Besides genetic synergy, what causes "no eyes" occurrences in ball pythons?

Poor incubation temperatures that were too high or fluctuated significantly

While genetic interaction between the Piebald gene and Super BEL complex genes is a primary cause of reduced or absent eyes, environmental factors can also lead to the condition of having 'no eyes.' Specifically, instances of this anomaly have been attributed to improper incubation conditions. If the incubation temperatures used during the egg stage are either excessively high or experience significant, unstable fluctuations, this environmental stress can result in the developmental failure resulting in eyeless hatchlings, regardless of the specific genetic combination.