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The naturally occurring accommodative response of the oscar, Astronotus ocellatus, to visual stimuli.
Observation of the naturally-occurring accommodative response of a highly visual teleost species provides the opportunity to study its stimulus-response accuracy. A video recording system, linked to a computer digitizing program, was used to measure accommodative changes in lens position in the oscar, Astronotus ocellatus, in response to known food stimuli. The largest lens deviations occurred along an axis c. 22 deg from the pupillary plane. Consistent underaccommodation was reported for the closest of targets, a finding reminiscent of accommodative lag reported in human studies.
Eye accommodation during prey capture behaviour in salamanders (Salamandra salamandra L.).
The eyes of fire salamanders were examined refractometrically before, during and after prey capture behaviour. It was ascertained that the refraction makes a myopic shift before the salamander turns to the prey. This means that fire salamanders use accommodation for distance estimation.
Velocity percepts of apparent laser speckle motion modulated by voluntary changes of visual accommodation: real-time, in-vivo measurements of the accommodative response.
This study examined negative volitional accommodation under open-loop viewing conditions by means of a coherent laser light pattern (633 nm) whose direction and velocity of motion is determined by the refractive state of the eye. Using the direct scaling procedure of free magnitude estimation, the subjects were required to quantitatively judge velocities of speckles when the retinal image of the subjects' eye was minimally influenced and when the subject was instructed to exert voluntary negative accommodation. Real-time, in-vivo measures of accommodation indicated that the dioptric strength of the crystalline eye lens was reduced under the condition of mental effort, and that the volitional accommodation values ranged between -0.26 and -1.90 D. The amplitude of these responses were noticeably correlated with individual measures of dark focus, so that larger dark focus values were associated with higher amplitudes of the voluntary negative response, and vice versa. By converting the dioptric strength of added optical lenses and the in-vivo measures of the eye lens curvature into angular velocities of laser speckles whose speed changes with focus relative the plane of stationarity, a specification of the proximal stimulus flow was obtained. The psychophysical functions describing the relationship between subjective speed and angular velocity generated either by placing lenses in front of the eye or by voluntary changes in accommodation had approximately the same appearance suggesting that the percepts reported by the subjects were valid and veridical estimates of the velocity of speckle movement.
Pupillary constriction evoked from the posterior medial lateral suprasylvian (PMLS) area in cats.
Pupillary constriction was evoked by systematic stimulation using a microelectrode in the upper medial bank of the middle suprasylvian sulcus in the parieto-occipital cortex of the cat. The pupillo-constrictor area corresponded to the rostral and middle parts of the posterior medial lateral suprasylvian (PMLS) area. This pupillo-constrictor area extended by 2-3 mm along the middle suprasylvian sulcus. It is suggested that this pupillo-constrictor area overlaps or lies in close proximity of a part of the region in PMLS area related to lens accommodation, in which unit activity temporally related to lens accommodation was recorded and from which lens accommodation was evoked by electric stimulation.
Afferent and efferent connections of the cortical accommodation area in the cat.
Accommodative responses were evoked by microstimulation of a circumscribed area in the lateral suprasylvian (LS) cortex of the cat. We studied anatomical connections of this area with WGA-HRP. We identified an accommodation-related area by systematic microstimulation of the LS cortex in each of nine cats. Accommodative and pupillary responses were monitored by an infrared optometer and a pupillometer, respectively. WGA-HRP was injected into the accommodation-related area where accommodative responses were elicited with low-intensity microstimulation, but pupillary responses were not evoked. Retrogradely labeled cells were found mainly in ipsilateral areas 17, 18 and 19, the pulvinar, the lateral posterior nucleus of the thalamus (LP) and the contralateral LS area. Fewer labeled cells were found in ipsilateral areas 20 and 21, the ventral lateral suprasylvian area (VLS), the splenial visual area (SVA) and the lateral geniculate nucleus (LGN). Anterogradely labeled terminals were located mainly in the ipsilateral LP, the rostral portion of the pontine nuclei and the superficial layers of the ipsilateral superior colliculus which corresponds to the representation of the central visual field. Less dense labeled terminals were also found in the ipsilateral nucleus of the optic tract (NOT) in two cats.
Convergence insufficiency and failure of accommodation following midfacial trauma.
