PubMed Health⌕ Search

Biomedical subjects

L Tychsen

Publications and source records attributed to L Tychsen.

At least 19 recordsLinked to original sources
PubMed2004

Pediatric transscleral sutured intraocular lenses: efficacy and safety in 43 eyes followed an average of 3 years.

PURPOSE: To report longer term results of transscleral sutured intraocular lens (TSSIOL) implantation in a sizable cohort of aphakic children, who were not suitable for contact lens wear and lacked adequate capsular support for sulcus fixation of an intraocular lens. METHODS: Clinical outcome data were collated by retrospective review after surgery on 43 consecutive eyes in 32 aphakic children (mean age at implantation = 10 years; 33% < or = age 7 years). Outcome measures included visual acuity, postoperative refractive error, postoperative complications, and rate of reoperation. Follow-up averaged 37 months. RESULTS: Visual acuity improved after surgery in 70% (30) of operated eyes (in 69% or 22/32 children). Fifty-one percent (22/43 eyes) improved by two lines or more. No patient suffered a loss of acuity or exacerbation of preexisting amblyopia. Postoperative refraction was within +/-2.0 D of the predicted refraction in 93% (40/43) of eyes. Complications, with the exception of one eye (2%), were minor/transient and resolved in the first week after surgery. Complications included small hyphemas (7%, 3/43 eyes), vitreous hemorrhage (5%, 2/43 eyes), and ocular hypertension or hypotony (5%). Two eyes (5%) exhibited episodes of iris capture of the IOL optic, one of which (2%, 1/43) eventually necessitated reoperation for IOL exchange. No retinal detachments or other retinal complications were encountered. CONCLUSION: TSSIOL implantation appears to be a safe and effective method for correcting aphakia in pediatric eyes that lack adequate capsular support. Safety over a follow-up period longer than the average 3 years reported here remains to be determined. The surgery is more difficult to perform than capsular-bag or sulcus implantation and potentially carries greater risks.

Adolescent↗
PubMed2001

Retinal and intraventricular cerebral hemorrhages in the preterm infant born at or before 30 weeks' gestation.

PURPOSE: To determine the prevalence of retinal hemorrhages and their association with cerebral intraventricular hemorrhages (IVH) in low-birth-weight preterm neonates born at or before 32 weeks' gestation. METHODS: We prospectively studied a consecutive series of 22 neonates (24-30 weeks' gestation; mean gestational age, 27 weeks; mean weight, 1065 g) admitted to the neonatal intensive care unit. Anterior segment and indirect ophthalmoscopic examination, as well as cranial ultrasonographic examination, were performed on day 1 and day 10 of life. The prevalence of retinal and intraventricular hemorrhage was tested statistically for association with obstetric and neonatal clinical variables. RESULTS: The prevalence of retinal hemorrhage was 9% (2/22; 95% CI, 3%-21%) on day 1 and 2% (1/22) on day 10. The prevalence of IVH was 27% (6/22; 95% CI, 9%-46%): 14% (3/22) on day 1 and 23% (5/22) on day 10. Retinal hemorrhages occurred with greater frequency in neonates born to women who had intrauterine infection (chorioamnionitis, P =.043) and low umbilical cord pH levels (P =.027). No association was found between the presence of retinal hemorrhage and IVH (P = 1.000), mode of delivery (ie, vaginal vs cesarean section, P = 1.000), birth weight (P =.476), or gestational age (P = 1.000). The presence of subconjunctival hemorrhage was associated with IVH (P =.046). CONCLUSIONS: Retinal hemorrhages occur in less than 10% of low-birth-weight neonates, ie, a prevalence one half that observed in term neonates (22%). The hemorrhages tend to resolve without sequelae in the first 10 days of life and occur more commonly in infants born to women with uterine infection. Retinal hemorrhages in very premature neonates are not predictive of IVH-related brain damage.

Cerebral Hemorrhage↗
PubMed2001

Pediatric secondary lens implantation in the absence of capsular support.

PURPOSE: To describe and evaluate alternate techniques for implanting intraocular lenses in children in the absence of adequate capsular support for traditional lens implantation. METHODS: Postoperative results of 18 eyes with posterior chamber intraocular lenses (PCIOLs) sutured to the ciliary sulcus and 10 eyes implanted with anterior chamber intraocular lenses (ACIOLs) were reviewed. Visual outcomes were divided into 2 groups: onset of aphakia during the critical period of visual development (< or = 9 years) and onset after the critical period (> 9 years). Visual outcomes and complications were recorded. RESULTS: Average follow-up was 10.3 months in the PCIOL group and 49.2 months in the ACIOL group. Eyes that became aphakic after the critical period of visual development achieved better overall final visual acuity than the eyes that became aphakic during the critical period; indeed, the eyes that became aphakic during the critical period did not achieve significantly improved vision. There were no complications in the PCIOL group. Complications in the ACIOL group included corectopia, haptic migration through the operative wound requiring removal, and pigment deposits on the lens. CONCLUSIONS: PCIOLs sutured to the ciliary sulcus offer a superior option to ACIOLs for correction of childhood aphakia in children lacking capsular support. ACIOLs had a high rate of serious complications (10%) in this small series. Secondary implantation with transsclerally sutured PCIOLs should be considered in complicated cases when more conservative options have been exhausted.

