This study evaluated all 47 adult patients meeting the inclusion criteria. Their mean age was 73 ± 2 (SEM) years. Thirty were female, and 17 were male. Their mean cup-to-disc ratio values were 0.84 ± 0.02 in the right eye and 0.86 ± 0.01 in the left. Their mean Humphrey 30-2 MD and PSD values were −13.72 and 10.70, respectively, for left eyes and −12.24 and 10.26 for right eyes (see
Table 1). The age, sex, and all right and left eye MD and PSD values for all 47 subjects are provided in
Table 2. Twenty-three subjects had severe visual field loss in both eyes, 9 had moderate loss in both eyes, and 15 had severe loss in one eye and moderate loss in the other. Eighty-eight percent of patients had undergone successful glaucoma surgery in either or both eyes,
18 stabilizing intraocular pressure bilaterally. Many of the clinical subjects qualifying for the present study were participants in a recently published surgical study
18 who collectively demonstrated very stable and low postoperative glaucoma medication use and IOP values, as well as very high intervisit Humphrey 30-2 stability and reproducibility. All six correlation coefficients (
R) for comparisons of MD and PSD at 6, 12, and 18 months versus presurgical baseline values in that study were clustered around 0.9 (range,
R = 0.863–0.957).
The mean intraocular pressure among participants in the present study was 10.1 ± 0.5 mm Hg in the right eye and 11.6 ± 0.6 mm Hg in the left. Only 27% of subjects were receiving any topical ocular hypotensive therapy in either eye with the clinical intent of enhancing IOP reduction. No oral ocular hypotensive agent was in use by any subject. Fifty-seven percent of subjects were prescribed topical carbonic anhydrase inhibitor eye drops with the intent of augmenting ocular vascular perfusion.
19
Figure 1 presents several select examples of paired visual fields that show a readily apparent nonrandom inverse tendency for focal zones of visual loss in one eye to be seen well by the fellow eye. Note that in these individuals, the alternating positive and negative complementarity between the right and left eye visual fields results in a much more normal binocular field than could be predicted by chance. The examples shown were chosen because they make the “jigsaw” phenomenon fairly obvious at a glance. Other individuals in the study had significant loss in the same quadrant or hemifield in both eyes, making bilateral compensatory effects far less obvious on cursory inspection of the fields. All patients were included in the statistical analysis.
Figure 2 shows an example of a patient with bilateral severe visual field loss who clearly does not demonstrate the jigsaw phenomenon. This 84-year-old female, whose data were included in both the
n = 47 and
n = 16 prospective analyses, had coexisting diabetes and systemic hypertension. Her severe bilateral concentric loss overlaps extensively in the peripheral field of both eyes; and the MD of the binocular field is actually worse than either eye on its own, despite taping of both upper lids to prevent ptosis during testing. It is nevertheless intriguing that during that testing she dynamically expanded the functionally more important inferior binocular field while sacrificing binocular function superiorly.
Figure 3 provides a 3-D projection heat map set for one specimen visual field pair, with results obtained by the actual natural focal pairings of all 74 visual field loci (
α) and the mean of 10,000 randomized isopterically equivalent pairings using the same left eye visual field data (
β). Note in this instance that the latter physiologically balanced pairings would render an improved but still severely defective binocular visual field, while the actual natural pairings render a binocular field that approaches normal.
Numerical analysis of the entire study population reaffirms the general strength of this tendency.
Figure 4 and
Table 3 illustrate and summarize the statistical findings from the full study group (
n = 47; 94 eyes). Among these eyes, the mean threshold value across the entire visual field (74 loci) was 18.9 dB for left eyes and 19.9 dB for right eyes (average 19.4), 4 dB lower than the better of the naturally paired concomitant loci (
α) at 23.4 dB (
P < 10
−15). This mean threshold value (
α) for concomitant direct pairings was significantly higher than was attainable from the same eyes when pairing was performed using the randomized coisopterically equivalent options (
β), which yielded 21.9 dB (
P < 10
−12). The natural bilateral overlay pairings (
α) provided function levels within 0.3 dB of the mean of the very highest of the 47 individual results among the 470,000 randomized pairings used to calculate
β values. Mirror-image pairings, in contrast, were statistically indistinguishable from the randomized coisopteric pairings.
Simultaneous binocular visual field testing carried out prospectively among the returning subset of 16 of the 47 patients confirmed that concomitant testing with both eyes open produced results essentially equivalent to the higher light attenuation threshold value of all 74 naturally paired bilaterally concomitant loci (
α) of the individual right and left visual fields. These subjects comprised 10 individuals with severe visual field loss in both eyes, 2 with moderate loss in both eyes, and 4 with a mixture thereof (
Fig. 5,
Table 4). Paired
t-test values showed a highly significant 6.2-dB difference between the binocular Humphrey 30-2 global index MD (−7.97 ± 1.1 dB) and the mean of the right and left MD values (−14.18 ± 1.3 dB; see
Table 1) obtained on retesting immediately beforehand among this cohort (
P < 0.0001). The mean difference between the randomized mean paired right and left visual field values and the true measured binocular values among this prospectively retested subgroup was 1.6 dB (
P < 0.005). The difference between the means of the very best of the 10,000 coisopteric randomized combinations of individual right and left visual fields and the natural bilateral pairings (
α) was only 0.25 dB, in favor of the best-of-10,000 (
P = 0.02). Remarkably, however, the mean difference between these optimal pairings and actual measured (simultaneous) binocular visual fields was statistically indistinguishable (0.4 dB in favor of the binocular field,
P = 0.93); both of these were >5 dB higher than the means of the right and left fields, and >2 dB higher than the mean of 10,000 randomized coisopteric pairings (
β) or mirror-image pairings (
χ).