Optokinetic nystagmus elicited by filling-in in adults with central scotoma

PURPOSE: Filling-in is the perceptual completion of physiological, pathologic, or artificial scotomas. Three patients are described, in whom optokinetic nystagmus (OKN) was present during filling-in. METHODS: Three patients with age-related macular degeneration with large central scotomas were included in the study. OKN was elicited with black and white stripes moving nasally to temporally or temporally to nasally at four velocities. OKN gain was measured using infrared oculography. RESULTS: While looking at the OKN stimuli, the patients either did not see the stimulus (without perceiving a positive scotoma) or filled in the scotoma and perceived the stripes. Simultaneously with filling in the scotoma, OKN eye movements were elicited in all three patients. The filling-in phenomenon was present for all stimulus directions and velocities, appeared within seconds, and was followed immediately by eye movements corresponding to OKN. OKN gains during filling-in were similar to those of age-matched control subjects without scotomas. No asymmetry was noted between temporal to nasal or nasal to temporal stimulation. CONCLUSIONS: Motion-sensitive areas of the visual cortex may be activated and trigger the generation of OKN, supporting an active process. Alternatively, OKN is suppressed when subjects are not filling-in, while the subjects are fixating the central scotoma or edges of the scotoma. That the subjects did not perceive positive scotomas suggests that an active process is more likely.     

Optokinetic nystagmus in strabismus: are asymmetries related to binocularity?

PURPOSE: Strabismus may be associated with an asymmetry of monocular horizontal optokinetic nystagmus (OKN). It is unclear whether OKN asymmetries are associated with deficiency in binocular and/or stereovision. In the current study, patients with different degrees of binocularity were investigated. METHODS: OKN was examined in the dominant and nondominant eyes of four groups of patients: (1) no measurable binocularity (NB), (2) poor binocularity (PB)-that is, showing binocularity on the Bagolini Test and/or rudimentary stereovision, (3) good binocularity (GB) with good stereoacuity after squint surgery, and (4) a control group. Monocular OKN was elicited with black-and-white stripes moving temporally to nasally (TN) or nasally to temporally (NT) at velocities of 15, 30, 45, and 60 deg/s. Eye movements were recorded with infrared oculography. RESULTS: Only subjects in the NB group showed a significant OKN asymmetry, with preference for TN stimulation in dominant and nondominant eyes. Subjects with PB did not have significant OKN asymmetries but reduced OKN gains in both stimulus directions. Subjects with GB had normal mean OKN gains without asymmetry. Larger OKN asymmetries were correlated with younger age at detection of strabismus if NB and GB were grouped together, but not if each group was analyzed separately. CONCLUSIONS: For the first time, a large groups of patients classified by level of binocular vision has been investigated. The results show that OKN gain and asymmetry are associated with the development of binocular vision. OKN investigation may be helpful to identify patients with binocularity or binocular potential in strabismus.     

Role of the stimulus size in the generation of optokinetic nystagmus in normals and in patients with retinitis pigmentosa

BACKGROUND: To find out the smallest stimulus size still able to elicit optokinetic nystagmus (OKN). To discuss the differences in the generation of OKN between normals and patients with tunnel vision. METHODS AND PATIENTS: OKN was elicited monocularly with black and white stripes of 2 degrees moving on a screen temporally-to-nasally or nasally-to-temporally at velocities of 15, 30, 45, and 60 degrees /s. In healthy subjects (n = 10) the size of the stimulus was gradually increased from minimal 8 degrees x 0.5 degrees to maximal 48 degrees x 10 degrees. OKN was elicited in retinitis pigmentosa (RP) patients (n = 2) with visual field reduced to the central 10 degrees. OKN gain was measured using infrared oculography. OKN response was considered as normal if it was within 2 standard deviations of the mean OKN of age-matched control groups (n = 29). RESULTS: In healthy subjects the size of the stimulus necessary to elicit normal OKN gain was smaller at low velocity of 15 degrees /s (16 degrees x 1 degrees ) than at higher velocities of 30, 45, and 60 degrees /s (16 degrees - 24 degrees x 3 degrees ). Normal OKN gain was measured in the RP patients only at the low velocity of 15 degrees /s. CONCLUSIONS: Small stimuli are sufficient in normals to elicit good OKN answers. Therefore, poor OKN gain in RP patients may not be explained by their tunnel vision only. We postulate that in these patients the reduction of gain is due to a multifactorial decrease of their visual perception related to disorders of the visual field, the visual acuity, and the contrast sensitivity.     

