*2.3. Rapid Campimetry*

Following the observation that a small light passed rapidly through the visual field defect is perceived as interrupted in the area of the defect, the central 10◦ visual field is tested in rapid campimetry with a bright test dot (140 cd/m2) on a dark screen (0.8 cd/m2) at a viewing distance of 40 cm (Figure 2). The visual field of the campimetry is extended temporally to 15◦ adjacent to the area of the blind spot to ensure that the patient understands the principle of the test by signalling the disappearance of the dot in the area of the blind spot. In the centre of the screen, there is a clearly visible cross as a fixation target (1.39◦ diameter) with lower brightness than the test marker.

The size of the test point was chosen to be as small as possible, such that it would not overlap the scotoma, while having good visibility at the same time. Because of the decreasing resolution from the centre to the periphery, the size of the test point increased with increasing distance from the fixation target. The optimal test point size was determined subjectively in pilot experiments (Table 2) and was 1.05 mm (0.16◦) near the fixation point at a distance of 40 cm between the subject and the screen, and increased by 0.11 mm per degree, such that it had a size of 2.72 mm (0.39◦) in the blind spot region. As the test point moves vertically, diagonally, and horizontally through the visual field, the size of the test spot changes automatically depending on the distance from the fixation point.

**Figure 2.** Rapid campimetry testing environment. Left Panel: Snapshot of the actual campimetry setting (with increased room lighting for better visualisation) with a volunteer fixating the centre of the testing area; left part of the image is masked to disable identification. Right panel: a sketch showing a person (P) looking at the monitor with a 40 cm distance (A) while an examiner (E) controls and runs the test on a different monitor.

**Table 2.** Various test point sizes in relation to position.


The most important difference in rapid campimetry in comparison to other visual-field testing methods is the running speed of the test point. The optimal running speed was determined subjectively on a narrow scotoma at a point approximately 8◦ from the fixation point, marked by a black ring (Figure 3). Different running speeds ranging from 0.18 cm/s to 24 cm/s were subjectively tested and the optimal speed was selected with which the scotoma was most reliably identified.

Using a too fast, 24 cm/s, or too slow, 0.18 cm/s, speed to run the test point disables the detection of the scotoma. Subjectively judged, the optimal speed of the test point seems to be ≈3 cm/s at 40 cm viewing distance from the screen. Here, it can be overlooked that the flat examination surface of the monitor results in an outward slowing of the velocity, since this variance at 10◦ results in about a 4% difference in velocity between the flat and curved surfaces. If the test point travels through the field of view at this speed along the seven vertical, diagonal, and horizontal paths mentioned in Figure 3, for a total length of ≈70 cm, then the test run passes through >1000 pixels ("test points"), depending on the resolution of the monitor (dpi). The specific screen area tested in rapid campimetry was 21.4 cm (442 pixels horizontally) by 14.1 cm (295 pixels vertically) and thus, for the test point progression of rapid campimetry (see below), ≈1400 test points. Due to the very fast update of the test point on the monitor (60 Hz), a subject perceives an uninterrupted line of light, that is, a point moving on the examination field of the monitor without interruption. The examination is completed within less than 30 s and the presence of absolute scotomas in the central 10◦ visual field can be largely excluded, if subjects see the test point uninterruptedly during the examination run.

**Figure 3.** The path tested in the screening procedure of rapid campimetry is shown in dashed lines. In the arc scotoma marked by a black ring, 8◦ from the fixation point, the optimum test point speed was determined. The test point changes its diameter with the distance from the fixation point; the greater the distance, the greater its diameter. In the outer of the three vertical test lines, the used size change is overdrawn. If one wants to determine the examined area in this area, then the area is calculated as the sum of two identical trapezoids.

The test point trajectory is, in principle, arbitrary. However, for better comparability of the results for "rapid campimetry", a certain pattern is specified for the test point course. Within less than a minute, the test point first runs at 15◦ through the blind spot, then on three vertical, two diagonal and two horizontal lines through the central 10◦ visual field (Figure 3). The pattern of this test point course was chosen to follow the nerve fibre course traversing arcuate scotomas as perpendicularly as possible. As Aulhorn wrote, this is the best way to accurately determine glaucomatous scotoma boundaries [17].

The testing screen is coupled with an observation screen to enable monitoring of the test point by the examiner during examination. If the subject signals the disappearance or reappearance of the test point, these points of the scotoma rim are marked and the coordinates of these points are stored. In the examination result, the two points (scotoma start and end) are connected by a grey line symbolizing the scotoma, as shown in Figure 1d.

