What is the role of visual field testing in the evaluation of primary open-angle glaucoma (POAG)?

Updated: Mar 16, 2020
  • Author: Kristin Schmid Biggerstaff, MD; Chief Editor: Inci Irak Dersu, MD, MPH  more...
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Answer

Perform automated threshold testing (eg, Humphrey 24-2) to rule out any glaucomatous visual field defects. A Humphrey visual field is shown below.

Humphrey visual field, right eye, showing patient Humphrey visual field, right eye, showing patient with advanced glaucomatous field loss. Notice both the arcuate extension from the blind spot (Bjerrum scotoma) and the loss nasally (nasal step), which often occurs early in the disease process. Courtesy of M. Bruce Shields, MD.

If the patient is unable to perform automated testing, Goldmann testing may be substituted.

Caveats about visual field analysis are outlined below (see also Other Tests).

New-onset glaucomatous defects are found most commonly as an early nasal step, temporal wedge, or paracentral scotoma (more frequent superiorly); generalized depression related to IOP level also can be found.

Swedish interactive thresholding algorithm (SITA)-based software algorithms may decrease testing time and boost reliability, especially in older patients.

Short wavelength automated perimetry or blue-yellow perimetry (SWAP) may provide a more sensitive method of detecting visual field deficits, especially in those previously labeled as ocular hypertensive. If the Humphrey visual field testing results are normal, SWAP should be considered to help detect visual field loss earlier. Recent studies suggest SWAP may detect visual loss/progression up to 3-5 years earlier than conventional perimetry, as well as in 12-42% of patients previously diagnosed with only OHT. Because the testing time may be lengthened, it may be tiring for some patients. However, new SITA-SWAP algorithm software may speed up the testing time and thus improve reliability.

Frequency doubling perimetry (also called frequency doubling technology or FDT, which is enhanced with MATRIX software) is a newer technology that projects an alternating pattern of gridlines onto a screen and stimulates specific neurons that may be damaged early in OHT or POAG. As in SWAP, this may also be able to help detect nerve fiber layer loss at an earlier stage in the glaucomatous disease process, thereby screening out more people who are currently misdiagnosed as having OHT instead of early POAG. Current sensitivities and specificities are continually improving, but continued baseline data is needed to determine in what setting this newer technology will prove to be most useful.

Examination results must take into account that visual field defects may not be apparent until over 40% loss of the nerve fiber layer has occurred. Therefore, the therapy should be based on the overall clinical picture and not on visual field testing alone (see Treatment).

The pupil size should be documented at each testing session, as constriction can reduce retinal sensitivity and mimic progressive field loss.

Risk factors, specifically for the development of glaucomatous field loss in OHT, have recently been studied, and it was found that several presumed risk factors (ie, presence of hypertension, diabetes, refractive error, race, family history of glaucoma, gender, smoking or ethanol use, disc area) were not significant for prediction of eventual field loss.

Significant positive predictive factors for progressive field loss included higher IOP, older age, presence of peripapillary atrophy, larger cup-to-disc ratio, smaller rim-disc area ratio, and cup asymmetry. A study by De Moraes et al found some of the same risk factors for visual field progression in treated glaucoma/POAG: female sex, African or Latin, exfoliation syndrome, older age, cornea thinner and decreased CCT, peak IOP 1.13 mm Hg higher, disc hemorrhage, and beta zone peripapillary atrophy. [7] Consequently, the relationship of risk factors for OHT and POAG compared with that of actual field loss development is much more complex than has been previously presumed.

The initial visual field baseline may need to be repeated at least twice on successive visits, especially if initial testing shows low reliability indices. Newer glaucoma progression analysis (GPA) software can help identify reliable perimetric baselines, and probability-based analyses of subsequent fields can assist in determining if there is true progression over time versus artifact. In follow-up, if a low risk of onset of glaucomatous damage is present, then repeat testing may be performed once a year. If a high risk of impending glaucomatous damage is present, then testing may be adjusted (as frequent as every 2 mo).

The rate of progression of visual field loss, as measured by mean deviation, is related to the amount of visual field loss present at initial presentation; the rate is greater the more loss is initially present. [8] A study by Nouri-Mahdavi et al suggests that accelerating the frequency of visual field testing from annually to biannually increases the ability to detect progression of glaucoma. [9]

In some patients with glaucoma, the addition of a 10-2 visual field (VF) test to the standard 24-2 VF test or modification of the 24-2 VF equipment to assess more test points may help to detect early central macular damage. [10, 11] In a prospective observational study of 100 eyes from 74 patients with glaucomatous optic neuropathy and a 24-2 VF test with mean deviation better than −6 dB, Traynis et al found that the 24-2 VF test failed to detect early glaucomatous damage in the central macula in 13 of 83 hemifields (15.7%) subsequently shown to be abnormal on 10-2 VF testing. Thus, the 10-2 VF test revealed abnormalities in 22.7% of the 22 eyes that appeared normal with 24-2 VF testing. [11] Among the abnormal hemifields on 10-2 VF testing, 68% were classified as arcuatelike, 8% as widespread, and 25% as other. [10, 11]


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