Optokinetic nystagmus: the effects of stationary edges, alone and in combination with central occlusion

In Experiment 1 we investigated the independent and combined effects of horizontal OKN of stationary edges and occlusion of the central retina. For a display 60 degrees wide moving at 30 degrees/sec a symmetrically placed pair of vertical nonoccluding bars suppressed OKN when near the center of the display but had no effect when 30 degrees apart. A 7 degrees-high 60 degrees-wide central occluder reduced OKN gain by 37%. However, a central occluder with edges only 30 degrees wide abolished OKN. In Experiment 2 this interaction between central occlusion and stationary edges was confirmed with a wider display over a range of stimulus velocities and configurations. A functional explanation of this interaction is presented.     

Look and stare optokinetic nystagmus in healthy subjects and in patients with no measurable binocularity. A prospective study

BACKGROUND: The aim of our study was to assess the difference between look and stare optokinetic nystagmus (OKN) in healthy subjects and in patients with early onset strabismus and no measurable binocularity. METHODS AND PATIENTS: OKN was elicited monocularly with black and white stripes moving horizontally or vertically at 15, 30, 45 and 60 degrees /s. Subjects were instructed either to follow individual stripes across the screen (look OKN) or to fixate stripes in the centre of the screen (stare OKN). We examined 20 healthy subjects (mean age 29 years; range 21 - 39), and 10 patients with no measurable binocularity (mean age 12.7 years; range 5 - 37). OKN gain was measured with photo-oculography. RESULTS: In both groups and at stimulation with the higher velocities gains for look OKN were significantly better than for stare OKN, and gains with horizontal stimuli were significantly better than with vertical stimuli (p < 0.05). In the group with no measurable binocularity horizontal look and stare OKN answers were significantly better for temporal-to-nasal stimulation than for nasal-to-temporal stimulation (p < 0.05). CONCLUSIONS: The performance of look or stare OKN influences the gain in healthy subjects and in patients with no measurable binocularity. Data about both modes of OKN stimulation are helpful to better interpret OKN responses especially in subjects with poor cooperation.     

Monocular optokinetic nystagmus in humans with age-related maculopathy

AIM—To investigate full field monocular optokinetic nystagmus (OKN) in patients with age-related maculopathy (ARM) and relative central scotoma.
METHODS—Six patients aged 59-88 years with bilateral ARM and an aged-matched control group of six patients aged 54-83 years were examined. Visual fields were assessed with a Humphrey field analyser using the threshold 30-1 routine. Monocular full field horizontal optokinetic stimuli were presented on a hemicylindrical screen subtending 172° horizontally and 50° vertically. The stimulus was a projected random dot pattern and three stimulus velocities were used, 30, 50, and 70°/s in both nasalward and temporalward directions. Each trial lasted between 30 and 40 seconds and eye movements were monitored using infrared oculography.
RESULTS—The ARM patients had relative central scotomas with an average depth of 10 dB. Neither the ARM nor the age-matched groups displayed any directional preponderance or a buildup of the slow phase eye velocity with time. No statistically significant difference in the gain was found between the two groups (p>0.05).
CONCLUSIONS—Marked central field loss in ARM does not significantly impair OKN gain. This supports the view that complete central retinal integrity is by no means essential and that the peripheral retina provides an important input to the generation of OKN.

