Tonic Accommodation Research Articles

The first experience of parallel measurements of objective accommodation parameters in children with myopia using various instruments: in search of a common denominator

Purpose: to study the relationship between the parameters of reflex and tonic accommodation measured using various objective methods.Material and methods. A comprehensive parallel study of objective accommodation parameters of 57 children (114 eyes) with low and moderate myopia (average -2.6 ± 1.4 D) aged from 8 to 12 years (average 9.9 ± 1.6 years) was carried out on three devices: Grand Seiko WAM-5500K, Acomoref 2 K-model Righton; TONOREF III, Nidek.Results. Both coincidences and differences of the indicators obtained by different methods as well as their correlations were revealed: positive - between the values of AR in the open field and in the virtual space (r = 0.23, r = 0.2); between the virtual responses to Righton K-2 and Nidek (r = 0.38); direct correlations of the accommodation response with accommodation tones. A correlation of average strength (r = 0.44) was found between the HAT on the Grand Seiko WR-5100K and the CMF on the Righton K2, which allows us to consider them as synonymous indicators. A negative relationship of CMF with PRA and SE refraction was found. A positive correlation of CMF with the rate of progression of myopia and a negative one with PRA suggests that a high CMF is a bad prognostic sign. However, CMF positively correlates with the magnitude of the accommodative response on all three devices. In this case, it turns out that an increase in CMF accompanies an increase in the amplitude of accommodation and, therefore, is not always a troublesome factor. Perhaps we are dealing with the limits of the norm for this indicator, which still need to be studied.Conclusion. With the help of objective methods of studying qualitatively different characteristics of one process, it is possible to investigate the actual and prognostic parameters of accommodation, which will allow us to offer an individualized approach to the treatment of patients with myopia using optical and drug instruments.

Spasm of Near Reflex: Objective Assessment of the Near-Triad.

PurposeTo characterize binocular steady-state accommodation, pupil and convergence responses (near triad) in spasm of near reflex (SNR) before and after optical and pharmacological intervention. To identify the putative source of SNR in the neural control schema of accommodation-vergence interaction using controls-engineering modeling.MethodsNear-triad of 15 patients with SNR (9 to 23 years) was recorded using an infrared photorefractor at 2m viewing distance for 120s during clinical presentation, after optical fogging intended to relieve spasm, with cycloplegia, post-cycloplegia and long-term follow-up visits. Data were also collected without cycloplegia in 15 age-matched controls. Schor (1999) model was used to computationally simulate accommodation and vergence responses of controls and SNR.ResultsBoth eyes of SNR exhibited significant myopia and refraction fluctuations (<1.0Hz) during clinical presentation [median (25th to 75th IQR) refraction: −1.7D (−3.2 to −0.8D); root mean squared (RMS) deviation: 1.1D (0.5 to 1.5D)], relative to controls [0.8D (−0.03 to 1.4D); 0.2D (0.1 to 0.3D)] (p < 0.001). These decreased after optical fogging, largely eliminated with cycloplegia and partially re-appeared in the post-cycloplegia and follow-up visits. SNR responses could be modeled by increasing the gain and decay time of tonic accommodation, vis-à-vis, controls. Pupil and convergence responses in SNR were similar to controls at all visits (p > 0.1).ConclusionsExaggerated fluctuations of steady-state accommodation may be a signature feature of SNR, even while their pupil and convergence responses may remain unaffected. These fluctuations may arise from the tonic accommodation controller, the properties of which could be potentially altered after optical fogging to relieve the disorder.

The Accommodation Response and Facility between Children and Young Adults

Tonic accommodation decreased with age among children. In young adults, late-onset myopia will develop due to occupational near vision demands. This study aims to investigate the accommodation response and facility between children and young adults, in emmetrope (non-myopic) and myope group. The accommodation response and facility of young adults and children were measured using monocular estimation method (MEM), monocular accommodative facility (MAF) and binocular accommodative facility (BAF) with an exposure of near task for 15 minutes. Near task has significantly increased the lag of accommodation in all groups (p&lt;0.05). However, the accommodation facility was not affected by near work in all groups (p&gt;0.05). Keywords: accommodation response, accommodation facility, myopes, emmetropes. eISSN: 2398-4287© 2020. The Authors. Published for AMER ABRA cE-Bs by e-International Publishing House, Ltd., UK. This is an open access article under the CC BYNC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer–review under responsibility of AMER (Association of Malaysian Environment-Behaviour Researchers), ABRA (Association of Behavioural Researchers on Asians) and cE-Bs (Centre for Environment-Behaviour Studies), Faculty of Architecture, Planning &amp; Surveying, Universiti Teknologi MARA, Malaysia. DOI: https://doi.org/10.21834/ebpj.v5i14.2168

Surround Propinquity and Tonic Accommodation.

