Optokinetic nystagmus in patients with central scotomas in age related macular degeneration

BACKGROUND: Reports on the impact of a loss in the central field of vision on optokinetic nystagmus (OKN) are varied. A study was therefore undertaken to reassess the role of the central retina in the generation of OKN in a large group of patients with age related macular degeneration. METHODS: Four groups of 20 patients were examined: a control group without scotoma and three groups with absolute central scotomas measuring 1 degrees--10 degrees, 11 degrees--20 degrees, and 21 degrees--30 degrees. OKN was elicited with black and white stripes moving nasally to temporally or temporally to nasally on a screen subtending 54 degrees x 41 degrees at four velocities (15, 30, 45, and 60 degrees /s). OKN gain was measured using infrared oculography. RESULTS: There was no significant difference in OKN gain between the control group and those with scotomas of 1 degrees--10 degrees and 11 degrees--20 degrees. A significant difference in OKN gain was found between the group with scotomas of 21 degrees--30 degrees and all other groups at stimulus velocities of 30, 45, and 60 degrees/s (p<0.05). OKN gain significantly diminished with increasing stimulus velocity (p<0.05). No statistically significant difference was found in OKN gain between stimuli moving temporally to nasally and nasally to temporally. CONCLUSION: Abnormalities of OKN gain were noted only in patients with large scotomas. An intact macula is therefore not necessary for the generation of OKN.     

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.     

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.     

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.     

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.     

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.     

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.     

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).     

Vertical optokinetic nystagmus and saccades in normal human subjects

PURPOSE: Optokinetic stimulation induces nystagmus that can be used to test the saccadic and visual-tracking systems in some patients with voluntary gaze palsies. The purpose of this study was to characterize vertical optokinetic nystagmus (OKN) in normal human subjects, comparing the dynamic properties of the quick phases with voluntary saccades of similar size and measuring the slow-phase responses to visual stimuli with a range of spatial and temporal frequencies. METHODS: Vertical OKN and saccades were recorded in 10 healthy adult subjects (age range, 24-54 years) using the magnetic search coil technique. The optokinetic (OK) stimulus subtended 72 degrees horizontally and 60 degrees vertically, consisted of black-and-white stripes with a spatial frequency of 0.04, 0.08, or 0.16 cyc/deg, and moved vertically at 10 to 50 deg/s. Vertical and horizontal saccades to visual targets separated by 1 degrees to 10 degrees were also elicited. RESULTS: Over 95% of quick phases were less than 10 degrees in amplitude; voluntary saccades of this amplitude range were slightly faster than quick phases of similar size. The amplitude-peak velocity relationships and amplitude-duration relationships of upward and downward fast movements (saccades or quick phases) were similar. Most vertical slow-phase OK responses showed greater gain for upward stimulus motion. OK gain decreased with increasing stimulus speed and increased spatial frequency, so that there was a general decrease in slow-phase velocity gain with increasing temporal frequency. CONCLUSIONS: In this study, the best OK responses were obtained using stripes with lower spatial frequencies and lower stripe speeds (0.4 cyc/deg at 10 deg/s). The dynamic properties of vertical quick phases of nystagmus are similar enough to those of voluntary saccades for OK stimulation to be used as a clinical test of the vertical saccadic system in individuals with voluntary gaze palsy.     

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.     

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.     

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.     

The relationship of luminous intensity and velocity for motion perception and maximum OKN elicitation

The psychophysiological aspects of the luminous intensity stimulus velocity relationship for perceiving a grating pattern and eliciting optokinetic nystagmus (OKN) with maximum slow-phase velocity were studied in two normal human eyes. The results show that (1) both the luminous intensity and target velocity (within the region from 16-56 deg/sec) have a linear relation to the perception of a grating pattern and eliciting of the maximum OKN. (2) The trends of the relation between perception and elicitation are similar, but the slopes of the regression lines are different. (3) No statistically valid directional effect is found on either visual perception or maximum OKN elicitation in humans who have normal binocular vision. (4) For a given stimulus velocity, OKN gain (slow-phase velocity/stimulus velocity) increases to a saturation point as the stimulus intensity increases. The maximum OKN gain decreases as the stimulus velocity increases.     

Adaptation of the vestibulo-ocular reflex in amblyopia

Adaptation of the vestibulo-ocular reflex (VOR) is demonstrated by changes in gain in response to discrepancies between visual and vestibular stimulation. The authors have investigated the effect of monocular asymmetries of OKN in amblyopia upon adapting the gain of the VOR. Adaptation was investigated by modifying the horizontal balance of the VOR. While monocularly fixating a head referenced spot for 2 min, subjects were sinusoidally oscillated on a chair inside an optokinetic drum that rotated in one direction (left or right) at the peak velocity of sinusoidal chair rotation. The VOR was then measured during continued sinusoidal body oscillation in darkness for 1 min. Imbalance of the horizontal VOR gain equalled the ratio of slow phase velocities in the rightward and leftward directions. After rotating the drum in the nasalward direction, an increase was observed in slow phase gain of the VOR in the nasalward direction for either eye of our amblyopes that was significantly greater than similar changes in gain for the normals. Increased VOR gains for the amblyopic group following temporalward stimulation were significantly less than the nasal aftereffect. Gain changes of the VOR in normals had similar magnitudes following nasal or temporal stimulation. These results suggest that disturbances of OKN in amblyopia are common to the pathways that modify the slow phase gain of the VOR.     

Optokinetic nystagmus as a measure of visual function in severely visually impaired patients

PURPOSE: To evaluate the efficacy of using optokinetic nystagmus (OKN) as an objective measurement of vision in severely visually impaired patients, in whom it is difficult to measure visual function reliably. Objective visual acuity (VA) measurements would be useful in the pre-and postoperative assessment of severely visually impaired patients who are potential candidates for visual rehabilitation strategies, such as retinal prostheses, neural and stem cell transplantation, and molecular approaches. METHODS: Full-field visual stimuli were used to evoke horizontal OKN responses in 17 subjects. Eye movements were recorded and analyzed to determine the maximum stimulus velocity (V(max)) at which subjects could maintain an OKN response. This endpoint was compared to logMAR VA and Goldmann visual field (VF) test RESULTS: results. V(max) was dependent on VA, VF, and the spatial frequency (SF) of the stimulus, yielding the equation V(max) = 14.2 . log(VA) - 6.20 . log(SF) + 0.22 . VF + 25.0. The findings suggest that V(max) in the presence of full-field OKN stimuli may provide an objective measure of VA and peripheral vision. CONCLUSIONS: OKN testing may be useful as an additional, more objective means of assessing visual function in a select group of severely visually impaired patients who are being considered as candidates for new visual rehabilitative strategies.     

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.     

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.     

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.     

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。