User blog comment:Suparockr/List of Plotholes throughout the series/@comment-2130543-20120718205943/@comment-1388547-20120719234555

Oculi seem pretty agile and tough. If they can dodge well enough to make themselves hard to target, and have enough armor to soak up some successful hits, I could see one getting through. GARDIAN lasers aren't strong enough to outright destroy fighters -- they're intended to kill torpedoes, or do enough damage to force fighters to break off for repairs, and I don't recall seeing any Oculi breaking off the attack. Also, the Normandy is only a single frigate with limited space for point defense, and GARDIAN lasers are noted to being susceptible to overheating and having to shut down if overwhelmed.