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Altitudinal visual field defects are commonly associated with ischaemic optic neuropathy and hemibranch artery or vein occlusion. Less commonly, altitudinal visual field defects can be seen in advanced glaucoma. Artefactual visual field defects are not uncommon; however, to our knowledge this is the first reported case of an artefactual uniocular altitudinal visual field defect due to an abnormally sensitive hemifield response with the automated Humphrey perimeter.
A healthy 61 year old woman was referred to the ophthalmology department by her optician who had noted a visual field defect in her left eye following a routine examination. The patient was asymptomatic and her past ocular history was unremarkable. Initial assessment of the visual field carried out by the optician appeared to show a superior altitudinal field defect in the left eye (Fig 1). Ocular examination revealed 6/5 corrected vision and normal intraocular pressures in either eye. There was no relative afferent pupil defect and both optic discs were healthy. Fundus examination was otherwise unremarkable. Confrontational visual field test failed to show any defect. Goldmann visual field testing confirmed normal fields in both eyes. Closer examination of the Humphrey field test carried out by the optician shows the defect to be artefactual.
Altitudinal visual field defects are most commonly associated with ischaemic optic neuropathy and hemibranch artery or vein occlusion. They can also be seen in patients with glaucoma, chiasmal lesions, and optic nerve lesions such as colobomas. Hysterical or malingering patients and individuals deliberately attempting to mislead the Humphrey machine can manifest visual field defects including altitudinal defects on perimetry.1,2
In this reported case the pattern deviation plot initially appears to show a superior altitudinal field defect. However, scrutiny of the threshold sensitivities on the grey scale data reveals that the patient had somehow achieved abnormally high sensitivities in the inferior hemifield only (highest value 50 dB). The threshold sensitivities for the superior hemifield appear normal to slightly high (highest value 37 dB). Hence the pattern deviation defect is not only artefactual but also paradoxical. One can only speculate as to the cause of this artefactual field defect. Patient anxiety often leads to false positive responses and this patient had 67% false positive errors. However, it is curious that this should occur in one hemifield and in one eye only. One must always consider the possibility of either technical problem in stimulus presentation or machine software problems in unexplained or anomalous visual field defects. However, it is difficult to explain the pattern of this visual field defect on the basis of machine failure. This case demonstrates the importance of looking at the pattern deviation in conjunction with the grey scale, threshold sensitivities and interpreting the visual field in the light of other clinical data.