Continuous Glucose Monitors in NZ: How a CGM Works, What It Costs, and Why Your Optometrist Cares

By the Rose Optometry optometrist team, Hamilton. General information only — it does not replace advice from your GP or diabetes team. Numbered references are listed at the end.

A continuous glucose monitor (CGM) is a small wearable sensor, usually worn on the back of the upper arm, that measures glucose around the clock and sends the readings to your phone. Instead of a single finger-prick number, you see where your glucose is, where it has been, and which way it is heading.

People are often surprised to find a glucose monitor in an optometry store. The reason is simple: diabetic retinopathy is a leading cause of preventable vision loss in working-age adults [1], and it can reach a sight-threatening stage without any symptoms [2].

How a CGM works

A fine filament sits just under the skin and measures glucose in the interstitial fluid — the fluid between your cells — rather than in blood. Two things follow from that:

• Readings run behind blood glucose. Glucose takes about 5 to 6 minutes to pass from blood into interstitial fluid [3], and total sensor delay has been measured at around 9 to 10 minutes [4]. The gap matters most when glucose is rising or falling quickly [5].
• A finger-prick meter still has a place. Guidelines say blood glucose testing should be used to confirm a CGM reading whenever it does not match how you feel [5].

CGM vs a finger-prick blood glucose monitor

Who uses a CGM in New Zealand?

• People with type 1 diabetes. Since 1 October 2024 Pharmac has funded certain CGMs for people with type 1 diabetes and a few similar insulin-deficient forms of diabetes [6,7]. If that is you, talk to your diabetes team first — a funded device may be your best option.
• People with type 2 diabetes. CGMs are not currently funded for type 2 diabetes in New Zealand [7], so people who want one buy their own.
• People without diabetes. There is currently no good evidence that wearing a CGM improves health or prevents diabetes in people who do not have it, and the meaning of glucose fluctuations in people without diabetes is uncertain [8]. If you are worried about your glucose, ask your GP for an HbA1c test — see blood sugar and HbA1c levels in NZ.

What does a CGM cost in NZ?

If you are not eligible for a funded device, you pay for sensors yourself, and each sensor is replaced when its wear time ends. The LinX 15-day CGM 4-pack is NZ$259 from Rose Optometry, with free NZ shipping on orders over $100. That is four sensors at 15 days each — about two months of monitoring, or roughly $65 per sensor.

Why an optometrist cares about your glucose

Long-term high glucose damages the small blood vessels of the retina. The trial evidence that controlling it protects the eye is strong:

• Type 1 diabetes (DCCT). Over a mean of 6.5 years, intensive treatment reduced the risk of developing retinopathy by 76% in people who started with none, and slowed progression by 54% in those with mild retinopathy [9].
• Type 2 diabetes (UKPDS). Tighter glucose control reduced small-vessel complications, mainly the need for retinal laser, by 25% over ten years [10].

Time in range is the share of the day glucose stays between 3.9 and 10.0 mmol/L; international consensus suggests more than 70% for most adults with diabetes [11]. More time in range is linked with less retinopathy: in an analysis of DCCT data, each 10-point lower time in range was associated with a 64% higher rate of retinopathy [12], and in 3,262 adults with type 2 diabetes wearing a CGM, those with the most time in range had about half the odds of vision-threatening retinopathy [13]. These are observational findings, not trials that targeted time in range, so they show a link, not proof of cause.

Two practical points from the consulting room:

• Your focus can shift when glucose changes. After very high glucose is brought down, a temporary long-sighted shift can appear within about a week and take from two weeks to about three months to settle [14]. Tell us if your glucose has been changing before we finalise a new glasses prescription.
• Have your retina checked when treatment is stepped up. In the DCCT, retinopathy worsened temporarily in 13.1% of people starting intensive treatment versus 7.6% on conventional treatment; lowering glucose more gradually was not shown to prevent this, and the long-term benefits of good control greatly outweighed it [15]. Current guidance is that retinopathy status should be assessed when glucose-lowering treatment is intensified [2].

New Zealand guidance is for retinal screening every two years for people with diabetes, sometimes extended to three years when there is no retinopathy and glucose control has been consistently good [16]. More in our guide to diabetic retinopathy and diabetes eye checks.

The LinX CGM sensor

We stock the LinX Continuous Glucose Monitoring System sensor (4-pack, NZ$259) as part of our wearables range. The manufacturer states a 15-day wear time per sensor and an IP68 water-resistance rating. It pairs with a companion app for real-time glucose, trend charts and high and low alerts. ✔ Stock on hand — ships NZ-wide from Rose Optometry, Hamilton.

How accurate is it? In a manufacturer-funded study of 87 adults with diabetes, LinX readings differed from laboratory glucose by 8.66% on average [17]. Independent data on LinX itself are not yet available; an independent study of the same manufacturer's earlier sensor found a larger average difference of 21.9% [18]. So treat it as a tool for seeing patterns, and confirm with a finger-prick before acting on an unexpected reading.

