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Tuesday / September 29.
HomeminewsData Casts Light on Normal Tension Glaucoma

Data Casts Light on Normal Tension Glaucoma

It is estimated that 300,0001 Australians over the age of 40 live with glaucoma, and that as many as 50% remain undiagnosed.2 In the Blue Mountains Eye Study,3 75% of previously undiagnosed Australian glaucoma patients were reported to have an intraocular pressure (IOP) of less than 22 mmHg, reinforcing the challenges of detecting normal tension glaucoma.

Figure 1

Specsavers’ dataset is beginning to reveal vital information about the diagnosis of normal tension glaucoma in primary practice.

In 2017, Specsavers started the rollout of optical coherence tomography (OCT) across its network as a part of a nationwide strategy to improve glaucoma detection. As previously reported, this resulted in a dramatic rise in detection of glaucoma across the Specsavers network. Latest figures show that 1.3% of Specsavers patients were referred for glaucoma in 2019, approaching the approximate prevalence rate of the condition indicated by international studies.

Enhanced visibility of the retinal architecture enabled by OCT has been hugely beneficial in supporting optometrists to detect early nerve fibre layer and ganglion cell loss. Equipped with this information, data shows optometrists have been more able to make consistent patient management decisions to perform clinically indicated visual field assessments, interpret structural and functional correlations, and then appropriately refer for ophthalmological intervention.

The Specsavers’ dataset now includes over 115,000 glaucoma referrals issued since 2016 and is enabling significant insight into glaucoma detection in Australia. Within the dataset, 75% of the referrals can be classified based on IOP at the time of referral.

Normal tension glaucoma referrals more than doubled in the period between 2016 and 2018 (Figure 1). Specsavers began its AU$40 million OCT roll out in October 2017 and two years later, all Specsavers stores were making use of this technology for every patient. The step-change seen as a result of OCT introduction is evident. The stabilisation of normal tension glaucoma referrals in the past 12 months is in line with previously reported Australian data,2,3 and suggests that OCT is a valuable case-finding tool for detecting normal tension glaucoma.

To begin to qualify this, Specsavers’ instated classification of glaucoma referrals in December 2018, whereby optometrists can indicate if the glaucoma referral they are making is for a ‘new detection’, ‘glaucoma suspect’ or ‘existing (glaucoma) diagnosis’. This allows for a closer look at patients who are being diagnosed with glaucoma for the first time.

Of those newly diagnosed with glaucoma since December 2018, 71.1% had IOPs below 22mmHg, in line with published Australian studies.2,3 Interestingly the data indicates that normal tension glaucoma is being detected at a similar rate across all age categories, suggesting that OCT can enhance detection of normal tension glaucoma in all age groups, not just younger patients.

A pivotal measure is the feedback from ophthalmology to confirm validity of these referrals. Emerging feedback data of 442 normal tension glaucoma referrals suggests accuracy is equivalent to existing Specsavers’ feedback data for all glaucoma referrals. Currently, the false positive rate for normal tension glaucoma referrals sits at 15%, with 29% of referrals being confirmed as glaucoma suspects and 56% diagnosed with glaucoma (total glaucoma referral false positive rate is 21%).

Glaucoma specialist A/Prof Mitchell Lawlor from Sydney Eye Surgeons has contributed to the emerging feedback data and says, “The process of capturing and reporting on ophthalmological feedback is crucial in verifying the increasing glaucoma detection rate. Feedback on appropriateness of referrals is key to driving systematic change that ensures the right people are referred at the right time for early treatment of glaucoma.”

References

1. Glaucoma Australia, 2020, What is Glaucoma, available at www.glaucoma.org. au/about-glaucoma/what-is-glaucoma

2. Keel S, Xie J, Foreman J, et al. Prevalence of glaucoma in the Australian National Eye Health Survey. Br J Ophthalmol. 2019;103(2):191-195. doi:10.1136/bjophthalmol-2017-311786

3. Mitchell P, Smith W, Attebo K, Healey PR. Prevalence of open-angle glaucoma in Australia: The blue mountains eye study. Ophthalmology. 1996;103(10):1661-1669. doi:10.1016/S0161 6420(96)30449-1

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