Adolescent↗
PubMed2000

Automated cover testing for binocular misalignment in awake monkeys using spectacle- mounted liquid crystal shutters.

PURPOSE: In humans, pathologic misalignment of the eyes (strabismus, or hetero-tropia) is readily detected using a clinical technique in which the visual axis of each eye is blocked briefly by a hand held occluder (i.e., the cover test, AKA the single cover test, or unilateral cover test). This manual technique is impractical for use in non-human primates. This paper reports the electronic hardware and computer software we have devised and adapted to perform an automated cover test in awake macaque monkeys (Macaca mulatta or rhesus, and Macaca nemistrina or pigtail) to facilitate the study of strabismus in this species. METHODS: Liquid crystal shutters (Displaytech LV2500OP-OEM) are mounted in aluminum spectacle frames which are positioned in front of the monkey's eyes by attaching the frame holder to an acrylic skull cap. The shutters are electrically actuated alternately to an "open" (transparent) or "closed" (opaque) state, occluding each eye in turn. The actuation signal (+/-5 volts) is generated by a single logic chip. The chip is driven by commercial data control and acquisition software (Spike 2, Cambridge Electronic Design) running on a Macintosh computer. Eye position and movement during this cover tests is monitored and recorded by the computer using surgically implanted scleral coils. Monkeys are rewarded for fixating small, moveable targets so that binocular misalignment can be measured with high precision at different or cardinal positions of horizontal and vertical gaze. RESULTS: The shutters produced occlusion of each eye as effective as that of an opaque plastic occluder used in previous experiments that required monocular viewing. Heterotropias were detected and recorded in monkeys and closely resembled those observed in human patients. It was also possible to detect heterophorias by actuating the shutters alternately. CONCLUSIONS: The shutters operated reliably, with negligible delay and transition times, providing automated, repeatable cover tests that are, in fact, in many respects superior to the standard clinical manual technique. In addition, their application to humans, using infrared electro-oculography instead of scleral coils to monitor eye position and movement, holds promise for future applications.

Animals↗
PubMed2000

Anomalous retinal correspondence: neuroanatomic mechanism in strabismic monkeys and clinical findings in strabismic children.

BACKGROUND: Anomalous retinal correspondence (ARC) is a neural adaptation to eye misalignment in which non-corresponding retinal points are linked in the visual cortex to provide binocular fusion. ARC within the striate cortex would require that horizontal neurons link right-eye and left-eye ocular dominance columns (ODCs) separated by a distance in the cortex proportional to the angle of strabismus. Two hypothetical mechanisms are possible: (1) The ODCs can be linked by axons of horizontal neurons that project monosynaptically from a right-eye to a left-eye ODC. The further apart the ODCs, the longer the axons; hence, axon length should be greater in subjects with strabismus than in healthy subjects (elongated axon, monosynaptic hypothesis). In this case, the clinical probability of developing ARC should be independent of the angle of strabismus, until an upper-limit angle of strabismus is reached equally to the maximal length of axons available to link nonadjacent ODCs, at which point an abrupt decline of ARC probability should be evident. (2) Alternatively, ODCs can be linked by a chain of horizontal neurons, the number of which increases as the distance among ODCs increases; axon length in subjects with strabismus would be expected to be the same as in healthy subjects (normal axon, polysynaptic hypothesis). In this case, the greater the angle of strabismus, the more horizontal neurons and synapses required for linkage, and the greater the probability of signal degradation. Thus, the clinical probability of developing ARC through a polysynaptic mechanism should be inversely proportional to the angle of strabismus. The purpose of this study was to test these 2 hypotheses neuroanatomically in primates and clinically in children. METHODS: For the neuroanatomic portion of the study, biotinylated dextran amine was injected into ODCs of area V1 to label individual neurons. The length of the horizontal axons from these neurons was then compared in strabismic and normal monkeys. In the clinical portion of the study, the medical records of 192 children with strabismus were reviewed retrospectively. The angle of strabismus (prism cover test) and the presence of ARC (Bagolini striated lenses, Worth/Polaroid 4-dot) were recorded. Plots of the presence of ARC as a function of the angle of strabismus were obtained. RESULTS: There was no significant difference in axon length between healthy (7. 02 +/- 0. 83 mm) and strabismic monkeys (6. 60 +/- 1. 07 mm) (P =.16). In children with strabismus, ARC decreased as the angle of strabismus increased (P <. 05). ARC was more prevalent in children who had primary or postsurgical deviations of </=4 degrees to 5 degrees (8-10 PD), corresponding to </=2 horizontal axon lengths in the foveal striate visual cortex. CONCLUSIONS: The visual cortex adapts to strabismus by combining information from paired ODCs of opposite ocularity that, because of the eye misalignment, are nonadjacent and separated by abnormally long distances across the striate cortex. The cortex appears to achieve the linkage, not by elongating neuronal axons, but by using chains of neurons that have normal-length axons. The visual cortex is most successful stochastically at achieving this linkage (ie, developing ARC) when the gap that must be bridged is no greater than 4 degrees to 5 degrees (8-10 PD), or the retinotopic distance in the foveal visual field is spanned by 2 normal V1 neurons.

