Purpose
There is a high potential for multifocal Visual Evoked Potential (mfVEP) techniques to objectively measure functional visual loss in glaucoma prior to Standard Automated Perimetry (SAP). We conducted a prospective, observational clinical study in a long-term cohort to evaluate the performance of Low Luminance Achromatic (LLA) and Blue-on-Yellow (BonY) mfVEP stimuli presentation in the detection of pre perimetric glaucoma.
Methods
Pre perimetric glaucoma (glaucomatous optic discs as judged by stereo disc photography and normal standard visual fields) subjects enrolled from a glaucoma clinic underwent complete ophthalmic examination including LLA mfVEP, BonY mfVEP, Ocular Coherence Tomography (OCT) and Heidelberg Retina Tomograph (HRT) at baseline and annually thereafter. SAP was performed at two baseline visits and followed up every 6 months. Criteria for minimum scotoma for the various functional tests were established. The mean follow up duration was 3.1±0.8 years.
Results
Seventy-two eyes of 46 subjects (Mean age 64.59±6.66 years) confirmed pre perimetric glaucoma. Of these, progression on SAP was detected in 17 eyes (23.6%). Despite a normal SAP at baseline in 72 eyes, low contrast mfVEP (22%), BonY mfVEP (26%), OCT (86%) and HRT (81%) showed abnormalities. Amongst 17 progressive eyes, abnormalities were detected on low contrast mfVEP (47%), BonY mfVEP (53%), OCT (82%) and HRT (88%) prior to detection on HVF. OCT and HRT borderline values were considered abnormal. Low contrast and BonY mfVEP identified hemifield changes 9±5.5 months prior to progression on HVF. The location of hemifield defect on low contrast mfVEP and BonY mfVEP corresponded topographically to the defect detected on HVF in 41% (7 out of 17) of eyes.<br />
Conclusions
Amongst functional tests, LLA and BonY mf VEP appear to have the potential to detect changes in function prior to standard automated perimetry (SAP) with moderate topographic correspondence. However, there was only a moderate level of correlation with structural change.