Ronald M. Hansen

Accuracy of eye position information for motor control

Two dimensional eye movements were recorded to show that subjects could return their eyes to a reference position following both saccades and slow phase of vestibular nystagmus suggesting eye position was signalled accurately during both movement types and this signal was closely timelocked to saccades. In addition, this signal could be used by naive subjects for oculomotor control without special training. Finally, subjects could strike blows within a few minutes of arc of a target localized only by eye position information suggesting both that motor systems detect eye position to better than 0.5° arc and that large errors in controlling eye position in the dark could be attributed to poor spatial memory.

Quality of retinal image stabilization during small natural and artificial body rotations in man.

Abstract Two-dimensional head rotations recorded from 2 subjects sitting still, without artificial head support, showed appreciable movement over the frequency range d.c. to 7 Hz. Capacity of vestibuloocular reflex and visually guided eye movements to null motion over this dynamic range was examined by simultaneously recording 2-dimensional head and eye rotations while sinusoidally rotating subjects over the frequency range 0.1 to 15 Hz using small amplitudes. At best, oculomotor compensation removed about 90% of head motion from eye motion in space. Representative compensation was poorer. Compensation for natural motions of unsupported heads while sitting and standing was also incomplete resulting in substantially more eye motion in space than was observed with head supported. These observations, coupled with recent demonstrations of plasticity of the vestibulo-ocular reflex, led us to suggest that the degree of compensatory oculomotor response is actively adjusted downwards so as to guarantee sufficient retinal image motion to prevent perceptual fading when the body is relatively stationary and is actively adjusted upwards, so as to guarantee sufficient retinal stability to prevent perceptual blurring when the body moves actively. Seen this way. the goal of oculomotor compensation is not retinal image stabilization, but rather controlled retinal image motion adjusted so as to be optimal for visual processing over the full range of natural motions of the body.

Accuracy of spatial localizations near the time of saccadic eye movements

Two-dimensional eye movements were recorded while subjects used a hammer to strike targets that were flashed-on briefly before, during or up to 750 msec after a horizontal saccade. Mean position of hammer blows was 20 min arc (SD = 67 min arc) from the target when the only cue to target location was eye position. Position of responses varied slightly with time of target exposure relative to the saccade. These results show that observers can closely monitor small changes in eye position during and near the time of saccadic eye movements.

Cycloplegic Refractions in Infants and Young Children

We studied groups of normal infants and infants with amblyopia and esoropia to determine the incidence of infantile astigmatism. Under cycloplegia, 19% of normal infants had astigmatism; this was at least twice the incidence in adults, but less than one-hale that found by noncycloplegic refractions of infants. During the first three postnatal years the incidence of astigmatism and distributions of spherical equivalents and anisometropia did not distinguish normal patients from most of those with esotropia and amblyopia.

Spatial localization during pursuit eye movements.

Abstract Two-dimensional eye movements were recorded while observers used ballistic arm movements to localize targets presented during smooth pursuit. Mean position of responses was 2′ arc ( SE = 3′arc ) from a target when localizations depended solely on eye position. Next, observers accurately struck an untracked target seen moving in the peripheral retina showing that eye position cues were used to compensate for retinal image motion caused by pursuit of other objects. Finally, observers used the method of adjustment to veridically set the path of a target to show that accurate localizations were not restricted to a motor task. These results show that observers are sensitive to changes in the position of the pursuing eye.

The Relation of Myopia and Astigmatism in Developing Eyes

The relation of astigmatism and myopia was analyzed in 298 myopic children, ages birth to 10 years. The mean spherical equivalent, determined by cyclopentolate retinoscopy, for the entire group was--2.9 diopters and did not change significantly with age. However, in 3-year-old children and younger, myopia progressed in eyes with greater than or equal to 1 diopter of cylinder and tended to increase through age 8 years in those having greater than or equal to 3 diopters of cylinder. Also, astigmatic errors greater than or equal to 1 diopter, especially of oblique orientation, were associated with higher degrees of myopia than nonastigmatic errors. These data from myopic children suggest that uncorrected astigmatism during a period of visual immaturity influences the course of myopia. Thus, naturally occurring astigmatic errors, that are frequent among infants and young children, appear to have a role similar to the vision blurring perturbations that trigger the development of myopia in young animals. Ascertainment and full correction of these refractive errors in young children may be important in assuring the best possible vision.