Previous studies of dark focus have found evidence of a propinquity response, in which subjects accommodate to the perceived distance of their surroundings despite being in absolute darkness. Their distance perception in a lighted room allows a spatial representation to persist within the darkened room. This study sought to establish the significance and magnitude of the propinquity response in a large sample of young adults, and to determine whether the propinquity response can be predicted by a subject's initial dark focus in an unknown dark room. Dark focus was measured with a dynamic infrared optometer (Plusoptix PowerRef 3) in 30 young adult subjects, 26 of whom were naive to the testing room and its dimensions. Dark focus was then measured at varying dioptric wall distances of 0.25-4D. The subject viewed the lighted room before each measurement. For each individual, the dark focus was plotted as a function of dioptric wall distance. The slope of this function was used as a measure of the propinquity response. The mean initial dark focus value was 1.05D (SD 1.04D) for the 26 naive subjects. The mean slope of the plot of dark focus as a function of dioptric wall distance was small (+0.097), yet highly statistically significant (P = .0002). The propinquity response function showed no statistically significant quadratic or cubic trends, and so may be considered linear. No statistically significant correlation was found between naive dark focus and propinquity response (r = +0.246, P = .226). Propinquity seems to be a small but statistically significant factor in dark focus measurements. Though it is unlikely to contaminate tonic accommodation measurements in large samples under normal laboratory conditions, a minority of individuals exhibit large propinquity responses equal to that of proximal accommodation in lighted conditions.

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Tonic accommodation predicts closed-loop accommodation responses

The purpose of this study is to examine the potential relationship between tonic accommodation (TA), near work induced TA-adaptation and the steady state closed-loop accommodation response (AR). Forty-two graduate students participated in the study. Various aspects of their accommodation system were objectively measured using an open-field infrared auto-refractor (Grand Seiko WAM-5500). Tonic accommodation was assessed in a completely dark environment. The association between TA and closed-loop AR was assessed using linear regression correlations and t-test comparisons. Initial mean baseline TA was 1.84diopter (D) (SD±1.29D) with a wide distribution range (−0.43D to 5.14D). For monocular visual tasks, baseline TA was significantly correlated with the closed-loop AR. The slope of the best fit line indicated that closed-loop AR varied by approximately 0.3D for every 1D change in TA. This ratio was consistent across a variety of viewing distances and different near work tasks, including both static targets and continuous reading. Binocular reading conditions weakened the correlation between baseline TA and AR, although results remained statistically significant. The 10min near reading task with a 3D demand did not reveal significant near work induced TA-adaptation for either monocular or binocular conditions. Consistently, the TA-adaptation did not show any correlation with AR during reading. This study found a strong association between open-loop TA and closed-loop AR across a variety of viewing distances and different near work tasks. Difference between the correlations under monocular and binocular reading condition suggests a potential role for vergence compensation during binocular closed-loop AR.

Stereoscopic Viewing Can Induce Changes in the CA/C Ratio.

Stereoscopic displays challenge the neural cross-coupling between accommodation and vergence by inducing a constant accommodative demand and a varying vergence demand. Stereoscopic viewing calls for a decrease in the gain of vergence accommodation, which is the accommodation caused by vergence, quantified by using the convergence-accommodation to convergence (CA/C) ratio. However, its adaptability is still a subject of debate. Cross-coupling (CA/C and AC/A ratios) and tonic components of vergence and accommodation were assessed in 12 participants (27.5 ± 5 years, stereoacuity better than 60 arc seconds, 6/6 acuity with corrected refractive error) before and after a 20-minute exposure to stereoscopic viewing. During stimulation, vergence demand oscillated from 1 to 3 meter angles along a virtual sagittal line in sinusoidal movements, while accommodative demand was fixed at 1.5 diopters. Results showed a decreased CA/C ratio (-10.36%, df = 10, t = 2.835, P = 0.018), with no change in the AC/A ratio (P = 0.090), tonic vergence (P = 0.708), and tonic accommodation (P = 0.493). These findings demonstrated that the CA/C ratio can exhibit adaptive adjustments. The observed nature and amount of the oculomotor modification failed to compensate for the stereoscopic constraint.

