Takahiro Niida

Repeated vergence adaptation causes the decline of visual functions in watching stereoscopic television

To evaluate visual fatigue when viewing stereoscopic TV, a technology expected to become the broadcasting display system of the future. Wide public acceptance of stereoscopic TV awaits resolution of many issues, including visual fatigue on viewing TV images. Visual fatigue was induced using a visual function simulator, consisting of prism and lens optical systems, while viewing stereoscopic TV. We assessed subject visual fatigue through subjective reports of symptoms and by the changes in visual functions. These functions included: viewer B [Js fusional break point, recovery point, accommodation step response, and visual evoked cortical potentials (VECP)]. Significant changes of some visual functions were found after watching simulated stereoscopic TV when the vergence load was heavy or when it changed over time; relative vergence limits decreased and the latency of VECP increased after watching, reflecting visual fatigue. After subjects rested, relative vergence limits recovered to pre-viewing levels. Our findings lead us to conclude that, aside from excessive horizontal binocular parallax, discontinuous changes in parallax is also a major factor that contributes to visual fatigue in the viewing of stereoscopic images. It also causes a decreased range of relative vergence, accommodation response, and a delay in the P100 latency of VECP.

Ocular dominance and patient satisfaction after monovision induced by intraocular lens implantation.

Purpose: To elucidate the relationship between ocular dominance and patient satisfaction with monovision induced by intraocular lens implantation. Setting: Eye Clinic, Kitasato University School of Medicine Hospital, Sagamihara, Kanagawa, Japan. Methods: The durations of exclusive visibility of dominant‐ and nondominant‐eye targets were measured in 16 patients with successful monovision and 4 patients with unsuccessful monovision to determine the characteristics of ocular dominance. The dominant eye was determined using the hole‐in‐card test (sighting dominance). The contrast of target in nondominant eye was fixed at 100%; the contrast of target in the dominant eye varied (ie, 100% to 80% to 60% to 40% to 20%) using rectangular gratings of 2 cycles per degree that were 4 degrees in size. Results: In the successful monovision group, the reversal thresholds (ie, exclusive visibility of the nondominant eye crosses over that of the dominant eye) were displayed only at low decreasing contrast (80% and 60%). However, in the unsuccessful monovision group, the reversal thresholds were at high decreasing contrast (20%) or not at all. The reversal thresholds in patients with unsuccessful monovision were at a significantly lower contrast than in patients with successful monovision (P<.05). Conclusions: Success and patient satisfaction in monovision patients were significantly influenced by the magnitude of ocular dominance. The balance technique seems to be a good method to evaluate the quantity of ocular dominance and prospectively evaluate the monovision technique.

Effects of dominant and nondominant eyes in binocular rivalry.

Purpose. To investigate the relation between sighting and sensory eye dominance and attempt to quantitatively examine eye dominance using a balance technique based on binocular rivalry. Methods. The durations of exclusive visibility of the dominant and nondominant eye target in binocular rivalry were measured in 14 subjects. The dominant eye was determined by using the hole-in-card test (sighting dominance). In study 1, contrast of the target in one eye was fixed at 100% and contrast of the target in the other eye was varied from 100% to 80% to 60% to 40% to 20%, when using rectangular gratings of 1, 2, and 4 cycles per degree (cpd) at 2°, 4°, and 8° in size. In study 2, contrast of the target in the nondominant eye was fixed at 100% and contrast of the target in the dominant eye was varied from 100% to 80% to 60% to 40% to 20%, when using a rectangular grating of 2 cpd at 4° in size. Results. In study 1, the total duration of exclusive visibilities of the dominant eye target; that is, the target seen by the eye that had sighting dominance was longer compared with that of the nondominant eye target. When using rectangular gratings of 4 cpd, mean total duration of exclusive visibility of the dominant eye target was statistically longer than that of the nondominant eye target (p < 0.05). In study 2, reversals (in which duration of exclusive visibility of the nondominant eye becomes longer than the dominant eye when the contrast of the dominant eye target is decreased) were observed for all contrasts except for 100%. Conclusions. The dominant sighting eye identified by the hole-in-card test coincided with the dominant eye as determined by binocular rivalry. The contrast at which reversal occurs indicates the balance point of dominance and seems to be a useful quantitative indicator of eye dominance to clinical applications.

Diurnal variation of human corneal curvature in young adults.

