In the accompanying article, the authors evaluated 10-2 visual field (VF) testing strategy and concluded that central VF pointwise linear regression (PLR) analysis was helpful in the detection of progression in advanced glaucomatous damage.[1] In this manuscript, we have highlighted the role of 10-2 VF testing strategy in the early diagnosis of mild-moderate glaucomatous defects and how this strategy influences the definition and clinical classification systems pertaining to glaucoma. The Paradigm Shift - Inception of 10-2 for Early Diagnosis in Glaucoma Suspects For a long time, it was thought that glaucomatous field defects involving the central 10 degree occur only in advanced stages of glaucoma, and traditionally 10-2 strategy was advised to document progression only when tubular vision was documented in 30-2 or 24-2 strategy.[2] Recently, it was well documented that sensitivity loss in the macular region was no longer regarded as a late manifestation of glaucoma, and VF analysis of this region should be undertaken irrespective of the stage of glaucoma. This paradigm shift in thought process generated good interest and various studies soon reported that detection of progressive VF loss was possible even in glaucoma suspects, by performing a VF test with an increase in the number of testing points on the central visual field (i.e., with 10-2 strategy).[3] These early VF defects were previously missed in the routine 24-2 strategy, thereby enhancing the importance of 10-2 strategy in glaucoma suspects.[3,4] How 10-2 Strategy Became the Key Ingredient in Functional Visual Field Testing - The Rationale The 24-2 and 30-2 threshold VF testing strategies assess a total of 54 and 74 points, respectively [Fig. 1a and b], each six degrees apart (three degrees from the horizontal and vertical meridians), with only 12 points tested within the central 10 degrees [Fig. 1c]. Furthermore, only four of these points were testing the central eight-degree macular region, the area which accounts for over 30% of the total retinal ganglion cells (RGCs) and over 60% of the visual cortex area. When only four points are tested, these strategies can easily miss paracentral scotomas at or near fixation, due to the macula being more sensitive than the rest of the retina.[5]Figure 1: (a and b) Graphic illustration displaying the total number of points checked in the visual fields, 30-2 and 24-2. (c and d) Illustration comparing the number of points checked in the central macular area in 24-2 (orange-colored squares) and 10-2 (black arrow)By comparison, the 10-2 threshold VF testing strategy assesses 68 points [Fig. 1d], five times as many points in the central 10 degrees, compared to the 24-2 and 30-2 testing strategies. These points are just two degrees apart from each other and just one degree from either side of the horizontal and vertical meridians.[6] As a result of this, greater sensitivity was noted, with many paracentral scotomas involving only a small area of the VF at or near fixation being detected with 10-2 tests, which may be missed with 24-2 and 30-2 tests.[7] What Do We Know From Existing Literature - The Scientific Travel Drance first illustrated how the central VF could be affected in early glaucomatous damage.[8] Teixeira et al. reported that more than 50% of eyes with mild-to-moderate glaucoma had defects within the central three degrees.[4] Further research strengthened the fact that central VF defects exist as commonly as peripheral VF defects in early glaucoma.[9] Schiefer et al. suggested that early central defects were usually more common in the upper VF and were deeper with an arcuate-like pattern that was closer to fixation than those in the inferior aspect.[10] Hood et al. found that 9% of normal 30-2 VFs in glaucoma suspects turned out abnormal with 10-2 testing.[11] Additionally, 30-2 underestimated the level of glaucomatous damage in 13% of the hemifields.[10] De Moraes et al. found that 11 eyes with normal 24-2 VF outside the central 10 degrees, showed arcuate defects within the central 10 degrees with 10-2.[12] Sullivan-Mee et al. reported that 6% of eyes without 24-2 field loss exhibited a 10-2 defect.[13] They also reported that 10-2 tests revealed damage missed by 24-2 tests in 35% of the ocular hypertensives, 39% of the suspected glaucoma cases, and 61% of the early glaucomatous field loss patients.[14] Zhang et al. threw light on the structural aspect, calling for the 10-2 test whenever there was a localized retinal nerve fiber (RNFL) layer defect in the inferior-temporal region of the retina, as it was likely to indicate significant macular damage due to glaucoma.[15] The Structure Function Correlation and the Hood Report - The Potential Game Changer? The new school of thought that has emerged is that the ganglion cell layer (GCL) damage can sometimes be the only manifestation of early glaucoma which can be picked up only in 10-2 VF strategy, and 10-2 VF functional defects correlate well with GCL structural defects, similar to how 24-2 VF defects correlate well with RNFL structural defects.[2,13] In the SPECTRALIS optical coherence tomography (S-OCT) (Heidelberg Engineering, Germany), Glaucoma Module Premium Edition, the Hood Glaucoma Report combines and organizes the most pertinent OCT data from the optic nerve head, RNFL, and macula, empowering ophthalmologists to detect glaucomatous damage and clinically correlate the information to VF location effectively. The structure-function comparison is done by rotating the RNFL and GCL thickness maps and overlaying them with the visual field test points simultaneously (i.e., 24-2 locations are relayed on the RNFL thickness map and 10-2 locations are relayed on the GCL thickness maps) [Fig. 2].[16]Figure 2: (a) Image showing the Hood Glaucoma Report in the Glaucoma Module Premium Edition (where the point tested in the visual fields are superimposed in the structural layers of the RNFL and GCL, respectively). (b) Visual fields of the same patient can be correlated with the Hood reportA Potential Blind Spot in Andersen’s Criteria? The Diagnostic Classification Dilemma Andersen’s criteria for glaucomatous field defects states that three or more contiguous non-edge points of the 30-2 printout should have P <5%, out of which at least one should have P <1%. However, there is no real mention of 10-2 testing strategy because, in reality, the presence of one non-edge (functional defect) point in the central 10 degrees may be suggestive of early glaucomatous change. The 24-2 or 30-2 programs fail to test this vulnerable region in detail and can falsely brand a patient with damage in the central retina as normal [Fig. 3]. Also, many of the so-called “glaucoma suspects” or “pre-perimetric glaucoma” may in fact have central damage, which would now be reclassified as “severe glaucoma” based on the clinical classification system currently employed. Moreover, clinicians should consider performing 10-2 tests in established glaucoma patients, too, to prevent misdiagnosis and/or misclassification of disease severity.Figure 3: Image showing the three practical permutations and combinations, with the highlighted scenario where 10-2 becomes imperative. (a) An abnormal 24-2 report with an abnormal 10-2 report. (b) A normal 24-2 report with an abnormal 10-2 report. (c) An abnormal 24-2 report with a normal 10-2 reportConclusion - The Recommended Way Forward To conclude, tests to analyze the macular region such as the 10-2 should be recommended to all patients in whom 24-2 and/or 30-2 tests are indicated, such as glaucoma suspects and ocular hypertensives. The tests for peripheral damage as well as central loss should be incorporated, instead of the “divide and treat” approach. However, it is also imperative to note that abnormalities in 10-2 may not always represent true functional loss due to glaucoma, calling for a structure-function clinical correlation. Even a normal 10-2 examination will provide an important baseline for future comparison. Though various challenges exist in the form of multiple visits, extended VF testing duration, appropriate training of personnel in conducting 10-2, and no precise guidelines, we recommend an alternating approach between 24-2 and 10-2 tests and to make sure both are done within the first two visits and take things on from there for glided glaucoma practice.