Factors influencing interocular blur suppression

An Important feauture of monovision correction is the ability of the binocular system to suppress blur from the defocused eye (interocular blur suppression). We conducted a study with three subjects and found that interocular blur suppression improved with higher levels of monocular defocus (addition powers in monovision) but was not affected by the eye defocused (sighting dominant or non-domninant) or by pupil size. The selection and management of monovision patients may be assisted by an understading of the understanding of the underlying suppression preocesses.     

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.     

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.     

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.     

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.     

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.     

Suppression behavior analyzed as a function of monovision addition power

Monovision, the use of a monocular addition for near viewing, is a clinical technique sometimes used to correct presbyopia. This technique attempts to maintain binocular function while requiring a degree of central suppression. We examined suppression behavior in spectacle monovision as a function of addition power. Suppression behavior was determined by measuring the length and frequency of periods of suppression for a range of monocular addition powers. Testing was conducted at viewing distances of 6 m and 40 cm. The most striking result is the existence of a near/distance differential: the monocular addition power required to stabilize suppression at near is greater than at distance. It was also found that suppression behavior may be stable even in the presence of a relatively high level of stereoscopic acuity. The relation between the contradictory needs for suppression and binocular functioning under monovision conditions is discussed.     

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.     

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.     

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.     

Short term responses to soft contact lens corrections for presbyopia

Eleven subjects were each fitted with five different soft contact lens corrections for presbyopia. The correction types were distance contact lenses with lookover spectacles, concentric bifocals, monovi-sion, modified monovision and progressive bifocal contact lenses. Subjects were asked to rate each contact lens correction in terms of distance, intermediate, near and peripheral vision, confidence when walking and climbing stairs, eye-hand co-ordination, performance on work tasks, vision difficulties in bright and dim ambient illumination and the correction most preferred for daily wear. There were few significant differences between ratings for the different corrections. Monovision, modified monovision and the concentric bifocal corrections were the preferred options for daily wear.     

The effect of monovision contact lens wear on driving performance

Background : A number of studies have highlighted the problems with driving reported by wearers of monovision contact lens corrections. In this study, we wished to investigate this further, by determining whether driving performance as measured on the open road under daytime conditions is worse when drivers wear their monovision contact lenses compared to their habitual correction. Methods : Thirteen subjects with healthy eyes and corrected visual acuity of 6/6 were selected. Each had worn monovision contact lenses for at least three months. All subjects had their driving performance assessed while driving their own vehicles on an open road course, with both monovision contact lenses and their other habitual correction (spectacles or unaided). Results : No statistically significant differences were found in driving performance when subjects wore their monovision contact lenses compared to when they wore their habitual distance correction. Conclusions : The results indicate that monovision does not adversely affect driving performance in daylight hours for adapted wearers. However, limitations in the study design are acknowledged, including the relatively small sample size, lack of standardisation of the habitual correction and the use of adapted wearers. Future studies are recommended to investigate these issues further.     

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。     

Peripheral visual acuity with monovision and other contact lens corrections for presbyopia

We have conducted two experiments to investigate the effect of monovision and other contact lens corrections for presbyopia upon peripheral visual acuity. In the first study, we measured binocular peripheral visual acuity using Landolt rings with seven subjects wearing a monovision correction. The Landolt rings were presented at eccentricities of 10, 20, 40, and 70 degrees on each side of the subject, with near additions of +1.50 D, +2.50 D, and no addition. We found no significant effect of monovision correction on peripheral visual acuity. In the second experiment we measured the peripheral visual acuity of 11 presbyopic subjects wearing distance contact lenses with lookover spectacles, soft progressive bifocal contact lenses, soft concentric bifocal contact lenses, monovision contact lenses, modified monovision contact lenses, and hard bifocal contact lenses using Koenig bar targets. There were no significant differences in peripheral visual acuity between any of the contact lens corrections for presbyopia.     

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.     