     

AN ASYMMETRY IN THE OPTOKINETIC NYSTAGMUS RESPONSE IN NORMAL INDIVIDUALS

Optokinetic nystagmus (OKN) was induced by using a modified projector system to provide a moving pattern of irregular spots of light. A systematic electro-oculographic study of horizontal and vertical OKN for a series of stimulus velocities from 10 to 100 degrees s-1 was conducted on 10 healthy young subjects. It was found that the vertical responses, in particular to upward-moving stimuli, were less well sustained at velocities above 30 degrees s-1 than the horizontal responses. In view of these observations, care should be taken in the interpretation of OKN results clinically, and only when the response is absent in one direction or an extreme asymmetry is present should clinical significance be attached. This applies particularly for the vertical OKN responses. Clearly, the use of stimulus velocities below 40 degrees s-1 is advised and the standard suggested by Holm -Jensen and Peitersen [Acta oto-lar. 88, 110-116 (1968)] of a target moving at 20 degrees s-1 seems a reasonable choice.     

Age related change of optokinetic nystagmus in healthy subjects: a study from infancy to senescence

BACKGROUND: Optokinetic nystagmus (OKN) gain is asymmetrical between temporal to nasal (TN) and nasal to temporal (NT) stimulation in infancy and decreases at older ages. The age at which OKN gain becomes symmetrical and decreases is debated. The aim was to investigate OKN over the whole lifespan in a large sample of healthy subjects. METHODS: In a prospective, cross sectional study OKN was tested monocularly using TN and NT small field stimulation. Stimulation velocity was 15 degrees /s and 30 degrees /s for children aged under 1 year (n = 97), and 15 degrees /s, 30 degrees /s, 45 degrees /s, and 60 degrees /s for older subjects (1-9 years, n = 66; 10-89 years, n = 86). Gain was measured using infrared oculography. RESULTS: Significant OKN gain asymmetry in favour of TN versus NT stimulation was found during the first 5 months of life (p<0.05). Only at 11 months of age was OKN symmetrical in 100% of the subjects. The percentage of children with symmetrical OKN decreased with increasing stimulus velocity. OKN gain increased in the second and third years (p<0.05 for 15 degrees /s), remained stable until 50 years of age, and showed a small but significant decrease afterwards for the tested velocities (between 6% and 18%, p<0.05). CONCLUSIONS: Infrared oculography is an accurate method to assess OKN, especially in children. Knowledge about change of OKN in healthy subjects could be helpful to interpret OKN in patients with abnormal binocular vision or lesions of the central nervous system.     

Asymmetry of the optokinetic nystagmus in lesion of the central nervous system

BACKGROUND: Unilateral lesions of the central nervous system (CNS) may be associated with a reduction of the optokinetic nystagmus (OKN) slow component in the direction of the lesion. The aim of our study was to assess the role played in these cases by the direct injury of the OKN pathways and/or by a possible associated visual field defect. METHODS AND PATIENTS: Monocular OKN was elicited with black and white stripes moving temporally-to-nasally (TN) or nasally-to-temporally (NT) at velocities of 15, 30, 45 and 60 degrees /s. Patients with cortical or chiasmal lesions associated with visual field defects were investigated. OKN was considered asymmetrical if the gain difference between TN and NT stimulation was not within 2 standard deviations of an age-matched control group (n = 86). RESULTS: We examined 12 patients with cortical lesions and 4 patients with chiasmal lesions. Asymmetric OKN gain was measured in 7 patients with cortical lesions associated with a visual field defect, and in 2 patients with chiasmal compression and bitemporal hemianopia. In 2 patients with isolated occipital lesions, OKN asymmetry was explained by the associated visual field defect. CONCLUSION: The interpretation of OKN asymmetry in patients with CNS lesions should not only consider a direct lesion of the OKN pathways but also a sensory deficit due to a visual field defect.     

