There are no such health requirement for student regarding the admission to the IIST course. Now professionally being an Aerospace Engineer or Avionics you have nothing to worry about the minus eye power. Having a negative eye power is quite common and it don't create any problem in your professional career until and unless you go for the army and other cases if there are requirements of eye health. In general there are no such regarding the engineers and if there exist then it would be for High power candidates having very low eye sight for 6.6,6/9 vision there are no problems in most of the case.

To know more about the IIST visit the link below:

https://www.careers360.com/university/indian-institute-of-space-science-and-technology-thiruvananthapuram

I hope this answer helps. All the very best for your future endeavors!