The pattern electroretinogram was recorded in patients with initial stages of visual field defects due to open-angle glaucoma and in age-matched normal subjects. Both normal subjects and glaucoma patients had a visual acuity above 0.8. Counterphasing checkerboard patterns were used as visual stimuli with a range of check sizes from 0.8 degree to 15 degrees at 7.8 reversals/s. Whereas the amplitude in glaucoma patients was nearly normal for large check sizes, it was significantly reduced for small check sizes (p = 0.003). Possibly two separate mechanisms that generate the pattern electroretinogram for small and large checks are differentially affected; they may be related to the magnocellular and parvocellular systems. The difference between normals and glaucoma patients was even more significant when the ratios of the amplitudes at small and large check sizes were compared (p less than 0.0002). When this ratios is used, the amplitude variability can be partly overcome and the pattern electroretinogram can be a sensitive indicator of ganglion cell function.

An alternating checkerboard pattern subtending a visual angle of 25 min arc is capable of eliciting remarkably high amplitudes of visually evoked potentials (VEP) outside a visual angle of 2.5 degree. These contributions cannot be neglected when evaluating a VEP response obtained with a larger field of stimulation. When the retina is consecutively stimulated by concentric frame-shaped stimuli, the algebraic sum of all single cortical responses augmented the cortical response obtained when stimulating the whole field simultaneously by approximately 30%. This finding may be explained by the inhibiting interactions within the receptive field organisation of the retina.

A target screen stimulus takes into account the necessity of larger checkerboard patterns with rising eccentricity. The target pattern should be calculated to fit the retinocortical magnification factor. This proposition is based on the working hypothesis that for maximal visual evoked potential (VEP) amplitude the stimulus should appear on the cortex as an undistorted checkerboard pattern. We describe the cortical response elicited by four different target screen stimuli based on a similar algorithm. No significant difference to normal checkerboard was found.

Loss of the crystalline lens into the vitreous cavity can lead to corneal damage and expulsive hemorrhage. In this technique, the lens is released from adhesions by vitrectomy and then extracted from the vitreous cavity by phacoemulsification using a special tip. No protective liquids are used to cover the retina. This technique was successful in 44 patients.

Along the processing chain in the visual pathway the pattern electroretinogram (PERG) is a better indicator of the peripheral function than the visual evoked potential (VEP). Therefore the PERG and the VEP will be impaired equally by disturbances before the ganglion cell layer (e.g., blurred image or retinal disease) and differently by further centrally located diseases (e.g., tumor compression of the optic nerve). Thus in patients complaining of reduced visual acuity who show disturbed VEP but a normal PERG, malingering can be definitely ruled out. Representative combinations of PERG and VEP findings are described.