purpose. In adult patients and in children of school age who have been treated with vigabatrin (VGB), persistent visual field defects have been reported as a side effect. To date, it is unknown to what extent VGB causes visual field loss in young children and mentally handicapped adolescents who cannot be tested with conventional perimetric methods. The purpose of the present study was to investigate VGB-induced visual field loss in these patients by using a noncommercial arc perimeter and a forced-choice, preferential-looking method.

methods. The visual field size was measured in 30 patients aged 1 to 15 years who had epilepsy and who were treated with VGB. The visual field of these patients was compared to the visual field of 70 control subjects.

results. In eight (27%) patients who had been treated with VGB, the visual field was constricted compared with the visual field of the children belonging to the control group.

conclusions. Arc perimetry shows that mentally handicapped patients and children younger than 6 years treated with VGB have visual field loss compared with the loss reported in adult patients receiving VGB.

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^{ 38 }The prevalence of visual field defects in adult patients who receive VGB ranges between 19%

^{ 23 }and more than 70%.

^{ 24 }In children who receive VGB, a prevalence of visual field defects between 42%

^{ 37 }and 71%

^{ 28 }has been found. However children younger than 6 years and children who were mentally handicapped (IQ <60) had to be excluded from these studies because their visual fields could not be assessed with conventional perimetric methods. In conventional perimetry, which was used to assess the visual field of adult patients and children of school age, patients have to maintain fixation of the central point in the perimetric sphere until the target is presented. When the target is seen, they have to press a button while fixation of the central point is maintained.

^{ 39 }Children younger than 6 years and mentally handicapped adolescents, however, are unable to understand and follow the instructions. Those who understand the instructions are unable to maintain fixation when the target appears, and/or they forget to press the button.

^{ 40 }

^{ 41 }

^{ 42 }

^{ 43 }

^{ 44 }Therefore, the influence of VGB on the extension of the visual field of infants and preschool children has not yet been tested. We therefore assessed the visual field with an improved arc perimeter

^{ 41 }

^{ 42 }

^{ 43 }

^{ 44 }using a sufficiently small stimulus, which was only 0.5 degrees of arc larger than the largest stimulus in the Goldmann perimeter. Our arc perimetry is based on the forced-choice, preferential-looking methods

^{ 41 }

^{ 42 }

^{ 43 }

^{ 44 }used in earlier studies to assess the visual field in infants. In contrast to conventional perimetry, the method we applied does not require the subjects to understand instructions. When the visual field is assessed with the arc perimeter, the patients are neither required to maintain fixation if they detect the target nor to press a button. The gaze is automatically attracted by a flickering central point. The target appears instead of the fixation point, and the patients are allowed to make an eye movement when the target is presented. The decision about whether the target was detected depends on the kind of eye movement performed when the target is present.

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^{ 44 }This method made it possible to examine the location and extension of the visual field in very young children and in mentally handicapped patients who had been treated with VGB.

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^{ 44 }Therefore, the visual field of the control subjects aged between 1 and 15 years is expected to have a normal size.

^{ 45 }an adapted German version of the WISC-III (Wechsler Intelligence Scale for Children-Revision III). Scores of cognitive functioning could not be tested in nine patients older than 6 years because they did not understand instructions. Thirteen patients had an IQ below 60 (HAWIK-R). In all children, the optokinetic nystagmus, threat response, eye movements, optical alignment, and pupillary reflex were normal. Spontaneous eye movements occurred to the left and to the right. All children reacted to acoustic and tactile stimuli in the left and right halves of space. Patients were excluded from arc perimetry if they had damage to the primary or secondary visual pathway, if they were unable to hold their head upright and if they did not open their eyes and did not direct their eyes spontaneously to the flickering fixation point in the perimetric arc. Six patients who had been treated with VGB had to be excluded from the study due to the listed exclusion criteria.

*t*-test:

*P*= 0.62). The visual fields of these children and adolescents were assessed with the arc perimeter because the children could not be tested with conventional perimetric methods. The children were unable to understand and follow the instructions, because they were too young or because they were mentally handicapped. Eight children were less than 6 years of age. Scores of cognitive functioning could not be tested in 10 patients older than 6 years because they did not understand instructions. Twelve patients had an IQ below 60 (HAWIK-R).

