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Having experienced similar fears concerning a non-ophthalmological health concern, I can tell you that all the anti-blindness supplements in the world are not going to get rid of your anxiety because you'll just worry that you're still not doing enough or doing it wrong or a thousand other things. Focus on dealing with the fear that you know exists rather than a hypothetical situation, that frightens you to think about.

Just in general, having a balanced diet that includes a variety of different fruits, vegetables and animal based proteins is enough to help eye (and most health) issues from growing unnexpectedly quickly. I don't think there are any magic foods to include that will keep your eyesight from worsening if it's a predisposition to do so.

Include some of all of these in your diet regularly, and moderate excessively fatty, salty and sugar added foods. Green leafy vegetables, mineral rich root vegetables, fatty fish, red meat. eggs, beans/lentils/legumes, nuts.
Eat vegetables of different colors, because certain colored vegetables will contain varieties of vitamins and such.

Not a doctor, but have some experience with nutrition.