PURPOSE To elucidate the diurnal variation of human corneal curvature with regard to gender and menstrual cycle. METHODS Changes in corneal curvature and intraocular pressure (IOP) were measured over 24 hours in 14 young adults using corneal topography and a non-contact tonometer. In study 1, seven males and seven females (after menses) were measured. In study 2, four females out of the seven volunteers who participated in study 1 were measured again during menses. RESULTS The females after menses showed a remarkable diurnal variation throughout 24 hours. A significant difference between the light-wake periods and dark-sleep periods of 0.83 +/- 0.15 D was found (P < .01). Corneal curvature was significantly flatter during menses than after menses in the light-wake period (P < .05). In the males, no significant diurnal change (0.21 +/- 0.12 D) was measured in corneal curvature. CONCLUSIONS Diurnal variation of corneal curvature was significant, approximately 0.83 D in young females after menses, and corneal curvature became flatter during menses in young females. Diurnal variation of corneal curvature is an important parameter for planning refractive surgery and contact lens wear.

Binocular function in patients with pseudophakic monovision.

Purpose To evaluate the relationship between ocular deviation and stereopsis and fusion in patients who had pseudophakic monovision surgery. Setting Department of Ophthalmology, Kitasato University Hospital, Kanagawa, Japan. Design Retrospective comparative case series. Methods Patients had surgical monovision correction with monofocal intraocular lens placement followed by routine postoperative examinations. The alternate prism cover test was used to measure motor alignment. Sensory tests for binocularity included sensory fusion determinations using the Worth 4‐dot test, near stereopsis test, and fusion amplitude measured with a prism bar. Patients with monovision were categorized as having small‐angle exophoria (≤10.0 prism diopters [&Dgr;]) or moderate‐angle exophoria (>10.0 &Dgr;). Results This study comprised 60 patients with a mean age of 70.2 years ± 7.7 (SD). The difference in the mean stereopsis values between patients with small‐angle exophoria and patients with moderate‐angle exophoria was statistically significant (P<.001). In the moderate‐angle exophoria group, 10 patients (62.5%) developed intermittent exotropia after surgery; however, no serious ocular deviation problems were observed. The fusion amplitudes in patients with pseudophakic monovision were approximately similar to normal values. Patients with moderate‐angle exophoria were more likely to fail the Worth 4‐dot test than those with small‐angle exophoria. Conclusions In patients with pseudophakic monovision having a near exophoria angle of more than 10.0 &Dgr;, the possibility of changes in ocular deviation and stereopsis after surgery is a concern. Moreover, the application of monovision in patients with a previous moderate‐angle exophoria should be carefully considered. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

Evaluation of Relative Afferent Pupillary Defect Using RAPDx Device in Patients with Optic Nerve Disease

ABSTRACT We previously reported the standard values of the amplitude and latency scores in the RAPDx device for evaluating relative afferent pupillary defect (RAPD). Here, we evaluated RAPD in patients with optic nerve disease by using these standard values. Twenty-eight patients with current or previous optic nerve disease were enrolled in this study. Additionally, the data of 84 healthy subjects from our previous report were used as control data. We measured the amplitude and latency scores using RAPDx. We then compared their mean values and the percentages of individuals with standard values within a certain range between the optic nerve disease group and healthy group. Additionally, we evaluated their correlation with visual acuity and the critical flicker fusion frequency in the optic nerve disease group. Both parameters were significantly higher in the optic nerve disease group than in the control group (p < 0.0001). The detection rate of RAPD when using the standard value of amplitude score was 75%. Additionally, both parameters showed a significant correlation with laterality-based differences in visual acuity and critical flicker fusion frequency values in the optic nerve disease group (r = 0.59–0.75, p < 0.001). The amplitude and latency scores determined using RAPDx are useful in evaluating RAPD, particularly the standard value of the amplitude score.

Differences in the Stimulus Accommodative Convergence/Accommodation Ratio using Various Techniques and Accommodative Stimuli

ABSTRACT Purpose: To investigate differences in the stimulus accommodative convergence/accommodation (AC/A) ratio using various techniques and accommodative stimuli, and to describe a method for determining the stimulus AC/A ratio. Methods: A total of 81 subjects with a mean age of 21 years (range, 20–23 years) were enrolled. The relationship between ocular deviation and accommodation was assessed using two methods. Ocular deviation was measured by varying the accommodative requirement using spherical plus/minus lenses to create an accommodative stimulus of 10.00 diopters (D) (in 1.00 D steps). Ocular deviation was assessed using the alternate prism cover test in method 1 at distance (5 m) and near (1/3 m), and the major amblyoscope in method 2. The stimulus AC/A ratios obtained using methods 1 and 2 were calculated and defined as the stimulus AC/A ratios with low and high accommodation, respectively, using the following analysis method. The former was calculated as the difference between the convergence response to an accommodative stimulus of 3 D and 0 D, divided by 3. The latter was calculated as the difference between the convergence response to a maximum (max) accommodative stimulus with distinct vision of the subject and an accommodative stimulus of max minus 3.00 D, divided by 3. Results: The median stimulus AC/A ratio with low accommodation (1.0 Δ/D for method 1 at distance, 2.0 Δ/D for method 1 at near, and 2.7 Δ/D for method 2) differed significantly among the measurement methods (P < 0.01). Differences in the median stimulus AC/A ratio with high accommodation (4.0 Δ/D for method 1 at distance, 3.7 Δ/D for method 1 at near, and 4.7 Δ/D for method 2) between method 1 at distance and method 2 were statistically significant (P < 0.05), while method 1 at near was not significantly different compared with other methods. Conclusions: Differences in the stimulus AC/A ratio value were significant according to measurement technique and accommodative stimuli. However, differences caused by measurement technique may be reduced by using a high accommodative stimulus during measurements.

