According to dictionaries (e.g. PIV), "okul/" is a root. So the in-Esperanto etymology of "okulo" is trivial: "okul·o", i.e., the root "okul/" with the noun word ending "-o". (Which, as "okul/" is a thing-y root, is in fact the base form of the word.)
As Lepticed's answer layes out, there's consensus among Esperanto etymologists, that "okul/" / "okulo" comes from Latin "okulus", also meaning "eye". But where did "okulus" come from? The entry in Konciza Etimologia Vortaro by André Cherpillod allows us to dig a bit deeper into the exter-Esperanto etymology of the word. It reads
okuloF. L ŏkŭlus ← HE ok. · HE → Sk अक्षि akṣ̂i, Gr ὤψ, Gt augo, Sl око, Li, akis, Arm Աչք aĉk. · L → I òcchio, Ks occhju, F œil, Oc uèlh, H ojo, Kt ull, P olho, Glg ollo, Srd ogu, Rm ochi. Ĝ → G Auge, Jd אויג uyg, Is auga, Nd oog, N øye, Dn øje, Sv öga, Vp Iog. · Sl → R Uk о́ко, Blr Вока, Po Ĉĥ oko, Bg око̀.
So according to Cherpillod, Latin (L) "ŏkŭlus" indeed comes (←) from Indo-European (HE for eo "hindeŭropa") "ok", from which corresponding words (for "eye") in many European and some Asian languages directly or indirectly derive (→). However, he lists no indication of any relation to the Esperanto number word "ok" (8), for which he gives a different etymology also from Indo-European:
okF (8). L octō ← HE okt. HE → Sk aṣ̂ṭan, Gr ὀκτώ, Ga ochto, Ir OĊT, Br eizh, G Nd acht, A eight, Is, átta, Sv åtta, Sl осмь Li aštuoni, Hd आठ āṭh, Pe hǎŝt̀. · L → I òtto, F huit, Oc uèit, Kt vuit, H ocho, P oito, Rm opt.
Kp: He okt «8», ak «pinto»; Gr ὀκτώ, ἄκρα «pinto»; L octō, ăcūtus «akuta»; Sl осмь «8», остръ «akra». Kalkulo sur ok fingropintoj, ne uzante la poleksojn. ☞ naŭ, kvin.
So Cherpillod sees some possible relation (whether causal or not) between the words for 8 and for peak, acute, sharp etc., and probably considers that this might be due to 8 being the maximum one can count on two hands with the fingertips, excluding the thumb (maybe because the thumb was used to touch the "current" finger while counting to keep track).
There's no mention of the Kabbalah, or of Jewish or Israelite languages other than Yiddish (Jd) in either of these entries, though. (If your theory was right, one would probably expect links to ancient or modern Hebrew or similar Semitic languages, which do exist for some other Esperanto words, but aren't known for "okulo" or "ok".) And as "okulo" can be readily explained as being derived from the Latin "okulus", it's very, very unlikely that any such connection would have guided Zamenhof's choice of that word.