Sensitivity and specificity of the step VEP in suspected functional visual acuity loss
- 289 Downloads
Early and accurate diagnosis of functional visual loss (FVL) allows optimum management. Visual evoked potentials (VEPs) offer a means of objectively estimating acuity and therefore could assist with early and accurate diagnosis. The aim of this study was to assess the sensitivity and specificity of the step VEP in diagnosing FVL.
A retrospective audit was conducted in 36 school-aged children presenting with reduced visual acuity and clinical suspicion of FVL. All had undergone step VEP testing as part of their investigation. Medical notes were reviewed, and where necessary, referring centres, general practitioners or electronic clinical portals were consulted to obtain longer-term outcome data.
Twenty-seven of the 36 patients (75 %) were classified as having had FVL: all had a normal step VEP spatial threshold. Nine patients (25 %) had an organic cause for their acuity loss, of whom seven had abnormal step VEP spatial thresholds: the other two patients had some functional overlay to their organic disease. The step VEP sensitivity was 78 % (95 % confidence interval 40–96 %), and specificity was 100 % (95 % confidence interval 84–100 %).
The high specificity of the step VEP for FVL warrants increased suspicion of an organic cause should the step VEP spatial threshold be abnormal.
KeywordsVisual evoked potentials Visual acuity Conversion disorder Functional visual loss
The authors thank the following for providing some of the patients described in this series: Dr. A Brown, Dr. J Dudgeon, Dr. R Bowman, Dr. S Gupta, Dr. I Hanna, Dr. I Hunter, Dr. N Kennedy, Dr. J Kerr, Dr. D Mansfield and Dr. M O’Regan.
Conflict of interests
- 1.Chen CS, Lee AW, Karagiannis A, Crompton JL, Selva D (2007) Practical clinical approaches to functional visual loss. J Clin Neurosci 14:1–7Google Scholar
- 3.Mace CJ, Trimble MR (1991) ‘Hysteria’, ‘functional’ or ‘psychogenic’? A survey of British neurologists’ preferences. J R Soc Med 84:471–475Google Scholar
- 4.Taylor D (1997) Non-organic visual disorders. In: Taylor D (ed) Paediatric ophthalmology. Blackwell Science Ltd, London, pp 765–771Google Scholar
- 5.Behrman J (1969) The visual evoked response in hysterical amblyopia. Br J Ophthalmol 53:839–845Google Scholar
- 14.McBain VA, Robson AG, Hogg CR, Holder GE (2007) Assessment of patients with suspected non-organic visual loss using pattern appearance visual evoked potentials. Graefes Arch Clin Exp 245:502–510Google Scholar
- 17.Tyler CW, Apkarian P, Levi DM, Nakayama K (1979) Rapid assessment of visual function: an electronic sweep technique for the pattern visual evoked potential. Investig Ophthalmol Vis Sci 18:703–713Google Scholar
- 18.Mackay AM, Bradnam MS, Hamilton R, Elliot AT, Dutton GN (2008) Real-time rapid acuity assessment using VEPs: development and validation of the step VEP technique. Investig Ophthalmol Vis Sci 49:438–441Google Scholar
- 20.Brown B, Lovie-Kitchin J (1993) Repeated visual acuity measurement: establishing the patient’s own criterion for change. Optom Vis Sci 70(1):45–53Google Scholar
- 21.Mackay AM, Hamilton R, Bradnam MS (2003) Faster and more sensitive VEP recording in children. Doc Ophthalmol 107:251–259Google Scholar
- 23.Victor JD, Mast J (1991) A new statistic for steady-state evoked potentials. Electroencephalog Clin Neurophysiol 78:378–388Google Scholar
- 24.Meigen T, Bach M (2000) On the statistical significance of electrophysiological steady-state responses. Doc Ophthalmol 98:207–232Google Scholar
- 25.Mackay AM (2003) Assessing children’s visual acuity using steady-state evoked potentials. University of Glasgow. PhD ThesisGoogle Scholar