*t*-test:

*P*= 0.71). The monocular visual fields of these children were also assessed on eight meridians within the arc perimeter. Spontaneous eye movements occurred to the left and to the right. All children reacted to acoustic and tactile stimuli in the left and right halves of space. In all children the optokinetic nystagmus, threat response, eye movements, optical alignment, and pupillary reflex were normal.

^{2}; background luminance, 5 cd/m

^{2}; target diameter 2 and 4 mm) and with the arc perimeter. All patients had an IQ above 81 (HAWIE and HAWIK-R). Spontaneous eye movements occurred to the left and to the right. All patients reacted to acoustic and tactile stimuli in the left and right halves of space. Optokinetic nystagmus was disturbed in 11 patients, and pursuit eye movements were disturbed in six. Threat response, optical alignment, and pupillary reflex were normal in all patents. Optokinetic nystagmus was tested by showing the children a rotating drum with black and white stripes of a frequency of 0.07 cyc/deg. Visual threat response was tested by moving a 14 × 14-cm object rapidly toward the child’s eyes.

^{2}. Background luminance was 0.03 cd/m

^{2}. The head position, fixation, and eye movements were controlled by an infrared-sensitive video camera displayed on a high-resolution monitor. During perimetric testing, an assistant controlled fixation of the central fixation point and eye and head movements on the video monitors. Two investigators independently judged whether an eye movement was directed toward a target. The investigators did not know where the targets would appear and received no information about whether the child had cerebral lesions or epileptic seizures or about the medication the child received. To exclude the presence of a hemispatial neglect, spontaneous eye movements were recorded when no visual stimulus was present in the perimetric arc.

^{2}. If the target was not detected, the measurement was repeated with a target luminance of 40 cd/m

^{2}, since targets with a luminance below 50 cd/m

^{2}had no light scatter.

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*t*-test. The significance of the difference of the percentage of visual field defects in the VGB group and the control group was tested using

*z*-test for percentages.

*r*). Correlations between the patients ages at the beginning of the VGB medication, the duration of VGB medication, VGB dosage, and size of the visual field defect were also calculated by using Pearson’s coefficient (

*r*). The significance of differences between the size of the visual field on a given meridian in the control groups were calculated with the Kruskal-Wallis ANOVA. Statistical evaluation was made with BiAS.

^{ 46 }

*n*= 30) were of normal size when tested on eight visual meridians. The size of the visual fields in the cerebral palsy group (control group 2) was almost identical with the size of the visual fields of the children in the normal control groups (control groups 1 and 3). The arithmetic means of the extensions of the nasal and temporal visual hemifields on eight meridians are summarized in Table 2 . The size of the normal visual field (i.e., the area in which all control subjects detected the targets) is shown in Table 3 . There were no significant differences in the size of the visual fields of the control groups on all eight meridians (Kruskal-Wallis-ANOVA: χ

^{2}> 1.15;

*df*= 5;

*P*> 0.05). All children responded promptly to the target, which was presented on eight meridians of each monocular visual hemifield.

*x*= 3.3° ± 0.7° [SD]). The size of the visual field measured with the Goldmann perimeter did not differ significantly from the measurement with the arc perimeter (Wilcoxon test: overestimations,

*z*= 0.54;

*P*> 0.05; underestimations,

*z*= −0.33;

*P*> 0.05; Pearson

*r*= 0.897;

*P*= 0.000003).

*z*-test:

*P*< 0.001. The difference between the area of visual field in the VGB group (right eye:

*x*= 5790 ± 441.1 cm

^{2}[SD]; left eye:

*x*= 5889 ± 452.3 cm

^{2}) and the control groups (right eye:

*x*= 6013 ± 19.0 cm

^{2}; left eye:

*x*= 5912 ± 18.1 cm

^{2}) was also highly significant (for both eyes,

*t*-test:

*P*< 0.01). The area of visual field defect and the percentages of visual field loss are summarized in Table 3 .

