Abstract
Purpose: :
To compare the diagnostic performance of mfVEP and SAP in eyes with high–risk ocular hypertension or early glaucoma.
Methods: :
185 individuals with high–risk ocular hypertension or early glaucoma ranged in age from 37 to 87 (mean ± SD: 61 ± 11 yrs). Pattern–reversal mfVEPs were obtained using VERIS, a 4–electrode array, and analyzed with custom software.1 SAP visual fields were obtained using the SITA–standard threshold algorithm within 22.3 (± 27) days of the mfVEP. Abnormalities on the mfVEP were defined using a variety of cluster criteria.2 Abnormalities on SAP were defined as pattern standard deviation (PSD) p < 0.05 or GHT ONL (OHTS criteria). A stereophotograph of each optic disc, taken within 19 (± 27) days of the mfVEP, was graded as either glaucomatous (GON) or normal (N) by two independent masked experts, disagreements were adjudicated by a third masked expert. Sensitivity for mfVEP or SAP was defined as the % of GON eyes that had an abnormality on the functional test. Specificity was defined as the % of N eyes that had a normal functional test.
Results: :
Disc photos from 50% of eyes were graded GON. In 71 subjects (38%) both eyes were graded GON. The average SAP mean deviation (MD) was 0.3 ± 2.1 dB (range +3.9 to –10.1 dB); average PSD was 2.3 ± 1.9 dB (range 1.0 to 16.1 dB). By OHTS criteria, 83 eyes (22%) had an abnormal SAP. The abnormality rate for mfVEP ranged from 14 to 45%, depending on the cluster criterion used. Using a criterion with a specificity2 of 90%, 102 eyes (28%) had an abnormal mfVEP. For criteria with specificities of 95% and 98.5%, respectively, 88 eyes (24%) and 52 eyes (14%) had an abnormal mfVEP. Concordance between SAP and mfVEP ranged from 75 to 81%. Sensitivity of SAP to detect GON, using OHTS criteria, was 29%, while specificity was 84%. Sensitivity of the mfVEP to detect GON, for cluster criteria with specificity between 84 and 87%, ranged from 28% to 32%.
Conclusions: :
The mfVEP and SAP performed in a similar manner. However, they agreed in only ∼80% of eyes, suggesting that they may detect slightly different deficits. The diagnostic performance of both SAP and the mfVEP were relatively poor when GON was used as a reference standard. This suggests that structural and functional abnormalities do not correlate well in early glaucoma, and questions use of one as a reference standard for the other. [1] Hood & Zhang 2000 [2] Fortune et al. 2004
Keywords: visual fields • electrophysiology: clinical • optic disc