Daily dose-response from short-term monocular deprivation in adult humans

Short-term monocular deprivation (MD) shifts sensory eye balance in favour of the previously deprived eye. The effect of MD on eye balance is significant but brief in adult humans. Recently, researchers and clinicians have attempted to implement MD in clinical settings for adults with impaired binocular vision. Although the effect of MD has been studied in detail in single-session protocols, what is not known is whether the effect of MD on eye balance deteriorates after repeated periods of MD (termed 'perceptual deterioration'). An answer to this question is relevant for two reasons. Firstly, the effect of MD (i.e., dose-response) should not decrease with repeated use if MD is to be used therapeutically (e.g., daily for weeks). Second, it bears upon the question of whether the neural basis of the effects of MD and contrast adaptation, a closely related phenomenon, is the same. The sensory change from contrast adaptation depends on recent experience. If the observer has recently experienced the same adaptation multiple times for consecutive days, then the adaptation effect will be smaller because contrast adaptation exhibits perceptual deterioration, so it is of interest to know if the effects of MD follow suit. This study measured the effect of 2-h MD for seven consecutive days on binocular balance of 15 normally sighted adults. We found that the shift in eye balance from MD stayed consistent, showing no signs of deterioration after subjects experienced multiple periods of MD. This finding shows no loss of effectiveness of repeated daily doses of MD if used therapeutically to rebalance binocular vision in otherwise normal individuals. Furthermore, ocular dominance plasticity, which is the basis of the effects of short-term MD, does not seem to share the property of 'perceptual deterioration' with contrast adaptation, suggesting different neural bases for these two related phenomena.

Binocular imbalance in patients after implantable collamer lens V4c implantation or femtosecond laser-assisted in situ keratomileusis for myopia with presbyopia

Aim

To investigate the long-term safety, efficacy, and binocular balance of monovision surgery using Implantable Collamer Lens (ICL) V4c implantation and Femtosecond Laser-Assisted in situ Keratomileusis (FS-LASIK) for the treatment of myopic patients with presbyopia.

Methods

This case series study involved 90 eyes of 45 patients (male/female = 19/26; average age:46.27 ± 5.54 years; average follow-up time:48.73 ± 14.65 months) who underwent the aforementioned surgery to treat myopic presbyopes. Data on manifest refraction, corrected distance visual acuity, dominant eye, presbyopic addition, intraocular pressure, and anterior segment biometric parameters were collected. The visual outcomes and binocular balance at 0.4 m, 0.8 m, and 5 m were documented.

Results

The safety index for the ICL V4c and FS-LASIK groups were 1.24 ± 0.27 and 1.04 ± 0.20 (p = 0.125), respectively. Binocular visual acuity (logmar) for 0.4 m, 0.8 m, and 5 m were -0.03 ± 0.05, -0.03 ± 0.02, and 0.10 ± 0.03 for the ICL V4c group, and -0.02 ± 0.09, -0.01 ± 0.02, and 0.06 ± 0.04 for the FS-LASIK group, respectively. The proportions of all patients with imbalanced vision at 0.4 m, 0.8 m, and 5 m distances were 68.89, 71.11, and 82.22%, respectively (all p > 0.05 between the two groups). There were significant differences in refraction between the balanced and imbalanced vision for patients at 0.4 m distance (for non-dominant eye spherical equivalent [SE]: -1.14 ± 0.17D and -1.47 ± 0.13D, p < 0.001), 0.8 m distance (for preoperative ADD:0.90 ± 0.17D and 1.05 ± 0.11D, p = 0.041), and 5 m distance (for non-dominant SE: -1.13 ± 0.33D and -1.42 ± 0.11D, p < 0.001).

Conclusion

ICL V4c implantation and FS-LASIK monovision treatment demonstrated good long-term safety and binocular visual acuity at various distances. After the procedure, the imbalanced patients' vision is primarily related to the age-related presbyopia and anisometropia progression caused by the monovision design.

Rapid Alternate Flicker Modulates Binocular Interaction in Adults With Abnormal Binocular Vision

Purpose

The current understanding of binocular processing is primarily derived from static spatial visual perception: this leaves the role of temporal information unclear. In this study, we addressed this gap by testing the effect of alternating flicker on binocular information processing in adults with abnormal binocular vision. Our goal was to determine which temporal frequency optimally balanced input from both eyes.

Methods

We took measurements in four groups of human adults: 10 normal adults with the individual's nondominant eye covered by a 2% neutral density filter (aged 25.60 ± 1.43 years, experiment 1), 9 nonamblyopic anisometropes (aged 24.33 ± 1.66 years, experiment 2), 7 amblyopes (aged 26.5 ± 1.64 years, experiment 3), and 7 treated amblyopes (aged 24 ± 3.21 years, experiment 4). The balance point (BP), where participants' two eyes are equally effective, was measured using a binocular orientation combination task at four spatial frequencies (SFs; 0.5-4 c/d) and five temporal frequencies (TFs; baseline and 4, 7, 10, and 15 Hz). Its log transformation |logBP| was taken into further analysis.

Results

We observed clear U-shaped temporal tuning of the |logBP| for the entire range of TFs (that we measured: trough occurred at 7 Hz). This pattern occurred and was significant in all four groups (P < 0.001). In addition, the effect of SFs on |logBP| was significant in normal, amblyopic, and treated amblyopic groups (all P < 0.001) and was marginally significant in the nonamblyopic anisometropic group (P = 0.086).