Horizontal and vertical look and stare optokinetic nystagmus symmetry in healthy adult volunteers

PURPOSE: Look optokinetic nystagmus (OKN) consists of voluntary tracking of details in a moving visual field, whereas stare OKN is reflexive and consists of shorter slow phases of lower gain. Horizontal OKN is symmetrical in healthy adults, whereas symmetry of vertical OKN is controversial. Horizontal and vertical look and stare OKN symmetry was measured, and the consistency of individual asymmetries and the effect of varying stimulus conditions were investigated. METHODS: Horizontal and vertical look and stare OKN gains were recorded in 15 healthy volunteers (40 degrees /s) using new methods to delineate look and stare OKN. Responses with right and left eye viewing were compared to investigate consistency of individual OKN asymmetry. In a second experiment, the symmetry of stare OKN was measured in nine volunteers varying velocity (20 degrees /s and 40 degrees /s), contrast (50% and 100%), grating contrast profile (square or sine wave), and stimulus shape (full screen or circular vignetted). RESULTS: There was no horizontal or vertical asymmetry in look or stare OKN gain for all volunteers grouped together. However, individual vertical asymmetries were strongly correlated for left and right eye viewing (look: r = 0.77, P = 0.0008; stare: r = 0.75, P = 0.001) and for look and stare OKN (r = 0.66, P = 7.3 x 10(-5)) because of a strong correlation for downward moving stimuli (r = 0.73, P = 0.002). Horizontal and vertical asymmetries were not significantly affected by variations in stimulus parameter. CONCLUSIONS: Although no horizontal or vertical OKN asymmetries existed for volunteers grouped together, vertical OKN was characterized by idiosyncratic asymmetries that remained consistent for an individual. Look and stare OKN gain is strongly associated for downward moving stimuli.     

The efficiency of the central and peripheral retina in driving human optokinetic nystagmus

Previous experiments to decide whether the gain of optokinetic nystagmus (OKN) is increased or decreased by occlusion of the central retina involved the use of stationary edges on the occluder and unmatched contrasts. With these factors controlled, it was confirmed that OKN gain is severely reduced by occlusion of the central retina but only at stimulus velocities above about 30°/sec. The gain of horizontal OKN was found not to increase with increasing width of the display if the lateral edges are blurred. The high gain of centrally driven OKN may be related to the ability of higher mammals to stabilize the images of objects at a given distance in a complex parallactic visual field.     

Torsional optokinetic nystagmus: normal response characteristics

BACKGROUND/AIMS: Few studies have investigated normal response characteristics of torsional optokinetic nystagmus (tOKN). The authors have investigated the effect of stimulus velocity and central/peripheral stimulation on tOKN. METHODS: Torsional OKN was elicited using a sinusoidal grating rotating at velocities of 3 degrees /s to 1000 degrees /s in clockwise and anticlockwise directions. To investigate the effect of central stimulation, stimulus size was varied from 2.86 degrees to 50.8 degrees. An artificial scotoma placed over a 50.8 degrees stimulus was varied from 2.86 degrees to 43.2 degrees to investigate peripheral stimulation. Eight subjects participated in each experiment and torsional eye movements were recorded using video-oculography. The mean slow phase velocity (MSPV) and gain were calculated. RESULTS: The maximum gain occurred in response to 8 degrees /s stimulation. The MSPV increased up to a stimulus velocity of 200 degrees /s achieving a maximum of 3 degrees /s in both directions. MSPV was linearly correlated with the log of stimulus velocity. The smallest field size, rotating at 40 degrees /s, evoked 10% of the gain elicited by the largest display. When the most peripheral stimulus was used, the gain was maintained at 50% of the gain evoked when the full display was used. CONCLUSIONS: A wide range of stimulus velocities can elicit tOKN and peripheral field stimulation contributes significantly to its response.     

Development of the optokinetic system in macaque monkeys

Optokinetic nystagmus in response to horizontal movement of a whole field random dot pattern was measured in infant macaque monkeys from the first week to about 5 months after birth using electrooculography. During monocular and binocular viewing conditions stimulus velocities were varied between 10 and 120 degrees/s. Monocular stimulation in the temporonasal direction yielded slow phase gain of the optokinetic system which was relatively constant for a given stimulus velocity over the whole period of observation. Gain during nasotemporal stimulation was also clearly present but significantly lower at early stages and increased during further development. This asymmetry of monocular horizontal optokinetic nystagmus (OKN) clearly depended on the stimulus velocity. At lower stimulus velocities (10-20 degrees/s) OKN was largely symmetrical at 2-5 weeks of age. At higher stimulus velocities (40 degrees/s) symmetry was reached at about 12 weeks of age or even much later (80-120 degrees/s).     

