Earlier glaucoma detection: Study finds progress, but at very slow rate

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Analyses of visual field data collected at centers across England showed the average level of severity of vision loss at the time of glaucoma detection decreased-improved-over time. Still, the rate of improvement between 1998 and 2012 was only 0.1 dB per year.

Trishal Boodhna

By Cheryl Guttman Krader; Reviewed by Trishal Boodhna, MSc

London-A study from England analyzing visual field loss at the time of glaucoma diagnosis shows the average level of severity decreased over a recent 15-year period.

However, the annual rate of change was low, indicating a need for strategies that will improve earlier disease detection, said Trishal Boodhna, MSc.

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“Detecting glaucoma sooner than later is important, because glaucoma-related vision loss is irreversible,” said Boodhna, a PhD student in Health Economics in Professor David Crabb’s Research Lab at City University London. “In addition, from a health economic perspective, the cost burden for treatment is lower for earlier versus more advanced stages of disease.

“Although our study indicates we are getting better at detecting glaucoma earlier in England, the question as to whether the rate of improvement is sufficient requires further exploration,” Boodhna said.

Available studies show that screening programs for glaucoma are not cost-effective. However, there has to be a middle ground between that approach and the opportunistic way glaucoma is usually detected in the United Kingdom, when people have routine eye exams with optometrists, he noted.

Analyzing the data

Trends in visual field severity at the time of glaucoma diagnosis were examined using data from Humphrey SITA visual fields recorded at four regionally different glaucoma clinics in England in the years 1998 to 2012. Approximately 433,000 visual fields were available, but after applying selection criteria requiring a mean deviation (MD) outside 95% normative limits in at least one eye and having at least two visits to the glaucoma clinic, tests representing the worse eye in only 26,131 patients were included in the study.

Patients were categorized as to the severity of their glaucoma at the time of diagnosis using the following criteria:

·      MD 0 to –6 dB = early

·      MD >–6 to –12 dB = moderate

·      MD >–12 dB = severe

 During the first 5 years of the study (1998 to 2002), 43% of patients presented with early disease and 29% presented with severe disease. During the last 5 years, 50% of patients presented with early disease and 22% had severe disease at diagnosis.

“Although these positive changes were statistically significant, the data still show that during the last 5 years, 1 in 5 patients had a severely damaged visual field at the time of glaucoma diagnosis,” Boodhna said. “We should be performing better.

A trend analysis was also conducted to determine the annual rate of improvement in the average level of glaucoma vision loss at presentation, and it was calculated to be 0.1 db per year or only 1.0 db per decade.

Study limitations

Boodhna noted the study has several limitations. Given its retrospective nature and lack of other clinical data it is not possible to control for the effect of visual comorbidities on the visual field (e.g., cataract) or for population variation. However, the sheer large scale of the data used means that the estimates are likely to be representative.

In addition, there is no information on the reliability of individual visual fields. However, it is also not considered to be a significant limitation constraining the validity of the analyses given the infrequent nature of unreliable visual fields and the large dataset being analyzed.

Boodhna also noted that because the study focused on detection of glaucoma based on visual field loss, it may have excluded some patients with early glaucoma that was detected on structural testing.

“The compilation of multisite electronic visual field records provides significant opportunity to audit service delivery and to identify areas for improvement, such as in glaucoma identification found in this study,” he said. “The fact remains that a significant proportion of patients are being diagnosed with advanced stage glaucoma when we should seek to be identifying them at the earliest stages.”

Trishal Boodhna, MSc

E: trishal.boodhna.1@city.ac.uk

This article was adapted from Boodhna’s presentation at the 2014 meeting of the Association for Research in Vision and Ophthalmology. Boodhna and his co-authors have no relevant financial interests to disclose.