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Biomedical subjects

L Hainline

Publications and source records attributed to L Hainline.

18 recordsLinked to original sources
PubMed2000

Childhood visual experience affects adult voluntary ocular motor control.

PURPOSE: To quantify the effects of childhood visual experience/chronic visual deprivation upon adult voluntary ocular motor control. METHODS: Eye movements of blind and sighted adults were elicited and videotaped in total darkness. The videotaped responses were digitized using an eye tracker, yielding data from 10 congenitally blind (infantile onset, blindness before age 1 year), 16 adventitiously blind, and 9 sighted persons. RESULTS: Multivariate analysis of variance, trend analyses and post hoc tests revealed that primary position fixational stability and consistency of return to primary position were lowest in the congenitally blind vs. the adventitiously blind group, and highest in the sighted. Duration of adventitious blindness reduced primary position stability but not consistency of return to primary position. Secondary position maximum amplitudes: congenitally blind mean, 14 degrees; adventitiously blind mean, 40 degrees; sighted mean, 47 degrees. Average velocity (a form of Main Sequence) increased significantly with amplitude in all three groups. CONCLUSIONS: Visual deprivation can greatly attenuate but does not abolish human voluntary eye movement. Adventitious blindness exerts minimal to profound effects, commensurate with age of vision loss.

Adaptation, Physiological↗
PubMed1997

Comparison of measures of visual acuity in infants: Teller acuity cards and sweep visual evoked potentials.

PURPOSE: This study compares the development of acuity in the same infants during one testing session using Teller acuity cards (TAC) and sweep visual evoked potentials (sVEP). We asked whether different testing methods in two centers would produce different developmental time courses. METHODS: Forty-eight infants were tested in two centers. The standard procedure for TAC was used. For sVEP acuity, the amplitude response curve derived from time-locked cortical activity was used to extrapolate to zero response, giving an acuity estimate for each infant. RESULTS: sVEP acuity was generally higher than TAC acuity. The rate of development was steeper for TAC than sVEP acuity with TAC starting at a much lower level. The ratio of sVEP to TAC acuity decreased exponentially with age reaching an asymptote of about 1.44 at 6 months. CONCLUSIONS: Results were indistinguishable between centers suggesting that comparison of acuity measures obtained using variations of these methods across centers is possible.

Aging↗
PubMed1997

Eye movement-based measures of development of spatial contrast sensitivity in infants.

This study presents spatial contrast sensitivity functions from 66 infants ranging in age from 12 to 146 days. Functions were derived using a behavioral method based on eye movements; in this method, the subject viewed drifting sinusoidal gratings while an experimenter, who did not know the direction of stimulus drift, voted on that direction based only on the record of the subject's eye movements. Results show that there is a marked increase in contrast sensitivity across age, as well as a modest shift of the peak of the function and of the acuity limit to higher spatial frequencies. However, when normalized with respect to peak frequency and peak sensitivity, the functions at all ages have the same general shape and can be fit with a standard template curve used to describe contrast sensitivity in the adult visual system; that is, even the youngest infants clearly show a drop in sensitivity at frequencies below the peaks of their functions.

Adult↗
PubMed1995

Binocular alignment and vergence in early infancy.

Vergence to static targets presented at five distances between 25 and 200 cm from the subject was measured in 631 infants aged between 17 and 120 days. Photographic images of the eyes were magnified and measured to yield information on the monocular and binocular eye positions for each target. Vergence data were fit by a linear function and compared to the vergence calculated from target distance and each infant's measured interpupillary distance. Differences in vergence across targets were also evaluated for each subject by calculating the change in angle of rotation for each eye. Many of even the youngest infants showed good ocular alignment both monocularly and binocularly, although the youngest infants showed the greatest variability in vergence. However, the median difference in vergence angle between the eyes for even the youngest group was < 4 deg (6.8 prism D), and some of this difference is attributed to versional eye movements and to slightly off-axis head position across trials. The average infant of 1-2 months showed substantially better vergence than has been reported in some recent studies. Apparently, oculomotor constraints are not a significant barrier to the development of the higher forms of binocularity that begin to emerge in the months immediately following the interval studied here, and may form the substrate for later developments in binocular vision.

Child Development↗
PubMed1994

Calibration of the Hirschberg test in human infants.

