J. Van Hof-Van Duin

Development of visuomotor behavior in normal and dark-reared cats

Summary The development of visuomotor coordination in light-deprived cats was compared with that of newborn animals, raised under normal circumstances, using behavioral tests. Two groups of light-deprived cats were studied: one of which was dark-reared for 4 months, the other for 7 months. After dark-rearing the cats were kept in animal rooms which were illuminated for 12 h each day. All cats spent at least 4 h each day in a big playroom, where toys were available. Obstacle avoidance, tracking of moving objects, optokinetic nystagmus, visually triggered extension, visually guided placing, visual cliff behavior and jumping were tested. All light-deprived cats revealed a complete recovery of visuomotor behavior; the 7-months deprived cats recovered within 10 weeks and the 4-months deprived ones within 7 weeks. The time period in which the various responses in both groups of light-deprived cats developed after dark-rearing was found to be roughly in accordance with that of normally visually inexperienced kittens after birth.

Early and permanent effects of monocular deprivation on pattern discrimination and visuomotor behavior in cats

Abstract Visuomotor behavior and pattern discrimination were studied in a group of cats raised with one eye closed by eyelid suturing 7–10 days after birth. At the age of 8–10 months the animals were forced to use their deprived eye by reversal of eye closure (closing the normal eye and opening the deprived one). Visuomotor behavior and pattern discrimination were tested before as well as after reverse closure, to compare performances of the deprived eye with those of the non-deprived eye. In order to get optimal visuomotor experience, the animals were kept in large playrooms for at least 4 h each day. Except for normal tactile placing responses, visually triggered extension responses and uncertain jumping, 2 years after reverse closure all other tests (visually guided reaching, visual cliff behavior, obstacle avoidance, tracking, jumping, and visual blink responses) still showed impairments; the optokinetic nystagmus was asymmetric. In contrast with this partial behavioral recovery, pattern discrimination in a simple nose-push training ☐ requiring no complicated visuomotor coordination was found to be positive. Discriminations of gratings of different orientations, starting 4 weeks after reverse closure, appeared to be normal, in comparison with performance using the non-deprived eye of the same cats tested before reverse closure. Form discrimination was also found to be positive; some monocularly deprived cats required more trials than normal cats in upright vs. reversed solid triangles discrimination, but succeeding form problems were mastered within the same range as found in normal cats. Apparently behavioral defects after monocular deprivation are due to deficiencies in visuomotor control rather than in pattern identification.

ACUITY ASSESSMENT OF NON‐VERBAL INFANTS AND CHILDREN: CLINICAL EXPERIENCE WITH THE ACUITY CARD PROCEDURE

The acuity card procedure was used to assess the visual acuity of 510 neurologically normal and abnormal infants and children. Acuity estimates were obtained for 93 per cent of 842 binocular and 279 monocular tests. The observed development of binocular acuity of normal fullterm and preterm infants agreed well with previous reports using the traditional forced‐choice preferential looking technique. Monocular tests seemed to support earlier suggestions that grating acuity may be relatively insensitive to strabismic amblyopia. Infants at risk of later neurological deficits but developing normally had only a slight delay in development of acuity, but there was a high incidence of acuity deficits (54 per cent) among those with severe neurological defects. The great majority of a group of multiply handicapped children had low acuity for age. Repeat tests showed a high degree of test‐retest consistency. The acuity card procedure was a successful and useful method for assessing the acuity of infants and children who cannot be tested with standard ophthalmological methods.

Visual field and grating acuity development in low-risk preterm infants during the first 2 1/2 years after term

The effect of early visual experience on visual field size and grating acuity development was studied longitudinally in 36 appropriate for gestational age (AGA) and 26 small for gestational age (SGA) low-risk preterm infants. These were selected out of 194 very low birth weight (VLBW) infants (birthweight less than 1500 g) born in 1985 and 1986. Criteria for inclusion as low-risk were the absence of neurological, respiratory, circulatory and alimentary problems in the neonatal period; no retinopathy of prematurity and no evidence of abnormality on the neonatal cranial ultrasound scans. Binocular field sizes were assessed using kinetic arc perimetry. Binocular grating acuity was tested by means of the prototype version of the acuity card procedure. Results were compared with norms obtained in control fullterms in earlier studies. Infants were tested at 6 weeks, 6, 6, 9 and 12 months of age from the expected term date. Twenty-two of these infants were retested at 2 1/2 years of corrected age. Visual field size and visual acuity estimates of (both AGA and SGA) low-risk, VLBW preterms and control fullterms overlapped at all test ages, except for a slight but significantly faster development of the upper and the lower visual field at 6 weeks corrected age in the preterm group. These results indicate that for clinical purposes visual experience before the expected term date has not only no measurable effect on the normal development of behavioural acuity, but also no accelerating effect on the development of peripheral vision.