Disjunctive optokinetic nystagmus in a naturally esotropic macaque monkey: interaction between nasotemporal asymmetries of versional eye movement and convergence

OBJECTIVE: To assess the interaction between versional and vergence eye movements in normal and strabismic monkeys. METHODS: Horizontal optokinetic nystagmus (OKN) and vergence were measured using the magnetic scleral search coil technique in a normal adult monkey and a strabismic monkey who had naturally occurring early-onset esotropia. Mean eye velocity and vergence angles were calculated during the slow phases of OKN. RESULTS: The strabismic monkey had a nasotemporal asymmetry of OKN favoring nasally directed motion in each eye. During monocular optokinetic stimulation, mean eye velocities were substantially greater for the adducting as compared to the abducting eye. The velocity of the abducting eye was between 55 and 80% of the velocity of the adducting eye (p < 0.01). As a consequence of the disjunctive movements, the eyes converged an average of 4 +/- 2.8 degrees during OKN. Saccadic analysis documented normal lateral rectus function in each eye. Neither an OKN asymmetry nor disjunctive OKN was observed in the normal monkey. CONCLUSION: Disjunctive OKN in the esotropic monkey suggests that the cerebral maldevelopment responsible for nasally biased OKN also contributes to nasal biases in vergence pathways.     

Human horizontal optokinetic nystagmus elicited by the upper versus the lower visual fields

A 30-deg-high horizontally rotating random-dot display was presented to the central field, and with its more central edge at vertical eccentricities of 0, 2.5, 5, and 10 deg above or below the horizon. Stimulus velocities of 25-100 deg/s and two directions of motion were presented. The mean gain of the slow phases of optokinetic nystagmus (OKN) for five subjects was significantly higher when the stimulus was presented to the lower visual field than when the stimulus was presented to the upper field. This difference was most pronounced when the display was displaced 5 deg from the fovea and moving below 100 deg/s. Our results are consistent with existing psychophysical and physiological evidence for the superiority of the upper retina. In addition, four of the five observors showed significant directional asymmetries.     

OKN asymmetries and binocular function in amblyopia

Asymmetrical optokinetic nystagmus (OKN) means that OKN has a lower gain (slow-phase eye velocity/stimulus velocity) for monocular temporalward than nasalward visual field motion. OKN tends to be asymmetric in amblyopia, leading to suggestions of a link between OKN asymmetry and binocularity in the literature. The present study measured OKN in 13 amblyopes and five normal subjects. In an attempt to identify those binocular cells used in the OKN response, the degree of OKN asymmetry was compared with binocularity assessed by two different techniques: (1) stereopsis and (2) interocular transfer of threshold elevation (IOT). Horizontal monocular OKN was recorded for three different stimulus velocities in each subject. All the amblyopes were found to be stereoblind, although three amblyopes showed OKN asymmetries close to those found for the normal group. More association was seen between interocular transfer of the threshold elevation and OKN asymmetry; not all amblyopes demonstrated reduced IOT, but those amblyopes with no IOT all had OKN asymmetries more than 125% of the mean of the normal group. However, no association was seen between the amount of OKN asymmetry and the degree of IOT. The results are discussed in terms of the role of different groups of binocular neurones for OKN and the effect of the sensitive periods of development on these binocular neurones.     

色觉和运动觉相互作用的客观判断

目的:确定正常人在不同运动速度绿、红光栅刺激时的等亮度点值,探讨色觉和运动觉相互作用特性。方法:自行研制能同时诱发运动觉和色觉的运动颜色光栅刺激器,用眼电图(electrooculograph,EOG)方法记录诱发视动性眼球震颤(optokinetic nystagmus,OKN),确定不同运动速度时受检查者OKN换相时的绿、红亮度比值(即等亮度点)。共测试16例(32只眼)正常人,男6人,女10人,年龄20～51岁。结果:于5个等级光栅运动速度:595,400,301,239和200mm/s,测得其对应等亮度点的均值分别为:0.525,0.425,0.397,0.391,0.367。经统计学分析,595mm/s组的等亮度点均值与其他各组间有非常显著性差异(P<0.01),其他组间的等亮度点均值均无显著性差异(P>0.05)。结论:运动速度快的情况下会影响人眼对颜色的感觉。眼科学报1997;13:186—188。     