PURPOSE: The Hirschberg ratio has been defined as the ratio of the change in angular position of the line of sight to the change in location of the first Purkinje image relative to the pupil center. This study was designed to determine empirically whether the adult value of the Hirschberg ratio (approximately 22 prism diopters/mm) is a suitable value to use for all ages. Because many structures in the eye are growing during the 1st year, it is possible that there could be some change in the Hirschberg ratio during this period. METHODS: A photographic technique was used to calculate the Hirschberg ratio for 323 infants between the ages of 27 and 365 days and for ten adult subjects. The study also measured angle lambda, the angle between the line of sight and the pupillary axis, in these populations. RESULTS: The Hirschberg ratio did not change with age during infancy and was similar for adults and infants both in value and in variance. Angle lambda, however, declined rapidly, from an extrapolated value of about 8.4 degrees at birth to near 5 degrees at 5 months, a change that is assumed to reflect axial growth of the eye. CONCLUSIONS: The results suggest that the same average Hirschberg ratio can be used to estimate angle of strabismus across age. The change in angle lambda is important to consider when evaluating angle of deviation from measures using the Hirschberg test.

Adult↗
PubMed1992

Development of accommodation and convergence in infancy.

Paraxial photorefraction was used to assess the development of accommodation and convergence in a large sample of infants under 1 year of age. The infants viewed small dolls placed at various distances (200-25 cm). The majority of infants at all ages demonstrated appropriate convergence for target distance, regardless of manifest refractive error. However, accommodation lagged behind convergence in development. Infants under 2 months tended to demonstrate either flat accommodation responses with a fixed plane of focus at around 30 cm, or accommodated appropriately for near targets, but failed to relax their accommodation sufficiently for the more distant targets. Thus, the focussing error increased with increasing target distance. Since the manifest refractive error was estimated by extrapolating the accommodation function to 0 diopters demand, these infants demonstrated spuriously myopic behavior. After 2 months, the majority of infants showing emmetropic behavior had accommodation responses that changed appropriately with target distance. However, infants with myopic or hyperopic manifest refractive errors displayed a variety of accommodative styles.

Accommodation, Ocular↗
PubMed1990

Screening infant vision with paraxial photorefraction.

Early screening for refractive errors is highly desirable. Techniques for doing this must be usable with noninstructable subjects (infants), noninvasive, and relatively easy to use. Photorefraction has been used to examine infants' refractive status. However, unless cycloplegia is used, the results can be difficult to evaluate, inasmuch as the subject's plane of focus is not known. This paper describes a photorefraction system that is being used for routine screening of young infants, without cycloplegia and without using highly skilled personnel. The major innovation is the systematic presentation of attractive targets at distances that present a range of demands to accommodation. Changes in the fundal reflections, seen in the photographs taken as the infant views the different targets, can be interpreted unequivocally to identify severe myopia and hyperopia, anisometropia, heterotropia, and anisocoria. The results can also be quantified and are compared with retinoscopic refractions.

Clinical Protocols↗
PubMed1988

The distribution of fixation durations in infants and naive adults.

The distributions of durations of fixations from infants and free-viewing adults are shown to be basically exponential for different stimulus conditions. It is found that fixation duration can be divided into two periods. One, the alpha-period, is a refractory period during which a saccade does not occur and fluctuates across fixations. The other, the beta-period, is a random variable intrinsic to each fixation and constitutes a waiting-time for a saccade that occurs with constant probability per unit time. It is shown that mean duration decreases when stimulus size increases. These results suggest that fixations are terminated by saccades triggered by non-foveal stimulation.

Adult↗
PubMed1985

Saccades and small-field optokinetic nystagmus in infants.

Developmental studies of infant eye movements may be a useful tool in the early diagnosis of visual abnormalities. We have measured saccades made by infants during the free scanning of stimuli differing in attentional value. When viewing stimuli with high attentional value, infants made saccades that had adult-like peak velocity/amplitude (main sequence) relationships, while for less interesting stimuli, their saccades were slower; saccadic oscillations were also more frequent for these stimuli. In studies of small-field horizontal and vertical optokinetic nystagmus, with binocular viewing, infants' horizontal OKN was of higher frequency and lower amplitude than their vertical OKN. Within vertical OKN, there was a clear asymmetry with reduced responsiveness to downward moving stimuli. This asymmetry declined for older infants; possible interpretations for this change are discussed.

