Key research and practical information to inform INS care
Reviewed by Fiona Rowe

This ‘tutorial’ format paper aims to translate key research findings and conclusions into practical terms, discuss their clinical utility and introduce a new clinical method that accurately measures the static visual deficits in infantile nystagmus (INS), predicts the improvements that may be expected from treatment and provides accurate outcome measures of treatment. The paper outlines that all patients with INS have the same nystagmus waveforms (NAFX) and variations whether there is an associated visual sensory deficit or not. The direct cause of these waveforms is a failure of calibration of the smooth-pursuit damping mechanism. Best-corrected visual acuity (BCVA) depends on the quality of the foveation periods alone, independent of the rest of the nystagmus waveform. There are a number of specific types of nystagmus including INS, fusion maldevelopment syndrome, nystagmus blockage syndrome and spasmus nutans. The main type of nystagmus in INS is pursuit-system nystagmus. INS evaluations should be made binocularly because occlusion can significantly change in the INS nature. A single distance VA measure is insufficient. Distance VA should consist of at least three measurements along with measurement of near VA. This is to provide an adequate measurement of total static visual function deficits. The author suggests three distinct measures of distance VA: binocular BCVA tested at the INS null and tested at 15 degrees to the right and left of the null. Use of these measurements can generate a HAFZ value. Surgical management can include null-shifting procedures, Anderson recessions plus tenotomy and reattachment of the remaining two rectus muscles, or tenotomy and reattachment of all four rectus muscles in the plane of the nystagmus. The author concludes that eye movement recording and the NAFX provide repeatable accurate nystagmus diagnosis and evaluation. Without access to eye movement recording, careful clinical observations and measurements can be used to inform management decisions.

A new clinical method for visual function evaluation including estimation and measurement of therapeutic effectiveness: lessons from infantile nystagmus research.
Dell’Osso L.
JOURNAL OF PEDIATRIC OPHTHALMOLOGY AND STRABISMUS
2021;58:188-95.