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Subtle glaucomatous damage detectable using 10-2 visual fields

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Humphrey Field Analyzer HFA II-i  

______________________________

Dr Jack Phu
BOptom(Hons) BSc
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).

 

44 OL Phu -Figure 1.jpg

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).

 

44 OL Phu - Figure 2

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.

Conclusion

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.

 

1. Jampel HD, Singh K, Lin SC, Chen TC et al. Assessment of visual function in glaucoma: A report by the American Academy of Ophthalmology. Ophthalmology 2011; 118: 986-1002.

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3. Budenz DL, Rhee P, Feuer WJ, McSoley J et al. Sensitivity and specificity of the Swedish interactive threshold algorithm for glaucomatous visual field defects. Ophthalmology 2002; 109: 6: 1052-1058.

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9. Kita Y, Kita R, Nitta A, Nishimura C, Tomita G. Glaucomatous eye macular ganglion cell complex thickness and its relation to temporal circumpapillary retinal nerve fiber layer thickness. Jpn J Ophthalmol 2011; 55: 3: 228-234.

10. Traynis I, de Moraes CG, Raza AS, Liebmann JM et al. The prevalence and nature of early glaucomatous damage in the central 10° of the visual field. JAMA Ophthalmol 2014; 132: 3: 291-297.

11. Hood DC, Raza AS, de Moraes GC, Liebmann JM, Ritch R. Glaucomatous damage of the macula. Prog Retin Eye Res 2013; 32: 1-21.

12. Park SC, Kung Y, Su D, Simonson JL et al. Parafoveal scotoma progression in glaucoma: Humphrey 10-2 versus 24-2 visual field analysis. Ophthalmology 2013; 120: 8: 1546-1550.

13. Park HL, Hwang BE, Shin HY, Park CK. Clinical clues to predict the presence of parafoveal scotoma on Humphrey 10-2 Visual Field using a Humphrey 24-2 Visual Field. Am J Ophthalmol 2015; doi: 10.1016/j.ajo.2015.10.007.

14. Araie M. Pattern of visual field defects in normal-tension and high-tension glaucoma. Curr Opin Ophthalmol 1995; 6: 2: 36-45.

15. Ahrlich KG, De Moraes CG, Teng CC, Prata TS et al. Visual field progression differences between normal-tension and exfoliative high-tension glaucoma. Invest Ophthal Vis Sci 2010; 51: 3: 1458-1463.

16. Koseki N, Araie M, Suzuki Y, Yamagami J. Visual field damage proximal to fixation in normal- and high-tension glaucoma eyes. Jpn J Ophthalmol 1995; 39: 3: 274-283.

17. Heijl A, Leske MC, Bengtsson B, Hyman L, Hussein M. Reduction of intraocular pressure and glaucoma progression: results from the Early Manifest Glaucoma Trial. Arch Ophthalmol 2002; 120: 1268-1279.

18. Burton R, Crabb DP, Smith ND, Glen FC, Garway-Heath DF. Glaucoma and reading: exploring the effects of contrast lowering of text. Optom Vis Sci 2012; 89: 9: 1282-1287.

19. Glen FC, Crabb DP, Smith ND, Burton R, Garway-Heath DF. Do patients with glaucoma have difficulty recognizing faces? Invest Ophthal Vis Sci 2012; 53: 7: 3629-3637.

20. Drance SM. The early field defects in glaucoma. Invest Ophthalmol 1969; 8: 1: 84-91.

21. Asaoka R. Mapping glaucoma patients’ 30-2 and 10-2 visual fields reveals clusters of test points damaged in the 10-2 grid that are not sampled in the sparse 30-2 grid. PLoS One 2014; 9: 6: doi: 10.1371/journal.pone.0098525.

22. Redmond T, Garway-Heath DF, Zlatkova MB, Anderson RS. Sensitivity loss in early glaucoma can be mapped to an enlargement of the area of complete spatial summation. Invest Ophthal Vis Sci 2010; 51: 6540-6548.

23. Khuu SK, Kalloniatis M. Spatial summation across the central visual field: Implications for visual field testing. J Vision 2015; 15: 1: 1-15.

24. Khuu SK, Kalloniatis M. Standard automated perimetry: Determining spatial summation and its effect on contrast sensitivity across the visual field. Invest Ophthal Vis Sci 2015; 56: 3565-3576.

25. Khuu SK, Kalloniatis M. Visual field testing within complete spatial summation. Invest Ophthal Vis Sci 2014; 55: ARVO E-Abstract 3534.

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