^{2}in the superonasal quadrant between 5° and 15° eccentricity, which corresponds to 46% of the superonasal quadrant field between 5° and 15° eccentricity in control subjects—an area of 78 cm

^{2}. This patient also had a 36-cm

^{2}defect in the inferonasal quadrant between 5° and 15° eccentricity, which is 46.2% of control subjects. In normal control subjects, this area of the visual field was 78 cm

^{2}.

^{2}in the superonasal quadrant between 30° and 50° eccentricity, which corresponds to 10.6% to 46.8% of the superonasal quadrant field between 30° and 50° eccentricity in control subjects—an area of 415 cm

^{2}. These patients also had a 44- to 132-cm

^{2}defect in the inferonasal quadrant between 30° and 65° eccentricity, which is 8% to 23.9% of that in control subjects. In normal control subjects, this area of the visual field was 553 cm

^{2}.

^{2}in the superotemporal quadrant between 30° and 60° eccentricity, which corresponds to 0.9% to 63.5% of the superotemporal field between 30° and 60° eccentricity in control subjects—an area of 883 cm

^{2}. One patient also had a 52-cm

^{2}defect in the inferotemporal quadrant between 30° and 60° eccentricity, which is 5.5% of that in control subjects. In normal control subjects, this area of the visual field was 946 cm

^{2}.

^{2}in the superotemporal quadrant between 60° and 85° eccentricity, which corresponds to 25.5% to 100% of the superotemporal quadrant field between 60° and 85° eccentricity in control subjects—an area of 517 cm

^{2}. Six of these patients also had a 97- to 561-cm

^{2}defect in the inferotemporal quadrant between 60° and 85° eccentricity, which is 13% to 75.2% of that in control subjects. In normal control subjects, this area of the visual field was 746 cm

^{2}.

^{2}in the superonasal quadrant between 30° and 50° eccentricity, which corresponds to 24.6% to 34% of the superonasal quadrant field between 30° and 50° eccentricity in control subjects—an area of 415 cm

^{2}. These patients also had a 108- to 198-cm

^{2}defect in the inferonasal quadrant between 30° and 50° eccentricity, which is 18.2% to 35.8% of that in control subjects. In normal control subjects, this area of the visual field was 553 cm

^{2}.

^{2}in the superotemporal quadrant between 5° and 15° eccentricity, which corresponds to 15.5% of the superotemporal quadrant field between 5° and 15° eccentricity in control subjects—an area of 78 cm

^{2}. This patient also had a 6.6-cm

^{2}defect in the inferotemporal quadrant between 5° and 15° eccentricity, which is 7.8% of that of control subjects. In normal control subjects, this area of the visual field was 78 cm

^{2}.

^{2}in the superotemporal quadrant between 60° and 85° eccentricity, which corresponds to 37.3% to 100% of the superotemporal quadrant field between 60° and 85° eccentricity in control subjects—an area of 517 cm

^{2}. These patients also had a 225- to 716-cm

^{2}defect in the inferotemporal quadrant between 60° and 85° eccentricity, which is 30.2% to 100% of that in control subjects. In normal control subjects, this area of the visual field was 746 cm

^{2}.

*r*= −0.0068;

*P*= 0.97), the duration of VGB medication (Pearson

*r*= 0.26;

*P*= 0.16), and the dose of VGB (Pearson

*r*= 0.18;

*P*= 0.33).

^{ 8 }who found visual field defects in 29% of 41 adults after treatment with VGB. Other researchers

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^{ 48 }have found visual field defects in up to 73% of the patients who were treated with VGB. Our results are in agreement with the findings of Best and Acheson

^{ 47 }who have shown that visual field defects due to VGB therapy do not progress when VGB medication is continued. They assume that there is no dose-dependent toxicity. Other investigators

^{ 49 }reported a slight increase in visual field when VGB medication was stopped. An improvement of the visual field after withdrawal of VGB has even been reported.

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*x*= 62.4 mg/kg), which was given to the children in the treated group. Visual field defects also developed during monotherapy with VGB.

