Electrophysiology of the eye in diagnosis of refractive anomalies in preschool children
DOI:
https://doi.org/10.13112/pc.1063Keywords:
ELECTROPHYSIOLOGY; REFRACTIVE ERRORS; EVOKED POTENTIALS, VISUALAbstract
Electrophysiological testing provides an objective and non-invasive method for assessing the visual pathway. The use of various electrophysiological procedures allows for precise characterization and localization of dysfunction within the visual system. In a newborn's eye, the density of neurons in the retina is significantly lower, as is the density of synapses both in the retina and the visual cortex. For these reasons, the visual acuity of a newborn is significantly lower compared to an adult. The development of vision is determined by the immaturity of the entire system from the retina, and fovea, through the visual pathway to the brain.
Refraction represents the relationship between the refractive power of light rays in the eye and the length of the eye without the use of accommodation. Thus, we differentiate between emmetropia (the normal state of a healthy eye) and ametropia (axial or refractive).
The process of emmetropization is most sensitive to errors during the first year of life if the stimulus for the development of retinocortical connections is inadequate, due to deprivation of visual signals, blurriness present in anisometropia, or deviation of the visual axis in strabismus. Refractive errors favor the development of numerous serious eye diseases. Eye diseases that cause visual impairment are often associated with high ametropia.
Each of the electrophysiological examinations assesses the function of the visual pathway at a specific level. The electrophysiological tests of visual function include:
- VEP (visual evoked potentials)
- ERG (electroretinogram)
- EOG (electrooculogram)
- PERG (pattern or structured electroretinogram)
- FERG (focal electroretinogram)
- MERG (multifocal electroretinogram)
Studies show that refractive errors blur the stimulus and cause defocusing, leading to significant changes in VEP (P100 latency and amplitude). VEPs are particularly sensitive to myopia compared to hyperopia, although both types of refractive errors cause image defocusing on the retina.
When conducting VEP tests, it is crucial to correct refractive errors as they significantly affect the interpretation of results. Therefore, the correction of refractive errors should be an indispensable part of these tests.
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