The uses and limitations of standard automatic perimetry. Roibeard Ó hÉineacháin reports
Alternative perimetry techniques may be used as a complementary test in glaucoma diagnosis, but not at the expense of standard automated perimetry (SAP), unless the patient cannot reliably perform the standard test and objective methods are available, suggests Gustavo De Moraes MD, MPH, Columbia University, New York, USA.
“There are a lot of alternatives to SAP, but you have to keep in mind that they have their limitations and, above all, these methods are not interchangeable. You also have to be specific about whether you are looking for detection of conversion to glaucoma or for detecting progression,” Dr De Moraes told the 7th World Glaucoma Congress in Helsinki Finland
He noted that 30-2 or 24-2 SAP – or its equivalent to other types of perimeters – remains the gold standard for assessing functional status in glaucoma and for monitoring functional changes. Research shows that monocular and binocular threshold sensitivities detected by SAP are significantly correlated with quality of life. However, these do not always equate with the ease with which patients can live their daily life.
Frequency doubling technology (FDT) has some advantages over SAP in that it appears to detect glaucomatous changes earlier and has less variable testing results in patients with more advanced disease. Although previous work suggested a similar application for short-wave automated perimetry (SWAP), more recent research showed it was not any better than SAP for detecting early functional damage. Moreover, it has high test-retest variability, which limits its usefulness for the diagnosis of early glaucoma and its ability to monitor the progression of the disease.
Electroretinography has also shown promise and has the advantage of being objective. It performs as well as SAP and FDT, and better than SWAP, in detecting early glaucoma and mapping regions of visual loss, but it has been largely abandoned because tests did not find favour with patients.
However, Felipe Medeiros MD and his associates have developed a more patient-friendly device that can be used with a smartphone. “This portable brain-computer interface makes electrophysiology a lot easier and gives you a good estimate of function in a more objective way than SAP,” said Dr De Moraes.
The device, called the NGoggle, consists of a wearable, wireless, dry electroencephalogram and electro-oculogram system and a head-mounted cell-phone-based display. It allows detection of multifocal steady state visual-evoked potentials associated with visual field stimulation.
Dr De Moraes noted that in a study by Dr Medeiros’ team, the device was able to distinguish between patients with and without glaucoma with equal specificity and greater sensitivity than SAP. The regions of the retina where the NGoggle device showed diminished sensitivity also corresponded to the pattern deviation plots obtained with SAP.
Gustavo De Moraes: Gustavo.firstname.lastname@example.org