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PubMed2002

Continuous measurement of accommodation in human factor applications.

It has long been sought to measure ocular accommodation continuously in human factor applications such as driving or flying. Open-field autorefractors such as the Canon R-1 could be converted to allow continuous, objective recording, but steady eye fixation and head immobilisation were essential for the measurements to be valid. Image analysis techniques utilised by newer open-view autorefractors such as the Shin-Nippon SRW-5000 are more tolerant to head and eye movements, but perhaps the technique with the greatest potential for the measurement of accommodation in human factor applications is photoretinoscopy. This paper examines the development of techniques for high temporal measurements of accommodation and reports on the tolerance of one such recent commercial instrument, the PowerRefractor (PlusOptiX). The instrument was found to be tolerant to eye movements from the optical axis of the instrument (approximately 0.50 DS change in apparent accommodation with gaze 25 degrees eccentric to the optical axis), longitudinal head movement (<0.25 DS from 8 cm towards and 20 cm away from the correct photorefractor to eye distance) and changes in background illuminance (<0.25 DS from 0.5 to 20 cd m(-2) target luminance). The PowerRefractor also quantifies the direction of gaze and pupil size, but is unable to take measurements with small pupils <3.7 +/- 1.0 mm.

Accommodation, Ocular↗
PubMed1986

Disparity-induced and blur-induced convergence eye movement and accommodation in the monkey.

The dynamics of vergence eye movement and of ocular accommodation were studied in two monkeys trained to track a haploscopically presented target that appeared to move in depth. The target was presented under four conditions: monocular viewing, normal binocular viewing, accommodation-open-loop binocular viewing, and "conflict" viewing, in which the accommodation and vergence stimuli did not correspond to those produced by any real target in three-dimensional space. The first and third conditions were chosen because in each case only one of the two primary cues that guide accommodation and vergence was operative: blur in the first case and disparity in the third. We usually studied responses to apparent target movement directly toward or away from the right eye, in which accommodation was measured. The latencies of the accommodation responses to steps toward the monkey were approximately 180 and 240 ms in the two monkeys, while in both monkeys the latencies of convergence were approximately 160 ms. Neither the vergence latencies nor the accommodation latencies were greatly different in monocular and binocular viewing. Responses to a sinusoidally moving target (frequencies 0.1-1.2 Hz; peak-to-peak amplitude 0.5-4 diopters or meter-angles) were studied in the first three of the above viewing conditions. In binocular viewing, even with accommodation open-loop, vergence and accommodation showed much smaller phase lags than in monocular viewing. Furthermore, in response to step changes, both vergence and accommodation velocities were higher in binocular viewing than in monocular viewing. Thus the dynamic control of both vergence and accommodation relies predominantly on disparity signals. At low frequencies (0.2 or 0.3 Hz) the monkeys showed only a modest ability to separate their accommodation and vergence responses when presented with conflicting blur and disparity cues. A simple linear calculation based on the data above was used to predict the responses in such situations. The predicted and observed responses were in reasonable agreement.

Accommodation, Ocular↗
PubMed1995

Visual accommodation as a cue for size.

Accommodation micropsia is examined in the general context of ocular accommodation as a cue for object size. The nature and limits of accommodation micropsia and arguments dealing with the possible contribution of accommodation to the perception of size are reviewed. Literature on the anomalous myopias, the intermediate-resting hypothesis, and theories of ciliary muscle innervation is examined critically in so far as it bears on the accommodation-micropsia hypothesis. The anomalous myopias and evidence for the intermediate-resting hypothesis are well documented, but without a mechanism for proprioceptive feedback from the ciliary complex about the state of accommodation it can only be concluded that such feedback would have to be indirect, either via the reflex link with vergence, or possibly through the agency of efference-copy neurones.

Accommodation, Ocular↗
PubMed1993

Amplitudes of accommodation of primate lenses refilled with two types of inflatable endocapsular balloons.

