expression, suru verb (irregular)
squint; narrow one's eyes
Describes partially closing the eyes, often to see better, against bright light, or when concentrating. Not inherently emotional.
彼は遠くの看板を見ようと目を細くした。
He narrowed his eyes to try to read the distant sign.
まぶしくて、思わず
It was so bright that I instinctively squinted.
expression, suru verb (irregular)
smile warmly; look fondly
Used when a gentle, affectionate smile makes the eyes narrow naturally. Often implies a soft, whole-face smile directed at someone.
祖母は孫の顔を見て目を細くした。
The grandmother smiled warmly at her grandchild.
彼女は彼に目を細くしてうなずいた。
She looked at him fondly and nodded.