Ocular dominance and the interocular suppression of blur in monovision

Presbyopic contact lens patients with monocular corrections (monovision) see clearly at all distances by virtue of an interocular suppression of anisometropic blur that occurs regionally between corresponding retinal areas. This suppression fails to occur with small high-contrast targets viewed under low luminance conditions. The effect of target size and contrast upon interocular suppression of blur was quantified by reducing contrast of a bright test spot, viewed binocularly while wearing various plus lenses monocularly, until the out-of-focus image was suppressed. The strength of interocular suppression was equivalent when the plus lens was before either eye. However, after subjects wore a plus lens over their nonsighting eye for one day, interocular suppression of blur became enhanced when the nonsighting eye was blurred, and it became reduced when the sighting eye was blurred. Successful monovision subjects suppressed blur at higher contrast levels than did unsuccessful subjects. These results suggest a possible clinical test for quantifying adaptation to monovision.     

Patterns of binocular suppression and accommodation in monovision

The binocular depth of focus of monovision wearers was compared to the sum of the two monocularly determined depths of focus. Observers fell into three groups based upon ocular sighting dominance. Complete binocular summation of the monocular depths of focus was observed in subjects without a preferred fixating eye. Subjects who preferred to fixate with one eye had difficulty suppressing blur of that eye while the binocular target was within the depth of focus of the nonpreferred eye. A third group showed partial summation of the two monocular depths of focus. Similar patterns of accommodative response, measured objectively with the SRI optometer, were observed in subjects wearing monovision corrections. Accommodative response to sinusoidal variations in blur was controlled primarily by the dominant sighting eye. These results demonstrate the effectiveness of interocular suppression of anisometropic blur in monovision correction and the influence of ocular dominance upon this suppression process.     

Effects of interocular blur suppression ability on monovision task performance

Suppression of anisometropic blur induced by monovision contact lenses was examined in 18 presbyopic subjects. Suppression ability was quantified by reducing the contrast of a bright test target, viewed by subjects wearing a monovision correction, until the blurred image was suppressed. Subjective success with monovision was evaluated using a patient survey and no correlation to blur suppression ability was found. Objective success was evaluated in terms of performance at three near work tasks, each requiring a different level of stereoscopic localization. A significant correlation was found between card filing performance (requiring a moderate level of stereopsis) and blur suppression ability. Correcting either the dominant or non-dominant eye for near in the monovision correction did not significantly affect blur suppression ability. There was no evidence for adaptation to monovision in terms of increasing blur suppression ability over time.     

Comparison of suppression, stereoacuity, and interocular differences in visual acuity in monovision and acuvue bifocal contact lenses.

PURPOSE: The relationship between visual acuity and stereoacuity has been well documented: as binocular visual acuity increases, stereoacuity improves. We compared interocular differences in visual acuity and stereoacuity in two presbyopic soft contact lens modalities, monovision and a new soft bifocal contact lens, the Acuvue Bifocal. The Acuvue Bifocal is hypothesized to show a smaller interocular acuity difference, increased stereoacuity, and decreased suppression over monovision at distance and near. METHODS: Monovision patients wearing Acuvue or Surevue soft contact lenses were tested for visual acuity, stereoacuity, and suppression at distance and near. Stereoacuity was tested with the Randot Stereotest (near) and the BVAT (distance). Suppression was evaluated with the Acuity Suppression Vectogram (near) and the BVAT (distance). Patients were then fit with the Acuvue Bifocal in each eye. After wearing the lenses for 1 week, the same tests of visual acuity, stereoacuity, and suppression were performed. RESULTS: The mean interocular acuity difference (IAD) at distance with monovision was 0.712 logarithm of the minimum angle of resolution (logMAR) (SD = 0.275) and 0.188 logMAR (SD = 0.252) (p < 0.001) with the Acuvue Bifocal. At near, the mean IAD with monovision was 0.420 logMAR (SD = 0.183) and 0.137 logMAR (SD = 0.147) (p < 0.001) with the Acuvue Bifocal. Of the monovision subjects, 89% (17 of 19) demonstrated suppression at near while only 26% (5 of 19) did with the bifocal lenses (statistically significant at p < 0.001). Stereoacuity at near improved from a median of 200 sec arc with monovision to 50 sec arc with the bifocal lenses. CONCLUSIONS: In this study, correcting presbyopia with the Acuvue Bifocal versus monovision resulted in a statistically significant decrease in the interocular difference in visual acuity at distance and near. The decreased interocular difference in visual acuity improved certain aspects of binocularity as demonstrated by a decrease in suppression and an increase in stereoacuity.     