A prospective evaluation of patients who had sustained midfacial trauma was carried out in order to determine the prevalence of impaired convergence and accommodation and to establish the risk factors for such defects. Of 52 patients in this study, 11 suffered accommodation and/or convergence disturbances. They included 6 males (17% of the male population) and 5 females (29% of the female population). Nine of these 11 patients sustained their injuries due to alleged assaults (24.3% of all assaulted patients) and 2 following simple falls (25% of all fall victims). Five patients complained of double vision for near (5/11 = 45.5%) and another 4 had blurred vision and/or difficulty with reading (4/11 = 36.4%). The remaining two were asymptomatic. Six patients were randomly selected to receive orthoptic exercises/treatment while the other five were monitored for signs of spontaneous recovery. Within six months of injury/surgery, 83% of the treated patients (n = 5) and 80% of the non-treated patients (n = 4) recovered to within the normal values of accommodation and convergence. No significant statistical relationship was found between the incidence of accommodation and/or convergence failure, and the cause or the type of fracture sustained. It may, however, be related to the severity of both the impact and the associated closed head trauma.
Heterophoria: a vergence adaptive position.
Previous experiments have shown that as the adaptive change becomes more complete with prolonged wear of a prism, the adaptive decay during monocular occlusion (MO) becomes slower; at the same time, adaptation to a further prism disparity becomes faster. If phoria is an adapted position of the oculomotor system then, as with prism adaptation, it should demonstrate an adaptive decay during MO. The rate of this decay should be inversely related to the rate of adaptation to a prism. In the first part of the paper, changes in the horizontal and vertical phorias were demonstrated at distance and near during 4 hr of MO. In the second part, adaptation to various prism disparities (horizontal and vertical) was monitored. The rates of adaptation were found to be inversely related to the rates of phoria decay during MO. The phoria position is, therefore, an adapted position of the vergence system.
Visual training programme applied to precision shooting.
A three month visual training programme was conducted at the CAR of Sant Cugat (Olympic Training Center). Eleven members of 'The Catalan Government Special Intervention Squad' were used in a clinical trial. Pre-test and post-test results were obtained for pistol shooting, visual function, and psychological and physical states. Statistical analysis indicated significant gains in visual function and pistol shooting scores after the programme, while psychological (anxiety) and physical condition remained the same. Some conclusive statements can be made with regard to the relation of visual function improvement and shooting performance increment, after analysing the data. This improvement is evident in statistically significant post-test gains in the following variables: 'phoria at distance, recovery points in fusional reserves at distance, analytical amplitude, negative relative accommodation, saccadic fixations, and accommodative facility at distance and at near. The rest of the controlled visual variables also showed clinical improvement.
Intraocular motility, electrophysiological tests and visual fields in drug addicts.
The effects of drugs on intraocular motility, retina function and central pathways in a drug addicts population have been studied. The study group were made up of 15 drug addicts. Fifteen healthy subjects who had never used drugs acted as a control group. Refractive state, accommodation, tonometry, assessment of pupillary reflexes, campimetry, visual evoked cortical potential (VECP) and ERG were performed in all cases. All the subjects studied used heroine, 12 used cannabis and 12 used cocaine. Refraction was normal in all cases. Accommodation amplitude in normal subjects ranged from 8.5 to 11.5 D, and from 3.5 to 9.5 D in the drug addicts group. Tonometry indicated a tendency to lower intraocular pressure values. Direct and consensual pupillary reflexes were normal in eight subjects, but were sluggish in the rest. Campimetry showed relative and absolute scotoma in five subjects. VECP were found to be normal in two of the cases, moderately pathological in six and pathological in the remaining seven cases. As for the ERG, it showed non-specific altered traces in 11 cases. Accommodation amplitude was lower than normal in 20 eyes. The decrease of VECP with altered traces but with an increase of latency, seem to indicate the presence of an alteration in the optical pathway or in the cortical centres. The findings in ERG point out a decrease of amplitudes and an increase of latency in more than half the population studied.
Dark focus and dark vergence: an experimental verification of the configuration of the dual-interactive feedback model.
Based on the dual-interactive feedback model, dark focus and dark vergence designate a point on a line describing the response AC/A ratio. In order to verify the relationship between dark focus and dark vergence, we predicted the dark vergence from the measured dark focus when the measurements were based on the response-based calculated and gradient AC/A ratios. For 10 subjects, the correlations between predicted and measured dark vergence values were high. The prediction was better when using the gradient AC/A ratio.
Hysteresis in accommodation.
Under certain conditions the accommodative response is not a simple function of accommodative stimulus, but depends as well upon the history of the stimulus. Experimental evidence points to multiple mode control of accommodation as being responsive: a high-gain feedback control mode responds to blur; a second mode causes a drift to bias set level when visual stimuli are removed. We extend a model consistent with these results and use it to predict the results of a new experimental paradigm, 'pushdown' accommodation. Finally, we extend the model to a third mode of behaviour, schematic accommodation, which encompasses instrument myopia, proximal accommodation and voluntary accommodation.
