Associated convergence and accommodative insufficiency.
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Accommodation, Ocular↗
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Effect of timolol on the amplitude and dynamics of accommodation.
There is still debate about whether the ciliary muscle is innervated by the sympathetic nervous system. We investigated the amplitude and the dynamics of accommodation under influence of the non-selective beta-blocker timolol. For this purpose the variations in thickness of the human lens during step-like changes in accommodation were measured with high-resolution A-scan echography. Results showed that the dynamics of accommodation, expressed in the time constants of the response, were affected as well as the amplitude.
Accommodation, Ocular↗
Cycloplegic refraction in children: single-dose-atropinization versus three-day-atropinization.
A new scheme for refractive measurements under atropine cycloplegia was tested in 90 strabismic children aged two to several years. Refraction was determined by an autorefractor (CANON R 10) 90 minutes after application of two drops of atropine (0.5% atropine children < 2 1/2 years; 1.0% atropine children > 2 1/2 years) and compared with the results after 3 days of receiving 1 atropine eyedrop 3 times daily. In 86.5% the spherical equivalents differ not more than 1.0 diopter (p = 0.05); the correlation was 0.99. Astigmatic corrections were in agreement in 95.5%, the axis of cylinders in 93.0% (p = 0.05); the correlations were 0.95 and 0.97. The residual accommodation 90 minutes after 2 drops of atropine was not more than 1 diopter in all children. The additional cycloplegic effect of the three-day-atropinization was only 0.5 diopters. This new type of application allows a more rapid and less toxic assessment of refraction than the usual three-day-atropinization.
Accommodation, Ocular↗
Accommodation power determined with transient pattern visual evoked cortical potentials in diabetes.
Changes of accommodation power by aging were measured with pattern reversal visual evoked cortical potentials (VECPs) in 45 normal subjects and 32 patients suffering from diabetes mellitus. Transient VECPs were recorded by increasing minus power lenses in front of the eye at one-diopter steps, up to the point where no VECP was recordable. It was found that the amplitude of the P100 component became attenuated linearly with increased accommodation stimulus. The regression line was calculated from the VECP amplitude vs. accommodation stimulus plots (in diopters) and the objective accommodation was determined by extrapolating the line to 0 microV amplitude. The measured accommodation power with pattern VECPs was attenuated significantly in the normal group over 40 years old and in diabetics, and also was found to be larger by approximately 2.5 diopters than that obtained subjectively by the near-point rule.
Accommodation, Ocular↗
Accommodative stimulus/response function in human amblyopia.
Three parameters are essential to describe static accommodative behavior in a comprehensive, quantitative manner: the slope of the stimulus/response curve, the depth of focus, and the tonic response. These parameters were obtained in amblyopes, former amblyopes, strabismus without amblyopia, and normals. Results showed that the accommodative response in the amblyopic eye was characterized by a reduction in the slope of the stimulus/response curve and increased depth of focus. Similar abnormalities but of lesser magnitude were found in the non-dominant eye of some former amblyopes and some strabismus without amblyopia. Orthoptic therapy always increased the slope of the stimulus/response curve in the amblyopic eye. We believe that the reduced accommodative responses found in amblyopic eyes reflect a primary sensory loss over the central retinal region that occurs as a result of prolonged, early, abnormal visual experience associated with the presence of strabismus and/or anisometropia.
Accommodation, Ocular↗
Does work with visual display units impair visual activities after work?
It is well established that visual display unit (VDU) operators complain of visual fatigue and visual stress during after-work hours. The present study was divided into two parts. In the first part, standard eye examinations were performed on a group of VDU workers (n = 32) and a control group (n = 15); those subjects who were found to have correct vision (n = 16 and 13, respectively) participated in the second part. The eye examinations revealed that on the average, the VDU workers suffered more than twice as many visual impairments as the controls. In those with correct vision, the near point of accommodation was measured at the beginning of the workday at the start of the week, and at the end of the workday, four days later. In the VDU group, the decrease in accommodation was uniformally distributed between zero and 1.0 diopter, whereas among the non-VDU workers, 77% of the decrease was between zero and 0.25 diopter. The dynamic range of accommodation in the VDU workers on the second examination was smaller than on the first. We conclude that some of the visual stress and visual fatigue that developed at work hindered visual activities after work.
