Visual field testing: timing and analysis in patients with primary open-angle glaucoma

The periodic assessment of vision function with visual field testing is a standard and important part of the management of primary open-angle glaucoma (POAG).¹ Automated achromatic static threshold perimetry is the preferred technique,^2-5 although other static and kinetic techniques are acceptable alternatives in patients who are unable to complete automated perimetry reliably or when the technology is not available.¹

Determining an optimal interval between visual field testing in an individual patient with POAG can be challenging. Like most things in glaucoma, care must be individualized. In addition to considering clinical characteristics and patient risk factors in scheduling follow-up examinations, the physician must consider the data set required for using statistical tools to analyze visual field changes over time. This article explores clinical features and risk factors that should be considered in scheduling follow-up visits for visual field testing and the two primary analytical strategies-event analysis and trend analysis-in current use for quantifying visual field changes.

Recommended follow-up intervals

As shown in the table, the recommended follow-up interval varies from 1 to 12 months-a relatively wide range-depending on patient characteristics. A follow-up interval as short as 1 month may be indicated for patients who are just learning to take fields and whose tests are unreliable, for those in whom progression is suspected, to confirm progression, or for those in whom target IOP is not achieved. With new visual field software, it may be advisable to obtain a few fields in the first several months to establish a solid baseline. Other clinical settings also may require a short follow-up interval. No patients have a recommended follow-up interval longer than 12 months; thus, visual field and optic nerve head evaluation should be done at least annually under the best of circumstances. Of course, visual field testing may not provide for far advanced glaucoma when the field is nearly extinguished.¹

In addition to automated achromatic threshold perimetry (AAP), several other visual field testing technologies are available. Visual field testing based on short-wavelength automated perimetry (SWAP) and frequency-doubling technology (FDT) may detect defects earlier than conventional white-on-white perimetry.⁶ To generate a useful measure of progression in an individual patient, the physician should employ a consistent testing strategy over time. It is not established whether SWAP or FDT will provide additional information about progression once AAP has demonstrated a glaucomatous defect.

The following factors should be considered when determining an appropriate follow-up interval for visual field testing and optic nerve evaluation¹ :