OCT and glaucoma

Debate highlights pros and cons of glaucoma diagnosis before visual field defects occur

Dermot McGrath

Posted: Friday, November 1, 2019

Ingrida Janulevičienė MD, PhD

The development and ongoing improvement of imaging technologies such as optical coherence tomography (OCT) will play an increasing role in the diagnosis, management and detection of progression in primary open-angle glaucoma (POAG) before visual field defects have occurred, according to Ingrida Janulevičienė MD, PhD, speaking at the European Society of Ophthalmology (SOE) meeting in Nice, France.

“We are not questioning the importance of visual field data but rather the management of glaucoma before visual field defects become apparent. The pure statistical output may miss clinically important defects,” said Dr Janulevičienė, Professor of Ophthalmology at the Eye Clinic of the Lithuanian University of Health Sciences, Kaunas, Lithuania.

Visual field testing is far from a perfect diagnostic tool, noted Dr Janulevičienė. The commonly used standard automated perimetry (SAP) 24-2 test pattern is disliked by patients, is prone to a high variability of mean deviation and does not detect early glaucomatous damage in most cases, she said.

The utility of visual field testing in newly diagnosed glaucoma patients is also questionable, pointed out Dr Janulevičienė.

“Performing a single visual field test per year is a common practice in newly diagnosed glaucoma patients. However, this approach is insufficient and probably as bad as not doing it at all,” she said.

In the United Kingdom glaucoma treatment study (UKGTS), repeated visual field tests were included at baseline and after 18 months and 24 months in 516 newly diagnosed POAG patients randomised to latanoprost or placebo eye drops. The test clustering enabled the researchers to detect statistically significant differences in visual fields between treated and untreated patients after an observation period of 12 months.

While this approach of clustering visual field tests using a linear regression model to identify rapid progressors is very interesting and promising, further validation is needed before it can be recommended in routine clinical practice, said Dr Janulevičienė.

“It holds promise but we need to bear in mind that simulations are all based on the assumption that visual field loss will occur linearly over time, an assumption for which there is really not good evidence,” she said.

The current role of imaging in the diagnosis of glaucoma is unclear but of great clinical importance, said Dr Janulevičienė.

“Using spectral domain OCT is not a sufficient stand-alone test for the detection of glaucoma or for triage use in primary care, but it has value in conjunction with clinical examination and perimetry,” she said.

Using OCT for evaluation of glaucomatous damage can help in early diagnosis by detecting progressive retinal nerve fibre layer (RNFL) thinning and can serve as an essential component in guiding management decisions, evaluating treatment efficacy and providing prognostic information about patients with increased risk for developing functional impairment, she concluded.

Gauti Jóhannesson MD

Presenting the case against diagnosing pre-perimetric glaucoma (PPG), Gauti Jóhannesson MD, Associate Professor at the Department of Clinical Sciences, Ophthalmology, Umeå University, Sweden, said that PPG is not even mentioned in the European Glaucoma Society guidelines.

“This poses a problem for obtaining a diagnosis. In the section on OCT and imaging the guidelines state that ‘no imaging device provides a clinical diagnosis’,” he said.

Another problem is the high frequency of false positives and artefacts in OCT images.

“We all have these fantastic high-tech gadgets in our clinics with bright red printouts, which intuitively leads and guides us towards pathology. However, they do raise the red flag a bit too often and mislead many clinicians to make a false positive diagnosis of glaucoma,” he said. One recent retrospective analysis of more than 2,300 OCT scans revealed artefacts in 46% of cases, he said.

There are also question marks over the reliability of detecting progression in OCT.

“We are used to working with visual fields and the normal databases are age adjusted. However, no OCT has age-correction for progression analysis in the commercial models currently available, so we are not taking into account the normal thinning of the retinal layers due to ageing, which might raise the red flag more than necessary,” he said.

Another issue is that POAG is often a mild disease in many patients, said Dr Jóhannesson.

“We know this from many randomised controlled trials with an untreated versus treated arm. More than 65% of the untreated normal tension glaucoma eyes in the Collaborative Normal Tension Glaucoma Study Group study did not progress during a five-year follow up,” he said.

Early detection may in turn lead to overtreatment with eyedrops containing preservatives that are damaging to the ocular surface and that may jeopardise the success of future filtration surgery, he added.

However, perhaps the most compelling argument against diagnosing PPG is the impact it has on the patient’s quality of life (QoL), said Dr Jóhannesson.

“I think in many cases we forget the person surrounding the eye. While advanced disease undoubtedly impacts on QoL, a literature review by Quaranta et al. found that falsely diagnosing patients as having glaucoma can significantly impact their QoL and well-being. In another study, 34% of patients reported at least a moderate amount of fear of blindness after glaucoma diagnosis, which dropped to 11% at five years. This indicates that a lot of the fear sits in the diagnosis and not in the actual visual disability caused by the visual field defects,” he concluded.

Ingrida Janulevičienė:
Gauti Jóhannesson: