The operation - done five years ago - caused the woman harm, pain, risk and anxiety, Singapore's medical watchdog concluded.
Dr Cheah Way Mun, 65, who practises at The Eye Centre at Mount Elizabeth Medical Centre, has also been made to pay for the cost of the hearing.
The Singapore Medical Council (SMC) said Dr Cheah used "inadequate", "improper and/or erroneous" measurement techniques when performing cataract surgery on the patient in 2009.
"Dr Cheah had caused harm to his patient, who had to undergo the pain, risk and anxiety of a second operation to correct the mistake," it said in a statement.
The doctor had also not taken into account an earlier measurement of her short-sightedness, which gave a different figure.
The woman, 58, had needed correction for severe myopia of about 1,300 degrees, but received a lens for myopia of about 400 degrees.
Following the surgery, she could not see properly with her left eye, and returned to see Dr Cheah five times within the space of a month.
Her poor eyesight after the surgery should have alerted Dr Cheah that the lens he had implanted was incorrect, said SMC. It was only on the fifth visit that he told the patient that he had put in the wrong lens.
He then apologised and offered to do a second operation to correct the mistake, without charge.
SMC's disciplinary committee, chaired by Professor John Wong, said that Dr Cheah had been slow to rectify his mistake.
It said: "As important as it is for a doctor to not make a mistake in the first place in the management and treatment of a patient, it is equally, if not more, important that if the doctor unfortunately does make a mistake, the doctor will quickly find out and promptly tell the patient about it."
Such misconduct damages public confidence, it added, and an unequivocal message that it cannot be condoned must be sent.
In mitigation, however, the committee noted that Dr Cheah had a long and unblemished record. It said that he had pleaded guilty and expressed remorse, and that the committee had no reason to doubt his sincerity.
But it did note that this mitigation was "somewhat diluted" as he "pleaded guilty at a very late stage of the inquiry".
Fortunately, the SMC added, the patient "was well after the second operation, and no permanent injury was caused to her".
But the woman's husband, Mr Bernard Huang, told The Straits Times that her eyesight never recovered fully.
Even when she wears spectacles, vision from her left eye - where the wrong lens was implanted - remains blurred.
"It's like looking through a car windscreen in the rain with no wiper," he said.
He was also upset that the doctor had initially refused to admit there was a mistake. He said that Dr Cheah told his wife that she needed to wear corrective spectacles, insisting that an improvement of only 300 degrees in the eye - leaving 1,000 degrees to be corrected by spectacles - was normal.
The implanted lens was supposed to do away with the need for high-prescription glasses.
It was only because they persisted in returning to the clinic every few days that the doctor finally told them he had made a mistake. The last straw was when Dr Cheah told the couple that they could sue him if they were unhappy with his treatment.
Mr Huang said: "Everyone makes mistakes and if he had told us that and apologised, we would not have pursued the matter."
This article was published on May 3 in The Straits Times.
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