OBJECTIVE: To investigate the maintenance of ocular accommodation by refilling the lenses of the eyes of youthful primates with inflatable endocapsular balloons. METHODS: The lenses of 21 cynomolgus monkeys were refilled following endocapsular phacoemulsification with a balloon that either approximates the shape of the non-accommodated lens or the accommodated crystalline lens. RESULTS: In nine of 15 successfully refilled lenses, we were able to perform automated refractometry to determine the amplitude of accommodation, ie, changes in refraction before and 1 hour after application of topical 4% pilocarpine hydrochloride to alter lens shape. At 2 weeks, 2 to 3 months, and 6 to 12 months after operation, mean (+/- SD) accommodation was 4.6 +/- 2.5, 2.5 +/- 0.5, and 1.7 +/- 0.7 diopters (D), respectively, in the lenses refilled with the nonaccommodation balloon (n = 5; preoperative value, 15.2 +/- 1.3 D), and it was 1.9 +/- 0.5, 1.3 +/- 0.9, and 1.8 +/- 0.9 D, respectively, in the lenses refilled with the accommodation balloon (n = 4; preoperative value, 17.0 +/- 2.9 D). CONCLUSION: The greater yield of accommodation with the nonaccommodation balloon is consistent with the recent theory on the mechanism of accommodation. Although the obtained accommodation was a small fraction of values determined prior to the operation and the small amplitude of accommodation decreased over time, the feasibility of refilling the lens with an inflatable endocapsular balloon, allowing at least some accommodation in the eyes of youthful primates, was demonstrated. Applied to humans, this procedure may allow accommodation following cataract surgery.

Accommodation, Ocular↗
PubMed2002

Clinical testing of accommodative facility: Part 1. A critical appraisal of the literature.

BACKGROUND: Accommodative facility testing is used in clinical care to assess functioning of the ocular accommodative system. The current clinical standard (binocular assessment using +/- 2.00 D lenses at 40 cm with a vectographic suppression check) was first described nearly 20 years ago as part of the last comprehensive review of the literature. The standard accommodative facility test imposes a variable requirement on patients of different ages who have a wide range of accommodative amplitudes. METHOD: In this article, we critically reviewthe present body of literature on accommodative facility testing, with emphasis on the relation between symptoms, accommodative amplitude, and the results found during accommodative facility testing. RESULT: We include discussion of the five broad categories of accommodative facility studies: (11 recommendations for testing criteria; (2) normative data investigations; (3) reliability and variability assessment; (4) relation between accommodative facility and symptoms; and (5) other relationships (e.g., effect of test parameters on accommodative facility). CONCLUSION: Given the substantial variation in demand when testing patients of different ages (amplitudes), it is not surprising that a significant variation in responses has been reported in the clinical accommodative facility literature. Future clinical investigation of accommodative facility would benefit from a systematic investigation into the relationship between age and amplitude. The presence or absence of symptoms needs to be considered so that results of testing can be analyzed in relation to the severity of binocular vision-related symptoms.

Accommodation, Ocular↗
PubMed2004

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

BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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.

Accommodation, Ocular↗
PubMed1997

Accommodation without feedback suggests directional signals specify ocular focus.

Accommodation was monitored continuously under open-loop conditions while subjects viewed a sinusoidally oscillating sine-wave grating (0.2 Hz; +/- 1 D; 2.7 c/d; 0.56 contrast) in a Badal optometer. The target was illuminated by monochromatic light (590 nm) or white light (3000 K) with longitudinal chromatic aberration (LCA) normal, doubled, neutralized and reversed. Subjects (12) accommodated well in white light with LCA normal and doubled (mean gains = 0.85 and 0.94), gain was reduced in the neutralized condition (0.54), in monochromatic light (0.43), and especially when LCA was reversed (0.30). The results suggest that accommodation responds to changes in the relative contrast of spectral components of the retinal image and perhaps to the vergence of light.

Accommodation, Ocular↗
PubMed2006

Dynamic performance of accommodating intraocular lenses in a negative feedback control system: a simulation-based study.

A dynamic model of ocular accommodation is used to simulate the stability and dynamic performance of accommodating intraocular lenses (A-IOLs) that replace the hardened natural ocular lens that is unable to change focus. Accommodation simulations of an older eye with A-IOL materials having biomechanical properties of a younger eye illustrate overshoots and oscillations resulting from decreased visco-elasticity of the A-IOL. Stable dynamics of an A-IOL are restored by adaptation of phasic and tonic neural-control properties of accommodation. Simulations indicate that neural control must be recalibrated to avoid unstable dynamic accommodation with A-IOLs. An interactive web-model of A-IOL illustrating these properties is available at http://schorlab.berkeley.edu.

