When the Gemarah tells us that a Suma (a blind person) is "Patur" from Mitzvot, does that mean to say that he is completely outside the realm of Mitzvot, and will get no reward for doing them, or does it mean that while he has no obligation, he still gets some reward, possibly a Kiyum Mitzvah?
The Gemara states about R` Yosef who was blind that he wondered whether he got more reward because he was blind and therefore non-obligated and did them anyways or less reward because he was non-obligated and so doing them was easier. Like when mom asks you to clean your room you don't want to but a day later you decide on your own that you want a clean room. What changed? You weren't being forced so it is easier.
I believe the Gemara's conclusion is that they receive less reward for the fulfillment. However, I have heard that since they are non-obligated, many times it's more meaningful to blind people so they would be fulfilling the imperative Rachamana liba bouy Hashem wants the heart.
The Gemara in Bava Kamma 87a indicates that a blind man is still within the realm of mitzvot and merits the reward of one for whom the mitzvah is optional rather than obligatory (mi she'eino metzuva v'oseh):
אמר רב יוסף מריש הוה אמינא מאן דאמר הלכה כר' יהודה דאמר סומא פטור מן המצות קא עבדינא יומא טבא לרבנן. מאי טעמא? דלא מפקדינא וקא עבדינא מצוות. השתא דשמעית להא דר' חנינא דאמר ר' חנינא גדול המצווה ועושה ממי שאינו מצווה ועושה, מאן דאמר לי: אין הלכה כרבי יהודה עבדינא יומא טבא לרבנן. מאי טעמא? דכי מפקדינא אית לי אגרא טפי.
Rav Yosef (who was blind) said: Originally, I would say that if one says the halacha is like Rabbi Yehuda who said that a blind person is exempt from the commandments, I will make a holiday for our rabbis. Why? For I'm not commanded yet keep the mitzvot. Now that I heard that which Rabbi Chanina said - for Rabbi Chanina said that one who is commanded and does is greater than one who is not commanded and does - if one says to me the halacha is not according to Rabbi Yehuda, I'll make a holiday for our rabbis. Why? Because if I'm commanded, I have even more reward.
(The clear implication is that even if we say a blind man is "patur", he still receives reward and is included in the mitzvot, just not the same level of reward as one who is "metzuvah" - obligated.)