Carried
The first image we see of Grandma is her being carried out, under the armpits, by Mommy and Daddy and essentially dumped into the sandbox. The imagery immediately shows us that Grandma is not treated in a very dignified way by Mommy and Daddy; they treat her like an object rather than a respected elder. The stage direction also indicates that she wears an expression of fear, which suggests that they haven't consulted her about where they are taking her. The image represents Grandma's lack of autonomy.
Lights Down
Albee has the lights turned up to represent the brightest time of day. When the lights are brought down, it represents in a dramatical visual way that Grandma is near death.
Final Tableau
The final tableau of the play is the Young Man laying his hands over Grandma's hands, in a pose of affection and care. After Grandma has been treated so horribly by the other characters, the Young Man treats her with a gentle respect. Even though he is dim-witted, he is kind to Grandma and gives her a warm and tender transition from life to death.