Accommodation, Ocular↗
PubMed1989

Reproducible stimulation of ciliary muscle contraction in the cynomolgus monkey via a permanent indwelling midbrain electrode.

To better study the pivotal role of the ciliary muscle in ocular accommodation and aqueous humor outflow, a technique was developed to permit long-term reproducible stimulation of the muscle via the normal efferent neuronal pathway in cynomolgus monkeys. Following a small midline craniotomy, the stereotaxic coordinates of the Edinger-Westphal (E-W) nucleus were localized by contrast ventriculoradiography. A bipolar stimulating electrode was stereotaxically positioned to generate the maximum accommodative amplitude, and then permanently affixed to the surrounding cranium. Once experience was gained, the implant procedure required approximately 3 h and was well-tolerated by the animals, which subsequently exhibited normal behavior and no apparent discomfort or neurological deficits. Most animals retained the implant seemingly permanently (8-42 months follow-up), although a few animals extruded them after 4-8 months. Electrode placement in the E-W nucleus was verified histologically. The stimulation current and frequency-accommodative response relationships varied remarkably little between eyes, animals, or experimental sessions, although there was moderate inter-animal variation in the maximum accommodative amplitude. Using square-wave pulses of 0.5 ms duration, maximum accommodation, averaging approximately 15 diopters, was achieved at approximately 700 microA and approximately 70 Hz, and was greater under pentobarbital than under halothane anesthesia. Topical application of carbachol, eserine and echothiophate to the eye induced more accommodation than did central electrical stimulation. Permanent implantation of a stimulating electrode into the E-W nucleus may facilitate study of ocular physiological parameters dependent upon ciliary muscle contraction.

Accommodation, Ocular↗
PubMed2000

The relation between accommodative facility and general binocular dysfunction.

This study was designed to evaluate the relation between accommodative facility and accommodative and binocular dysfunctions. We determined whether failure to achieve 8 cycles per minute of binocular accommodative facility or 11 cycles per minute of monocular accommodative facility tends to be associated with these dysfunctions. Forty eight subjects, ages 10-30 years were examined and classified into four groups: 13 subjects with accommodative dysfunctions, 11 patients with binocular dysfunctions, 12 subjects with accommodative and binocular dysfunctions and 12 control subjects with refractive errors but no accommodative or binocular anomalies. Monocular and binocular accommodative facility was conducted using +/- 2.00 D flip lenses. In general, statistical analysis indicates that subjects with binocular and accommodative (ocular motor) anomalies performed significantly poorer than subjects of normal group on monocular and binocular facility tests. Monocular accommodative facility results showed more information about the dysfunction of the patient compared with the results of the binocular accommodative facility. In general data supported a relation between reduced accommodative facility and a general binocular dysfunction (accommodative or binocular) which demonstrates the importance of the accommodative facility test in diagnosing an accommodative or binocular anomaly.

Accommodation, Ocular↗
PubMed2006

Accommodation and the relationship to subjective symptoms with near work for young school children.

The aim of this work was to study the relation between subjective symptoms at near and ocular accommodation in terms of the amplitude of accommodation and the relative accommodation. A secondary aim was to discuss the diagnosis of accommodative insufficiency. The chosen cohort was examined on two occasions with 1.8 years in between. The first examination included 72 children, 43 boys (mean age 8.1 years, ranging from 5.8 to 9.8) and 29 girls (mean age 8.3 years, ranging from 6.2 to 10.0). The second examination included 59 of these children, 34 boys (mean age 9.9 years, ranging from 7.8 to 11.7) and 25 girls (mean age 10.1 ranging from 8.0 to 11.8). Subjective symptoms at near work (headache, asthenopia, floating text, facility problems) were recorded and the amplitude and the relative accommodation, both positive and negative, were measured. The result from the questionnaire showed that at the first examination more than one-third of the children (34.7%) reported at least one subjective symptom when doing near work and 42.4% at the second examination. No symptoms were found among children younger than 7.5 years, but for children between 7.5 and 10 years old at the first examination, the prevalence of at least one symptom was 47.2%. At the second examination, symptoms were reported also for the youngest children, i.e. from the age of 8 years. The discrimination ability for the amplitude of accommodation, both monocular and binocular, was significant. In the first examination the difference between the mean for the two groups (i.e. with and without at least one symptom) was around 2.00 D monocular and 3.00 D binocular. Corresponding figures from the second examination was a difference between the mean for the two groups of around 3.50 D monocular and nearly 4.00 D binocular. We suggest that accommodation measurements should be performed more routinely and regularly, maybe as screening, especially in children over 8 years of age.

