Motor and sensory characteristics of infantile nystagmus

Abstract

Background/aims: Past studies have explored some of the associations between particular motor and sensory characteristics and specific categories of non-neurological infantile nystagmus. The purpose of this case study is to extend this body of work significantly by describing the trends and associations found in a database of 224 subjects who have undergone extensive clinical and psychophysical evaluations.

Methods: The records of 224 subjects with infantile nystagmus were examined, where 62% were idiopaths, 28% albinos, and 10% exhibited ocular anomalies. Recorded variables included age, mode of inheritance, birth history, nystagmus presentation, direction of the nystagmus, waveform types, spatial and temporal null zones, head postures and nodding, convergence, foveation, ocular alignment, refractive error, visual acuity, stereoacuity, and oscillopsia.

Results: The age distribution of the 224 patients was between 1 month and 71 years, with the mean age and mode being 23 (SD 16) years and 16-20 years respectively. By far the most common pattern of inheritance was found to be autosomal dominant (n = 40), with the nystagmus being observed by the age of 6 months in 87% of the sample (n = 128). 139 (62%) of the 224 subjects were classified as idiopaths, 63 (28%) as albinos, and 22 (10%) exhibited ocular anomalies. Conjugate uniplanar horizontal oscillations were found in 174 (77.7%) of the sample. 32 (14.3%) had a torsional component to their nystagmus. 182 (81.2%) were classed as congenital nystagmus (CN), 32 (14.3%) as manifest latent nystagmus (MLN), and 10 (4.5%) as a CN/MLN hybrid. Neither CN nor MLN waveforms were related to any of the three subject groups (idiopaths, albinos, and ocular anomalies) MLN was found in idiopaths and albinos, but most frequently in the ocular anomaly group. The most common oscillation was a horizontal jerk with extended foveation (n = 49; 27%). The amplitudes and frequencies of the nystagmus ranged between 0.3-15.7 degrees and 0.5-8 Hz, respectively. Periodic alternating nystagmus is commonly found in albinos. Albino subjects did not show a statistically significantly higher nystagmus intensity when compared with the idiopaths (p>0.01). 105 of 143 subjects (73%) had spatial nulls within plus or minus 10 degrees of the primary position although 98 subjects (69%) employed a compensatory head posture. Subjects with spatial null zones at or beyond plus or minus 20 degrees always adopted constant head postures. Head nodding was found in 38 subjects (27% of the sample). Horizontal tropias were very common (133 out of 213; 62.4%) and all but one of the 32 subjects with MLN exhibited a squint. Adult visual acuity is strongly related to the duration and accuracy of the foveation period. Visual acuity and stereoacuity were significantly better (p<0.01) in the idiopaths compared to the albino and ocular anomaly groups. 66 subjects out of a sample of 168 (39%) indicated that they had experienced oscillopsia at some time.

Conclusions: There are strong ocular motor and sensory patterns and associations that can help define an infantile nystagmus. These include the nystagmus being bilateral, conjugate, horizontal uniplanar, and having an accelerating slow phase (that is, CN). Decelerating slow phases (that is, MLN) are frequently associated with strabismus and early form deprivation. Waveform shape (CN or MLN) is not pathognomonic of any of the three subject groups (idiopaths, albinos, or ocular anomalies). There is no one single stand alone ocular motor characteristic that can differentiate a benign form of infantile nystagmus (CN, MLN) from a neurological one. Rather, the clinician must consider a host of clinical features.

Figures

Figure 1

A schematic classification for infantile nystagmus based on the possible association with one of two nystagmus waveforms (congenital nystagmus (CN) and manifest-latent nystagmus (MLN)) and various associated anomalies.

Figure 2

A schematic illustration of nystagmus waveforms (A) pendular nystagmus, (B) an accelerating velocity exponential slow phase jerk nystagmus (CN), (C) a decelerating exponential slow phase jerk nystagmus (MLN), (D) a linear or constant velocity slow phase jerk nystagmus (MLN). In (A) a slow phase is followed by a slow phase while in (B)–(D) a slow phase is followed by a fast phase.

Figure 3

The age distribution of the 224 subjects who were involved in the case study. Mode = 16–20 years and mean 23 (SD 16) years.

Figure 4

The distribution of waveform types seen among the idiopath (n = 139), albino (n = 63), and ocular anomaly (n = 22) subject groups for all 224 subjects.

Figure 5

The distribution of the 12 classes of waveforms seen in 182 subjects who exhibited a CN. P/AP = pendular/asymmetrically pendular, Pfs = pendular with foveating saccades, J = pure jerk, Jef = jerk with extended foveation, PC = pseudocycloid, DJ = dual jerk, Bdj = bidirectional jerk, J and DJ = jerk and dual jerk hybrid, Pfs and PC = pendular with foveating saccades and pseudocycloid hybrid, P/AP and PC = pendular/asymmetrical pendular and pseudocycloid hybrid, PC and DJ = pseudocycloid and dual jerk hybrid, Multiple = more than two different CN oscillations.

Figure 6

A schematic illustration of the four types of manifest latent nystagmus (MLN). During binocular viewing the eyes exhibit one of four states: stability (type 1 MLN), square wave jerks (type 2 MLN), torsional nystagmus (type 3 MLN), or a horizontal MLN (type 4 MLN). All four types show a typical MLN during monocular viewing with the fast phase beating toward the viewing eye.

Figure 7

The distribution of the position of the null zone for 143 of the subjects with CN. Note: subjects with manifest latent nystagmus (n = 27), periodic alternating nystagmus (n = 17), and hybrid oscillations (n = 8) were excluded from the original pool of 195 subjects.

Figure 8

The distribution of binocular logMAR visual acuities for the idiopath (n = 133), albino (n = 55), and ocular anomaly (n = 20) groups.

Figure 9

The distribution of logMAR visual acuity levels in the 41 subjects who exhibited foveation. All acuity measures were recorded during binocular viewing of a 6 metre distant acuity chart.