To become Ophthalmologists you have to first complete MBBS (Bachelor of Medicine and Bachelor of Surgery) course and then go for the postgraduate degree in ophthalmology like MS (Master of Surgery), MD (Doctor of Medicine), etc. After completing PG course in this field you can also pursue doctoral courses in this field. You can also go for research studies in this course in various institutions and research centres.

After diploma in this course you will be left no where as you will be required to go higher studies in it.
Incase you want to take up job after diploma itself then you can get job in areas like:

Research labs
Nursing homes
Military Health services
Pharma companies
Content writing


All the best!