The influence of field size upon the spatial frequency response of optokinetic nystagmus

The range of target velocities that stimulate optokinetic nystagmus (OKN) was examined as a function of spatial frequency of drifting gratings and field size. OKN responded optimally to coarse gratings with upper spatial frequency limits of 16, 8 and 4 c/deg for 2°, 10° and 45° test fields respectively. These upper spatial frequency limits for optimal responses were related to spatial resolution of moving gratings at the edges of the test field. At low spatial frequencies OKN had an upper slow phase velocity limit that increased with field size. The upper velocity limit was influenced more by proximity of test field edges to the fovea than by test field area. The upper velocity limit was reduced at higher spatial frequencies by a constant temporal frequency limit of 24 Hz. This fixed temporal frequency limit was independent of field size and was related to the CFF for detecting moving gratings. Reduction of stimulus area increased apparent speed of low stimulus velocities and enhanced fast phase frequency of OKN. Pursuit OKN replaced involuntary OKN at stimulus velocities below a lower velocity limit. An empirically derived schematic was developed to describe the spatio-temporal stimulus space for OKN as limited by sensory and motor factors.     

Peripheral astigmatism in emmetropic eyes

The long-term aim of the work introduced here is to investigate the influence of off-axis aberrations on human vision, especially for subjects with a large central scotoma. The latter use their peripheral vision in spite of its poor off-axis optical quality, and a correction of the off-axis aberrations might be of great assistance. The eccentric fixation angles used by these subjects can be up to 20-30 degrees. In this initial study we have measured oblique astigmatism, the major off-axis aberration, in 20 emmetropic eyes in 10 degrees steps out to 60 degrees nasally and temporally using a 'double pass' setup. The results show very large individual differences and the oblique astigmatism also varies from nasal to temporal side. In an off-axis measurement angle of 30 degrees the astigmatism varied between subjects from 1 to 7-D, with a mean astigmatism of about 4-D on the nasal side and about 1.5-D lower on the temporal side. At 60 degrees temporally, the mean astigmatism was 7-D. At 60 degrees nasally, all subjects had astigmatism larger than 8-D and the mean astigmatism was 11-D. The results indicate that any attempt to correct the off axis astigmatism in an eye with central scotoma cannot be based on central refraction; instead, individual measurements are necessary.     

Human optokinetic nystagmus in response to moving binocularly disparate stimuli

Physiological and behavioral evidence shows that the directionally preponderant subcortical control of optokinetic nystagmus (OKN) in lower mammals is supplemented in higher mammals by bidirectional cortical control. It is hypothesized that this cortical control allows higher mammals to cope with the parallactic movement of the scene produced by linear motion of the body. In particular, it is hypothesized that a coupling between OKN and stereopsis allows higher mammals to stabilize the images of objects within the plane of fixation while ignoring motion signals from objects at other distances. According to this hypothesis the gain of the slow phase of OKN should be highest for binocularly fused moving stimuli and attenuated for binocularly disparate displays. The results of Experiment 1 confirmed this prediction although the effects of accommodation were not ruled out completely. In Experiment 2 a display moving in one direction was presented across the central retina at the same time as one moving in the opposite direction was presented in the upper and lower periphery. It was found that subjects do not show OKN in the direction of the peripheral display unless it is binocularly fused and the central display is disparate. In Experiment 3 a stationary display of dots was superimposed on a moving display. It was found that OKN is not inhibited by the stationary display when it has a horizontal disparity and the moving display is fused. Experiment 4 found that horizontal OKN is disrupted by the sudden introduction of a vertical disparity in the stimulus. Since accommodative state was kept constant in the last three experiments, the data show that binocular disparities can help a person to stabilize selectively the image of one moving display while ignoring conflicting motion signals from another display.