Documenta Ophthalmologica

, Volume 79, Issue 1, pp 1–23 | Cite as

Foveation dynamics in congenital nystagmus I: Fixation

  • L. F. Dell'osso
  • J. Van Der Steen
  • R. M. Steinman
  • H. Coleewijn


Congenital nystagmus (CN) has been described as a ‘fixation’ nystagmus implying an inability to fixate a target. However, each cycle of CN contains a target-foveation period during which the eye velocity is at, or near, zero. Prolongation of foveation time, reduction of retinal image velocity and cycle-to-cycle foveation repeatability all contribute to increased visual acuity. We developed several methods to accurately measure the dynamics of foveation in CN; their use is illustrated on an individual with typical idiopathic CN and no afferent defects. During eight 5-second intervals of fixation on a stationary target, the horizontal standard deviation (SD) of the mean foveation position (FPOS) was 12.82 minarc and the SD of foveation velocity was 118.36 minarc/sec. The SD of the means of total eye position and of the non-foveating peak of the CN were 43.17 and 25.32 minarc respectively. The mean foveation-time interval (eye velocity ⩽4°/sec) was 57.27 msec. The SD FPOS for the best 1-second interval (4 successive CN cycles), in a typical 5-second record, was 0.71 minarc. Histograms revealed peaks of eye position at 0 ± 10 minarc and of eye velocity at 0 ± 240 minarc/sec. The small vertical component of the CN (16 minarc peak-to-peak) had a SD of 6.56 minarc. A nystagmus foveation function related to visual acuity was derived that was more sensitive than CN intensity. The increased visual acuity resulting from the use of convergence or base-out prisms was due to increased foveation time. Although it might appear that CN is a defect of fixation, this individual with CN had strong fixation reflexes in the sense that he was able to accurately (within 1 minarc) achieve (interbeat) and maintain (intrabeat) target foveation for appreciable periods of time. Our data support the hypothesis that individuals with idiopathic CN do not have a primary disturbance of fixation.

Key words

Congenital nystagmus foveation fixation 


General Terms


Average values during distance fixation


Congenital nystagmus


Fixation at distance with prisms


Gaze angle


Nystagmus foveation function


Standard deviation (STD)

CN Waveforms


Jerk with extended foveation


Left pseudocycloid


Pendular with foveating saccades


Pseudopendular with foveating saccades

Calculated (Statistical) Terms


Mean eye position


Mean foveation period position


Mean frequency of CN


Mean foveation period velocity


CN intensity (PPA*freq)


Mean non-foveating peak position


Mean peak-to-peak amplitude


Mean post-saccadic velocity


Mean range of eye position during foveation period


Mean time (duration) of foveation period


The SD of FPOS as a percentage of EPOS


The SD of NFP as a percentage of EPOS


REP as a percentage of PPA


TFOV as a percentage of the CN period (1/freq)


The NFF = (TFOV)(freq)/[(SD FPOS)(SD FVEL)]


Approximation to the NFF = k(TFOV)(freq)/(SD FPOS)


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Copyright information

© Kluwer Academic Publishers 1992

Authors and Affiliations

  • L. F. Dell'osso
    • 1
    • 2
    • 3
  • J. Van Der Steen
    • 5
  • R. M. Steinman
    • 4
  • H. Coleewijn
    • 5
  1. 1.Ocular Motor Neurophysiology Laboratory, Veterans Affairs Medical CenterUSA
  2. 2.Department of NeurologyCase Western Reserve University and University Hospitals of ClevelandCleveland
  3. 3.Department of Biomedical EngineeringCase Western Reserve University and University Hospitals of ClevelandCleveland
  4. 4.Department of PsychologyUniversity of MarylandCollege Park
  5. 5.Department of PhysiologyErasmus UniversityRotterdamThe Netherlands

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