These are the Rebbe's letters to individuals about their own situations. Throughout, the Rebbe instructed people to consult an expert doctor and follow his guidance; anyone facing a medical question should do the same.
The Rebbe's guidance to people with eye problems:
Consult an expert and follow his instructions. If the specialist has nothing to offer, consult another (IK 1360, 2556, 5707). Before any drastic step, such as surgery or removing an eye, first try every other possible treatment, and be strong in bitachon (IK 1784, 1895, 1947).
Be careful with kiddush and havdalah on wine. Chazal say this adds to "מאור עיניו של אדם" (IK 1784, 1947, 3688, 3757, 4408, 4880, 5180, 5647). Following minhag Yisrael, dip the fingers in the wine left over from havdalah and touch the eyes from the outside (IK 4041).
Add in the "light" of Torah. Studying pnimiyus haTorah, the מאור שבתורה, adds to the light of one's eyes (IK 1947, 4880, 5180, 6615).
Check tefillin and mezuzos (IK 3688, 5707).