Rashi on Genesis 19:11/רש"י על בראשית י״ט:י״א

1פתח THE DOOR (literally, opening) — This means the hollow space (opening) through which people go in and out.

2בסנורים This is an attack of blindness (cf. Yoma 28b)

3מקטן ועד גדול FROM SMALL TO GREAT — The small had begun this wrongdoing — as it is said, (Genesis 19:4) “both young and old” — therefore the punishment started with them (Genesis Rabbah 50:8).