Adaptation to monovision

Many patients who begin wearing monovision contact lenses report that it requires days or weeks for them to become adjusted to the anisometropia; however, it is not clear if there are measurable improvements in their vision during this period. We therefore studied both the objective and subjective characteristics of adaptation to monovision over a period of 8 weeks. Sixty presbyopic subjects wore high water content hydrogel lenses in the study. During the 8 weeks of monovision wear, there were no significant changes in the subjects' visual acuities (distance, intermediate, or near) in high- and low-luminance conditions, near stereopsis, or interocular blur suppression characteristics. Nevertheless, the subjects reported significant improvement in various aspects of visual performance during the same period. Forty-eight percent of the subjects reported complete tolerance to the vision with their correction within the first week of monovision wear and a total of 78% of subjects were completely satisfied with the monovision correction at the completion of 8 weeks wear. The improved tolerance to monovision may be related to changes in aspects of vision other than those measured in this study or may reflect a psychological adjustment to the anisometropia.     

Monocular acuity in the presence and absence of fusion.

Because little is known about monocular acuity during binocular fusion, acuity of the right eye was measured in binocularly normal subjects, with the fellow eye open or fully occluded. The target was flashed for 65 ms or presented sinusoidally for 1 s. Subjects had both eyes optimally focused, or the right eye defocused by +3.00 D. Monocular acuities were equivalent during fusion or occlusion when both eyes were optimally focused. Acuity of the defocused eye was reduced when the fellow eye was open compared to when it was occluded. Suppression of the blur, therefore, produced a measurable reduction in recognition thresholds. As monocular acuity was not measurably affected by the fellow eye when each eye was in focus, the finding that monocular vision is improved with the fellow eye occluded should be ascribed to something other than suppression or more sensitive spatial measures of the suppression should be obtained.     

The effects of monocular refractive blur on gait parameters when negotiating a raised surface.

Falls in the elderly are a major cause of mortality and morbidity. Elderly people with visual impairment have been found to be at increased risk of falling, with poor visual acuity in one eye causing greater risk than poor binocular visual acuity. The present study investigated whether monocular refractive blur, at a level typically used for monovision correction, would significantly reduce stereoacuity and consequently affect gait parameters when negotiating a raised surface. Fourteen healthy subjects (25.8 +/- 5.6 years) walked up to and on to a raised surface, under four visual conditions; binocular, +2DS blur over their non-dominant eye, +2DS blur over their dominant eye and with their dominant eye occluded. Analysis focussed on foot positioning and toe clearance parameters. Monocular blur had no effect on binocular acuity, but caused a small decline in binocular contrast sensitivity and a large decline in stereoacuity (p < 0.01). Vertical toe clearance increased under monocular blur or occlusion (p < 0.01) with a significantly greater increase under blur of the dominant eye compared with blur of the non-dominant eye (p < 0.01). Increase in toe clearance was facilitated by increasing maximum toe elevation (p < 0.01). Findings indicate that monocular blur at a level typically used for monovision correction significantly reduced stereoacuity and consequently the ability to accurately perceive the height and position of a raised surface placed within the travel path. These findings may help explain why elderly individuals with poor visual acuity in one eye have been found to have an increased risk of falling.     

The suppression effect of simulated anisometropia

Although there is evidence that differential interocular image clarity degrades binocular performance (for example, reducing stereo sensitivity) little is known about how this sensitivity reduction occurs. As there is evidence that suppression scotomas are induced in the more defocused eye, the presence and approximate size of suppression scotomas induced with uni-ocular defocus was investigated in five binocularly normal subjects. The targets comprised a fusional lock and a suppression check for each eye and the task of each subject was to report the presence of the suppression check with varying amount of defocus. There was a range of simulated anisometropia over which suppression did not occur (approximately +/- 0.50 DS). Thereafter the probability of suppressing a small foveal target increased approximately linearly until the target was always suppressed. Greater amounts of simulated anisometropia produced larger suppression scotomas. However, less anisometropia was required to produce an equivalent sized suppression scotoma if greater amounts of fusional detail were provided. These results suggest that the decrement in binocular performance which accompanies simulated anisometropia may occur because of localized inhibition in the more defocused eye and is not solely due to loss of resolution in that eye.     