Adult↗
PubMed1985

Changes in visual functions of children exposed as infants to prolonged illumination.

The visual system can be modified by early experience. Many infants requiring extensive medical treatment spend time in neonatal intensive care units in which they experience prolonged and relatively intense illumination. Visual functions were measured in a group of 7-year-old children who, as infants, were in intensive care for treatment of neonatal jaundice. Using procedures disguised as games, these children were tested for spatial and temporal resolution, receptor functions, and binocular vision. Especially in children whose eyes had not been shielded, deficits were found in color vision, spatial contrast sensitivity, and stereopsis, but not in rod vision.

Child↗
PubMed1984

Characteristics of saccades in human infants.

Infants (14-151 days) and adults were shown two-dimensional geometric forms or stimuli from a set of highly textured patterns. Their eye movements were recorded by an infrared corneal reflection eye movement recorder as they freely scanned the stimuli. For both infants and adults, linear relationships were found between the peak velocities of fast eye movements and their amplitudes (main sequences). Infants viewing texture stimuli had main sequences with slopes comparable to those of adults. Infants viewing simple geometric forms made slower saccades. They also showed more eye movement oscillations which analyses showed were probably back-to-back saccades. Both the slower saccades and saccadic oscillations were attributed to factors related to the attentional value of the stimuli.

Adolescent↗
PubMed1984

Orientational asymmetries in small-field optokinetic nystagmus in human infants.

Optokinetic nystagmus (OKN) is a pattern of reflexive eye movements which occurs when portions of the visual field are in continuous motion. Gratings moving at 7 deg/s either horizontally (left or right) or vertically (up or down) were presented on a viewing screen subtending 30 degrees by 22 degrees. Horizontal (HOKN) and vertical (VOKN) OKN were recorded under binocular viewing conditions from infants and adults. Eye movements were recorded by means of an infrared corneal reflection eye movement recorder. OKN to horizontal and vertical stimuli was different in pattern for infants. Infants' HOKN was of significantly higher frequency and lower amplitude than their VOKN. Infants below 4 months of age also showed an asymmetry within VOKN between upward and downward stimulus motion, with markedly lower gains and more variable slow phase following movements for downward moving stimuli. No differences were found in HOKN to the right and left. There was also no evidence of a build-up of slow phase velocity over time. Infants' fast phases showed peak velocity/amplitude relationships like those of adults, and like those of infant saccades recorded in a previous study of infants' fast eye movements. Across all directions of stimulus movement, infants had lower slow phase gains and OKN frequencies, and larger slow phase amplitudes than adults. The characteristics of infants' OKN are discussed in relation to those observed in other species and in adult clinical patients with eye movement disorders.

Adolescent↗
PubMed1984

Rocket-ship psychophysics. Assessing visual functioning in young children.

A set of psychophysical procedures is described for rapidly measuring visual functions such as spatial contrast sensitivity, flicker fusion, and rod and cone two-color increment thresholds in young children. The psychophysical procedures, disguised as electronic space games, use a forced-choice paradigm combined with the method of descending limits. Because children enjoy the tasks and are highly motivated, the tests yield good sensory thresholds in a short period of time. However, when thresholds from 6-8-year-old children are compared with those of adults, the children have slightly higher thresholds for all of the functions tested. The differences are ascribed to the tendency of children to adopt a guessing strategy when stimuli are close to threshold.

Adolescent↗
PubMed1982

The retina of the newborn human infant.

We have examined a pair of eyes from a normal, full-term infant who died at 8 days as a result of accidental injury. Eyes were obtained immediately after death, fixed, and sectioned for light microscopy. Results from both eyes were substantially the same. The macular region was still drastically immature at 1 week. Even though a foveal depression existed, all cell layers were still present across it. Furthermore, the inner nuclear layer was divided into two separate layers. The receptor layer was reduced to one or two cells thick; receptors had both inner and outer segments, but they were very short and stumpy. The region of immaturity covered about 5 degrees of the retina. These findings suggest that the central region of a human infant's retina is probably not fully functional at birth.

Humans↗