Foveation dynamics in congenital nystagmus IV: vergence
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To evaluate foveation dynamics and characteristics of vergence eye movements during fixation of static targets at different distances and while tracking a target moving in depth in a subject with congenital nystagmus (CN).
Eye movements of a well-studied subject with CN were recorded using the magnetic search coil technique and analyzed using the OMtools software, including the eXpanded Nystagmus Acuity Function (NAFX).
Both the phase planes and NAFX values during fixation of targets at various near distances were equivalent to those during fixation of a far target. When applied to vergence data, the NAFX values (“binocular” NAFX) were higher than for the individual eye data. Vergence tracking of targets moving in depth was demonstrated and was accurate for targets moving at speeds up to ~ 35°/sec.
Target foveation qualities during fixation of targets at various near distances were equivalent to that during fixation of a far target. Stereo discrimination was limited by the foveation quality of the eye with the higher NAFX waveform. Foveation period slopes during vergence tracking demonstrated vergence movements despite the ongoing CN oscillation. Similar to what we found with fixation, pursuit, and the vestibulo-ocular systems, these findings establish that vergence in both static and dynamic viewing conditions functions normally in the presence of the CN oscillation.
KeywordsCongenital nystagmus Infantile nystagmus syndrome Vergence Tracking
Infantile nystagmus syndrome
Expanded nystagmus acuity function
Jerk right with extended foveation
Pseudo-pendular with foveating saccades
Left eye horizontal
Left eye horizontal error
Right eye horizontal
Right eye horizontal error
Target distance velocity
Target vergence velocity
This work was supported in part by the Office of Research and Development, Medical Research Service, Department of Veterans Affairs.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflicts of interest.
Statement of human rights
All procedures performed in studies involving human participants were approved by the appropriate institutional committee and were in accordance with the ethical standards of the University of Maryland and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
Statement on the welfare of animals
This article does not contain any studies with animals performed by any of the authors.
Informed consent was obtained from the individual participant included in the study.
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