I'll begin with the basics,
Firstly, the ELIGIBILITY CRITERIA :
Candidate should complete 10+2 with minimum 50% marks, subjects being physics, chemistry and biology.

Second, if you plan on PRACTICING OPTOMETRY, the PRE-REQUISITE REQUIREMENTS are:
(A) Bachelors degree, that is,  Bachelor of clinical optometry (B. Optom)
ELIGIBILITY TO PURSUE B. OPTOM?
1) 50% marks in PCB and English from a recognized board in your 10+2
2)age limit: 17 years as on 31st December (in the year in which you're applying for the entrance exam)
If you satisfy the above mentioned criteria, you get the eligibility to appear for EYECET examination.

DURATION OF B. OPTOM COURSE : 4 years
(3 years of studies + 1 year internship)

(B) FOR DIRECT ADMISSION TO THIRD YEAR B. OPTOM COURSE
ELIGIBILITY CRITERIA : Candidates who have completed their 10+2 must have a 2 year diploma course in Optometry along with a minimum of 40%marks from an institution that is recognized by the Indian optometric association and BVP.

AGE LIMIT FOR DIRECT ADMISSION INTO 3RD YEAR B. OPTOM : 19 years
Also, they'll have to appear for the EYECET entrance examination.

The various optometric courses that you can consider studying include :
1) B.sc ophthalmic techniques (Hons)
2)B.sc optometry
3) Bachelor of optometry
4) Bachelor of optometry and vision science
5) Diploma in optometry
6) Diploma in optometrical science (DOS)
7) Diploma in ophthalmology
8) Diploma in Ophthalmic assistance
9)Optician and refractionist course

If you plan on pursuing masters degree in optometry, you can proceed for pursuing M. Optom. It is post graduation course of 2 years duration.
Admissions into M. Optom courses are based on  entrance examination results.

Diploma Courses: For two years duration.You can go for it after completing your 12th. There are certificate courses of 1-year duration. Bachelor Degree Courses are 1) Optometry (B.Opto) 2) Bachelor of Science (B.Sc) The duration of these courses is 4 years.

There are 2 types of courses in optometry, namely, Certificate courses and bachelor degree.
Certificate courses are of 1 year and bachelor degree of 4 years.
These days you can pursue Master's as well as M.phil in optometry.
Institutes are as follows: AIMS, Delhi
Bharati Vidyapeeth
Government medical college Nagpur
Government medical college Surat
And a couple of colleges in Punjab.