Another interpretation. He said to them: Since you covered the matter from me [hid Sarah's true status], the son whom you raise up will be a covering of the eyes [blind, or one who must shield his eyes].
Abimelech's Words to Sarah and the Covering of the Eyes
Yalkut Shimoni on Torah 91:3
דָּבָר אַחֵר, אָמַר לָהֶם אַתֶּם כִּסִּיתֶם מִמֶּנִי אֶת הָעַיִן בֵּן שֶׁאַתֶּם מַעֲמִידִים יִהְיֶה כְּסוּת עֵינַיִם.