Accommodation, Ocular↗
Functional differences between free alternators and non-alternators successfully treated for strabismic amblyopia.
Visual acuity was examined in patients successfully treated for strabismic amblyopia, and with equal refractive error in the two eyes (no more of 4 diopters of hyperopia). Patients able to freely alternate fixation showed equal visual acuity in the two eyes without optical correction. An optical correction in front of the ex-amblyopic eye was needed, in order to achieve equal visual acuity in patients unable to freely alternate fixation. No correction was necessary for the sound eye. This difference is attributed to a residual anomaly of accomodation of the ex-amblyopic eye. It is concluded that the concept of cure of strabismic amblyopia based on the attainment of equal visual acuity needs re-evaluation.
Accommodation, Ocular↗
Vergence adaptation: a review.
The present review aims to discuss the current researches on the ability of the vergence system to adjust to new information. A concomitant or non-concomitant binocular retinal disparity caused by a prism or an anisometropic prescription can be adapted to such that the induced phoria of fixation disparity reduces back to the original value. The features and mechanisms of this normal adaptation and also the response in subjects with abnormal binocular vision are discussed. The less extensive work on the adaptive ability of the accommodative vergence system is also reviewed.
Accommodation, Ocular↗
Cataract surgery and IOL implantation. More than 40 years of personal experience. My present criteria and considerations.
The author refers his personal experience with different types of IOL since 1950. After an initial period of enthusiasm (1950 to 1961) the author abandoned the techniques of Ridley, Strampelli and Dannheim, because of the considerable incidence of severe complications directly related to the IOL. Over many years he emphasized the serious postoperative complications which appeared in the course of the years, even with the different new types of IOL which acquired a certain prestige. With the new posterior chamber lenses placed in the capsular bag, the results became more encouraging and the author resumed IOL implantation with this type of lenses after an adequate period of observation and experimentation. The present criteria, technique and results of the author are discussed together with some considerations on future research work to develop new techniques for substitution of the opacified lens and also to attempt to restore accommodation.
Accommodation, Ocular↗
The accommodative response, refractive error and mental effort: 1. The sympathetic nervous system.
The accommodative response of 12 emmetropic subjects was measured for an array of numbers located at -1, -3 and -5 dioptres using an objective infra-red optometer. Responses were compared for passive (reading numbers) and active (adding numbers) conditions. The imposition of mental effort induced a significant increase in mean response for the -1 D stimulus, a response equivalent to the passive condition at -3 D and a reduction in response at -5 D. Mental effort induced similar responses for the -1 D and -3 D locations when sympathetic innervation to the ciliary muscle was blocked with the beta-receptor antagonist timolol maleate. Responses for the -5 D location were, however, significantly increased. It is proposed that sympathetic inhibition can modify the effect of mental effort on near accommodative responses.
Accommodation, Ocular↗
Follow-up results of a combination of accommodation and convergence insufficiency in school-age children and adolescents.
A follow-up over a period of 1-4.7 years was done on nine patients between the ages of 9-16 years, who had a combination of accommodation and convergence insufficiency without any known history of head trauma, febrile illness or drug use. The initial examinations disclosed exophoria and/or exotropia in near fixation, markedly low amplitudes of accommodation in both eyes, and remote near points of convergence in all patients. There was no correlation between the severity of convergence insufficiency and that of accommodative insufficiency. The extent of convergence insufficiency remained unchanged except for one patient who had a gradual and complete recovery and two other patients who underwent resection of both medial rectus muscles. The amplitude of accommodation recovered in varying degrees in six patients, while it decreased further in two other patients during the follow-up period. On initial examination, these two patients had the most remote near point of convergence (20 cm) and the lowest accommodative amplitude (less than 2 D) in common.
Accommodation, Ocular↗
Antonie Cramer's explanation of accommodation.
In the middle of the last century the question of the origin of accommodation was still unsolved. At the suggestion of Donders, Cramer used in 1851 a microscope to demonstrate that accommodation has to be ascribed to an increase in the curvature of the lens. Donders himself had several instruments made for the same purpose. These are still present in the collection of the Royal Netherlands Ophthalmic Hospital.