Unexpected improvement after prolonged posttraumatic vegetative state

An 18-year-old girl suffered a severe head injury in a traffic accident. As a result, she was vegetative for about 21/2 years. She then showed signs of a gradually returning responsiveness. Six years after the accident, she is now able to comprehend and communicate, shows considerable interest in her surroundings and is able to establish interpersonal relationships. Moreover, the improvement is still continuing. Her severe contractures, however, prevent her from making full use of these regained mental capacities. Such a mental recovery after such a long-lasting vegetative state of traumatic origin has not previously been described.

Visual defects in children after cerebral hypoxia

Visual functions were examined in 18 survivors of perinatal hypoxia/ischemia with mild to severe neurological sequelae, aged between 3 months and 17 years, and in two patients, aged 8 and 13 years, who had suffered postnatal hypoxic events. All but two patients showed clear visual deficits ranging from mild defects in visual acuity, visual field size, and/or optokinetic nystagmus to blindness. In 5 patients, the visual field was restricted to tunnel vision, a finding which appeared to be specifically related to the hypoxic/ischemic nature of the brain damage. The severity of the visual defects after perinatal hypoxia was related to the occurrence of neonatal seizures, later neurological outcome, and gestational age at birth. This is discussed in relation to previous studies of the effects of perinatal hypoxia/ischemia.

Effects of very low birth weight (VLBW) on visual development during the first year after term

Behavioural visual functions were assessed in 155 very low birth weight (VLBW) infants during the first 12 months after expected term. Visual development was examined (mainly cross-sectionally) at 6 weeks, 3, 6, 9, and 12 months of corrected age by assessment of visual acuity, visual fields, optokinetic nystagmus and visual threat response. Many VLBW infants showed visual impairments (54.2%). No single visual function appeared to be specifically susceptible to impairments, deficits were often apparent across a range of functions. Visual impairments were observed at all test ages, and could already be assessed at 6 weeks of corrected age. The highest incidence of visual impairments was scored at 6 months corrected age. Beyond 6 months, less deficits were observed, suggesting in many infants a delayed rather than a permanently impaired visual development. In some infants deficits became evident at a later stage, after an apparently normal initial development. The results suggest that VLBW infants are at risk for impaired visual development.

Optokinetic and spontaneous nystagmus in children with neurological disorders.

Binocular and monocular optokinetic nystagmus (OKN) was examined with EOG recordings in 26 visually impaired children with neurological disorders, aged 2.5 months to 15 years. Spontaneous and/or latent nystagmus, complicating the assessment of OKN, was seen in 73% of the children. Binocular OKN in 21 patients with positive visual functions was symmetrical in 5 cases, asymmetrical in 12 cases and could not be elicited in 4 patients. Monocular OKN was nearly always asymmetrical, with usually a superiority of the temporal-to-nasal (TN) components. Five blind children, 4 of them cortically blind, showed positive binocular and monocular OKN, suggesting that neural control of OKN in humans may be at least partly independent of the cortex. This, together with results from some of the sighted patients, indicates that in humans, cortical and subcortical contributions to OKN, and particularly to monocular nasal-to-temporal (NT) OKN, may be more complicated than had been thought.

