Humphrey Field Analyzer HFA II-i
Dr Jack Phu
School of Optometry and Vision , Science, Centre for Eye Health, NSW
The gold standard of functional assessment in glaucoma is standard automated perimetry (SAP), using instruments such as the Humphrey Visual Field Analyzer (HVFA).1
The test pattern that is most commonly used in glaucoma assessment is the 24-2 grid, due to its ability to detect the most common glaucomatous visual field defects within a reasonable time and with less variability than a 30-2 grid.2 The Swedish Interactive Thresholding Algorithm (SITA) of the HVFA offers benefits when using the 24-2: it is quick, has less test-retest variability, has excellent sensitivity and specificity for glaucoma, and is reasonably well-tolerated by patients.3-5
However, while the 24-2 has been widely accepted as the standard for visual fields testing in the majority of glaucoma cases, the 10-2 pattern has also been proposed to be used in some exceptional cases, aside from other retinal diseases such as bullseye maculopathy and age-related macular degeneration. The 10-2 pattern tests the central 10 degrees with two-degree spacing of the points, resulting in 68 points tested within the central visual field. This compares to the 24-2 or 30-2, which test only 12 points within that central area (Figure 1).
Figure 1. Schematic for HVFA 30-2 and 10-2 test patterns. Red circles denote points that are tested with both points.
Blue circles show the boundary of the 10-degree test region of the 30-2 and 24-2, which miss the rest of the central points of the 10-2.
Most notably, the 10-2 is useful in cases of advanced glaucoma, where only the central-most visual field remains,6 where there is no point in testing more peripheral locations. When using the 10-2 pattern, it can also be seen that visual field loss is not necessarily concentric and symmetrical, but biased towards the superonasal region, with the inferotemporal region most commonly intact within the central 10 degrees, a finding that can be masked by the wider (six degrees) spacing of the 24-2. Therefore, a 10-2 visual field could be more useful in monitoring such patients.7
More recently, the 10-2 has been suggested as an alternative or adjunct to the conventional 24-2 pattern even for earlier stages of glaucoma. One reason for this is that increased test point density has been shown to have superior detection ability for early visual field defects.8
The papillomacular bundle was previously thought to be relatively spared in early glaucoma due to its higher density of retinal ganglion cells;9 however, recent studies have shown that some defects in early glaucoma may be detected using the 10-2, in the context of a normal 24-2 result,10 due to early macular changes in glaucoma.11
The ability of the 10-2 to detect defects has been shown not only in event analysis, but also trend analysis over time in cases of parafoveal scotomas.12 A representative patient is shown in Figure 2, where a 30-2 visual field reveals classical a nasal step defect (A) but misses central depressions as close as three degrees away (B), and points flagged as abnormal centrally (C) are more precisely described with the 10-2 (D).
Figure 2. Right and left eye 24-2 and 10-2 visual field results for a patient with NTG (truncated for clarity).
The 10-2 visual field is able to more accurately map out the losses in central vision that appear suspicious in the 24-2 result.
It is not always practical to perform both 24-2 or 30-2, and 10-2 on the same patient on the same day for reasons including patient fatigue, length of the consultation and work flow. Studies have suggested a high index of suspicion in cases where there are defects within the central 10 degrees found on the 24-2 pattern, that is, the central 12 points, even at relatively low levels of significance of p < 5%, alongside an abnormal macular ganglion cell-inner plexiform layer (GCIPL) thickness.13
Another subgroup of patients that may benefit from 10-2 testing is those with normal- or low-tension glaucoma (NTG). Patients with NTG have been shown to have visual field loss that is closer to fixation in comparison to high-tension glaucoma or exfoliative glaucoma.14-16 While NTG may progress slower over time,17 its propensity to affect the central visual field may make it more impactful on day-to-day life.18,19 In these patients, a 10-2 visual field could be considered to monitor for such defects.
One limitation in 10-2 visual fields is that it cannot detect peripheral field defects that are common in glaucoma.20 A 10-2 result cannot be directly compared to a 24-2 or 30-2 result, and therefore, performing one type of test at one visit essentially means a lack of a comparable result over time for the other.
There is also a lack of in-built statistical packages that facilitate objective measures of trend analysis over time with the 10-2. The structure-function relationship between the 10-2 and objective measures of retinal structure is also not well-established. More studies are required to overcome these limitations, but the future of visual field testing for glaucoma may be test patterns with differing densities across the visual field,21 which respect the differences in spatiotemporal characteristics that facilitate increased sensitivity for disease detection, particularly in early stages.22-25 Future testing patterns could incorporate points from both 30-2 and 10-2 test patterns into one.
The 10-2 pattern plays an important role in functional testing for glaucoma, not only in end-stage disease but also in its early stages and in cases where perimetric defects may affect the central points first, such as in NTG. Threats to central vision can severely affect quality of life in glaucoma patients, and these are best detected with 10-2 rather than the conventional 24-2 or 30-2. Due to its inability to detect peripheral defects, the 10-2 should be considered in conjunction with conventional 24-2 or 30-2 patterns for patients with glaucoma.
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