Hospital eye services have been hit with increased workload partly caused by new scanning technology at optometrists - including big chains like Specsavers.
Imaging technology to check customers for potential problems like glaucoma is becoming widespread in optometry practices, which is funnelling more referrals into the public system.
Specsavers now uses the technology on all of its customers and says this, as part of a wider assessment, helps pick up disease that would otherwise go undetected. The company says it will soon have New Zealand data, but in Australia more than 80 per cent of referrals are appropriate, leading to diagnosis and treatment.
However, some ophthalmologists are wary of such widespread testing - including more than 400,000 scans at Specsavers a year - because potential problems can turn out to be nothing to worry about.
Such "incidentaloma" cause more workload in a health system already struggling to cope with an ageing population also sickening with conditions like diabetes. A number of Kiwis permanently lost sight in recent years because of ballooning wait lists.
"Optical coherence tomography (OCT)" is imaging technology that gives detailed information about the retina, which helps detect disease. Specsavers finished a roll out of the technology to its 52 stores in September 2018, with more than 485,000 scans expected in the following 12 months.
A Ministry of Health memo prepared for Health Minister David Clark ahead of a July 2018 meeting with the United Kingdom-headquartered company noted OCT was already available at many other optometrists.
"Specsavers Optometrists propose to scan all patients as part of the pre-test screening routine, and expect this to detect an additional 100 cases of eye disease per week," Clark was advised in the memo, released under the Official Information Act.
"There is concern that this will lead to an increase in patients being referred to DHBs for unexpected findings, or for interpretation of findings of uncertain clinical significance."
The Royal Australian and NZ College of Ophthalmologists (Ranzco) had stated testing such as OCT wasn't needed if a patient didn't have symptoms or a relevant medical history, the ministry noted. That position was developed for a wider "choosing wisely" campaign , led by health workers worried about unnecessary procedures and treatment.
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Ranzco recommended members at DHBs audit referrals to see if referrals from Specsavers are appropriate.
After some DHBs told the ministry about an increased workload, it wrote to all health boards to ask about the issue. Auckland, Hawke's Bay, and Taranaki DHBs all confirmed increased referrals from optometrists.
Dr Peter Hadden, chair of the New Zealand branch of the Royal Australian and NZ College of Ophthalmologists (Ranzco), said the increase in demand couldn't be definitively attributed, given no comprehensive audits or studies had been done.
"But you would think [optometrists use of OCT] must have had something to do with it. They are picking up stuff that hasn't been seen before, and some of it is important. On the other hand, they are picking up a lot of stuff that isn't important."
Whangarei-based ophthalmologist Dr Brian Kent-Smith, a past chair Ranzco's NZ branch, said his own opinion was indiscriminate use of any medical test was ill advised.
"Unnecessary tests will lead to unnecessary follow-up appointments, either at the DHB or in a private practice. Someone - the taxpayer, the individual or the insurance company - is going to pay for that."
A spokesman for Specsavers said the company had not been made aware of any concerns about its use of OCT, but would expect it to increase referrals to DHBs, particularly because currently about half of the 115,000 Kiwis estimated to have glaucoma remain undiagnosed.
"The OCT has beneficially brought into play technology's ability to identify possible signs of glaucoma that the naked eye and other equipment just can't see."
Every Specsavers patient has a pre-examination process including an OCT scan. Based on results as well as the patient's history, the optometrist considers further tests and assessments.
"If the combination of the pre-examination results, visual field and findings during the examination suggest a significant risk of glaucoma in-line with the Ranzco NZ guidelines then, in discussion with the patient, a referral is made to an ophthalmologist.
"It does seem that some practitioners are under the false impression that Specsavers uses the OCT in isolation when this is just not the case."
The Specsavers spokesman said detailed New Zealand data will soon be available, but in Australia, 83 per cent of referrals are later confirmed to be appropriate, leading to diagnosis and treatment.
"This is very positive in that it means our optometrists are making significant inroads into impacting the 50 per cent undiagnosed glaucoma population. Of course, this is a collaborative initiative and should Ranzco NZ choose to refine their referral criteria then we will be the first to adopt the updated guidelines."
An Auckland DHB spokeswoman said the DHB continued to see very high growth in demand for ophthalmology services, with a 10 per cent increase in first surgical appointments and 14 per cent increase in follow-up appointments in the 2018/19 financial year.
"This growth appears to be consistent across all referral pathways - i.e referrals from Specsavers are consistent with those via other routes - and we forecast a similar increase in demand in this financial year."
A Ministry of Health spokesman said it hadn't been advised of any DHBs having trouble dealing with volumes of referrals from Specsavers practices,
"DHBs have robust processes for the triage of any new referral and the ongoing management of ophthalmology patients. The ministry and DHBs welcome service improvements that include the earlier detection and appropriate referral of patients with eye disease."
DHBs, ophthalmologists and the ministry have worked to clear backlogs in some areas. In the past two years, Auckland, Canterbury, Nelson-Marlborough, Northland and Southern DHBs have reported a total of 37 "adverse events" where delays resulted in patients losing sight.
Asked if the building demand risked a repeat of such incidents, Dr Peter Hadden said that was possible.
"I guess it depends on how well resourced or not the health system is. It is up to us, too - we have got to triage and decide who is worthy to be seen, and what priority to give them."