Binocular visual field in adults with horizontal strabismus and driving requirements

Forty-nine subjects were included: 20 with exotropia mean age 40.89 years (SD15.46) mean angle of deviation for distance and near of −21.70PD (13.44) and −22.70PD (14.69) and 19 with esotropia mean age 43.25 years (SD18.96) mean angle of deviation 17.63PD (11.07) and 18.37PD (12.34). Ten subjects with orthotropia mean age 41.90 years (SD13.54), mean stereoacuity of 24.50 seconds (SD 30.86) were included (Table 1). There was no significant difference in the respective ages between the 3 groups (p = 0.90, p = 0.98).

Table 1 Baseline Characteristics Between Groups.Visual acuity

There were no significant difference in binocular BCVA between esotropes, exotropes and subjects with orthotropia (p = 0.10 and 0.10, p = 0.09). There was no significant difference in the BCVA of amblyopic eyes (0.02 p = 0.99) between patients with esotropia and exotropia, although they were significantly reduced compared to subjects with orthotropia (0.45, p < 0.01, 0.43, p < 0.01) (Table 1). For the fellow eyes, there was no significant difference between esotropes and subjects with orthotropia (0.06, p = 0.08) or between esotropes and exotropes (0.04, p = 0.85). There was, however, a significant difference between the BCVA of the fellow eye of patients with exotropes and those with orthotropia (0.10, p = 0.028) (Table 1). For the inter-eye difference in BCVA, there was no significant difference between patients with esotropia and exotropia (difference 0.036, p = 0.92). There was, however, a significant difference in the inter-eye difference in BCVA between patients with esotropia or exotropia compared to subjects with orthotropia (0.40, p = 0.004 and 0.36, p = 0.01).

Visual fields

In orthotropes all false positive (FP) errors were 0% and all false negative (FN) errors were 0% apart from one patient who had 10%. In esotropes all FP errors were 0% apart from one patient had 10% and all FN errors were 0% apart from one patient had 10% FN. In exotropes all FP errors were 0% apart from 5 patients had 10%,10%,11%,20% and 22% and all FN errors were 0% apart 2 patients had 10% and 11%. The extent of the visual fields for patients with esotropia, exotropia and orthotropia are provided in Table 2.

Table 2 Visual fields characteristics between groups.Monocular fields

The presence of an esotropia or exotropia were significant factors in the horizontal extent of the visual field of the amblyopic eyes (p < 0.01) and fellow eyes (p < 0.01). Age (p = 0.21, p = 0.20), and visual acuity of the fellow or amblyopic eyes (p = 0.45, p = 0.17) were not significant. There were also no significant associations between the horizontal extent of the visual field (VF) of either the amblyopic or fellow eyes and the refractive errors of patients with esotropia (p = 0.44) and exotropia (p = 0.39). Similarly, there was no significant association between the horizontal extent of the MVF and visual acuity of the amblyopic (p = 0.16 and p = 0.66) or fellow eyes (p = 0.82 and p = 0.43) eyes of patients with esotropia and exotropia, respectively.

The horizontal extent of the VF of the amblyopic eyes of patients with esotropia (98.70 degrees SD 19.76) and exotropia (104.75 degrees SD 16.93) was significantly smaller than eyes with orthotropia (121.00 degrees SD 3.16) by 22.3 degrees (p = 0.004) and 16.25 degrees (p = 0.045), respectively (Fig. 1A) with higher coefficient of variance (CoV) of 20.02% and 16.59% than that of orthotropes (2.61%). There was no difference in the extent of the monocular horizontal field of the amblyopic eye between the esotropes and exotropes (6.05 degrees p = 0.49).

Fig. 1figure 1

Horizontal extent of the visual field of the amblyopic (A) and fellow eye (B) eye of patients with esotropia, exotropia and subjects with orthotropia.

For the fellow eyes, there was a significant difference in the horizontal extent of the VF between patients with esotropia and orthotropia by 20 degrees (p = 0.006) but not between patients with esotropia and exotropia (1.8 degrees p = 0.485). There was, however, no difference in the extent of the horizontal VF of the non-amblyopic eye of exotropes and subjects with orthotropia (18.20 degrees p = 0.068) (Fig. 1B).

