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Editors Selection IGR 22-3

Examination methods: HRT versus stereo fundus camera in Japan

Comment by David Greenfield on:

19551 A pilot study to detect glaucoma with confocal scanning laser ophthalmoscopy compared with nonmydriatic stereoscopic photography in a community health screening, Ohkubo S; Takeda H; Higashide T et al., Journal of Glaucoma, 2007; 16: 531-538

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It is well established that no single test such as IOP measurement is an effective method for screening populations for glaucoma. Population-based studies suggest that half of all individuals with POAG have IOP levels consistently below 22 mmHg; and most individuals with elevated pressures at a screening measurement do not have optic nerve damage. Several prior studies have suggested that computerized imaging of the optic nerve and peripapillary retinal nerve fiber layer may be useful for glaucoma diagnosis in population-based screenings. This is a potentially desirable approach since some machines are small enough to be portable, and they facilitate one's ability to identify abnormal structural features by enabling the clinician to compare a subject to a population of age-matched 'normals'.

Ohkubo et al. (831) compare the diagnostic precision of optic disc assessments using a non-mydriatic stereo fundus camera with the Heidelberg Retina Tomograph (HRT2, Heidelberg Engineering, Germany) for glaucoma diagnosis 1173 Japanese persons enrolled in a health screening project. Glaucoma was established using criteria including disc abnormality and unconfirmed visual field defect in at least one eye in 60 of the 1173 subjects. Depending on how 'borderline' HRT images were analyzed, the authors found the HRT to have a lower sensitivity (60-72%) for glaucoma detection compared to the non-mydriatic camera (95%). Several points are noteworthy. The reported sensitivity/specificity values may be confounded by the fact that suspected visual abnormalities were not confirmed with additional field testing, and the usual occurrence is that such abnormalities are not repeatable.

Glaucoma detection may be most effective when targeted at populations at high risk, and using a combination of evaluation methods

Moreover, the HRT2 normative data is based largely on 110 British Caucasians and may not be applicable to Japanese subjects (often myopic with tilted discs). Second, a very high percentage of HRT images (92%) were of acceptable quality (standard deviation below 50 microns) demonstrating the feasibility for obtaining useful quantitative data for interpretation at the time of screening. Third, although the prevalence of NTG is high in Japanese persons, this study is consistent with the literature in that most patients identified with glaucoma at the time of screening have an IOP below 22 mmHg. Finally, overall a small percentage of eyes were identified as glaucomatous. Glaucoma detection may be most effective when targeted at populations at high risk, and using a combination of evaluation methods.

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