Single figure indices for the steady-state accommodative response.
The slope of the regression line fit is often used to characterize an accommodation response-stimulus curve. It is argued that comparisons based on this parameter alone may be misleading, as also may be those using the intercept or correlation coefficient of the regression line. It is suggested that it would be more useful to compare curves on the basis of a combination of all three regression line parameters, together with the stimulus interval over which the fit is derived. A new parameter, the accommodative error index which is effectively the mean of the magnitude of the response error divided by the correlation coefficient, is proposed to achieve this.
Push-up amplitude of accommodation and target size.
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Binocular convergence in man during total sleep deprivation.
It was proposed that binocular convergence (lateral phoria) for near and far vision would reflect the states of visual functioning and that there would be a progressive reduction in phoria during sleep deprivation. Six young male subjects underwent two conditions of sleep deprivation on separate occasions. One condition incorporated a high visual load and the other a low load. Exercise and sound were balanced. Lateral phoria for near and far vision was carefully measured, regularly, before, during and after sleep deprivation. It was found that a reduction in convergence (exophoria) for both near and far vision became increasingly apparent with progressive sleep deprivation, especially with near vision and under high visual load. The near vision measure, which included accommodation convergence, appeared to be more sensitive to sleep deprivation generally, whereas far vision tended to produce a greater differentiation between the conditions. The implications of these findings for REM sleep and oculomotor innervation are discussed.
Model of visual focussing involving extraocular muscles and the causes of myopia and glaucoma.
The classical model of visual focus has increased curvature of the lens for accommodation and flattening of the lens for far vision, with both determined by ciliary muscle tension. This new model proposes that change in the focal length is a second modulator of acuity. This model also proposes that the extraocular muscles are the more important neuromuscular entities for both lens and focal length changes. At accommodation there would be relaxation of the recti muscles and contraction of the superior oblique muscle. This increases focal length while allowing the ciliary muscle ring to contract, releasing tension on the lens capsule. Far object focus is due to contraction of the recti muscles. These pull on the sclera, stretching the zonule fibers taut to give flattening tension of the lens capsule. The myopic eye, in addition to a highly curved lens, also has longer focal length and is misaligned in the orbit. Ageing glaucoma is hypothesized as due to: 1. excessive curvature of an ageing lens; 2. chronic contraction of the recti in compensatory effort to flatten the lens and shorten the focal length; 3. the overcontracted recti pull to excess, stretching the inner tissue and distorting the Schlemm canal and its access mesh area to inhibit efflux of aqueous fluid.
On the nature of myopia and the mechanism of accommodation.
An experiment in which pressure was applied to the globe of the eye by artificially-induced contraction of the superior oblique muscles produced two effects: 1) Dual vision, consisting of two separate, superimposed, retinal images, one blurred and one clear; and 2) A 5 diopter increase in myopia. It was concluded that the pressure, transmitted through the sclera to the vitreous, forced the vitreous against the back of the lens, flattening the periphery but not the axial (central) region, resulting in a high degree of negative spherical aberration, combined with accommodation. This suggests that accommodation can be actuated by contraction of the extraocular muscles. When the pressure was released, it took several years for the dual image to subside. This suggests that when the lens is released after a long period of accommodation, the return to the unaccommodated state is extremely slow, and that a significant factor in the etiology of myopia is repeated long periods of accommodation in which periods of rest are insufficient to allow the lens to return completely to the unaccommodated state.
Improving the precision of biological age determinations. Part 2: Automatic human tests, age norms and variability.
In order to eliminate variability due to test operators, procedures for measuring 12 physiological functions that are candidate biomarkers of aging have been automated. Data was collected from a norm group of 2462 male and female office workers using an instrument which requires no test operators, administers all 12 tests in about 45 min. per subject, computes biological age, prints out results, and stores data on floppy disks for transfer to other computers for analysis. This report a) describes the instrumentation and test procedures, b) presents normal age/sex standards for each of the 12 biomarkers, c) reports the variance of the data for each biomarker by sex, d) lists sources of biomarker variance, e) discusses criteria for biomarker selection and f) examines implications for information loss when biomarker data is combined to calculate biological age. After eliminating chronological age as a variable, the standard deviations of the frequency distributions of predicted age for individual biomarkers were found to vary from .226 to 1.075, a range of more than 4 to 1. Procedures are discussed for improving the ratio of useful-to-useless variance in calculating biological age.