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Prevalence of undetected glaucoma significantly higher among older patients

A cross-sectional study of patients screened for recruitment into the Early Manifest Glaucoma Trial indicates that the incidence of undetected glaucoma increases with age although the severity of undetected disease may be similar in all age groups with one-third of cases having severe disease and a small percentage actually blind in one eye from the disease.

The study’s investigators invited all people aged from 55 to 79 years who were living in the catchment area of Malmö, Sweden and for whom there were no recent records at the Malmö University Hospital Ophthalmology Department to participate. Of a total of 32,918 invited citizens, 77.5 per cent participated, and among these, 406 (1.23 per cent) had previously undetected glaucoma.

The researchers found that the prevalence of undetected glaucoma was significantly higher among older patients, rising from 0.55 per cent among those aged 55 to 59 years to 2.73 per cent among those 75 to 79 years. Early-stage glaucoma was more frequent in the youngest group, those aged 55 to 59 years. The extent of field loss was similar in all patients aged 60 years and older. Most of the glaucomatous eyes in each age cohort had early disease.

Among those identified as having glaucoma, visual field defects were mild in 35 per cent and moderate in 32 per cent. Around two-thirds of those screening positive for glaucoma had unilateral disease, and 134 subjects (33 per cent) had advanced visual field loss in at least one eye. Although none of those screened were blind in both eyes, 3.4 per cent of the newly diagnosed patients were unilaterally blind because of glaucoma.

The screening examination involved measurement of visual acuity, refractive error and intraocular pressure using Goldmann tonometry and monoscopic fundus colour photography. Those who screened positively underwent a postscreening examination which included visual field testing with the 24-2 Full-Threshold program of the Humphrey Field Analyzer.

In 86 per cent of eyes, the diagnosis of glaucoma was based on the presence of repeatable visual field defects. In nine per cent of eyes the diagnosis was based on visual field loss plus corresponding optic nerve changes. In five per cent of eyes, the diagnosis was based on disc appearance only because useful visual fields were not available.

The authors of the study noted that these findings support those of previous research which has shown that around half of cases of glaucoma in the general population are undetected. However, they pointed out that the rate of undetected glaucoma in their population was most likely an underestimate since the criteria they used may have missed some cases with normal IOP. Moreover, in other populations with higher proportions of patients of African descent the incidence of undetected glaucoma could be considerably higher.

(Heijl et al, Ophthalmology, “Prevalence and Severity of Undetected Manifest Glaucoma, Results from the Early Manifest Glaucoma Trial Screening”, 2013 doi: 10.1016/j. ophtha.2013.01.043).