Tracking ketones as well? See our guide to continuous ketone monitors.

Common questions

Do I need a prescription to buy a CGM in NZ?

No. You can buy a CGM sensor directly. Never change insulin or other medication based on readings without talking to your GP or diabetes team.

How long does a CGM sensor last?

It depends on the sensor. The LinX sensor has a manufacturer-stated wear time of 15 days, after which you apply a new one. A 4-pack covers about two months.

Is a CGM as accurate as a finger prick?

Not exactly. It measures interstitial fluid rather than blood and runs several minutes behind [3,4], and accuracy varies between devices [17,18]. Confirm with a finger prick if a reading does not match how you feel [5].

Is a CGM worth it if I do not have diabetes?

There is no good evidence that it improves health in people without diabetes [8].

How often should I have a diabetic eye check?

Every two years for most people with diabetes in New Zealand, more often if retinopathy is found [16]. Our optometrists provide diabetic eye examinations in Hamilton — book at roseoptom.co.nz.

References

1. Cheung N, Mitchell P, Wong TY. Diabetic retinopathy. Lancet. 2010;376(9735):124-136. doi:10.1016/S0140-6736(09)62124-3
2. American Diabetes Association Professional Practice Committee. 12. Retinopathy, neuropathy, and foot care: Standards of Care in Diabetes—2026. Diabetes Care. 2026;49(Suppl 1). doi:10.2337/dc26-S012
3. Basu A, Dube S, Slama M, et al. Time lag of glucose from intravascular to interstitial compartment in humans. Diabetes. 2013;62(12):4083-4087. doi:10.2337/db13-1132
4. Schmelzeisen-Redeker G, Schoemaker M, Kirchsteiger H, et al. Time delay of CGM sensors: relevance, causes, and countermeasures. J Diabetes Sci Technol. 2015;9(5):1006-1015. doi:10.1177/1932296815590154
5. American Diabetes Association Professional Practice Committee. 7. Diabetes technology: Standards of Care in Diabetes—2026. Diabetes Care. 2026;49(Suppl 1). doi:10.2337/dc26-S007
6. Pharmac. Decision to fund continuous glucose monitors, insulin pumps, and insulin pump consumables. 29 August 2024. pharmac.govt.nz
7. Pharmac. Continuous glucose monitors and insulin pumps. Updated 16 September 2026. pharmac.govt.nz
8. Johansson M, Dower JA, Lipska KJ. Continuous glucose monitoring for persons with and without diabetes. JAMA Intern Med. 2026;186(9):1182. doi:10.1001/jamainternmed.2026.2769
9. Diabetes Control and Complications Trial Research Group. The effect of intensive treatment of diabetes on the development and progression of long-term complications in insulin-dependent diabetes mellitus. N Engl J Med. 1993;329(14):977-986. doi:10.1056/NEJM199309303291401
10. UK Prospective Diabetes Study Group. Intensive blood-glucose control with sulphonylureas or insulin compared with conventional treatment and risk of complications in patients with type 2 diabetes (UKPDS 33). Lancet. 1998;352(9131):837-853. doi:10.1016/S0140-6736(98)07019-6
11. Battelino T, Danne T, Bergenstal RM, et al. Clinical targets for continuous glucose monitoring data interpretation: recommendations from the International Consensus on Time in Range. Diabetes Care. 2019;42(8):1593-1603. doi:10.2337/dci19-0028
12. Beck RW, Bergenstal RM, Riddlesworth TD, et al. Validation of time in range as an outcome measure for diabetes clinical trials. Diabetes Care. 2019;42(3):400-405. doi:10.2337/dc18-1444
13. Lu J, Ma X, Zhou J, et al. Association of time in range, as assessed by continuous glucose monitoring, with diabetic retinopathy in type 2 diabetes. Diabetes Care. 2018;41(11):2370-2376. doi:10.2337/dc18-1131
14. Okamoto F, Sone H, Nonoyama T, Hommura S. Refractive changes in diabetic patients during intensive glycaemic control. Br J Ophthalmol. 2000;84(10):1097-1102. doi:10.1136/bjo.84.10.1097
15. Diabetes Control and Complications Trial Research Group. Early worsening of diabetic retinopathy in the Diabetes Control and Complications Trial. Arch Ophthalmol. 1998;116(7):874-886. doi:10.1001/archopht.116.7.874
16. Ministry of Health. Diabetic Retinal Screening, Grading, Monitoring and Referral Guidance. Wellington: Ministry of Health; March 2016.
17. Liu Y, Chen Y, Chen Y, et al. Accuracy and safety of the LinX continuous glucose monitoring system in adults with diabetes. Diabetes Obes Metab. 2026 (early view). doi:10.1111/dom.71392
18. Kölle J, Eichenlaub M, Mende J, et al. Performance assessment of three continuous glucose monitoring systems in adults with type 1 diabetes. J Diabetes Sci Technol. 2024;18(6):1424-1432. doi:10.1177/19322968231159657