視線 is a neutral 'gaze' or 'line of sight', while 睨み specifically implies a sharp, intimidating, or watchful look.
Etymology
Noun form of the verb 睨む (にらむ, to glare at), derived from the continuative stem (連用形). The kanji 睨 is composed of 目 (eye) and 兒 (child, but here a phonetic component), suggesting a fixed, staring eye.