The Neurovascular Retina in Retinopathy of Prematurity

The continuing worldwide epidemic of retinopathy of prematurity (ROP), a leading cause of childhood visual impairment, strongly motivates further research into mechanisms of the disease. Although the hallmark of ROP is abnormal retinal vasculature, a growing body of evidence supports a critical role for the neural retina in the ROP disease process. The age of onset of ROP coincides with the rapid developmental increase in rod photoreceptor outer segment length and rhodopsin content of the retina with escalation of energy demands. Using a combination of non-invasive electroretinographic (ERG), psychophysical, and image analysis procedures, the neural retina and its vasculature have been studied in prematurely born human subjects, both with and without ROP, and in rats that model the key vascular and neural parameters found in human ROP subjects. These data are compared to comprehensive numeric summaries of the neural and vascular features in normally developing human and rat retina. In rats, biochemical, anatomical, and molecular biological investigations are paired with the non-invasive assessments. ROP, even if mild, primarily and persistently alters the structure and function of photoreceptors. Post-receptor neurons and retinal vasculature, which are intimately related, are also affected by ROP; conspicuous neurovascular abnormalities disappear, but subtle structural anomalies and functional deficits may persist years after clinical ROP resolves. The data from human subjects and rat models identify photoreceptor and post-receptor targets for interventions that promise improved outcomes for children at risk for ROP.

Development of ERG responses: The ISCEV rod, maximal and cone responses in normal subjects

Purpose: Summarize ISCEV ERG responses from normal infants and children. Methods: The amplitudes and implicit times of the ISCEV rod, maximal dark-adapted and cone responses from a total of 409 normal infants (n=128), children and adult controls were compiled. The subjects, aged 1 week to 52 years, were divided into seven age groups, including four in infancy (<52 weeks). The response parameters for each age group were summarized as percentiles. Results: In each ISCEV condition, the youngest infants (1–5 weeks) had significantly smaller amplitudes and longer implicit times than adults. Amplitude increased and implicit time decreased systematically with age. Conclusions: The developmental changes in ERG responses are significant. The medians and ranges herein provide provisional norms against which the ERG responses from pediatric patients can be compared

Photoreceptor function in infants and children with a history of mild retinopathy of prematurity.

Five infants and children with a history of mild retinopathy of prematurity (ROP) were tested for postulated alterations in rod photoreceptor function. The photoreceptor responses were derived from the electroretinographic alpha waves. Postreceptoral components, the beta wave and the oscillatory potentials, were also examined. The saturated amplitude and sensitivity of the rod photoreceptor responses were low, except for the sensitivity in one patient. The beta-wave sensitivity was low, but saturated amplitudes were within the 95% prediction interval for normal. The amplitudes of the oscillatory-potential responses were also attenuated. The results indicate that retinal dysfunction may be present in patients with a history of mild ROP long after the ROP has completely resolved. Additionally, the data suggest that the photoreceptors are the primary site of retinal dysfunction in mild ROP.

Effect of carotenoid supplementation on plasma carotenoids, inflammation and visual development in preterm infants

Objective:Dietary carotenoids (lutein, lycopene and β-carotene) may be important in preventing or ameliorating prematurity complications. Little is known about carotenoid status or effects of supplementation.Study Design:This randomized controlled multicenter trial compared plasma carotenoid levels among preterm infants (n=203, <33 weeks gestational age) fed diets with and without added lutein, lycopene and β-carotene with human milk (HM)-fed term infants. We assessed safety and health.Result:Plasma carotenoid levels were higher in the supplemented group at all time points (P<0.0001) and were similar to those of term HM-fed infants. Supplemented infants had lower plasma C-reactive protein (P<0.001). Plasma lutein levels correlated with the full field electroretinogram-saturated response amplitude in rod photoreceptors (r=0.361, P=0.05). The supplemented group also showed greater rod photoreceptor sensitivity (least squares means 6.1 vs 4.1; P<0.05).Conclusion:Carotenoid supplementation for preterm infants raises plasma concentrations to those observed in HM-fed term infants. Carotenoid supplementation may decrease inflammation. Our results point to protective effects of lutein on preterm retina health and maturation.