The Zimbabwe Broadcasting Corporation said Mugabe, who left for Singapore last Saturday, "had eye surgery in the Asian country a few years ago" and had returned for a "routine medical check-up".
This week's trip there is Mugabe's third there this year.
Public hospitals in Zimbabwe often suffer from chronic shortages of drugs and staff as the economy has struggled to rebound following years of mismanagement.
Mugabe's ZANU-PF party was forced to postpone a rally yesterday at which he was due to address supporters, triggering speculation about his whereabouts.
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Early in 2015, he tripped and fell as he left a podium after addressing supporters who had gathered at Harare airport to welcome him back from a foreign trip.
The same year he also read a speech to parliament apparently unaware that he had delivered the same speech before.
Mugabe's party is sharply divided over his succession. Vice-president Emmerson Mnangagwa and Mugabe's wife Grace are seen as likely contenders to take over in the event of his death or retirement.
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