Learning/inattention artefact a more likely explanation.
I was interested to read Bekkelund et al’s account of an apparent
‘visual field constriction’ related to use of gabapentin (1).
Unfortunately, the authors seem to have overlooked the most common cause
of this type of visual field defect: artefact. Automated testing will
often give this pattern of ‘field defect’ in subjects who have difficulty
concentrating, have trouble following instructions, or are simply learning
to do the test. Usually, this type of artefact is apparent from the
‘reliability indices’ on the printout from the Humphrey Field Analyser
(2). Unfortunately, these data were edited out of Bekkelund’s field
plots, but this learning/inattention artefact can be present even if the
‘reliability indices’ appear to be good. It is common for this type of
‘field defect’ to appear variable and then resolve with repeated testing,
as the subject learns how to carry out the test. A similar report, of
‘reversibility of vigabatrin-induced visual field defect’ is also most
likely to represent learning/inattention artefact (3). Clinicians should
be aware of the limitations of automated testing when screening for visual
field defects.
1. Bekkelund SI, Lilleng H, Tonseth S. Gabapentin may cause
reversible visual field constriction. Br Med J 2006; 332:1193.
2. Heijl A, Patella VM. Essential Perimetry: The Field Analyzer
Primer, 3rd ed. Dublin, CA: Carl Zeiss Meditec Inc; 2002.
3. Versino M, Veggiotti P. Reversibility of vigabatrin-induced
visual-field defect. Lancet 1999 Aug 7;354(9177):486.
Competing interests:
TE was first author of the original paper on vigabatrin and visual field defects (reference 1 in Bekkelund's paper), and has received honoraria and travel expenses from the manufacturers of vigabatrin. He has been a paid adviser on medico-legal issues related to vigabatrin and visual fields.
Rapid Response:
Learning/inattention artefact a more likely explanation.
I was interested to read Bekkelund et al’s account of an apparent
‘visual field constriction’ related to use of gabapentin (1).
Unfortunately, the authors seem to have overlooked the most common cause
of this type of visual field defect: artefact. Automated testing will
often give this pattern of ‘field defect’ in subjects who have difficulty
concentrating, have trouble following instructions, or are simply learning
to do the test. Usually, this type of artefact is apparent from the
‘reliability indices’ on the printout from the Humphrey Field Analyser
(2). Unfortunately, these data were edited out of Bekkelund’s field
plots, but this learning/inattention artefact can be present even if the
‘reliability indices’ appear to be good. It is common for this type of
‘field defect’ to appear variable and then resolve with repeated testing,
as the subject learns how to carry out the test. A similar report, of
‘reversibility of vigabatrin-induced visual field defect’ is also most
likely to represent learning/inattention artefact (3). Clinicians should
be aware of the limitations of automated testing when screening for visual
field defects.
1. Bekkelund SI, Lilleng H, Tonseth S. Gabapentin may cause
reversible visual field constriction. Br Med J 2006; 332:1193.
2. Heijl A, Patella VM. Essential Perimetry: The Field Analyzer
Primer, 3rd ed. Dublin, CA: Carl Zeiss Meditec Inc; 2002.
3. Versino M, Veggiotti P. Reversibility of vigabatrin-induced
visual-field defect. Lancet 1999 Aug 7;354(9177):486.
Competing interests:
TE was first author of the original paper on vigabatrin and visual field defects (reference 1 in Bekkelund's paper), and has received honoraria and travel expenses from the manufacturers of vigabatrin. He has been a paid adviser on medico-legal issues related to vigabatrin and visual fields.
Competing interests: No competing interests