Korean J Ophthalmol.  2014 Feb;28(1):49-65. 10.3341/kjo.2014.28.1.49.

Evaluation of Hemifield Sector Analysis Protocol in Multifocal Visual Evoked Potential Objective Perimetry for the Diagnosis and Early Detection of Glaucomatous Field Defects

• Mousa MF
• Cubbidge R
• Al-Mansouri F
• Bener A

• KMID: 1792094
• DOI: http://doi.org/10.3341/kjo.2014.28.1.49

Abstract

PURPOSE
Multifocal visual evoked potential (mfVEP) is a newly introduced method used for objective visual field assessment. Several analysis protocols have been tested to identify early visual field losses in glaucoma patients using the mfVEP technique, some were successful in detection of field defects, which were comparable to the standard automated perimetry (SAP) visual field assessment, and others were not very informative and needed more adjustment and research work. In this study we implemented a novel analysis approach and evaluated its validity and whether it could be used effectively for early detection of visual field defects in glaucoma.
METHODS
Three groups were tested in this study; normal controls (38 eyes), glaucoma patients (36 eyes) and glaucoma suspect patients (38 eyes). All subjects had a two standard Humphrey field analyzer (HFA) test 24-2 and a single mfVEP test undertaken in one session. Analysis of the mfVEP results was done using the new analysis protocol; the hemifield sector analysis (HSA) protocol. Analysis of the HFA was done using the standard grading system.
RESULTS
Analysis of mfVEP results showed that there was a statistically significant difference between the three groups in the mean signal to noise ratio (ANOVA test, p < 0.001 with a 95% confidence interval). The difference between superior and inferior hemispheres in all subjects were statistically significant in the glaucoma patient group in all 11 sectors (t-test, p < 0.001), partially significant in 5 / 11 (t-test, p < 0.01), and no statistical difference in most sectors of the normal group (1 / 11 sectors was significant, t-test, p < 0.9). Sensitivity and specificity of the HSA protocol in detecting glaucoma was 97% and 86%, respectively, and for glaucoma suspect patients the values were 89% and 79%, respectively.
CONCLUSIONS
The new HSA protocol used in the mfVEP testing can be applied to detect glaucomatous visual field defects in both glaucoma and glaucoma suspect patients. Using this protocol can provide information about focal visual field differences across the horizontal midline, which can be utilized to differentiate between glaucoma and normal subjects. Sensitivity and specificity of the mfVEP test showed very promising results and correlated with other anatomical changes in glaucoma field loss.

Keyword

Glaucomatous field loss; Multifocal visual evoked potential; Objective perimetry; Standard automated perimetry

MeSH Terms

Adult
Aged
*Early Diagnosis
Evoked Potentials, Visual/*physiology
Female
Follow-Up Studies
Glaucoma/complications/*diagnosis/physiopathology
Humans
Intraocular Pressure/*physiology
Male
Middle Aged
Reproducibility of Results
Retrospective Studies
Scotoma/*diagnosis/etiology/physiopathology
Visual Field Tests/*methods
Visual Fields/*physiology
Young Adult

Figure

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  Fig. 1 The typical multifocal visual evoked potential signal is divided into two parts (windows) according to implicit time. The signal window between 0 to 200 msec and the noise window between 300 to 500 msec. Signal to noise ratio is calculated based on this division of the waveform.

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  Fig. 2 The five allocated hemi-rings and their corresponding fellows in both hemispheres (A). The allocated six sectors and their corresponding fellows in both hemispheres (B). SR = superior hemi-ring; IR = inferior hemi-ring; SS = superior sector; IS = inferior sector.

• 

  Fig. 3 The 58 segments of the right visual field. The field is divided into two identical hemifields across the horizontal meridian; each segment has a similar correspondent in the opposite hemifield. (A) Signal to noise ratio (SNR) value is calculated for each segment. The average SNR of wedge sectors (B) and semicircular sectors; peripheral and central sectors (C,D) are calculated to compare their values to fellow corresponding sectors on the opposite hemifield.

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  Fig. 4 Receiver operating characteristic analysis for the glaucoma suspect group by multifocal visual evoked potential testing in the glaucoma suspect group.

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  Fig. 5 Receiver operating characteristic analysis for the glaucoma group by multifocal visual evoked potential testing in the glaucoma suspect group.

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  Fig. 6 Box plot of signal to noise ratio (SNR) values of multifocal visual evoked potential in normal, glaucoma suspect, and glaucoma groups. There was a significant difference between the mean values among the three study groups.

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  Fig. 7 Box plot of the difference in signal to noise ratio (SNR) values of multifocal visual evoked potential in normal, glaucoma suspect, and glaucoma groups. There was a significant difference between the mean values among the three study groups.

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