tato 'viśan vanaḿ candra
jyotsnā yāvad vibhāvyate
tamaḥ praviṣṭam ālakṣya
tato nivavṛtuḥ striyaḥ
tatah -- then; avisan -- they entered; vanam -- the forest; candra -- of the moon; jyotsna -- the light; yavat -- as far; vibhavyate -- as was visible; tamah -- darkness; pravishtam -- entered; alakshya -- noticing; tatah -- thereupon; nivavrituh -- they desisted; striyah -- the women.
In search of Krishna, the gopis then entered the depths of the forest as far as the light of the moon shone. But when they found themselves engulfed in darkness, they decided to turn back.
The gopis entered a part of the forest so dense that even the light of the full moon couldn't penetrate it. This scene is also described in the Vishnu Purana:
pravishto gahanam krishnah
padam atra na lakshyate
nivartadhvam sasankasya
naitad didhiti-gocarah
"One gopi said, 'Krishna has entered such a dark part of the forest that we cannot possibly see His footprints. Therefore let us turn back from this area, which even the light of the moon cannot reach.' "