Night myopia is reduced in binocular vision.

Night myopia, which is a shift in refraction with light level, has been widely studied but still lacks a complete understanding. We used a new infrared open-view binocular Hartmann-Shack wave front sensor to quantify night myopia under monocular and natural binocular viewing conditions. Both eyes' accommodative response, aberrations, pupil diameter, and convergence were simultaneously measured at light levels ranging from photopic to scotopic conditions to total darkness. For monocular vision, reducing the stimulus luminance resulted in a progression of the accommodative state that tends toward the subject's dark focus or tonic accommodation and a change in convergence following the induced accommodative error. Most subjects presented a myopic shift of accommodation that was mitigated in binocular vision. The impact of spherical aberration on the focus shift was relatively small. Our results in monocular conditions support the hypothesis that night myopia has an accommodative origin as the eye progressively changes its accommodation state with decreasing luminance toward its resting state in total darkness. On the other hand, binocularity restrains night myopia, possibly by using fusional convergence as an additional accommodative cue, thus reducing the potential impact of night myopia on vision at low light levels.

Agreement between clinical and laboratory methods assessing tonic and cross‐link components of accommodation and vergence

BackgroundSeveral tests are available to optometrists for investigating accommodation and vergence. This study sought to investigate the agreement between clinical and laboratory methods and to clarify which components are actually measured when tonic and cross‐link of accommodation and vergence are assessed.MethodsTonic vergence, tonic accommodation, accommodative vergence (AC/A) and vergence accommodation (CA/C) were measured using several tests. Clinical tests were compared to the laboratory assessment, the latter being regarded as an absolute reference. The repeatability of each test and the degree of agreement between the tests were quantified using Bland‐Altman analysis.ResultsThe values obtained for each test were found to be stable across repetitions; however, in most cases, significant differences were observed between tests supposed to measure the same oculomotor component. Tonic and cross‐link components cannot be easily assessed because proximal and instrumental responses interfere with the assessment. Other components interfere with oculomotor assessment. Specifically, accommodative divergence interferes with tonic vergence estimation and the type of accommodation considered in the AC/A ratio affects its magnitude. Results on clinical tonic accommodation and clinical CA/C show that further investigation is needed to clarify the limitations associated with the use of difference of Gaussian as visual targets to open the accommodative loop.ConclusionsAlthough different optometric tests of accommodation and vergence rely on the same basic principles, the results of this study indicate that clinical and laboratory methods actually involve distinct components. These differences, which are induced by methodological choices, must be taken into account, when comparing studies or when selecting a test to investigate a particular oculomotor component.

Reduced vergence adaptation is associated with a prolonged output of convergence accommodation in convergence insufficiency.

Convergence insufficiency (CI) is a developmental visual anomaly defined clinically by a reduced near point of convergence, a reduced capacity to view through base-out prisms (fusional convergence); coupled with asthenopic symptoms typically blur and diplopia. Experimental studies show reduced vergence parameters and tonic adaptation. Based upon current models of accommodation and vergence, we hypothesize that the reduced vergence adaptation in CI leads to excessive amounts of convergence accommodation (CA). Eleven CI participants (mean age=17.4±2.3 years) were recruited with reduced capacity to view through increasing magnitudes of base out (BO) prisms (mean fusional convergence at 40 cm=12±0.9Δ). Testing followed our previous experimental design for (n=11) binocularly normal adults. Binocular fixation of a difference of Gaussian (DoG) target (0.2 cpd) elicited CA responses during vergence adaptation to a 12Δ BO. Vergence and CA responses were obtained at 3 min intervals over a 15 min period and time course were quantified using exponential decay functions. Results were compared to previously published data on eleven binocular normals. Eight participants completed the study. CI's showed significantly reduced magnitude of vergence adaptation (CI: 2.9Δ vs. normals: 6.6Δ; p=0.01) and CA reduction (CI=0.21 D, Normals=0.55 D; p=0.03). However, the decay time constants for adaptation and CA responses were not significantly different. CA changes were not confounded by changes in tonic accommodation (Change in TA=0.01±0.2D; p=0.8). The reduced magnitude of vergence adaptation found in CI patients resulting in higher levels of CA may potentially explain their clinical findings of reduced positive fusional vergence (PFV) and the common symptom of blur.

