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PubMed1992

Refractive accommodative esotropia: a surgical problem?

Among the reasons given for surgery in refractive accommodative esotropia (RAET) are (1) frequent functional deterioration and (2) high prevalence of cyclovertical strabismus and oblique muscle dysfunctions. Of 30 patients with RAET, corrected with glasses and followed for an average of seven years only one deteriorated. We tested a second group of 53 patients with RAET for A- and V-patterns and dysfunction of the oblique muscles. Pseudo-A- and V-patterns occurred without glasses but were absent when glasses were worn during the measurement. Dysfunctions of the oblique muscles were observed without glasses but were clinically insignificant. Our data do not support the reasons cited above for performing surgery in RAET.

Accommodation, Ocular↗
PubMed1997

Normal heterophoric changes: 20 years' follow-up.

BACKGROUND: Evaluation of changes in the heterophoric condition of 100 normal individuals over a 20-year period. METHODS: A retrospective study was undertaken. Charts of 100 normal men were reviewed. Individual changes in the heterophoric status were recorded over a 20-year period. The average value of the phoria at age 18-22 years was compared with the average value at age 34-38 years. Measurements were taken for near and distance fixation. No one was heterotropic. Changes in convergence and accommodation were also calculated. RESULTS: A 0.9 +/- 1.7 prism diopter increase in esophoria for distance fixation and a 0.6 +/- 2.5 prism diopter increase in exophoria for near fixation were found. These changes were statistically significant (P < 0.001 and P < 0.02 respectively). The near point of convergence receded by 0.5 +/- 1.1 cm (P < 0.001), and a decrease in accommodation over time of 2.8 +/- 1.4 diopters was found (P < 0.001). CONCLUSION: An increase in esophoria for distance fixation and a exophoria for near fixation was found in a 20-year follow-up of 100 normal subjects.

Accommodation, Ocular↗
PubMed1981

Biofeedback of accommodation to reduce functional myopia.

Functional myopia may be defined as the refractive condition of the eye due to spasm of the ciliary muscle. As a result of the ciliary muscle spasm, the crystalline lens becomes more convex, creating a myopic refractive condition. The normal increase and decrease in the refractive power of the crystalline lens is know as accommodation and is controlled by the autonomic nervous system innervation to the ciliary muscle. Previous studies have reported that voluntary control of accommodation is possible by biofeedback training (Cornsweet & Crane, 1973; Randle, 1970). The present research investigated the application of biofeedback control of accommodation to reduce functional myopia. A double-reversal, multiple-baseline design was used to conduct the experiment. The results revealed that the three adult male subjects achieved the preset criterion, a 1/2-diopter reduction from initial baseline to a subsequent baseline. Further analysis of the data revealed even greater changes between initial baseline and feedback periods. Although generalization to a nonexperimental environment was not trained, each subject showed a reduction in myopia and an increase in visual acuity. The results of the experiment clearly demonstrated that functional myopia is subject to voluntary control.

Accommodation, Ocular↗
PubMed1995

The optics of the eye-lens and lenticular senescence. A review.

Although the lens of the eye is structurally a biological tissue, it functions as an optical element providing one third of the refracting power of the human eye, and a variable focus in younger years. Throughout a life-time the optical properties of the eye-lens alter, resulting in changes in function: there is a gradual depletion of the focussing amplitude from infancy to middle age, and a loss of transmittance in the later decades of life. The optical properties of the lens depend on its power, which in turn is determined by its physical dimensions (curvatures and thickness) and its refractive index as well as transmissivity and the organization of its internal components. The power of the functional lens is, however, modifiable by virtue of the lens being attached via the zonule to the ciliary muscle. The contraction and relaxation of the latter respectively increases and decreases lens power in accordance with innervations determined by the physical distance of external objects to be imaged on the retina. This review will consider many of these features and how alterations in any of them may lead to changes in lenticular function. However, as we have recently devoted a detailed study to presbyopia [1] its mechanism will not be considered here.

Accommodation, Ocular↗
PubMed1995

Accommodation power determined with visual evoked cortical potentials in psychogenic visual disturbances.

Accommodation power was measured with pattern visual evoked potentials in 12 normal subjects and three patients suffering from psychogenic visual disturbances and accommodation failure. Steady-state visual evoked cortical potentials recorded by increasing a minus-power lens in front of the eye in 1 diopter steps. The regression line was established from the visual evoked cortical potential amplitudes vs accommodation stimulus plot, and the objective accommodation power was determined by extrapolating the line to zero amplitude. The accommodation power measured by visual evoked cortical potentials was larger by approximately 2 diopters than that obtained subjectively by near-point rule in normal subjects. The subjective accommodation power was remarkably low for their age in each patient but the objective power was normal. These results suggest that the decrease of accommodation in these patients was caused by psychogenic mechanisms, and visual evoked cortical potential measurements of accommodation could provide helpful information for diagnosis.

Accommodation, Ocular↗
PubMed1994

Clinical and laboratory investigations of the relationship of accommodation and convergence function with refractive error. A literature review.

