Since eyes are soft tissue, fingers will have no problem penetrating them. If you miss and hit bone, you will not cause serious injury to the person no matter how tough your fingers are. If you miss, the attempt will probably enrage the attacker so much that you will have a tougher time defeating him than you would have had without the attempt. When it comes to attacks to the head, the safest bet is always elbow attacks. Elbows can inflict lots of damage without being damaged themselves. If it becomes necessary and the opportunity arises, thumb eye gouges are always an option.
As far as strengthening the fingers, the traditional method is to drive the fingers repeatedly into a bucket of dried beans, gradually working your way up to using a bucket of sand. Another way is to drive the fingers repeatedly, but softly, into a makawara board; after a few months, you will be able to drive them in with great force.