Clues to a neurologic diagnosis include a head size that is larger or smaller than normal, developmental delay, optic nerve abnormalities, and a falling off of the growth curves, Dr. Drack noted.
“In these cases, you definitely need to do magnetic resonance imaging (MRI) of the brain,” she said. “That may give you the answer.”
If the MRI is negative, proceed with electro-retinography (ERG), targeted genetic testing, or optical coherence tomography (OCT).
“A negative MRI should not be the last test in a nystagmus workup,” she said.
For vision-related nystagmus, look for iris transillumination, trouble seeing in the dark, photophobia in bright light, and/or a very high refractive error, Dr. Drack noted.
“You have to do a cycloplegic refraction, because untreated high refractive error can cause nystagmus,” she said.
Iris transillumination, in particular, can reveal if there is a need for OCT. If the child has trouble seeing in different lighting, an ERG test can help narrow the diagnosis.
“A visual evoked potential test can be helpful, but in my experience, it’s not as helpful as other tests,” she said.
At this point, consider genetic testing. For example, albinism has around 15 associated genes, some of which cause platelet and lung disorders.
“Parents may want pre-implantation genetic testing or other help with family planning,” Dr. Drack said.
Pediatric ophthalmologists must work closely with geneticists and genetic counselors to direct testing.
“We are much more familiar with these diagnoses than are geneticists,” she said.