Influence of cycloplegia with topical cyclopentolate on higher-order aberrations in myopic children

To investigate the influence of cycloplegia with topical cyclopentolate on wavefront aberrations in myopic children. This is a prospective, comparative study. Twenty-eight myopic children with a mean age of 7.25 ± 2.55 were enrolled in this study. We evaluated refraction and wavefront aberrations before and after cycloplegia with 1% cyclopentolate hydrochloride. Ocular and corneal aberrations were simultaneously measured and compared with each other. Individual Zernike components were also analyzed up to the sixth order. All these parameters were compared before and after cycloplegia. Ocular higher-order aberrations (HOAs) significantly increased after cycloplegia (P=0.012 for spherical-like and P=0.015 for total HOAs). Corneal HOAs did not change after cycloplegia. When corneal and ocular HOAs were compared, the ocular HOAs were significantly smaller than the corneal HOAs in spherical-like aberrations (P<0.001) and total HOAs (P=0.006). As for individual Zernike components, ocular aberration generally showed smaller or equivalent values in comparison with corneal aberration. In addition, each Zernike component showed a large standard deviation. Internal optics compensates for corneal HOAs in myopic children, and paralysis of tonic accommodation with cyclopentolate considerably affects ocular HOAs. However, inter-individual variation in each Zernike component is quite large in myopic children.

Influences of Cycloplegia with Topical Atropine on Ocular Higher-Order Aberrations

To investigate the influence of cycloplegia with topical atropine on higher-order aberrations (HOAs) of the eye in children. Prospective, noncomparative study. Twenty-three eyes of 23 subjects (11 boys and 12 girls) with hyperopia, ranging in age from 3 to 12 years (average, 5.74 years), were enrolled in this study. Refraction and wavefront aberration were evaluated before and after cycloplegia with topical instillation of 1% atropine solution administered twice daily for 1 week. Ocular and corneal HOAs were measured simultaneously, and individual Zernike components were analyzed for a 6-mm pupil up to the 6th order. All these parameters were compared before and after cycloplegia. Ocular and corneal HOAs before and after cycloplegia. Cycloplegia with topical atropine significantly increased spherical equivalent refraction from +1.92±1.53 diopters (D) to +3.10±1.61 D (P<0.01, paired t test). Ocular HOAs significantly increased from 0.282±0.086 μm to 0.316±0.087 μm for coma-like aberrations (P=0.02), from 0.169±0.058 μm to 0.192±0.076 μm for spherical-like aberrations (P=0.02), and from 0.333±0.093 μm to 0.377±0.095 μm for total HOAs (P=0.01). Corneal HOAs did not change after cycloplegia. As for individual Zernike components, significant changes were found in C3(1) and C4(0) after cycloplegia (P<0.05). The induced changes in C4(0) were correlated significantly with those in spherical equivalent refraction (Pearson's correlation coefficient, R=0.45; P=0.03). Cycloplegia with atropine induced significant hyperopic shift and increases in ocular HOAs in children, leading to reduction in optical quality of the eye. It may be that physiologic tonic accommodation plays a role in improving retinal image quality by decreasing HOAs and refractive errors. The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Effect of heterophoria type and myopia on accommodative and vergence responses during sustained near activity in children

The influence of phoria-type and myopia on changes to vergence and accommodation during prolonged near-task was examined in 53 children. Participants were classified into phoria and refractive categories based on near phoria and cycloplegic refraction respectively. Measures of near phoria, binocular (BA) and monocular accommodation (MA) were obtained before and during a 20min task when children binocularly fixated a high-contrast target at 33cm through best corrective lenses. Vergence adaptation and accommodative adaptation were quantified using changes to near phoria and tonic accommodation respectively. The direction and magnitude of vergence adaptation was modified by the phoria-type (p<0.001). Emmetropic exophores displayed convergent (less exo than baseline) adaptation while esophores showed divergent shifts (less eso than baseline) in phoria upon prolonged fixation. Myopic children also followed a similar pattern but showed greater divergent (or less convergent) shift (p<0.001) in vergence adaptation for all phoria categories compared to emmetropes. Phoria-type also influenced the pattern of BA vs. MA (p<0.001) such that exophores showed BA>MA while esophores showed MA>BA in both refractive groups. Accommodative adaptation was higher in myopes (p=0.010) but did not demonstrate a significant effect of phoria (p=0.4). The influence of phoria-type on vergence adaptation and the pattern of BA vs. MA relates primarily to the varying fusional vergence demands created by the direction of phoria. The greater divergent (or less convergent) shift in vergence adaptation seen in myopes (compared to emmetropes) could be attributed to their higher accommodative adaptation. Nevertheless, the adaptive patterns observed in myopic children do not appear to explain their high response AV/A ratios identified as a risk factor for myopia development.

