ABSTRACT
The review discusses literature data on the clinical relevance of functional assessment of magno- (M), parvo- (P), and koniocellular (K) pathways. It also covers the differential contribution of the M, P, and K channels to visual impairments and how it determines the prognosis, early diagnosis, and treatment choice in patients with neurodegenerative diseases of the retina and brain. Selective changes in the performance of the visual channels are investigated by the example of glaucoma and optic neuritis in multiple sclerosis (MS) patients. A detailed analysis of pattern electroretinogram and visual evoked potentials in response to pattern stimuli of varying luminance and chromatic contrast in glaucoma and MS and characteristic functional alterations (objective markers of pathology of the visual pathways) are presented.
Subject(s)
Vision Disorders , Visual Pathways , Electroretinography/methods , Evoked Potentials, Visual/physiology , Humans , Photic Stimulation/methods , Vision Disorders/diagnosis , Vision Disorders/etiology , Vision Disorders/physiopathology , Visual Pathways/diagnostic imaging , Visual Pathways/physiopathologyABSTRACT
In this paper, technical details of visual evoked potentials (VEP) assessment and pattern electroretinography (PERG) are reviewed. Both methods are used to perform an objective functional examination of visual channels and to clarify the level, at which they have been damaged. Contributions of parvo- (P), magno- (M) and koniocellular (K) systems to the morphology of PERG and VEP responses are discussed with account to test conditions, selectively supportive of the activity of particular cell populations. The review analyzes the physiological role of such stimulation parameters as brightness and color contrast of the pattern elements as well as spatial and temporal frequency in detecting dysfunction of color channels and mistuning of the P- and M- pathways. Different times taken for neuronal integration and signal conduction along the M- and P- pathways determine the timing of the P- and M- VEP components, allowing us to judge their contribution to VEP morphology from the same recording.
Subject(s)
Electroretinography/methods , Evoked Potentials, Visual , Visual Pathways/physiopathology , Diagnostic Techniques, Ophthalmological , HumansABSTRACT
UNLABELLED: Early diagnosis of primary open-angle glaucoma (POAG) is closely connected with detection of normal age-related changes in the retina. It is also essential to develop reliable methods for quantitative evaluation of retinal nerve fiber layer (RNFL) thickness and retinal ganglion cells (RGCs) structure and function as well as to extend opportunities for inter-instrumental comparisons. AIM: to assess the function of RGCs from parvo- and magnocellular pathways by means of pattern electroretinography and to evaluate the degree of retinal sensitivity loss and RNFL thickness using new methods of analysis in normal aging and the early stage of POAG. MATERIAL AND METHODS: Four groups were formed: group 1 - young healthy participants, group 2 - aged controls, group 3 - glaucoma suspects, and group 4 - early-stage POAG patients. In all groups we investigated the MD and PSD indices of static computer perimetry (HEP, Heidelberg Edge Perimeter, SAP and FDF tests) and RNFL thickness provided by HRT III (Heidelberg Engineering). Pattern electroretinograms (PERGs) were recorded with the RETImap system (Roland Consult) at the check sizes of 0.8° and 16°. For steady-state and transient PERGs the 0.8°/16° and N95/P50 ratios were calculated, respectively. RESULTS: There was a statistically significant difference in PERG amplitudes to 0.8° checks (p=0.0001) and in 0.8°/16° ratios (p=0.0001) between the groups 1 and 2. Differences between the groups 2 and 3 as well as 3 and 4 were statistically significant only as to 0.8° checks (p=0.03 and p=0.001, respectively). Responses to 16° checks were alike in all groups. We have also applied original formulas to determine the relative loss of RGCs and their axons and the congruence coefficient for morphological and functional parameters in normal aging and the early stage of POAG. CONCLUSION: The discovered age-related PERG changes convincingly indicate a greater parvocellular RGC loss as compared to magnocellular. Thus, the PERG ratio (0.8°/16°) should be corrected for the subject's age. The proposed indices of relative decline in retinal light sensitivity and RNFL thinning have been shown to be useful for quantifying the loss of RGC bodies and axons in normal aging and early-stage glaucoma.
