I was asked a great question in clinic recently about the effectiveness of Omega 3 sources that are not fish based i.e. Vegan Omega 3 options and Flax Seed.  (Most all brands of Omega 3 source are fish such as PRN Omega 3 or Nutrasea Dry Eye Formula or I-VU)

From clinical experience, folks never seemed to have much success for dry eye treatment with flax seed Omega 3 based supplements or flax seed use.  I did not know exactly why but a great podcast from Dr. Peter Attia clarified the answer (reference below).

Although flax seed does indeed have Omega 3, its form is 'ALA'.  Our bodies can not use ALA directly and the conversion from ALA to our usable forms (EPA & DHA) is simply not very efficient.  Massive amounts of ALA would be required to approach the large doses of EPA / DHA that I commonly recommend for dry eye treatment.   

There is one vegan product derived from algae that does have EPA and DHA (no conversion required) - NutraVege Plant Based Omega 3.  Great!... however it is cost prohibitive for most folks for dry eye therapy with EPA/DHA dosages of ~1200mg daily.   (mEYEspa does not carry this product)

 Dr Morris

Reference: The Drive Podcast - Dr Peter Attia December 9, 2019
#83 – Bill Harris, Ph.D.: Omega-3 fatty acids