Studies of the relationship of clinical and laboratory measures of accommodation and convergence function with refractive error are reviewed. There are inconsistencies in results from study to study presumably due, in part, to methodological differences. However, some basic trends can be outlined. In studies in young adults, accommodation in darkness (dark focus), optical reflex accommodation, and proximally induced accommodation are less in myopes than in emmetropes and hyperopes. It also appears that nearpoint esophoria is associated with higher rates of myopia progression in children. Implications for myopia etiology are discussed.

Accommodation, Ocular↗
PubMed1995

Nearwork-induced transient myopia: a critical review.

The literature on nearwork-induced transient myopia (NITM) is reviewed, with NITM being defined as the short-term myopic far point shift immediately following a sustained near visual task. A majority of these investigations demonstrated the presence of NITM for a variety of test parameters, e.g., visual acuity, contrast sensitivity and far point. Overall, these studies reported relatively small myopic shifts, with a mean of approximately 0.40 D and a range from 0.12 to 1.30 D. The subsequent decay is characterized by an exponential function with a relatively short time course. While the precise etiology and implications of NITM remain unclear, speculations regarding its origin and relevance to clinical myopia are discussed. Studies that did not demonstrate NITM are also reviewed.

Accommodation, Ocular↗
PubMed1993

Accommodative response changes with age measured by pattern electroretinogram.

To evaluate whether the transient pattern electroretinogram reflects accommodation, we studied the amplitudes of the P-N component of transient pattern electroretinograms that were elicited in normal volunteers by reversing the checkerboard pattern. The stimuli were presented at a rate of three-reversals per second at a viewing distance of 20 cm. Each subject wore a lens that corrected for distance vision. The ophthalmic lenses were placed in front of the eye. A +12-diopter lens was used first, followed by lenses in decreasing 1-diopter steps, including minus lenses, until no response was recordable. The P-N amplitude was then plotted against increased accommodative stimulus. The graph showed a rapid increase to around 4 diopters, and then a slow decrease with increasing minus lens power. The gradually decreasing part of the graph became steeper under cycloplegic conditions. The amplitude of accommodative response was defined as the difference in diopters between the lens powers for eliciting an electroretinogram amplitude after cycloplegia was achieved and in the untreated pupil. The amplitude of accommodative response attenuated significantly in those subjects older than 40 years.

Accommodation, Ocular↗
PubMed1977

Blur: a sufficient accommodative stimulus.

Experiments under a variety of open and closed loop feedback configurations demonstrate that accommodative responses to target blur are equivalent to those to defocus blur; this supports blur as the 'sufficient' neurological stimulus to accommodations. The hunting action of accommodation compensates for the even error aspect of blur and also adaptively minimizes any close loop error components while finally accepting open loop components.

Accommodation, Ocular↗
PubMed1981

Myopic astigmatism a substitute for accommodation in pseudophakia.

The power of an intraocular lens can be calculated before surgery to make the eye emmetropic or ametropic. The physiological mechanism of accommodation however, cannot be restored with an inelastic lens. An increased depth of focus in the implanted eye can be predicted through optical principles alone, if the postoperative ametropia of the implanted eye is a simple myopic astigmatism. This increased depth of focus without accommodation was tested in artificial ametropia and found to be used in nature by the seal. To increase the precision of intraocular lens calculation the average change in corneal power induced at surgery is used to predict the postoperative corneal power. By controlled suture release in the postoperative phase, the amount of induced corneal astigmatism is adjusted to obtain a simple myopic astigmatism. Patients with an intraocular lens and a simple myopic astigmatism as a residual ametropia, are spectacle independent most of the time. They need their glasses only for driving or prolonged reading. The methods used to calculate the postoperative cornea, the postoperative anterior chamber depth and the intraocular lens are described with the corresponding calculator programs for the HP 41C calculator. Clinical results and measurements of the depth of focus are shown in a series of 50 successive implant cases.

Accommodation, Ocular↗
PubMed1984

[Consequences of presbyopia for the dynamics of sight and work at a terminal].

For 100 persons of different age the visual charge for the accommodation was examined by an objective procedure. Already at the age of 40 the dynamic range of accommodation decreases. This decrease could be a reason for the loss of mobility during work at VDUs, as it has been observed in a group of persons aged 40 to 55 years.

Accommodation, Ocular↗
PubMed1984

Influence of edge sharpness on the accommodation of the human eye.

Using a subjective method of laser refractometry, the accommodation behavior of six subjects toward real targets with various degrees of blur, dependent on the viewing distance, were investigated monocularly and binocularly. Despite the sharpness of the target, the nominal value is only reached incompletely with a lag of accommodation, because accommodation tends to be as minimal as possible. Increasing blurring leads to a drift of accommodation towards the resting position of accommodation. The resulting underaccommodation causes further physiological blurring of the retinal image of the targets. The approach of the targets to the resting position of accommodation leads to a higher precision of adjustment and less drift. Subjective components (accommodative laziness, cognitive demand) influence the accommodation and increase the phenomenons discovered.

