Abstract
Purpose: :
To compare the performance in the early detection of loss of function in glaucoma of two electrophysiology tests, the multifocal visual evoked potential (mfVEP) and the multifocal electroretinogram (mfERG), with one visual field test, the Frequency-Doubled Perimetry (FDP).
Methods: :
Full-threshold Humphrey Visual Field (HVF) perimetry was used to identify patients with asymmetry visual field loss in whom one eye had no visual field defects detectable and was classified as the "unaffected" eye, while the other had well-defined visual field defects in one hemifield and was classified as the "affected" eye. Fourteen patients were identified who underwent mfVEP, mfERG and FDP tests. To provide better coverage of the visual field, we used an mfVEP stimulus with 120 sectors and applied local spatial averaging to improve the signal-to-noise ratio. For the mfERG recordings the global flash paradigm was used to emphasize and evaluate the inner retinal response contributions, or what we call the "Optic Nerve Head Component" (ONHC). Stimulation for both mfVEP and mfERG and analysis for mfVEP were performed with the VERIS 5 Science system. Custom software that objectively evaluates ONHC was used for analyzing the mfERG data. For the FDP test, we used the 30-2 FDT Threshold program (Humphrey).
Results: :
For the 14 affected eyes, the mfVEP with inter-ocular comparison, mfERG, and FDP demonstrated an abnormality in the same location in all eyes, confirming the HVF results. In the 14 unaffected eyes, FDP revealed visual field defects in 8 eyes (53.3%). The mfERG showed an abnormality in 6 of 14 eyes (42.8%), while in 5 of these 6 eyes the defective area had the same hemifield location as detected by FDP. In one unaffected eye the mfERG detected an abnormality, while FDP results were normal. In the 8 unaffected eyes that FDP detected an abnormality, 6 eyes had visual field defects in a different location compared to the affected eye. In these 6 eyes, mfERG showed an abnormality in 3 eyes and mfVEP with inter-ocular comparison demonstrated local unilateral abnormality in 2 eyes consistent with FDP and mfERG results.
Conclusions: :
Our comparisons suggest that there is about 50 % probability that the mfERG and FDP detect visual dysfunction in unaffected eyes of patients with early glaucoma. In most cases the abnormalities found by the two tests are located in the same hemifield. In these highly asymmetry cases the mfVEP with inter-ocular comparison showed good agreement with the HVF results, but clearly does not address the question of possible dysfunction in the unaffected eye.
Keywords: neuro-ophthalmology: diagnosis • optic nerve • clinical research methodology