Recognising early glaucoma
Diagnosis hinges on understanding of risk factors and test interpretation.
Anders Heijl, MD
Both computerised perimetry and structural tests are sensitive for detecting early glaucoma, but there is potential for false positives with each, cautioned Anders Heijl MD at the ESCRS/EGS Glaucoma Day meeting in Paris, France.
Dr Heijl, Lund University, Malmö, Sweden, discussed considerations for building certainty when diagnosing glaucoma. For example, patient age and IOP are two meaningful factors to think about. He illustrated his point with findings from a prediction model based on the population screened for the Early Manifest Glaucoma Trial.
“It is rather unlikely that younger patients with low IOP have glaucoma. Our suspicion should be much higher in older patients and with higher IOPs,” Dr Heijl said.
When glaucoma is suspected, documentation of corresponding structural or functional damage is necessary to establish the diagnosis. Looking at perimetry, clinicians need to differentiate glaucomatous field loss from cataract-related defects.
Cataract results in a diffuse loss of threshold sensitivity and progressive cataract leads to darker greyscale maps. Glaucomatous visual field loss is primarily localised, resulting in field defects with shape. A diffuse loss component develops in later stages, and with progression defects deepen and even more importantly increase in area.
“Very early glaucomatous field loss, however, is often visible only in the probability maps, not in the greyscale maps, but is still diagnostic if confirmed in a second or third tests,” said Dr Heijl.
He cautioned that pre-perimetric glaucoma is a “rather risky diagnosis”, which should be avoided, and noted that false positive diagnoses are common in normal subjects with large discs.
Although OCT can be both sensitive and specific for diagnosing glaucoma, because of the large amount of data on an OCT printout, clinicians must beware of the potential for mass significance.
“There are many analyses in the OCT printout, and it is very likely that at least one will be significant even if the subject is perfectly normal,” Dr Heijl said.
He presented examples of false OCT flags in normal eyes and cited a paper discussing “red disease” that emphasised the importance of correlating findings from structural and functional tests along with the common occurrence of OCT segmentation/image acquisition errors.
Dr Heijl also cautioned against diagnosing glaucoma when uncertainty exists, noting the potential harm.
“Receiving a diagnosis of glaucoma reduces quality of life and can lead to problems with anxiety and fear of blindness. Patients with suspect or uncertain glaucoma should usually be followed, but should usually not receive a diagnosis or be treated,” Dr Heijl said.
Anders Heijl: firstname.lastname@example.org