The condition of 30 people who are losing their eyesight has worsened because of significant delays in treatment at Dunedin and Southland hospitals.
Six of the worst-affected patients have had severe eyesight loss.
A further 4600 people have received letters from Southern District Health Board (DHB) this week saying their eye operations are overdue.
"Out of the 30, we've identified that six of these patients have had severe loss of vision," interim chief executive Chris Fleming told Morning Report.
"Twenty-four of the patients have had to have additional health interventions."
Some patients waited five times as long to be seen as they clinically should have, he said.
Mr Fleming said the problem was first noticed in Southland in August 2015 and the DHB took steps to put in additional resourcing.
"We have reduced the backlog in Southland by 54 percent and we're on track to having that cleared by July. We only have started to gain traction in Dunedin in August of this year."
Dunedin woman Deborah Whitty said she had finally secured an appointment for December after a year's delay.
Ms Whitty said she hadn't had any communication from the DHB and her appointment was made after her GP started chasing up the hospital about three weeks ago.
"If that hadn't happened would I still be waiting until next year?"
Her eyesight needs to be monitored due to Type 1 diabetes, and Ms Whitty said she was not in danger of losing her vision.
'Big increase' in patient numbers
The DHB said its ophthalmology departments had struggled to keep up with a big increase in patients suffering from eye diseases that cause blindness.
"Southern DHB has seen a significant increase in the number of patients with chronic sight-threatening eye disease requiring assessment and treatment such as diabetic retinopathy, glaucoma and macular degeneration," said Nigel Millar, the DHB's chief medical officer.
"In recent years new treatments have become available, which have undoubtedly been positive for patients as they offer possible benefits for conditions that were previously difficult to treat. However, they require frequent follow up appointments.
"The DHB's systems of care and treatment delivery in ophthalmology has struggled to keep up with this increase in demand," Dr Millar said.
The DHB has reported 30 of the delayed cases as serious adverse events to the Health Quality Safety Commission and called in an external team to investigate.
It has apologised to 4618 patients, most of whom have been waiting at least twice as long as they should have been.
It said it was hiring more staff, and making "every possible effort" to identify the patients most at risk of losing their eyesight.
"We fully acknowledge that we did not provide the follow up care and treatment within the clinically recommended time frame, and sincerely apologise for this," Mr Fleming said.
The DHB was "ramping up" its action to reduce the backlog and ophthalmologists were seeing highest risk patients first.
"We believe we have already addressed the most serious at-risk patients. There is a chance as we go through the further list we may find some more and that's why we're putting all our energy and effort in, including monitoring these numbers monthly now so we do not make the same mistake going forward."
The DHB is aiming to clear the backlog at Southland Hospital around July 2017. It is yet to give a timeframe for Dunedin.
The DHB's board was sacked last year and a commissioner appointed after its deficit blew out past $30 million.
- Southern DHB has written to 4618 patients whose ophthalmology appointments are overdue.
- 1379 are patients at Southland Hospital and 3239 at Dunedin Hospital. This equates to 28 percent of total ophthalmology appointments in Southland being overdue and 37 percent of total ophthalmology appointments in Dunedin.
- The majority of the patients (63 percent) are waiting twice the expected time for appointments than has been clinically recommended.
- There are 30 cases where there has been some deterioration of eyesight during delays, (ie the care and treatment has not been provided within the clinically recommended timeframe): 21 in Southland and 9 in Dunedin.