模拟单眼视对视觉拥挤效应的影响

目的：建立单眼视的模拟方法及周边视觉拥挤效应的测量方法，并利用该方法评估模拟单眼视下的周边视觉拥挤效应是否较正常情况更严重。方法：实验研究。于2015 年3-11 月期间选取温州医科大学眼视光学院在校健康学生和教师20例。正常对照时，双眼均给予清晰的视标（模糊度数为0 D）；模拟单眼视时，左眼给予清晰的视标，右眼给予模糊的视标（模糊度数分别为0.75、1.50、2.50、3.50 D，顺序随机）。视觉拥挤效应的目标视标的偏心度（Ecc）为2.5°、5.0°、7.5°（顺序随机），阈值测量方法为心理物理学的阶梯法。通过比较模拟单眼视状态与正常对照状态的视觉拥挤效应的特征和差异，评估模拟单眼视对视觉拥挤效应的影响。不同模糊度数及不同Ecc时视觉拥挤效应的比较采用双因素重复测量方差分析，组间两两比较采用Bonferroni矫正过的t检验。结果：视觉拥挤效应显著依赖于模糊度数（F=13.37，P<0.001）和Ecc（F=296.90，P<0.001）。模糊度数与Ecc的交互作用显著（F=4.03，P<0.001）。当Ecc分别为7.5°、5.0°时，不同模糊度数下测得的视觉拥挤效应差异均有统计学意义（F=8.59，P<0.001；F=3.74，P=0.01），模糊度数越大，视觉拥挤效应越重。当Ecc为2.5°时，不同模糊度数下测得的视觉拥挤效应差异均无统计学意义（F=1.13，P=0.34）。结论：相比于正常对照情况，模拟单眼视下的视觉拥挤效应加重，并且与模糊眼的模糊度数及目标视标的Ecc相关。     

Monovision: a review

In presbyopia, patients can no longer obtain clear vision at distance and near. Monovision is a method of correcting presbyopia where one eye is focussed for distance vision and the other for near. Monovision is a fairly common method of correcting presbyopia with contact lenses and has received renewed interest with the increase in refractive surgery. The present paper is a review of the literature on monovision. The success rate of monovision in adapted contact lens wearers is 59-67%. The main limitations are problems with suppressing the blurred image when driving at night and the need for a third focal length, for example with computer screens at intermediate distances. Stereopsis is impaired in monovision, but most patients do not seem to notice this. These limitations highlight the need to take account of occupational factors. Monovision could cause a binocular vision anomaly to decompensate, so the pre-fitting screening should include an assessment of orthoptic function. Various methods have been used to determine which eye should be given the distance vision contact lens and the literature on tests of ocular dominance is reviewed. It is concluded that tests of blur suppression are most likely to be relevant, but that ocular dominance is not fixed but is rather a fluid, adaptive, phenomenon in most patients. Suitable patients can often be given trial lenses that allow them to experiment with monovision in real world situations and this can be a useful way of revealing the preferred eye for each distance. Of course, no patient should drive or operate machinery until successfully adapted to monovision. Surgically induced monovision is less easily reversed than contact lens-induced monovision, and is only appropriate after a successful trial of monovision with contact lenses.     

Factors influencing success of monovision contact lens fitting: survey of contact lens diplomates.

BACKGROUND: Contact lenses are frequently fitted so that one eye is focused for distance and the other for near (monovision) in order to reduce the dependence of presbyopic patients on bifocal spectacle correction. METHODS: We surveyed Diplomates in the Cornea and Contact Lens section of the American Academy of Optometry (N = 179) regarding their estimates of success with monovision fitting and factors influencing their perception of success. Results were statistically analyzed to determine the fitting philosophies of responders estimating that they achieve high success rates (HSRs) and low success rates (LSRs), respectively. RESULTS: Completed surveys were returned by 98 Diplomates (54.8%), who estimated an overall success rate of approximately 71.7% with monovision; 50.5% "totally successful" (wear monovision correction full-time without problems or need for additional correction) and 21.2% "successful" (wear monovision full-time, but experience some symptoms of blur or other discomfort, may wear over-correction at times for driving or detailed near work). Sighting dominance was the most frequently used method to determine the distant eye, followed by the plus-lens test. The HSR group tended to be more likely to take occupational factors into account when deciding which eye to use for the distance lens, and they used more flexibility in determining the near-add power. The LSR group discontinued monovision sooner than the HSR group, who continued treatment for longer than 4 weeks during the adaptation period much more often for all add ranges. CONCLUSIONS: Practitioners who regard monovision treatment as very successful have somewhat different fitting philosophies than those who regard monovision as unsuccessful. Implementation of highly successful practitioners' fitting techniques may increase success with monovision contact lens fitting.     

