He was lying in bed with his eyes opened for hours.でも、He was lying in bed with his eyes open for hours. でも、英語としていけると思います。
He was lying in bed with his eyes opened for hours.ですと、誰かに目開けられているニュアンスもありますが…
He was lying in bed with his eyes open for hours.なら、普通の自然な文です。
上記の文なら、openは形容詞、openedは動詞になると思います。
his eyes being openも、openは形容詞と思います。
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