Patient/Sex | Age at Time of Perimetry (mo) | Dose VGB | Duration of VGB Medication (mo) | Kind of Epilepsy |
---|---|---|---|---|

AS/M | 148 | 12.5 mg/kg + orphiril | 81 | Lennox |

RO/M | 158 | 33.3 mg/kg | 84 | Focal seizures |

PA/F | 147 | 60 mg/kg | 90 | Temporal lobe epilepsy |

FA/F | 108 | 66 mg/kg + pirimidon + phenytoin | 88 | Infantile spasms |

ME/M | 108 | 35.7 mg/kg + valproic acid + sultiam | 60 | Infantile spasms |

BT/M | 84 | 56.8 mg/kg + ergenyl | 48 | Focal seizures |

BG/M | 96 | 55.6 mg/kg | 22 | Grand mal seizures |

OK/M | 67 | 73.5 mg/kg | 48 | Grand mal seizures |

Eye | Visual Field Meridian | Contr 1 Norm Pat (n = 30) | Contr 2 Cereb Palsy (n = 20) | Contr 3 Norm (n = 20) |
---|---|---|---|---|

Left | Temp VF hor meridian | x = 87.5° | x = 88.2° | x = 88.0° |

SD = 1.4° | SD = 2.0° | SD = 1.3° | ||

Left | Temp VF 165° meridian | x = 87.2° | x = 87.6° | x = 87.4° |

SD = 1.2° | SD = 2.0° | SD = 1.2° | ||

Left | Temp VF 150° meridian | x = 85.9° | x = 83.0° | x = 81.7° |

SD = 0.91° | SD = 2.7° | SD = 1.9° | ||

Left | Temp VF 120° meridian | x = 56.6° | x = 56.1° | x = 55.3° |

SD = 1.9° | SD = 1.4° | SD = 1.2° | ||

Left | Temp VF 90° meridian | x = 51.8° | x = 53.4° | x = 52.8° |

SD = 1.9° | SD = 3.7° | SD = 3.2° | ||

Left | Temp VF 210° meridian | x = 87.3° | x = 86.2° | x = 87.2° |

SD = 1.2° | SD = 0.9° | SD = 1.2° | ||

Left | Temp VF 240° meridian | x = 76.4° | x = 76.3° | x = 76.1° |

SD = 1.6 | SD = 1.5° | SD = 1.4° | ||

Left | Temp VF 270° meridian | x = 67.5° | x = 66.8° | x = 66.8° |

SD = 3.05° | SD = 2.2° | SD = 2.1° | ||

Left | Nasal VF hor meridian | x = 47.1° | x = 47.0° | x = 47.4° |

SD = 1.4° | SD = 1.8° | SD = 1.6° | ||

Left | Nasal VF 15° meridian | x = 46.7° | x = 46.6° | x = 46.9° |

SD = 1.3° | SD = 1.5° | SD = 1.4° | ||

Left | Nasal VF 30° meridian | x = 46 | x = 46.5° | x = 46.9° |

SD = 1.0 | SD = 1.6° | SD = 1.4° | ||

Left | Nasal VF 60° meridian | x = 45.6 | x = 46.1° | x = 46.3° |

SD = 0.8 | SD = 1.2° | SD = 0.9° | ||

Left | Nasal VF 330° meridian | x = 46.5° | x = 46.4° | x = 46.8° |

SD = 1.2° | SD = 1.7° | SD = 1.4° | ||

Left | Nasal VF 300° meridian | x = 50 | x = 52.2° | x = 51.0° |

SD = 1.8 | SD = 2.8° | SD = 2.0° | ||

Right | Temp VF hor meridian | x = 87.3° | x = 88.0° | x = 87.5° |

SD = 1.6° | SD = 2.0° | SD = 1.8° | ||