Accommodation, Ocular↗
PubMed1988

Accommodation motor neurons in the foveate teleost Paralabrax clathratus: horseradish peroxidase labeling and axonal morphometry, with comparisons to other ciliary nerve components.

Although much is known about the optics and mechanism of ocular accommodation in teleost fishes, there is to date no description of the neurons innervating the muscle of accommodation, the lens retractor. I have identified accommodation motor neurons in the kelp bass, Paralabrax clathratus, by backfilling the lens retractor nerve (a branch of the short ciliary nerve) with the retrograde tracer horseradish peroxidase. These neurons comprise a subpopulation of relatively large unipolar neurons in the ciliary ganglion. Backfilling either of the remaining ciliary nerve branches (which innervate mainly cornea and iris) labels smaller cells in the ciliary ganglion as well as sensory neurons in the profundus ganglion and sympathetic neurons in the trigeminal sympathetic ganglion. No labeled cells were found in the brain in any of these experiments. I have also examined the lens retractor nerve and the corneal-iridal branch of the short ciliary nerve by electron microscopy. Counts of axons in these nerves from animals of different sizes suggest postembryonic growth of axon number in the corneal-iridal branch but not in the lens retractor nerve. The latter comprises approximately 100 myelinated and a few unmyelinated axons. Its diameter spectrum shows a preponderance of large-diameter axons, but the myelin sheaths are unusually thin (mean axon diameter: 7.5 micron; mean ratio axon diameter/fiber diameter: g = 0.81 for 830-gram animal). The results indicate that kelp bass accommodation motor neurons lie primarily if not entirely within the ciliary ganglion. Some of their axons are the largest in the short ciliary nerve, but their sheath thicknesses are apparently not optimal with respect to conduction velocity.

Accommodation, Ocular↗
PubMed2006

Development of an accommodating intra-ocular lens--in vitro prevention of re-growth of pig and rabbit lens capsule epithelial cells.

Cataract surgery is routinely performed to replace the clouded lens by a rigid polymeric intra-ocular lens unable to accommodate. By implanting a silicone gel into an intact capsular bag the accommodating properties of the natural lens can be maintained or enhanced. The implantation success of accommodating lenses is hampered by the occurrence of capsular opacification (PCO) due to lens epithelial cell (LEC) growth. In order to prevent LEC proliferation, a treatment regime using actinomycin D, cycloheximide and water was developed. The effectiveness of treatment was analyzed using an in vitro, MTT-based cell culture system and an ex vivo pig eye model in which the implanted lens-in-the-bag is cultured as a whole. LEC were exposed to treatment solutions for 5 min, then the cells were allowed to recover and to re-colonize the substratum. MTT conversion by cells was transiently inhibited by cycloheximide dissolved in water and by water alone. Exposure to actinomycin D resulted in a lasting inhibition of MTT conversion and consequently cell proliferation. These in vitro data could not be fully reproduced in the ex vivo pig eye model due to essential differences between both models. Treatment with actinomycin D containing solutions, however, resulted in a nearly complete absence of cells on the capsular wall. The pig eye model is a promising approach to further evaluate the effects of peri-surgical treatment during the accommodating intra-ocular lens implantation.

Animals↗
PubMed1986

Pharmacokinetics of topically applied cyclopentolate HCl and tropicamide.

The time course of accommodative loss after the topical application of 0.5% and 1.0% concentrations of cyclopentolate HCl and tropicamide was measured over a 20-min interval in 50 age- and sex-matched subjects between 20 and 30 years of age. Computer-assisted measures of residual accommodation provided detailed data on the temporal aspects of the cycloplegia induced by these commonly utilized drugs when used alone or with the topical anesthetic proparacaine HCl. The pattern of recovery of ocular accommodation from cycloplegia was also measured over a 5-h period, starting 2 h after drug application. The results show that latency, depth of cycloplegia, and rate of accommodative loss are regulated to drug type and concentration, and are influenced by the iris coloration of the test eye. The rate of onset of cycloplegia was not accelerated in blue or brown irides by the preadministration of proparacaine. Regardless of iris pigmentation, recovery from tropicamide cycloplegia was much faster than recovery from cyclopentolate cycloplegia. In contrast, the depth of cyclopentolate cycloplegia present in brown irides during the recovery phase was much greater than in blue irides. Mechanisms to explain these observations are proposed and clinical implications of these findings are presented.