Binocular visual fieldsVertical fields

The sizes of the vertical extent of the BVF are presented in Table 2. The vertical extent of the BVF was not related to the presence of an esotropia or exotropia (p = 0.49), age (p = 0.43), size of the tropia (p = 0.43) or visual acuity of the amblyopic (p = 0.86) and fellow (p = 0.31) eyes.

Horizontal fields

There were significant differences in the horizontal extent of the BVF in patients with esotropia, exotropia and normal eyes (p < 0.01) (Fig. 2).

Fig. 2figure 2

Horizontal extent of binocular visual field in patients with esotropia and exotropia, and subjects with orthotropia.

The presence of a tropia (esotropia or exotropia) was the significant factor in the horizontal extent of the BVF (p = 0.005). The difference in the horizontal extent of the BVF between esotropes and orthotropes was −18.21 degrees (p = 0.009) and −15.46 degrees for exotropes (p = 0.007). There was, however, no significant difference in the horizontal extent of BVF between exotropes and orthotropes (−2.75 degrees p = 0.84). Age (p = 0.21), visual acuity of the amblyopic (p = 0.47) and fellow eye (p = 0.22), and size of the tropia (p = 0.10) were not significant. There was also no significant association between the BVF and the degree of anisometropia for either patients with esotropia or exotropia (p = 0.22, p = 0.72).

There was, however, a significant non-linear association between the horizontal extent of the BVF of patients with esotropia and the angle of deviation (R2 = 0.63, p = 0.005) (Fig. 3) but not for those with exotropia (p = 0.45). Horizontal extent of VF (HVF) \(HVF = e^}}}\).

Fig. 3: Horizontal extent of the binocular VF and angle of deviation in esotropes.figure 3

Horizontal extent of VF (HVF) \(HVF = e^}}}\).

The ratio of the horizontal extent of the BVF to the sum of the MVF was related to the size of the tropia (p = 0.017), VA of the fellow (non-amblyopic) eye (p = 0.016) and the diagnosis (esotropia, exotropia or orthotropia) (p = 0.014), but not the VA of the amblyopic eye (p = 0.98). The ratio of the BVF to the sum of the MVF was similar between esotropes and exotropes (p = 0.88), but smaller in orthotropes (0.58) compared to either esotropes (0.63, p < 0.01) or exotropes (0.66, p < 0.01) (Supplementary Fig. 1).

The ratio of the horizontal extent of the VF of the amblyopic to non-amblyopic eye or the ratio of non-amblyopic eye to binocular field was not associated with the difference in VA between the amblyopic and fellow eyes (p = 0.21 and p = 0.81). Similarly, there was no significant difference in the ratio of the horizontal extent of the VF of amblyopic to fellow eyes between esotropes and orthotropes or exotropes (p = 0.97, p = 0.96) or between exotropes and subjects with orthotropia (p = 0.99). There was no difference in the ratio of the horizontal extent of the BVF on the side of amblyopic/right eye to fellow eye side (p = 0.31) (Supplementary Fig. 2).

The HE of BVF on the amblyopic side was significantly smaller for esotropes (p = 0.004) compared to exotropes (p = 0.008) and orthotropes (p = 0.003). There was no difference between exotropes and orthotropes (p = 0.45).

Points missed in the visual field

There were more points missed for the amblyopic eyes of patients with esotropia 9.85 (8.73) than those with orthotropia 1.30 (2.16) (p = 0.003) but not compared to those with exotropia 7.37 (6.78) (p = 0.58). There was also a significant difference between exotropes and orthotropes (p = 0.02).

There were more points missed in the BVF for the amblyopic eyes of patients with esotropia 8.00 (8.21) than those with orthotropia 1.90 (4.01) (p = 0.02), but not exotropia 4.00 (3.25) (p=0.44). There was no difference between exotropes and orthotropes (p = 0.40).

In 31.6% (6 of 19) of the patients with esotropia, the horizontal extent of their binocular field was below 120 degrees and as such would not meet the driving standard. These patients had a smaller angle of deviation (mean 11PD, min 4PD, max 16PD) than those whose binocular field was >120 degrees (mean 25PD, min 10PD, max 45PD), (p = 0.002). There were no differences in either near or distance visual acuity (p = 0.78, p = 0.55) between them. No patients with exotropia and no subjects with orthotropia had a horizontal BVF of less than 120 degrees.

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