Evidence that convergence rather than accommodation controls intermittent distance exotropia

This study considered whether vergence drives accommodation or accommodation drives vergence during the control of distance exotropia for near fixation. High accommodative convergence to accommodation (AC/A) ratios are often used to explain this control, but the role of convergence to drive accommodation (the CA/C relationship) is rarely considered. Atypical CA/C characteristics could equally, or better, explain common clinical findings. Nineteen distance exotropes, aged 4-11 years, were compared while controlling their deviation with 27 non-exotropic controls aged 5-9 years. Simultaneous vergence and accommodation responses were measured to a range of targets incorporating different combinations of blur, disparity and looming cues at four fixation distances between 2 m and 33 cm. Stimulus and response AC/A and CA/C ratios were calculated. Accommodation responses for near targets (p = 0.017) and response gains (p = 0.026) were greater in the exotropes than in the controls. Despite higher clinical stimulus AC/A ratios, the distance exotropes showed lower laboratory response AC/A ratios (p = 0.02), but significantly higher CA/C ratios (p = 0.02). All the exotropes, whether the angle changed most with lenses ('controlled by accommodation') or on occlusion ('controlled by fusion'), used binocular disparity not blur as their main cue to target distance. Increased vergence demand to control intermittent distance exotropia for near also drives significantly more accommodation. Minus lens therapy is more likely to act by correcting overaccommodation driven by controlling convergence, rather than by inducing blur-driven vergence. The use of convergence as a major drive to accommodation explains many clinical characteristics of distance exotropia, including apparently high near stimulus AC/A ratios.

Cycloplegic and Noncycloplegic Refractions of Chinese Neonatal Infants

To examine Chinese neonatal infants with both cycloplegic and noncycloplegic retinoscopy and to compare the distribution of refractive errors for the two techniques. Cycloplegic retinoscopy was performed by two experienced pediatric ophthalmologists on 81 neonatal infants randomly selected from a group of 185 neonates who had undergone noncycloplegic retinoscopy. All infants were between 1 day and 6 days of age and were born without incident at full term. The mean cycloplegic spherical equivalent (CSE) was highly hyperopic (+3.55 diopters [D] ± 2.39 D). The mean noncycloplegic spherical equivalent (nCSE) was +0.58 D ± 2.32 D. The high reliability of the refractive measurements was demonstrated by high correlations between examiners (CSE: OD, r = 0.96; OS, r = 0.97; nCSE: OD, r = 0.94; OS, r = 0.93 OS) and between eyes (CSE: examiner 1, r = 0.94; examiner 2, r = 0.95; nCSE: examiner 1, r = 0.95; examiner 2, r = 0.97). The correlation between CSE and nCSE was much lower (examiner 1: OD, r = 0.76; OS, r = 0.73; examiner 2: OD, r = 0.72; OS, r = 0.70). Prevalence of astigmatism was very low (1.6% ≥ 1.0 D). The level of hyperopia was very high in these infants, and the offsetting tonic accommodation demonstrated by the difference between CSE and nCSE was much higher than in any previous report. Low amounts of infantile hyperopia and high astigmatism are associated with future myopia in the West. The Chinese neonates in this study had high amounts of hyperopia and little astigmatism, yet they are at high risk to become myopic.

Effect of proximity on the open-loop accommodative response of the eye

We evaluated the relative contribution of proximal accommodation to the open loop accommodative response under open and closed loop conditions of vergence using 0.2 cycles per degree (c deg− 1) difference of Gaussian (DoG) targets at two test distances on five subjects. Accommodative responses were measured using a power refractor. Results show significant difference in the open loop accommodative response at the two distances under both open and closed loop conditions of vergence. Results obtained were applied to Hung and co-workers' [Investig. Ophthalmol. Vision Sci. 1991, 32, 2985–2991] proximal model of equations to find the relative contribution of proximal accommodation for the observed differences in the accommodative response. Results obtained show that the 0.2 c deg− 1 DoG stimulus at 0.4 m does not truly open the accommodation loop and the response obtained does have a significant level of proximal accommodation contribution. However, it can be used as a target to measure the relative changes in tonic accommodation and convergent accommodation responses and cannot be used for absolute measures when used at closer distances.

