Comparing multifocal VEP and standard automated perimetry in high-risk ocular hypertension and early glaucoma.

PURPOSE

To compare the diagnostic performance of multifocal visual evoked potential (mfVEP) and standard automated perimetry (SAP), in eyes with high-risk ocular hypertension or early glaucoma.

METHODS

Both eyes of 185 individuals with high-risk ocular hypertension or early glaucoma were evaluated. Subjects ranged in age from 37 to 87 (mean +/- SD: 61 +/- 11 years). Pattern-reversal mfVEPs were obtained by using VERIS (Electro-Diagnostic Imaging, San Mateo, CA) with a four-electrode array and were analyzed with custom software. SAP visual fields (SITA-standard; Carl Zeiss Meditec, Inc., Dublin, CA) were obtained within 22.3 +/- 27.0 days of the mfVEP. Stereo disc photographs and Heidelberg Retina Tomograph (HRT) images were obtained during one visit, which was within 24.8 +/- 50.4 days of the mfVEP and 33.1 +/- 62.9 days of the SAP visual field. Abnormalities on the mfVEP were defined by using a variety of cluster criteria: SAP with pattern standard deviation (PSD) P </= 0.05 or glaucoma hemifield test (GHT) outside normal limits, according to OHTS criteria (SAP-OHTS). In separate analyses cluster criteria were used to determine SAP abnormalities. Disc photographs were graded as either glaucomatous optic neuropathy (GON) or normal by two independent masked experts, and disagreements were adjudicated by a third masked expert. The overall Moorfields regression analysis (MRA) result from the HRT was used as a separate diagnostic classification. All eyes classified as "borderline" by the MRA were assigned to the normal category (i.e., "within normal limits"). Sensitivity for mfVEP or SAP was defined as the percentage of GON eyes that had an abnormality on the functional test. Specificity for mfVEP or SAP was defined as the percentage of eyes with normal optic disc structure that had normal functional test

RESULTS

results. Disc photographs from 50% of eyes were graded GON. Both eyes were graded GON in 71 (38%) of the 185 subjects. Exactly half as many eyes were abnormal by HRT MRA. The average SAP mean deviation (MD) was +0.3 +/- 2.1 dB; average PSD was 2.3 +/- 1.9 dB. By OHTS criteria, 83 (22%) of the 370 eyes had an abnormal SAP. Depending on the cluster criterion used, the proportion of eyes with an abnormal SAP ranged from 8% to 26% and with an abnormal mfVEP, from 14% to 45%. A criterion with an estimated specificity in normal subjects of 91% resulted in 102 (28%) eyes with an abnormal mfVEP. For criteria with estimated specificities of 95% and 99%, respectively, 88 (24%) eyes and 52 (14%) eyes had an abnormal mfVEP. Agreement between SAP and mfVEP ranged from 75% to 81%. The sensitivity of SAP-OHTS to detect GON (using the disc photograph as diagnostic standard) was 29%, whereas specificity was 84%. Sensitivity of the mfVEP to detect GON, for cluster criteria with disc structure specificity between 84% and 87%, ranged from 28% to 32%. When the HRT MRA was used as the diagnostic standard, sensitivities of both functional tests to detect GON increased to 42%.

CONCLUSIONS

The diagnostic performance of mfVEP was similar to that of SAP. However, the two modalities agreed in only approximately 80% of eyes, suggesting that they may detect slightly different functional deficits.