Factors influencing success and failure in monovision

This study compared the visual performance of 70 successful and 18 failed monovision (MV) wearers, measured before contact lens dispensing. Compared with successful MV wearers, the failed group showed greater levels of ghosting at distance and near, lost more stereoacuity at 6 m, and lost slightly more near visual acuity. The failed MV group was also older on average than the successful group. Both groups showed worse visual acuity at distance and near with MV than at spectacle baseline, as well as worse stereoacuity at 6 m and 40 cm. Discriminant analysis indicated that distance ghosting, distance stereoacuity, and age were predictive of both success and failure (78% sensitivity; 82% specificity). An investigation, before lens fitting, of other effects of monocular blur on binocular function, as well as an assessment of personal characteristics such as motivation and the nature of visual demands, may further improve the accuracy of prediction of patient success with MV found in this study.     

Monovision contact lens wear and occupational task performance

The effects of monovision (MV) contact lens wear on the performance of occupational-type nearpoint tasks was evaluated on 18 presbyopic subjects (ages 44 to 67 years) by comparing MV performance (MV condition) to that with distance contact lenses with reading glasses (BV condition). Each subject had correctable distance visual acuity of 6/6 (20/20) in each eye, at least 60 sec arc of near stereopsis, good ocular health, and no previous MV experience. Time performance and error performance for 3 nearpoint occupational tasks (pointers and straws, card filing, and letter editing) were measured with the MV correction and BV correction. Measurements were taken at dispensing and at 2 weeks and 8 weeks after dispensing. Subjects were instructed to wear the MV soft spherical contact lenses at least 8 h per day. We measured BV time performance to be better than MV time performance by 2.8 to 5.7% and also measured an increased number of errors with MV.     

Stereopsis in presbyopes wearing monovision and simultaneous vision bifocal contact lenses

One of the advantages suggested for contact lens bifocals over monovision treatment of presbyopia is that there may be less impairment of binocular function. We evaluated nearpoint stereoposis on the Titmus stereotest for 10 presbyopic patients. Testing was done under five conditions; monovision and binocular correction with each of four marketed simultaneous bifocal contact lenses. Simultaneous vision bifocals tested produced at least as much reduction in stereopsis as monovision compared to baseline spectacle correction. Repeat testing of bifocal stereopsis with best near over-refraction suggested that a substantial portion of the stereo reduction could be attributed to insufficient effective adds with the bifocal contacts.     

Comparison of multifocal and monovision soft contact lens corrections in patients with low-astigmatic presbyopia.

PURPOSE: The purpose of this study was to assess visual performance and patient satisfaction with two presbyopic soft contact lens modalities. METHODS: A crossover study of 38 patients with presbyopia was conducted. Patients were randomized first into either multifocal (Bausch & Lomb SofLens Multifocal) or monovision (SofLens 59) for 1 month. Visual performance was measured with high- and low-contrast visual acuity at distance and near and near stereoacuity. Patients' satisfaction was measured by the National Eye Institute Refractive Error Quality of Life Instrument questionnaire and by recording the patient's final lens preference. RESULTS: Patients maintained at least 20/20 binocular vision with both multifocal (MF) and monovision (MV) contact lenses under high-contrast conditions at distance and near. Under low-contrast conditions, patients lost less than a line of vision from the best spectacle correction to either multifocal or monovision contact lens correction at distance (pMF = 0.001, pMV = 0.006). Under low-contrast conditions at near, multifocal wearers lost five to six letters and monovision wearers lost two letters of vision (pMF < 0.001, pMV = 0.03, pMF/MV = 0.005). The average stereoacuity decreased by 79 s arc with monovision vs. multifocal contact lenses (p = 0.002). On the NEI-RQL, patients reported worse clarity of vision (pMF = 0.01, pMV < 0.001), more symptoms (pMF = 0.09, pMV = 0.01), and an improvement in their appearance with contact lens wear (pMF < 0.001, pMV < 0.001). Seventy-six percent of patients reported that they preferred multifocal contact lenses, and 24% preferred monovision contact lenses (p = 0.001). CONCLUSION: The majority of our patients preferred multifocals to monovision, most likely because the Bausch & Lomb SofLens Multifocal provides excellent visual acuity without compromising stereoacuity to the same degree as monovision.