Accommodation functions: Co-dependency and relationship to refractive error

We assessed the extent to which different accommodative functions are correlated and whether accommodative functions predict the refractive error or the progression of myopia over a 12 month period in 64 young adults (30 myopes and 34 non-myopes). The functions were: amplitude of accommodation; monocular and binocular accommodative facility (6 m and 40 cm); monocular and binocular accommodative response to target distance; AC/ A and CA/ C ratios, tonic accommodation (dark focus and pinhole), accommodative hysteresis, and nearwork-induced transient myopia. Within groups of related accommodative functions (such as facility measures or open-loop measures) measurements on individuals were generally significantly correlated, however correlations between functions from different groups were generally not significant. Although accommodative amplitude and pinhole (open loop) accommodation were significantly different in myopes than in non-myopes, these functions were unrelated to myopia progression. Facility of accommodation and accommodative lag was independent predictors of myopia progression.

Sympathetic innervation of ciliary muscle and oculomotor function in emmetropic and myopic young adults

Purpose: Evidence exists for an additional inhibitory accommodative control system mediated by the sympathetic branch of the autonomic nervous system (ANS). This work aims to show the relative prevalence of sympathetic inhibition in young emmetropic and myopic adults, and to evaluate the effect of sympathetic facility on accommodative and oculomotor function. Methods: Profiling of ciliary muscle innervation was carried out in 58 young adult subjects (30 emmetropes, 14 early onset myopes, 14 late onset myopes) by examining post-task open-loop accommodation responses, recorded continuously by a modified open-view infrared optometer. Measurements of amplitude of accommodation, tonic accommodation, accommodative lag at near, AC/A ratio, and heterophoria at distance and near were made to establish a profile of oculomotor function. Results: Evidence of sympathetic inhibitory facility in ciliary smooth muscle was observed in 27% of emmetropes, 21% of early-onset myopes and 29% of late-onset myopes. Twenty-six percent of all subjects demonstrated access to sympathetic facility. Closed-loop oculomotor function did not differ significantly between subjects with sympathetic facility, and those with sympathetic deficit. Conclusions: Emmetropic and myopic groups cannot be distinguished in terms of the relative proportions having access to sympathetic inhibition. Presence of sympathetic innervation does not have a significant effect on accommodative function under closed-loop viewing conditions.

The Effect of a β -Adrenoceptor Antagonist on Accommodative Adaptation in Hong Kong Children

Purpose: Increased susceptibility to nearwork-induced accommodative adaptation has been suggested as a risk factor for myopia development. We investigated whether accommodative adaptation may explain in part the high prevalence of myopia in Hong Kong children and examined the effect of β -antagonism with topical timolol maleate on accommodative adaptation.Methods: Thirty children (10 emmetropes and 20 myopes) aged between 8 and 12 years were recruited. Tonic accommodation was measured before and after 5 min of video game–playing using an open-field Shin-Nippon autorefractor. Measurements were repeated 30 min after timolol instillation.Results: Children with progressing myopia demonstrated accommodative adaptation following the near task, whereas stable myopes showed counter-adaptive, hyperopic accommodative changes. Timolol increased the magnitude of accommodative adaptation in the stable myopes but had little effect on responses of the progressing myopes or emmetropes.Conclusions: Neuropharmacological modulation of the accommodative system may have a possible etiological role in the progression of myopia.

Effect of unilateral forced nostril breathing on tonic accommodation and intraocular pressure

Unilateral forced nostril breathing (UFNB) has specific measurable effects on the autonomic nervous system. Ocular accommodation, which is controlled by the autonomic nervous system, would be expected to be under the influence of UFNB when it is applied. The purpose of this study was to investigate the effect of UFNB on the resting state of the accommodation system, i. e. tonic accommodation (TA), along with measures of intraocular pressure (IOP), blood pressure and heart rate. TA levels were measured using the Shin-Nippon autorefractor before and after 20 minutes of UFNB. IOP, blood pressure and heart rate, which are known to be affected by UFNB, were also measured with a non-contact tonometer and an automated blood pressure monitor respectively. Right and left UFNB produced slight, but not significant changes in TA. However, there was a tendency for left UFNB to produce a greater decrease in TA in subjects with higher base-line TA levels. Right UFNB produced a statistically significant decrease in IOP while the effect of left UFNB on IOP was not significant. UFNB produced changes in IOP consistent with previous reports. As studied in this trial, UFNB did not have any significant effect on TA. Further studies using a larger sample size are required to investigate the effect of UFNB on the autonomic inputs to the ciliary muscle of the eye and the subsequent measures of tonic accommodation.