Ocular dominance testing

Clinicians typically apply the distance correction to the dominant sighting eye when fitting monovision contact lenses on presbyopic patients. This study investigates if this form of dominance testing correlates with a second type of dominance testing, the eye that will accept the least plus power when viewing a distance target binocularly. The plus lens test more closely simulates the condition under which the patient will be using the monovision correction. The theory is that the nondominant eye will accept more plus to blur than the dominant eye. Our study population consisted of subjects from the ages of 10 to 72 years. Fifty (64%) of the 78 subjects preferred the same eye by the plus lens testing as they did for sighting dominance. Seven subjects (9%) showed the opposite eye dominance with the plus lens test, and 21 subjects (27%) demonstrated no preference in the plus lens testing. The results could indicate that same-eye dominance on both tests may enhance the changes of a successful monovision adaptation.     

Change in refractive anisometropia in presbyopic adults wearing monovision contact lens correction.

BACKGROUND: Researchers studying the refractive development of infant monkeys suggest that monocular refractive error changes in response to induced ametropia; specifically, slightly blurring one eye may cause a difference to develop between each eye's correction (anisometropia) when none existed before wearing the correction. The important question of whether similar changes occur in humans has not been addressed. METHODS: We compared premonovision correction and the correction after at least 12 months of monovision soft contact lens wear (artificially induced anisometropia prescribed to focus one eye for near and the other for distance so that bifocal glasses are not needed) for 62 healthy predominantly female soft contact lens wearers and (a) 62 age- and sex-matched spectacle wearers and (b) 62 age- and generally sex-matched contact lens wearers. Control patients wore corrections of like power and had similar follow-up periods. RESULTS: Development of anisometropia occurred significantly more frequently among monovision wearers than among spectacle (p = 0.043) or contact lens wearing controls (p = 0.025). Changes in anisometropia greater than or equal to 0.50 D, with amounts up to 1.25 D, occurred in 29% of monovision wearers. CONCLUSIONS: Changes in refractive correction occur for adults who have monocular blur intentionally induced with monovision contact lenses. Similar changes may also occur after refractive surgery if one eye is corrected for a different distance than the other. Care should be taken when counseling presbyopic patients so that they are aware of the possibility of inducing refractive changes after monovision correction.     

一种新型多空间频率眼优势度测量方法及其在弱视中的应用

目的利用眼间噪音掩盖技术结合快速对比敏感度测试技术（qCSF）测量弱视患者眼优势度,分析其可行性。方法实验研究。共10例成人弱视患者（弱视组）和17例正常成人对照者（正常组）参与了本研究。双眼先后作为测试眼和非测试眼,给非测试眼分别呈现空间滤波后的噪音和空白背景,测量测试眼的对比敏感度曲线,两者的差值即为非测试眼对测试眼的抑制度。测试时为有效地排除弱视眼对比敏感度损伤对测量结果造成的干扰,设定噪音图案的对比度值为噪音对比度阈值的5倍。数据采用重复测量的方差分析进行比较。结果弱视组不同空间频率抑制度大小眼间差异存在统计学意义（F=24.25,P＜0.01）;而正常组不同空间频率抑制度大小眼间差异无统计学意义（F=0.32,P＞0.05）。此外,弱视组的弱视眼对其对侧眼的抑制度显著低于正常组的非优势眼对其优势眼的抑制度（F=24.29,P<0.01）;弱视组对侧眼对弱视眼的抑制度略微高于正常组优势眼对其非优势眼的抑制度,但差异无统计学意义（F=3.81,P＞0.05）。结论弱视患者存在显著的眼间相互抑制不平衡,表现为弱视眼不能有效抑制对侧眼,而弱视对侧眼对弱视眼的抑制水平与正常人相当。我们认为这一现象可能是导致弱视患者双眼空间视觉损伤的基础。     

Simulating refractive errors: source and observer methods

There are two principal methods of simulating refractive errors. Either the retinal image can be defocused by an optical system, usually a positive lens, placed in front of an observer's eye (observer method), or the source of the retinal image can be defocused as it is projected onto a screen or photograph (source method). There are significant differences between the two methods, differences that make it difficult to compare results. However, the source method, which is the more artificial, seems to be superior for a number of reasons. The results of these two methods can be compared using a common or interchangeable parameter for specifying the level of defocus. A convenient parameter is the size of the defocused image of a point, measured either in image space (linear or angular diameter on the retina) or in object space (angular diameter of the blur disc projected back into object space), with the angular diameter measured from the respective nodal point of the eye. Methods of measuring the angular blur-disc diameter for both methods are discussed and the validity of the formula omega = D delta L, is investigated, where omega is the angular diameter of the blur disc, D is the observer's pupil diameter, and delta L is the dioptric defocus.     