Accommodation, Ocular↗
PubMed1985

Transdermal hyoscine (Scopolamine). A preliminary review of its pharmacodynamic properties and therapeutic efficacy.

Hyoscine (scopolamine) is a competitive inhibitor of the muscarinic receptors of acetylcholine and it has been shown to be one of the most effective agents for preventing motion sickness. However, a relatively high incidence of side effects and a short duration of action has restricted the usefulness of this agent when administered orally or parenterally, and to counter this a novel transdermal preparation of hyoscine has been developed. Pharmacokinetic studies indicate that this new method for administering hyoscine controls the absorption process and the rate of drug entry into the systemic circulation over an extended period (72 hours), providing a means of delivery which is similar to a slow intravenous infusion. However, recent evidence suggests that the response to transdermal hyoscine treatment is variable and this may reflect pharmacokinetic differences between individuals. Controlled therapeutic trials have indicated that a single transdermal hyoscine patch is significantly superior to placebo and oral meclozine (meclizine) in preventing motion sickness. Trials comparing transdermal hyoscine with oral dimenhydrinate have failed to establish any significant differences in efficacy between the 2 drugs in small numbers of subjects, although there was always a more favourable trend towards the transdermal system. In patients with acute vertigo, transdermal hyoscine and oral meclozine were equally efficacious and both were significantly better than placebo in reducing the number of attacks of vertigo. Although transdermal hyoscine has been associated with a lower incidence of side effects than orally or parenterally administered hyoscine hydrobromide, adverse systemic effects have still been frequently reported. Most commonly cited have been dry mouth, drowsiness and impairment of ocular accommodation, including blurred vision and mydriasis (some ocular effects reported may be due to finger-to-eye contamination). Adverse central nervous system (CNS) effects, difficulty in urinating, rashes and erythema have been reported only occasionally. Thus, preliminary evidence suggests transdermal hyoscine may offer an effective and conveniently administered alternative for the prevention of motion-induced nausea and vomiting in certain situations. However, the duration of its clinical effectiveness, and its relative efficacy and tolerability compared with other agents needs to be confirmed in a few additional well-designed studies.

Administration, Topical↗
PubMed1988

Modification of the Canon Auto Ref R1 for use as a continuously recording infra-red optometer.

The Canon Auto Ref R1 has been modified to allow continuous recording of accommodation while retaining its capacity to record in 'single-shot' static mode. Possible alternative principles of modification are discussed with emphasis placed on the method used in this paper. Preliminary results are presented for both a novel dynamic model eye and an emmetropic real eye. The system described provides a useful research tool in the study of ocular accommodation dynamics.

Accommodation, Ocular↗
PubMed2004

True three-dimensional displays that allow viewers to dynamically shift accommodation, bringing objects displayed at different viewing distances into and out of focus.

Under natural viewing conditions, viewers do not just passively perceive. Instead, they dynamically scan the visual scene by shifting their eye fixation and focus between objects at different viewing distances. In doing so, the oculomotor processes of accommodation (eye focus) and vergence (angle between lines of sight of two eyes) must be shifted synchronously to place new objects in sharp focus in the center of each retina. Accordingly, nature has reflexively linked accommodation and vergence, such that a change in one process automatically drives a matching change in the other. Conventional stereoscopic displays force viewers to try to decouple these processes, because while they must dynamically vary vergence angle to view objects at different stereoscopic distances, they must keep accommodation at a fixed distance--or else the entire display will slip out of focus. This decoupling generates eye fatigue and compromises image quality when viewing such displays. In an effort to solve this accommodation/vergence mismatch problem, we have built various prototype displays that can vary the focus of objects at different distances in a displayed scene to match vergence and stereoscopic retinal disparity demands and better simulate natural viewing conditions. By adjusting the focus of individual objects in a scene to match their stereoscopic retinal disparity, the cues to ocular accommodation and vergence are brought into agreement. As in natural vision, the viewer brings different objects into focus by shifting accommodation. As the mismatch between accommodation and vergence is decreased, natural viewing conditions are better simulated and eye fatigue should decrease.

Accommodation, Ocular↗