Observational/Prospective Study for Benchmarking the Management of Glaucoma With Selective Laser Trabeculoplasty (SLT) or Trabecular Stent Bypass Microsurgery, Using the Diopsys Visual Evoked Potential/Pattern ERG Protocols

The VEP and PERG have been proven and accepted as a viable clinical tool in the assessment of diseases of the retina ganglion cells. The Diopsys® Neuro Optic Vision Assessment Vision (NOVA) Testing System generates a battery of retinal responses evoked by viewing horizontal/checkerboard grating patterns with optimized contrast levels and visual field sizes.

Electrophysiological tests evaluate the function of the different structures constituting the visual nervous pathways (retina, optic nerve, optic tract, and chiasm, radiation and cerebral cortex). Among the various electrophysiological examinations, two very important tests are Electroretinograms (ERGs), which study the various retinal components, and Visual Evoked Potentials (VEPs) which study the visual pathway. These tests provide objective information on the function of the visual system even in those cases in which opacities of dioptric means (cataract, corneal leukoma) do not allow the direct observation of the retina and optic nerve, and may provide functional information in advance of structural changes.

Maculopathy and neuropathies are included in the long list of diseases of the visual pathway that permanently impair visual function. As there are considerable evidences related to the nature and evaluation of maculopathy and glaucomatous neuropathy, objective and reliable techniques are needed for visual function evaluation. By using PERG recordings, doctors are able to differentiate between normal subjects and subjects with ocular hypertension notwithstanding a normal optic disc and VF. PERG can provide important diagnostic information regarding the functional integrity of the macula and ganglion cells.

Based on a longitudinal study from Bascom Palmer Eye, abnormal retina function was recorded by PERG eight years before structural damage to the RNFL was detected. The study suggests that for glaucoma suspects it takes two years for a 10% change in PERG amplitude while it takes ten years for 10% change in RNFL.

The Diopsys® NOVA-pERG is a retinal biopotential that is evoked when a temporally phase-reversed horizontal/checkerboard grating pattern of constant total luminance is viewed. The contrast and viewing angle of the stimulus is optimized to elicit detection of dysfunction of the macula or the retinal ganglion cells selectively. The two NOVA-PERG reporting protocols are Contrast Sensitivity (CS) and Concentric Stimulus Fields (CSF). CS is optimized to detect dysfunctions of the retina that are sensitive to discrimination between different contrast levels while the CSF is optimized to localized pathologies in specific regions of the retina such as central vision and macula. Currently both protocols utilize steady-state technology.