Right | Temp VF 15° meridian | x = 86.0° | x = 87.0° | x = 87.3° |

SD = 1.4° | SD = 1.7° | SD = 1.7° | ||

Right | Temp VF 30° meridian | x = 85.8° | x = 87.7° | x = 82.1° |

SD = 1.1° | SD = 1.8° | SD = 2.2° | ||

Right | Temp VF 60° meridian | x = 56.6° | x = 56.8° | x = 56.3° |

SD = 2.0° | SD = 2.2° | SD = 1.5° | ||

Right | Temp VF 90° meridian | x = 52.5° | x = 53.3° | x = 52.9° |

SD = 2.9° | SD = 3.3° | SD = 3.2° | ||

Right | Temp VF 330° meridian | x = 86.9° | x = 86.2° | x = 86.6° |

SD = 1.5° | SD = 0.8° | SD = 1.3° | ||

Right | Temp VF 300 meridian° | x = 76.5° | x = 76.8° | x = 76.4° |

SD = 2.0° | SD = 1.9° | SD = 1.7° | ||

Right | Temp VF 270° meridian | x = 69.1° | x = 67.2° | x = 66.3° |

SD = 3.9° | SD = 2.6° | SD = 2.4° | ||

Right | Nasal VF hor meridian | x = 47.5° | x = 47.1 | x = 47.4° |

SD = 1.4° | SD = 1.8 | SD = 1.7° | ||

Right | Nasal VF 165° meridian | x = 47.2° | x = 46.5° | x = 47.3° |

SD = 1.3° | SD = 1.7° | SD = 1.7° | ||

Right | Nasal VF 150° meridian | x = 46.6° | x = 46.4° | x = 46.5° |

SD = 1.1° | SD = 1.6° | SD = 1.6° | ||

Right | Nasal VF 120° meridian | x = 45.9° | x = 46.0° | x = 46.1° |

SD = 1.0° | SD = 1.3° | SD = 1.2° | ||

Right | Nasal VF 210° meridian | x = 46.7° | x = 46.6° | x = 46.7° |

SD = 1.2° | SD = 1.4° | SD = 1.4° | ||

Right | Nasal VF 240° meridian | x = 52.2° | x = 51.9° | x = 52.3° |

SD = 2.9° | SD = 2.2° | SD = 2.3° |

^{2}> 1.5;

*df*= 5;

*P*> 0.05). The numbers indicate the arithmetic mean (

*x*) and the standard deviation (SD) of the extension of the visual field on a given meridian.

A. Right Eye | ||||||||||||
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Left Visual Hemifield | Right Visual Hemifield | |||||||||||

Eccentricity of Investigated Areas (deg) | Eccentricity of Investigated Areas (deg) | |||||||||||

Upper quad. | 30–50 | 15–30 | 5–15 | 5–15 | 15–30 | 30–60 | 60–85 | |||||

Lower quad. | 30–65 | 15–30 | 5–15 | 5–15 | 15–30 | 30–60 | 60–85 |

Areas of Visual Field | Areas of Visual Field | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|

Control subjects | ||||||||||||

Upper quad. | 415 cm^{2} 100% | 262 cm^{2} 100% | 78 cm^{2} 100% | 78 cm^{2} 100% | 262 cm^{2} 100% | 883 cm^{2} 100% | 517 cm^{2} 100% | |||||

Lower quad. | 553 cm^{2} 100% | 262 cm^{2} 100% | 78 cm^{2} 100% | 78 cm^{2} 100% | 262 cm^{2} 100% | 946 cm^{2} 100% | 746 cm^{2} 100% | |||||