Visual Field Measurements in Monocularly Deprived and Normal Cats

SummaryVisual fields of 15 monocularly deprived (MD) cats and 2 monocularly tested normal adult cats, were measured using stationary stimuli at fixed distances in the horizontal plane. Compared to the visual fields of monocularly tested normal cats, those of the deprived eyes of MD cats were found to be restricted to the ipsilateral hemifield up to the midline. This finding appeared to be permanent since it was measured both in cats tested early (4 cases) and late (11 cases) after deprivation. In addition, it seemed to be independent whether the nondeprived eye was closed by reverse suturing (13 cases), or was left open after deprivation and closed only temporarily during testing (2 cases).Visual fields were also found to be restricted to the ipsilateral hemifield, if MD cats were tested at several levels above the horizontal plane or in a hemisphere (23 cm radius) in which the superior and inferior segment of the visual space could be tested (6 cases).The results are controversial to those of Sherman (1973) who described the visual fields of MD cats to be restricted to the monocular (60–90 ° ipsilateral) segment. The differences observed in our results compared to those of Sherman could not be explained by experimental factors, since testing MD cats by the method employed by Sherman (8 cases) also resulted in visual fields covering the monocular as well as the binocular part of the ipsilateral side. Consequently, Shermans hypothesis (1974b), that for MD cats the geniculocortical pathways dominate in the visual behavior and that retinotectal pathways are somehow suppressed, could not be confirmed by our results. In our experiments the visual behavior demonstrated by MD cats seemed to be developed mainly through retinotectal pathways. In MD cats in which after the deprivation period the non-deprived eye remained open, the monocular part seemed to be of more importance than the binocular segment; permanent closure of the normal eye seemed to lead to a further shift towards the binocular segment. Therefore, in non-reverse sutured MD cats some suppression of retinotectal pathways by imbalanced corticotectal pathways may be present, but not as elaborate as described by Sherman. This slight suppression is overcome by reverse suturing.The mechanism of release from suppression of retinotectal pathways is unknown, its possible localisation is discussed.Visual fields of 15 monocularly deprived (MD) cats and 2 monocularly tested normal adult cats, were measured using stationary stimuli at fixed distances in the horizontal plane. Compared to the visual fields of monocularly tested normal cats, those of the deprived eyes of MD cats were found to be restricted to the ipsilateral hemifield up to the midline. This finding appeared to be permanent since it was measured both in cats tested early (4 cases) and late (11 cases) after deprivation. In addition, it seemed to be independent whether the nondeprived eye was closed by reverse suturing (13 cases), or was left open after deprivation and closed only temporarily during testing (2 cases). Visual fields were also found to be restricted to the ipsilateral hemifield, if MD cats were tested at several levels above the horizontal plane or in a hemisphere (23 cm radius) in which the superior and inferior segment of the visual space could be tested (6 cases). The results are controversial to those of Sherman (1973) who described the visual fields of MD cats to be restricted to the monocular (60–90 ° ipsilateral) segment. The differences observed in our results compared to those of Sherman could not be explained by experimental factors, since testing MD cats by the method employed by Sherman (8 cases) also resulted in visual fields covering the monocular as well as the binocular part of the ipsilateral side. Consequently, Shermans hypothesis (1974b), that for MD cats the geniculocortical pathways dominate in the visual behavior and that retinotectal pathways are somehow suppressed, could not be confirmed by our results. In our experiments the visual behavior demonstrated by MD cats seemed to be developed mainly through retinotectal pathways. In MD cats in which after the deprivation period the non-deprived eye remained open, the monocular part seemed to be of more importance than the binocular segment; permanent closure of the normal eye seemed to lead to a further shift towards the binocular segment. Therefore, in non-reverse sutured MD cats some suppression of retinotectal pathways by imbalanced corticotectal pathways may be present, but not as elaborate as described by Sherman. This slight suppression is overcome by reverse suturing. The mechanism of release from suppression of retinotectal pathways is unknown, its possible localisation is discussed.

Effects of perinatal hypoxia on visual development during the first year of (corrected) age

Visual development was assessed in 124 infants (112 preterms and 12 fullterms) who had suffered from perinatal hypoxia and in 55 control preterm infants during the first year of corrected age. Using behavioural techniques, visual functions were tested during follow-up visits in the Sophia Childrens Hospital. Corrected ages at testing ranged from 3 months to 1 year. During this period, infants with perinatal hypoxia showed more abnormalities in visual functions than preterm control infants. Gestational age at birth did not influence the outcome of visual development after perinatal hypoxia. Most visual impairments were demonstrated at 3 and 6 months of age. All infants with severe neuro-developmental handicaps showed visual deficits, although neuro-developmental abnormalities and visual deficits could be present as isolated phenomena. Ultrasound abnormalities related well with visual dysfunctions. Prospective studies of infants with visual deficits and a history of perinatal hypoxia are indicated.