Accommodation, Ocular↗
PubMed1986

Phaco-Ersatz: cataract surgery designed to preserve accommodation.

Phaco-Ersatz represents a new approach to cataract surgery and the correction of aphakia. The procedure involves the removal of the cataractous cortex and nucleus while preserving the lens capsule and its zonular attachments. The empty lens capsule is then refilled with biocompatible and optically suitable clear gel. A physiologic lens is recreated in situ. Experimental work with human cadaver eyes and rabbit and cat eyes in vivo demonstrates this surgical feasibility. A review of the literature reveals contradicting theories regarding the physical laws and lens properties governing accommodation. The accommodative potential of the ersatz lens has not been tested, but it may be speculated that this recreated lens may, in fact, possess some accommodative properties. Experimental investigations in this area represent the logical extension of intraocular lens implant development.

Accommodation, Ocular↗
PubMed1986

The effect of anticholinergic drugs on the inner eye muscles.

Using 12 healthy volunteers, we tested the para-sympatholytic effects on the eye. In a randomized crossover double-blind trial, hyoscine-N-butylbromide was tested against saline. Before (20 or 40 mg IV) and up to 45 min after the injection, pupillar light reaction, accommodation, visual acuity, and nyctometer values were measured. The range of accommodation diminishes according to dosage: 9-15 min after the injection, the inhibition is maximum; 45 min after the injection, only a small effect remains, even using the 40 mg dosage. Pupillary reaction is little affected by either dosage, and the pupil diameters at the end of the reaction are only slightly greater after the injection of either dosage than after placebo injection. The time constant of the reaction remains unchanged. Visual acuity and nyctometer values remain unchanged under the influence of hyoscine-N-butylbromide. The results are discussed with respect to the potential ability of a patient to meet the requirements of modern traffic. According to our findings, there are no ophthalmologically-based reasons for an emmetropic person to assume impaired driving abilities after a single injection of hyoscine-N-butylbromide of up to 40 mg. If the accommodative capacity of a patient is impaired whose hyperopia is not fully corrected, the ability to drive in modern traffic may be impaired. After a single dose of 20 mg hyoscine-N-butylbromide (i.e., 1 ampule Buscopan), the impairment of even these patients does not last longer than about 45 min.

Accommodation, Ocular↗
PubMed1982

Proximal and accommodative convergence and age.

The authors have estimated the phoria for distant and near fixation in two groups of subject (mean age 27. 5+/- 4.4 and 59.2 +/- 8.2 years). Different accommodative stimuli were induced by adding minus lenses for distant fixation and plus lenses for near fixation. Statistical analysis of the experimental data indicates that, for distant fixation, the value of phoria per unit of accommodative stimulus is significantly lower presbyopic than in nonpresbyopic subject. Also, during near fixation, the accommodative convergence (AC/A ratio) is more reliable in the presbyopic subjects when the accommodative stimulus is progressively reduced. This varying behavior indicates in presbyopic subjects that proximal convergence is of greater relative importance in the determination of the fusion-free position. In nonpresbyopic subjects, accommodative convergence is the more important component.

Accommodation, Ocular↗
PubMed1988

Central motor control in concomitant strabismus.

Basic research in the field of oculomotor physiology has advanced rapidly during the last decade. The new knowledge has been largely incorporated into the research and the clinical practice of neurology and neuroophthalmology [14, 16], but the influence on strabismus research has been rather limited [15]. This presentation will point out the elements of basic research that are believed important for our understanding of concomitant strabismus. The description will concentrate on the role of different central motor factors, mainly brainstem mechanisms, in the genesis and development of infantile esotropia or convergent strabismus, i.e. strabismus with an early onset in life [8]. Strabismus of late onset seems less enigmatic, since it probably originates from abnormalities of the vergence system, particularly its coupling with accommodation.

Accommodation, Ocular↗
PubMed1988

Accommodative esotropia following surgical correction of congenital esotropia, frequency and characteristics.

This study was undertaken to look at the development of accommodative esotropia, which occurs following the surgical correction of congenital esotropia. A retrospective review was done on all congenital esotropia patients operated on by one of the authors from 1974 through mid-1984. The criterion of a minimum of 3 years postsurgical follow-up was met by 101 patients. Of these patients, 52 developed accommodative esotropia, 25 within 3 months of surgery and 27 from 3 to 60 months after surgery. The average preoperative refractive error in the early group was +3.90 and +1.95 in the later group. The average time to develop accommodative esotropia in this group with later onset was 27 months following the initial surgery. It would appear that if the preoperative refractive error is +3.00 or more, and especially if the preoperative deviation responds to spectacles with a reduction of 15 prism diopters or more, then it is very likely that glasses will be required for accommodative esotropia very soon following surgery. There appear to be no clues as to which patients will need glasses later for accommodative esotropia.

Accommodation, Ocular↗