At the end of the test session, the examiner recognizes the suspected scotoma at the marked points at which the test point became invisible (off points) or visible again (on points). The scotoma can subsequently be delineated as in ordinary kinetic perimetry ("scotoma delineation campimetry"; duration approximately 1–10 min for one eye depending on the size of the VF defects) by moving the test point vertically, as, for example, shown in Figure 1e. Identifying the scotoma boundary accurately is facilitated by reducing the running speed of the test point, e.g., by a factor of 4 or 8.

If the examined area of each test point run is to be determined and set in relation to the square visual field with the horizontal and vertical diameter of the 10◦ area, and if the edge length of this square is 14.1 cm, then the total area to be examined is 198.81 cm2. The path tested in the screening procedure is shown in dashed lines in Figure 3. The test point changes its diameter with distance from the fixation point; the greater the distance from the fixation point, the greater its diameter. In the outer of the three vertical test lines, the size change used is exaggerated for clarity. The examined area is calculated approximately as the sum of two identical trapezoids, which are shifted vertically. Minimal deviations result from the fact that the test point change is linear only for lines running directly from the fixed point. The two trapezoids therefore have very slightly curved lines in the direction of travel. If they are placed next to each other, they approximately form a rectangle with half the running distance of the test point and the sum of the largest diameter of the test point at the top and the smallest diameter in the middle of the path. The area tested in rapid campimetry then adds up to a total of 13.41 cm<sup>2</sup> of the total 198.81 cm<sup>2</sup> from the three vertical, two identical diagonal, and two identical horizontal paths of the test point, and thus 6.75% of the paracentral visual field to be examined (Table 3).


**Table 3.** Area calculation of the tested visual field fractions during the test run.

#### **3. Results**

The case observation of F.H.'s scotomas is shown in Figure 1. The novel method of rapid campimetry verified the two subjectively observed scotomas. Figure 1d shows the result at the end of the test run of the rapid campimetry, and Figure 1e shows the result of the scotoma delineation campimetry. The red and green dots connected with a grey dotted line represent the scotoma's start and end.

Five additional subjects (detailed in Methods) with a glaucomatous VF defect were included in this study to compare VF defects between SAP and rapid campimetry. Unintentionally, all five subjects had no SAP evidence of a VF defect in the fellow eye, which thus served as reference.

In general, there was an excellent agreement between rapid campimetry and SAP. All eyes without VF defects presented without abnormalities in either test (Figure 4). Similarly, the area and extent of the grey/black shaded regions of the VF defects in SAP corresponded to the scotoma line delineated by the rapid campimetry (Figure 5).

In combination with scotoma delineation campimetry, the following results are obtained for each subject compared to SAP: In subject 1, HFA detected scotomas in the upper visual field and normal sensitive retina between these scotomas. Scotoma delineation campimetry found instead a continuous arcuate scotoma in the same location. In subject 2, both HFA and campimetry demonstrated comparable findings showing an upper quadrant scotoma (Figure 5). In the lower visual hemifield of the left eye of subject 3, there was a relative scotoma in the centre of the arcuate scotoma, which scotoma delineation campimetry identified as an absolute scotoma. In subject 4, both campimetry and SAP depicted a similar arcuate scotoma in the superior VF of the right eye. Finally, subject 5 has an upper arcuate scotoma at a site of relative scotoma that rapid campimetry classified as an absolute scotoma.

**Figure 4.** Eyes with normal visual field of subjects 1–5. The blind spot was detectable at 15◦ for all subjects except subject 2 (S2) with rapid campimetry. SAP = standard automated perimetry. OD = right eye; OS = left eye; S: subject; SAP: standard automated perimetry.

**Figure 5.** Eyes with visual field defects of subjects 1–5 compared between 10-2 SAP vs. rapid campimetry and scotoma delineation campimetry. SAP = standard automated perimetry. OD = right eye; OS = left eye; S: subject.

#### **4. Discussion**

The aim of this proof-of-concept study was to compare the novel visual field examination technique, rapid campimetry, with the established standard automated perimetry (SAP) in a case series regarding the detection of glaucomatous defects. In this six-subject sample, we found strong agreement between SAP and rapid campimetry in identifying VF defects in all eyes.

#### *4.1. Increasing Attention via Fast Stimulus Movement*

In the established SAP, the response behavior of the examinees is strongly dependent on their attention, since they are supposed to judge the appearance of a test point just at the threshold of perception and in weak contrast with the surroundings. The image change occurs so weakly or slowly that it is easily overlooked, but it is necessary in this form to define the threshold of perception [18]. One of the most important functions of the retina, namely, enabling the perception of rapid movement, was important in evolution because detection of the movement of a prey animal or enemy provided a survival advantage [19]. The perception of fast motion, however, is not tested in threshold perimetry. Notably, in order to identify retinal areas without light perception, i.e., whether there are absolute scotomas, fast motion can be used in combination with high contrast, with several key advantages, such as hardly strained participant attention.
