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Editors Selection IGR 24-3

Perimetry: Testing strategies

Comment by Kouros Nouri-Mahdavi on:

53773 Parafoveal Scotoma Progression in Glaucoma: Humphrey 10-2 versus 24-2 Visual Field Analysis, Park SC; Kung Y; Su D et al., Ophthalmology, 2013; 120: 1546-1550

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Park and colleagues compared the incidence of visual field deterioration in a group of 50 eyes with initial paracentral scotomas (IPFS) followed for an average of > 5 years with both 24-2 and 10-2 testing strategies of Humphrey Field Analyzer (average MD at baseline: −2.7 ± 1.5 dB). An IPFS was defined as presence of ≥ 3 adjacent test locations with p < 0.05 within the central 10 degrees of fixation, one or more points with p < 0.01 located at the innermost paracentral points, and no scotoma outside the central 10 degrees in either hemifield. Using more (presence of two progression locations) or less (at least one progressing test location) stringent criteria for pointwise linear regression analysis (PLR), they found a much higher proportion of progressing eyes with the 10-2 strategy (48% vs. 22% with the less stringent criteria; p = 0.007).

..involvement of the central 10 degrees, which is visually the most important region of the visual field, a denser grid would be beneficial for earlier detection of glaucoma deterioration

This manuscript formally confirms our suspicion that in eyes with involvement of the central 10 degrees, which is visually the most important region of the visual field, a denser grid would be beneficial for earlier detection of glaucoma deterioration. The density of retinal ganglion cells is much higher in the central macular region compared to more peripheral areas and the ganglion cell receptive fields are much smaller in this region; therefore, localized arcuate areas of visual field loss can fall in between the test locations of the 24-2 grid, which are 6 degrees apart (and even farther diagonally). The pessimists among us could, however, argue that because of the higher number of pointwise linear regressions done on 10-2 test locations (64 vs. 12), one would expect to have a higher number of (falsely) progressing test locations. We are not told how many locations were improving on the 10-2 and 24-2 series, but a comparison of the number of improving vs. worsening locations would have been helpful. Also, a description of patterns of clustering of deteriorating test locations on 10-2 tests would have emphasized the validity of the findings. Although the overall number of VFs performed during the follow-up was similar in the two groups, it is not clear whether the number of VFs in progressing groups was similar between the 10-2 and 24-2 tests. The sensitivity of regression analyses is highly dependent on the number of available VFs and it would have been important to rule out a bias towards a higher number of 10-2 tests in progressing eyes although this would not likely explain the large difference in proportion of progressing eyes between the two test series.

The findings of this study once again emphasize the necessity of customizing testing strategi

The findings of this study once again emphasize the necessity of customizing testing strategies to each patient's need. Some of eyes with IPFS tend to show progression outside of the central 10 degrees and therefore, concurrent testing with 24-2 and 10-2 strategies seems indicated as the authors suggest. Whether the findings of this study can be applied to eyes with involvement of the central 10 degrees as an extension of a peripheral defect remains to be demonstrated but it seems plausible that using the 10-2 strategy as an adjunct would be the appropriate approach in such eyes as well. The results also suggest that in eyes with IPFS, if only one test is to be performed, the 10-2 is the preferred strategy. The authors are to be commended for this important contribution to the glaucoma progression literature.

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