Poor fixation-and-following behavior in infants and young children can stem from a wide range of underlying causes. Diagnostics with imaging modalities such as fundus photography, fundus autofluorescence, fluorescein angiography, and optical coherence tomography are possible but typically require anesthesia. The saccadic vector optokinetic perimeter (SVOP), with its built-in eye-tracking system, was intended as a substitute for standard visual field testing in young children, but it still requires some cooperation and some degree of fixation.
Visual electrophysiology tests designed specifically for pediatric patients do not require anesthesia or pupil dilation. Tests that are based on flash stimulation do not require fixation. These tests provide objective assessments of the various groups of photoreceptor cells in the retina and of the entire optical pathway up to the visual cortex. More specifically, a combined recording of electroretinography (ERG) and visual-evoked potentials (VEP) can functionally dissect the visual pathway and identify the site of dysfunction in pediatric patients, whether the retina, optic nerve, or visual cortex is the primary cause of vision loss.
One feature of modern visual electrophysiology systems is that ERGs and VEPs can be recorded simultaneously, which is particularly convenient when recording infants and young children. Furthermore, once the electrodes are in place, flash and pattern tests can be performed sequentially within a single test session. In a webinar hosted by Diagnosys, Dr. Oliver Marmoy from Great Ormond Street Hospital (GOSH), London, demonstrated that a full suite of tests, including electrode placement, can be performed on a young child in under 30 minutes.
Flash ERGs adaptations for young children
In the early 1990s, GOSH developed an alternative protocol for electroretinography (ERG) testing in children, which is now widely used internationally. This approach categorizes retinal abnormalities into the rod system, the rod photoreceptor, the cone system, and those affecting the inner retina, which are reflected as individual components of the ERG waveforms.
A key aspect of this protocol is that it requires only 5-10 minutes of testing time, with natural pupils and minimal dark adaptation. It uses skin electrodes, which are safe for infants and young children. It also consists of delivering handheld flash stimulation from a sufficiently remote distance to minimize intimidation and enable testing in alert children of all ages. For infants and young children, interaction and play, with cartoons, music, and sounds, are used to garner attention and gaze for a successful recording.
“What’s that sound: a cow, a dog, a cat, a sheep, a duck, or a bell?” The ColorFlash from Diagnosys is optimized for testing children and infants with short attention spans and features built-in animal sounds.
During Dr. Marmoy’s 30-minute test session, we can observe him engaging his young subject with cartoons, play, and treats. In tests involving pattern stimuli, we can see him alternating between the stimulus test and the cartoons to get the child to fixate on the screen.
Glasgow sweep VEP
The Glasgow sweep Visually Evoked Potentials (sweep VEP) is an ISCEV extended protocol for objectively assessing visual acuity. It was designed for children and patients who have difficulty maintaining fixation. The method uses a thresholding algorithm that automatically adjusts the checkerboard size of the pattern VEP until the final threshold is reached. In a webinar hosted by Diagnosys, Dr. Ruth Hamilton from the Royal Hospital for Children, NHS Greater Glasgow & Clyde, Glasgow, U.K., demonstrated the method. The spatial frequency limit, which determines visual acuity, is based on the spatial frequency of the final step identified by the algorithm. This method can assess visual acuity from 20/20 to 20/2000.
Pattern stimulus adaptations for young children
Clinical researchers in the Netherlands developed a method of superimposing an animated cartoon on a pattern stimulus. This cartoon, known to children as La Linea, is drawn in a single line and depicts a man who is talking and moving around, with music in the background. The minimalist cartoon is optimal for this application that seeks minimal interference with the pattern stimulus. Although intended for children, it was evaluated on fifteen healthy adults. The researchers took the opportunity to record and analyze gaze movement on a continuum from fixation to saccades. The researchers found that, in pattern VEP, the P100 amplitude and peak time were reduced when they presented the cartoon compared with the standard test using the fixation point. While the reduction was deemed statistically significant, it was much smaller than the clinical limit range. Researchers concluded that the cartoon superimposed on the pattern stimulus was promising for young subjects.
Pattern VEPs for gene therapy monitoring in young children
The ophthalmology industry views the U.S. Food and Drug Administration (FDA) approval of Luxturna in 2017 and the European Medicines Agency (EMA) approval in 2018 as landmark milestones for retinal gene therapy. Diagnostic methods that helped Luxturna successfully complete drug trials included full-field stimulus test (FST) and multiluminance mobility tests (MLMT). However, because both tests require patient participation, clinicians understandably encounter difficulties getting young children to complete them reliably. Yet young children with RPE65 can develop visual impairment early.
Pattern VEPs need minimal cooperation and provide objective measures of the visual cortex. This test method was evaluated as a potential alternative to FST and MLMT for patient management of young children treated with Luxturna. The results were published in a recent study by clinical researchers affiliated with the Great Ormond Street Hospital for Children NHS Foundation Trust, the University College London, and The Tony Kriss Visual Electrophysiology Unit. This was a retrospective study of 27 eyes in children treated with Luxturna from 2020 to 2023. The researchers found that pattern VEPs in children were reproducible and showed increased amplitude after treatment.
An industry committed to advancing pediatric ophthalmology
Children too young to communicate with doctors about their visual health are particularly vulnerable. Visual electrophysiology can help. Its test modalities are objective and have been adapted for young children. Modern protocols do not require anesthesia or mydriasis. Clinicians have demonstrated the practicality of these protocols in diagnosing and managing very young patients. New visual electrophysiology studies focused on infants and young children continue to be published, adding to our knowledge base. Collectively, the visual electrophysiology community remains dedicated to advancing pediatric ophthalmology.