordinary leave/ with out pay) up to 2-5 years with the permission of department.(Para 10 of G.O.No. 1541-Edn.(S) dated 15/12/77).,No. 33- End dt. 7/3/90, and No. 181-SE DT. 8/10/2009 para 4 (ii).