How to add an optional dependency and run some specific code if it's present

[tawny flicker]

I'd like to add Entity Culling as an optional dependency to my mod. If this mod is present, I'd like to use its renderedEntities field (in the EntityCullingModBase class) instead of the vanilla regularEntityCount (in the WorldRenderer class). I still want to fallback to the vanilla field if Entity Culling is not installed, because I don't want my mod to have a dependency when it's not necessary.
I'm not sure how I can add Entity Culling as a dependency that is optional. Furthermore, I don't know how to check if a specific mod is installed or not

[lunar flare]

FabricLoader.getInstance().isModLoaded("entityculling")

then do everything that touches entityculling in separate classes