Louise Gagnon

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Improving the paediatric eye examination can be achieved with several small steps, according to Mr Jeff Locke, a past co-president of the Canadian Orthoptic Society. Mr Locke is an orthoptist/instructor and team lead in the visual electrophysiology lab at IWK Health in Halifax, Nova Scotia, Canada.

“We can streamline things and make the examination 1% better by being more competent in assessing visual acuity, checking for binocular single vision, and knowing what visual electrophysiology can do in this age group,” he said.

For vision to be normal, stimuli need to get through our optics to the retina, for the retina to relay to the optic nerve and for the optic nerve to relay to the cortex. “Acuity can be based on what aspects of the pathway are stimulated,” Mr Locke explained.

To benchmark 20/20 vision in an infant, the testing types and acuity being measured need to be altered. “We need to shift to more detection-based acuity versus recognition,” he said. In pre-verbal children, forced-choice preferential looking (FPL) tests such as Cardiff and Teller are not the most accurate in detecting and managing amblyopia, he pointed out. He noted that it is easy to become complacent with FPL tests and stop documenting those earlier learned tests.

As a child reaches more visual milestones as they age from newborn to 1 year, the physician can perform more complex testing. “It does not mean that those tests administered during earlier milestones [when a child was younger] are no longer useful,” he explained. “They can add great qualitative aspects to your vision examination.”

Indeed, vision testing in infants needs to have qualitative more than quantitative assessments, Mr Locke explained. A quantitative test such as the FPL test serves as a benchmark for normal vision in infants and provides a value over time, he noted. That said, qualitative tests are quick to perform and can aid in detecting asymmetry in vision, he added.

In terms of vision assessment tests, Mr Locke pointed to research which concluded that optokinetic nystagmus induction methods have been found to be suboptimal in determining visual acuity thresholds. He noted, however, that they can be a great qualitative indicator of the visual pathway since intact pursuit and saccadic centres are needed, as is normal cranial nerve innervation to the extra-ocular muscles.

Mr Locke pointed out that more recent research

 has suggested a strategy for a paediatric visual acuity examination. “[The study authors] advised for best compliance to start with binocular visual acuity with Cardiff at 50 cm, followed by induced tropia,” he said.

“Once these are successfully completed, you can then try monocular visual acuity at 50 cm with your FPL Cardiff [test]. Their view was that assessing both FPL Cardiff at 50 cm and induced tropia allows for more accurate visual assessment and allows practitioners to obtain more information should they lose cooperation [from the paediatric patient].

An educated assumption is being made based on observational data and detection-based acuity with paediatric examinations, Mr Locke explained. “When trying to make a comparison between detection type of acuities, like with forced-choice preferential looking, we are likely overestimating acuity, and it becomes challenging to detect mild to moderate levels of amblyopia,” he said.

“Each detection type of acuity has shown validity in assessing the paediatric population, but the sensitivity in detecting amblyopia is variable among tests. None appear to be as robust as crowding-based testing.”

The goal needs to be to maximise the visual examination by combining multiple methods of detection-based testing, not only to increase the sensitivity but also to gain more general knowledge of the paediatric patient’s ocular health, Mr Locke said. “Do as much as you can binocularly [assessment] while the child is getting comfortable with you, but at the same time, you are extracting data.”

The eye lane triangle method is demonstrated, including positions for the examiner and patient. (Image courtesy of Mr Jeff Locke)

Mr Locke stressed that the FPL test outcome should not be the only endpoint in a paediatric vision assessment. “Make your exam 1% better by adding a qualitative measurement into the mix,” he said. And for those who do not use the FPL test, Mr Locke advised setting a grading standard across the clinic for fixation testing to help follow amblyopia over time, noting that children do not need to be old enough to respond verbally before binocularity is assessed.

There are, however, some objective methods being employed to provide a sense of binocularity. “We can test motor fusion capability in infants, and newer investigations in the use of the FPL test in stereopsis are emerging,” he said. Detecting stereopsis will help to guide a care plan and add confidence to the visual acuity assessment, Mr Locke noted.

He said that the challenge with visual electrophysiology in paediatrics is that most of the tests require an infant or toddler who is being assessed to cooperate for accurate results to be obtained; this means the tests are not always practical, with the exception of the electroretinogram (ERG), which can be done under sedation.

“The ERG is our bread and butter, but they cannot localise dysfunction specifically to the macula,” he said. Visually evoked potentials (VEPs) offer an objective measurement at the cortex, but anomalies at any level of the optic pathway (optics, macula, optic nerve, optic pathway) can result in VEP pathology, he noted.

Another clinical pearl that Mr Locke offered is that assessors should avoid having their backs turned to their paediatric patients. He suggested placing the computer screen where information is being inputted in such a way as to maintain a line of sight to the child being assessed.

This article is based on a presentation at the virtual 31st annual Jack Crawford Day paediatric ophthalmology update. Mr Locke has no financial disclosures related to this content.

1. Kutschke PJ. Preverbal assessment for amblyopia. Am Orthopt J. 2005;55:53-61.

2. Nanda KD, Blaha B, Churchfield WT, et al. Induced tropia test and visual acuity testing in nonverbal children. J Binocul Vis Ocul Motil. 2018;68:134-136.

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