I have seen a trial suggesting that take up by the body drops off at about 2grams DHA a day. Individuals will obviously vary, metabolism stored fats etc so you will just have to work it out for yourself.
For most quality fish oils I have seen (and that is not many) about 5 teaspoons a day will give you 2 grams. Check the label.
Fish oil contains a range of fats including shorter chain and omega nines. This site will give you details.
http://www.nutritiondata.com/fatty-acids.html
Flax seed has wider effects as you are probably aware and can search on this site. From my reading it is important to take in a balance so a little quality olive oil etc is also worth keeping in mind. You will need to look up the short names.
Some do try much higher doses. Very high doses are reported as leading to blood thinning. The Linnus Pauling site deals withside effects of high dosages.
Please do let us know how you get on. Hopefully dry eyes will reduce and vision colour preception etc will stabilise or improve but it does take a while.
Please do discuss dietary changes with your advisor - they are powerful as is evident from the taxol DHA post above.
RB