Evaluation of visual function in preschool-age children using a vision screening protocol

Purpose To evaluate the relationship between uncorrected visual acuity and refraction and binocular function using a vision screening protocol. Methods In total, 760 children (3–6 years old) who were enrolled in 4 nursery schools in Otawara, Japan, were recruited; a total of 1,520 eyes were examined. We assessed uncorrected near visual acuity, manifest refraction, stereopsis, and eye position. Subjects were divided into 4 subgroups according to the lowest uncorrected near visual acuity value compared between the 2 eyes: group 1 (visual acuity [VA] ≤0.00 [logarithm of the minimum angle of resolution]), group 2 (VA 0.15–0.05), group 3 (VA 0.52–0.22), and group 4 (VA >0.52). These parameters were compared among the groups. Results The sample number of each of the 4 sub-groups was as follows: group 1, 608; group 2, 114; group 3, 27; and group 4, 11. The median spherical equivalent values were −1.13 diopter (D) in group 1 and −1.00 in group 2, which were more myopic than group 4. Median cylindrical power in group 1 was 0.25 D, and was the lowest among all groups. In group 1, median anisometropia was 0.38 D and median corneal astigmatism value was 1.13 D; both values were lowest in group 1. With regard to binocular function, 89.6% of the subjects in group 1 had 60 arcseconds or better in near stereopsis and 98.8% had no detectable strabismus, which were significantly different from the findings in the other groups. The percentage of subjects in group 1 who had 80 arcseconds or worse in near stereopsis was 10.4%. In contrast, 90.9% of the subjects in group 4 had 80 arcseconds or worse in near stereopsis, and 18.2% had intermittent or manifest strabismus. Conclusion We suggest that examination of refraction and stereopsis in preschool-age children undergoing vision screening is an important supplement to visual acuity testing.

Evaluation of Sensory Dominance Using Binocular Rivalry as Related to Ocular Deviations

Introduction and Purpose To investigate the relationship between sensory dominance and ocular deviations. Patients and Methods Sixty-three patients were evaluated with a new device for the measurement of exclusive visibility during binocular rivalry. The patients were consisted of twenty-three with exotropia (XT), twenty with intermittent exotropia [X(T)], twenty with exophoria (XP), respectively. Device is composed of two retinometers, their holders in which angle and position can be adjustable and a PC for data storage and analysis. In each of eyes, exclusive visibility of one stimulus during binocular rivalry was measured for 60 sec, and the strength of ocular dominance was evaluated by the difference of exclusive visibility between dominant and nondominant eye. Results The difference of exclusive visibility time between dominant and nondominant eye were 9.8 ± 3.7 sec in the XT group, 6.1 ± 4.1 sec in the X(T) group and 2.2 ±1.5 sec in the XP group, respectively. There were significant differences between XT and X(T) (P < 0.01) as well as between XT and XP (P < 0.001). Conclusions The present result indicates that sensory dominance was obviously influenced by ocular deviations since exclusive visibility of dominant eye was prolonged with decreasing the opportunity of normal binocular vision such as XT or X(T).

Saccadic reaction times in alternating cover.

Abstract Purpose: The aim of this study was to compare saccadic reaction times (SRTs) during the alternating cover with SRTs during monocular viewing. Methods: Seven subjects with intermittent exotropia, eight subjects with esophoria and ten control subjects were participated. The normal-task was to fixate the central fixation point until the peripheral target appeared randomly either 5 degrees to the right or left. In the alternating cover task (AC-task), the cover was switched from the fixating eye to the other eye, central fixation target was simultaneously extinguished and peripheral target was lit. An infrared limbal-tracking system and electro-oculogram were used for measurements of eye movements. The study followed the tenets of the Declaration of Helsinki. We certify that there is no conflict of interest. Results: In AC-task, the average SRTs of control subjects, subjects with exophoria and subjects with intermittent exotropia were 224.2 ± 46.5 ms, 198.2 ± 45.3 ms and 227.3 ± 69.9 ms, respectively. On the other hand, the average SRTs of control subjects, subjects with exophoria and subjects with intermittent exotropia in normal-task were 200.7 ± 37.8 ms, 178.2 ± 34.6 ms and 185.4 ± 54.1 ms, respectively. Conclusions: The SRTs of most control subjects, subjects with exophoria and subjects with intermittent exotropia in AC-task were prolonged compared to normal-task.