Patients | ||||||||||||

AS | ||||||||||||

Upper quad. | 194 cm^{2} 46.82% | 132 cm^{2} 25.53% | ||||||||||

Lower quad. | 116 cm^{2} 20.98% | 253 cm^{2} 33.91% | ||||||||||

RO | ||||||||||||

Upper quad. | 407 cm^{2} 46.09% | 517 cm^{2} 100% | ||||||||||

Lower quad. | 191 cm^{2} 26.60% | |||||||||||

PA | ||||||||||||

Upper quad. | 36 cm^{2} 46.15% | |||||||||||

Lower quad. | 36 cm^{2} 46.15% | |||||||||||

FA | ||||||||||||

Upper quad. | 88 cm^{2} 21.20% | 136 cm^{2} 26.31% | ||||||||||

Lower quad. | 132 cm^{2} 23.87% | 97 cm^{2} 13.00% | ||||||||||

ME | ||||||||||||

Upper quad. | 75 cm^{2} 18.10% | 192 cm^{2} 37.14% | ||||||||||

Lower quad. | 90 cm^{2} 16.27% | 270 cm^{2} 36.19% | ||||||||||

BT | ||||||||||||

Upper quad. | 44 cm^{2} 10.60% | 190 cm^{2} 36.75% | ||||||||||

Lower quad. | 44 cm^{2} 7.96% | |||||||||||

BG | ||||||||||||

Upper quad. | 48 cm^{2} 11.56% | 8 cm^{2} 0.91% | 364 cm^{2} 70.41% | |||||||||

Lower quad. | 48 cm^{2} 8.68% | 522 cm^{2} 69.97% | ||||||||||

OK | ||||||||||||

Upper quad. | 561 cm^{2} 63.53% | 517 cm^{2} 100% | ||||||||||

Lower quad. | 52 cm^{2} 5.5% | 561 cm^{2} 75.20% |

B. Left Eye | ||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|

Left Visual Hemifield | Right Visual Hemifield | |||||||||||||

Eccentricity of Investigated Areas | Eccentricity of Investigated Areas | |||||||||||||

Upper quad. | 60–85 | 30–60 | 15–30 | 5–15 | 5–15 | 15–30 | 30–50 | |||||||

Lower quad. | 60–85 | 30–60 | 15–30 | 5–15 | 5–15 | 15–30 | 30–65 |

Areas of Visual Field | Areas of Visual Field | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|

Control subjects | ||||||||||||

Upper quad. | 517 cm^{2} 100% | 883 cm^{2} 100% | 262 cm^{2} 100% | 78 cm^{2} 100% | 262 cm^{2} 100% | 262 cm^{2} 100% | 415 cm^{2} 100% | |||||

Lower quad. | 746 cm^{2} 100% | 946 cm^{2} 100% | 262 cm^{2} 100% | 78 cm^{2} 100% | 262 cm^{2} 100% | 262 cm^{2} 100% | 553 cm^{3} 100% | |||||

Patients | ||||||||||||

AS | ||||||||||||

Upper quad. | ||||||||||||

Lower quad. | ||||||||||||

RO | ||||||||||||

Upper quad. | 294 cm^{2} 56.87% | 141 cm^{2} 33.97% | ||||||||||

Lower quad. | 313 cm^{2} 41.96% | 198 cm^{2} 35.80% | ||||||||||

PA | ||||||||||||

Upper quad. | 12 cm^{2} 15.54% | |||||||||||

Lower quad. | 6.6 cm^{2} 7.8% | |||||||||||

FA | ||||||||||||

Upper quad. | 219 cm^{2} 42.36% | |||||||||||

Lower quad. | 225 cm^{2} 30.16% | |||||||||||

ME | ||||||||||||

Upper quad. | 193 cm^{2} 37.33% | 102 cm^{2} 24.58% | ||||||||||

Lower quad. | 240 cm^{2} 32.17% | 108 cm^{2} 18.22% | ||||||||||

BT | ||||||||||||

Upper quad. | ||||||||||||

Lower quad. | ||||||||||||

BG | ||||||||||||

Upper quad. | 517 cm^{2} 100% | |||||||||||

Lower quad. | 746 cm^{2} 100% | |||||||||||

OK | ||||||||||||

Upper quad. | ||||||||||||

Lower quad. |

^{2}) between these eccentricities is dealt with in the sixth and seventh rows. Percentages indicate the portion of the visual field area that corresponds to the area given in square centimeters. An area between 30° and 50° eccentricity in the upper quadrant of left visual field has, for example, an extension of 415 cm

^{2}, which corresponds to 100% of the area between 30° and 50°. The patients’ initials are listed in the first column. The third and the fourth rows indicate the eccentricities of the borders of the visual fields in the upper (upper) and in the lower (lower) quadrants in a given visual hemifield being investigated. The rows below indicate areas of visual field defects (cm

^{2}). Percentages indicate the portion of the visual field loss that corresponds to the area of visual field defect given in cm

^{2}. Patient AS, for example, had a visual field defect measuring 194 cm

^{2}in the superonasal quadrant between 30° and 50° eccentricity. This corresponds to 46.8% of the superonasal quadrant field between 30° and 50° eccentricity in control subjects.

**Figure 1.**

**Figure 1.**