Conclusions

Alternating flicker around 7 Hz may be the optimal temporal frequency for balancing eyes in human adults with binocular imbalance.

Internal neural states influence the short-term effect of monocular deprivation in human adults

The adult human visual system maintains the ability to be altered by sensory deprivation. What has not been considered is whether the internal neural states modulate visual sensitivity to short-term monocular deprivation. In this study we manipulated the internal neural state and reported changes in intrinsic neural oscillations with a patched eye open or closed. We investigated the influence of eye open/eye closure on the unpatched eye's contrast sensitivity and ocular dominance (OD) shifts induced by short-term monocular deprivation. The results demonstrate that internal neural states influence not only baseline contrast sensitivity but also the extent to which the adult visual system can undergo changes in ocular dominance.

Do monocular myopia children need to wear glasses? Effects of monocular myopia on visual function and binocular balance

Objective

This study aims to compare the binocular visual functions and balance among monocular myopic adolescents and adults and binocular low myopic adolescents and explore whether monocular myopia requires glasses.

Methods

A total of 106 patients participated in this study. All patients were divided into three groups: the monocular myopia children group (Group 1 = 41 patients), the monocular myopia adult group (Group 2 = 26 patients) and the binocular low myopia children group (Group 3 = 39 patients). The refractive parameters, accommodation, stereopsis, and binocular balance were compared.

Results

The binocular refractive difference in Group 1, Group 2, and Group 3 was -1.37 ± 0.93, -1.94 ± 0.91, and -0.32 ± 0.27 D, respectively. Moreover, uncorrected visual acuity (UCVA), spherical equivalent (SE) and monocular accommodative amplitude (AA) between myopic and emmetropic eyes in Group 1 and Group 2 were significantly different (all P < 0.05). There was a significant difference in the accommodative facility (AF) between myopic and emmetropic eyes in Group 2 (t = 2.131, P = 0.043). Furthermore, significant differences were found in monocular AA (t = 6.879, P < 0.001), binocular AA (t = 5.043, P < 0.001) and binocular AF (t = -3.074, P = 0.003) between Group 1 and Group 2. The normal ratio of stereopsis according to the random dots test in Group 1 was higher than in Group 2 (χ2 = 14.596, P < 0.001). The normal ratio of dynamic stereopsis in Group 1 was lower than in Group 3 (χ2 = 13.281, P < 0.001). The normal signal-to-noise ratio of the binocular balance point in Group 1 was lower than Group 3 (χ2 = 4.755, P = 0.029).

Conclusion

First, monocular myopia could lead to accommodative dysfunction and unbalanced input of binocular visual signals, resulting in myopia progression. Second, monocular myopia may also be accompanied by stereopsis dysfunction, and long-term uncorrected monocular myopia may worsen stereopsis acuity in adulthood. In addition, patients with monocular myopia could exhibit stereopsis dysfunction at an early stage. Therefore, children with monocular myopia must wear glasses to restore binocular balance and visual functions, thereby delaying myopia progression.

Rapid alternate monocular deprivation does not affect binocular balance and correlation in human adults

Recent studies show that the human adult visual system exhibits neural plasticity. For instance, short-term monocular deprivation shifts the eye dominance in favor of the deprived eye. This phenomenon is believed to occur in the primary visual cortex by reinstating neural plasticity. However, it is unknown whether the changes in eye dominance after monocularly depriving the visual input can also be induced by alternately depriving both eyes. In this study, we found no changes in binocular balance and interocular correlation sensitivity after a rapid (7 Hz), alternate and monocular deprivation for one hour in adults. Therefore, the effect of short-term monocular deprivation cannot seem to be emulated by alternately and rapidly depriving both eyes.Significance statementPrevious work has shown that short-term binocular function disruption, which its most extreme form is monocular deprivation, could induce neural plasticity in adult visual system. In this study, we found a balanced deprivation of binocular function could not induce a neuroplastic change in human adults. It appears that ocular dominance plasticity in human adults is unique in so far as it is only driven by an input imbalance not balanced deprivation of binocular function.

Children with Dyslexia Have Altered Cross-Modal Processing Linked to Binocular Fusion. A Pilot Study

Introduction

The cause of dyslexia, a reading disability characterized by difficulties with accurate and/or fluent word recognition and by poor spelling and decoding abilities, is unknown. A considerable body of evidence shows that dyslexics have phonological disorders. Other studies support a theory of altered cross-modal processing with the existence of a pan-sensory temporal processing deficit associated with dyslexia. Learning to read ultimately relies on the formation of automatic multisensory representations of sounds and their written representation while eyes fix a word or move along a text. We therefore studied the effect of brief sounds on vision with a modification of binocular fusion at the same time (using the Maddox Rod test).

Methods

To check if the effect of sound on vision is specific, we first tested with sounds and then replaced them with proprioceptive stimulation on 8 muscular sites. We tested two groups of children composed respectively of 14 dyslexic children and 10 controls.

Results

The results show transient visual scotoma (VS) produced by sensory stimulations associated with the manipulation of oculomotor balance, the effect being drastically higher in the dyslexic group. The spatial distribution of the VS is stochastic. The effect is not specific for sounds but exists also with proprioceptive stimulations.

Discussion

Although there was a very significant difference between the two groups, we were not able to correlate the (VS) occurrence with the dyslexic’s reading performance. One possibility to confirm the link between VS and reading impairment would be to find a specific treatment reducing the occurrence of the VS and to check its effect on dyslexia.