Accommodation, Ocular↗
Refilling the lens with a inflatable endocapsular balloon: surgical procedure in animal eyes.
In this report we describe the surgical details involved in refilling the lenses of 13 rabbit and 3 primate eyes using an inflatable endocapsular balloon to restore accommodation. The procedure involves endocapsular phacoemulsification through a small "buttonhole" or "dumbbell" anterior capsulotomy or minicircular capsulotomy and the simultaneous preservation of capsular integrity, including the zonules and ciliary muscles. An inflatable balloon made of thin silicone membrane is then inserted into the empty capsular bag. A liquid silicone polymer is injected into the balloon through a delivery tube, and the empty capsular bag is refilled by the inflated balloon. The procedure was found to be reproducible, and an accommodation of 6 D was confirmed in one primate eye. Capsular opacification occurred, but the proliferation and migration of residual lens epithelial cells could be hindered by abundant refilling. This lens-refilling technique may provide restoration of accommodation in future cataract surgery.
Accommodation, Ocular↗
The increasing sclerosis of the human lens with age and its relevance to accommodation and presbyopia.
By means of a fine conical probe and a miniature dynamometer, the resistance to penetration of different lens layers was measured. In clear human lenses the power of resistance of the lens nucleus increases with age, mostly due to the "hardening" of the nucleus. A distinct hardening of the nucleus as opposed to the cortex has been found to occur in lenses as young as 20 years of age. This "firmness" of the lens nucleus, occurring between the ages of 20 and 60 years, coincides with the decrease in accommodation range and the onset of presbyopia.
Accommodation, Ocular↗
New evidence for the intermediate position of relaxed accommodation.
Experimental evidence is presented that the focus of the eye tends to return passively to an individually characteristic intermediate resting position or dark-focus whenever (1) the stimulus to accommodation is degraded or (2) when the quality of the image is independent of focus. Based on measurements of the dark-focus with a laser optometer, it is possible to predict the magnitude of night, empty field, and instrument myopia on an individual basis. The role of the intermediate dark-focus as a factor in accommodation also provides an explanation for the paradoxical variation of visual acuity with observation distance. Applications to night myopia and night driving are described, and implications for clinical practice are discussed.
Accommodation, Ocular↗
Anteroposterior shift in rigid and soft implants supported by the intraocular capsular bag.
We compared the depth of the anterior chamber and the optimal distance refraction in a group of patients with soft and rigid intraocular implants under pilocarpine (maximal ciliary contraction) and cyclopentolate (maximal ciliary relaxation) in order to determine if lens movement might account for the apparent accommodation phenomenon. Lens shifts ranging from 1.5 to 0.02 mm and refractive variations up to 1 D were found. However, the discrepancies between amount of shift and refractive variations suggest that lens movement does not play a relevant role in this phenomenon.
Accommodation, Ocular↗
Focusing and accommodation in the brown kiwi (Apteryx australis).
Brown kiwis are an endangered species of nocturnal, flightless birds which are native to New Zealand. The resting focus of two specimens has previously been studied by retinoscopy in a zoo while the birds were restrained by their keeper (Sivak and Howland 1987). Those birds appeared to be hyperopic (farsighted) by 2-7 D. In this study, examination with infrared photorefraction of the focusing of two unrestrained, feeding birds showed that they could focus objects at infinity and objects in their immediate environment and that they had modest powers of accommodation. Measurements on two 6 month old kiwi chicks showed their corneal radius of curvature to be between 2.90 and 3.00 mm (117 D and 101 D in power).
Accommodation, Ocular↗
Instrument myopia conceptions, misconceptions, and influencing factors.
The literature on instrument myopia is reviewed, with the review organized around three principal objectives. One is to describe and discuss various factors that may influence the degree to which instrument myopia is manifested, including monocular vs. binocular viewing, age, direction of focus, illumination level, fatigue, magnification, astigmatic variations, optical decentration, perceived proximity of the target and peripheral surround, and experience. The second objective is to discuss the intermediate resting state conception of accommodation, its application to instrument myopia, and its strengths and weaknesses as applied to the available literature. The third objective is to summarize the salient problems in the instrument myopia literature, and to present a set of recommendations for guiding future work.
Accommodation, Ocular↗