What important fact do we find out about the grandfather in the first three lines of the poem "Grandfather" by Oliver Shelley?

In the poem "Grandfather" by Oliver Shelley, the poet makes great use of visual imagery. The first three lines establish the relationship between the narrator and the subject. On line one, the narrator refers to the grandfather as "Our grandfather," showing that the narrator is directly related to the subject. The use of "our" also reveals that the narrator has a sibling or a cousin. The poet uses visual imagery to present the grandfather as sitting "by the sea" on "[h]is deck chair." The chair is atop a rug belonging, at least in part, to the speaker, as it is referred to as "our rug" which the grandfather's chair is settling into "the stones" by the sea.
Finally, and perhaps most importantly, the grandfather is revealed to be blind, which helps to explain why "his face takes sunlight like thirst." Throughout the remainder of the poem, the narrator shows that the grandfather absorbs and appreciates his experiences in ways that don't require sight. Somewhat ironically, Shelley does a great job of using visual imagery to show how one can appreciate the world without being able to see it.