The influence of ocular dominance on monovision--the influence of strength of ocular dominance on visual functions

PURPOSE: Monovision is a method of correction for presbyopia. We have reported the advantage of conventional monovision (the dominant eye is corrected for distance). In this study, we investigated the influence of interocular imbalance of dominancy on the visual function. SUBJECTS AND METHODS: Ten healthy subjects without any ophthalmologic disease participated. After cycloplegia, the eyes of the subjects were corrected by soft contact lenses with an artificial pupil (diameter: 3.0mm). The dominant eye was corrected for distance, and the difference in lens power between the lenses was 2.5 D. The subjects were classified into two groups by strength of the imbalance of sensory dominance, which was determined by using binocular rivalry. Binocular visual functions (visual acuity at various distances, contrast sensitivity, near stereoacuity) were compared between the two groups. RESULTS: Subjects with strong imbalance of sensory dominance showed decreased near visual acuity as well as decreased binocular summation of contrast sensitivity at low spatial frequencies. On the other hand, near stereoacuity was not affected by the imbalance of sensory dominance. CONCLUSION: These results suggest that strong imbalance of sensory dominance interferes with binocular visual functions in monovision. Thus, the evaluation of ocular dominance is crucial for clinical applications of monovision.     

The Orientation Selectivity of Dichoptic Masking Suppression is Contrast Dependent in Amblyopia

PurposeWe aimed to study the effect of stimulus contrast on the orientation selectivity of interocular interaction in amblyopia using a dichoptic masking paradigm.MethodsEight adults with anisometropic or mixed amblyopia and 10 control adults participated in our study. The contrast threshold in discriminating a target Gabor in the tested eye was measured with mean luminance in the untested eye, as well as with a bandpass oriented filtered noise in the other eye at low spatial frequency (0.25 c/d). Threshold elevation, which represents interocular suppression, was assessed using a the dichoptic masking paradigm (i.e. the contrast threshold difference between the target only and masked conditions), for each eye. Orientation selectivity of the interocular suppression as reflected by dichoptic masking was quantified by the difference between the parallel and orthogonal masking configurations. Two levels of mask''s contrast (3 times or 10 times that of an individual''s contrast threshold) were tested in this study.ResultsThe strength of dichoptic masking suppression was stronger at high, rather than low mask contrast in both amblyopic and control subjects. Normal controls showed orientation-dependent dichoptic masking suppression both under high and low contrast levels. However, amblyopes showed orientation-tuned dichoptic masking suppression only under the high contrast level, but untuned under the low contrast level.ConclusionsWe demonstrate that interocular suppression assessed by dichoptic masking is contrast-dependent in amblyopia, being orientation-tuned only at high suprathreshold contrast levels of the mask.     

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.     

Interocular Suppression as Revealed by Dichoptic Masking Is Orientation-Dependent and Imbalanced in Amblyopia

PurposeWe investigate the orientation tuning of interocular suppression using a dichoptic masking paradigm in adult controls and amblyopes.MethodsFourteen adults with anisometropic or mixed amblyopia and 10 control adults participated in our study. Contrast sensitivity was measured by presenting a target Gabor in the tested eye and mean luminance in the untested eye (monocular) and by presenting a target in the tested eye and a bandpass oriented filtered noise in the other eye (masked). Interocular suppression was defined as the thresholds difference between the monocular and masked conditions for each eye. Interocular suppression was measured under parallel and orthogonal suppression configurations. The peak spatial frequency of the target and mask was 0.25 c/d in experiment 1 (low), 1.31 c/d in experiment 2 (mid), and 6.87 c/d in experiment 3 (high).ResultsThe masking suppression induced by the amblyopic eye was less strong than that induced by the fellow eye. The suppression from the fellow eye was similar to that observed in the controls. Interocular suppression under parallel configuration was less strong than under orthogonal configuration in amblyopes at low and mid spatial frequency, but not at high spatial frequency.ConclusionsWe demonstrate that the abnormal interocular masking in amblyopia displays the expected characteristic of orientation selectivity expected of normal controls at low and mid spatial frequency, but not at high spatial frequency. The dichoptic masking imbalance between the eyes of amblyopes results in a net suppression of the amblyopic eye during binocular viewing, modeling clinical suppression.     

Intra- and interocular colour-specific activation during dichoptic suppression

A new psychophysical method, based on dichoptic suppression, is introduced to study intra- and interocular colour activations. An experiment is performed which shows that activation of a specific colour in one eye may cancel suppression of the same colour in the ipsi-lateral eye or in the contra-lateral eye at non-corresponding retinal locations. A control experiment shows that the effect is not due to an overall response-bias to the activated colour. The colour-specific intra- and interocular activation might play a role in various colour-based percepts known in the literature.