Adaptation, Ocular↗
PubMed1999

Visual recovery after a year of craniopharyngioma-related amaurosis: report of a nine-year-old child and a review of pathophysiologic mechanisms.

BACKGROUND: The probability of visual recovery in tumor-related optic neuropathy usually correlates with the severity and duration of optic pathway compromise. Recovery of visual acuity to normal levels is unexpected after profound loss of vision extending for a period of weeks and months. METHODS: A 9-year-old girl who had neurosurgical resection of a craniopharyngioma compressing the optic chiasm and optic tract was followed up serially with neuroimaging and clinical examinations over a 6-year period. RESULTS: Within 3 months of the diagnosis of craniopharyngioma, the girl's vision was reduced to no-light-perception blindness when she viewed with the more involved eye. The blindness correlated with an amaurotic (i.e., >3.6 log unit) relative afferent pupillary defect and an absence of any response when tested with visual field perimetry. After more than a year of total blindness and cessation of all neurosurgical and radiation therapy, visual acuity recovered to a normal level (20/25), the afferent pupillary defect improved, and sensitivity in a portion of the temporal hemivisual field was restored. In the follow-up that has extended for 5 years from the time of recovery, stability of the restored vision has been documented. CONCLUSION: Children who have tumor-related loss of vision due to damage to the anterior visual pathways may be capable of recovery after intervals of blindness that would be considered irreversible in adults. The mechanism of the recovery in our patient may have been decompression-related restoration of axoplasmic flow, followed by gradual remyelination of visual fibers, which allowed reorganization of connections to the lateral geniculate nucleus to optimize synaptic transmission.

Blindness↗
PubMed1999

Effect of infantile strabismus on visuomotor development in the squirrel monkey (Saimiri sciureus): optokinetic nystagmus, motion VEP and spatial sweep VEP.

PURPOSE: To determine whether squirrel monkeys made artificially strabismic in infancy had ocular fixation abnormalities, directional asymmetries of horizontal optokinetic nystagmus (OKN) and asymmetries of motion visually evoked potentials (MVEPs) similar to those of humans with infantile strabismus. METHODS: Esotropia was produced in a newborn squirrel monkey by surgical tenotomy of both lateral rectus muscles. The alignment and eye rotations of the monkey were examined longitudinally and VEP testing was performed at the age of one year. Visual acuity was measured using spatial frequency sweep VEPs (SSVEP) in response to grating stimulation. OKN was tested under conditions of monocular viewing using full-visual-field, vertically oriented, moving stripes. MVEPs in response to horizontal motion were recorded with the animal sedated to reduce the possibility of eye movement artifact. RESULTS: The artificially strabismic squirrel monkey displayed a constant, committant esotropic strabismus accompanied by latent nystagmus. Monocular SSVEP acuity was subnormal in one eye, consistent with mild monocular strabismic amblyopia. The monkey demonstrated asymmetric OKN favoring nasally-directed stimulus motion when viewing with either eye. Monocular MVEPs were also characterized by a horizontal asymmetry with a directional bias inverted 180 degrees between the right and the left eyes. The eye movements and MVEP asymmetries were similar to those observed in strabismic macaque monkeys and humans with early-onset strabismus. Neither the OKN asymmetry nor the MVEP asymmetry was evident in a normal squirrel or normal macaque monkey. CONCLUSION: The artificially strabismic squirrel monkey is an appropriate eye movement and VEP model for the study of neural mechanisms in human infantile strabismus.

Animals↗
PubMed1998

Asymmetric motion visually evoked potentials in infantile strabismus are not an artifact of latent nystagmus.

BACKGROUND: Patients who have infantile strabismus exhibit a directional asymmetry of motion visually evoked potentials (MVEPs) recorded under conditions of monocular viewing. The majority of these patients also have latent nystagmus, raising the possibility that the MVEP asymmetry is an artifact of the nystagmus. To explore this issue, we correlated MVEPs and eye movements under conditions that eliminated or increased latent nystagmus. METHODS: MVEPs and eye movements were recorded under conditions of monocular viewing in three adults who had combined infantile-onset strabismus and latent nystagmus. The subjects viewed vertically oriented grating stimuli that oscillated horizontally at temporal frequencies of 6.6 to 11.0 Hz by use of spatial frequencies of 1 to 3 cycles/degree. Quantitative eye movement recordings of latent nystagmus and horizontal pursuit/optokinetic nystagmus were also obtained. RESULTS: Eye movement recordings showed that the latent nystagmus was absent or markedly diminished when the viewing eye was in a 45-degree adducted position, whereas nystagmus velocity increased 10 to 40 times (to 2.2 to 4.5 degrees/second) when the viewing eye was in an abducted position (p < 0.05). MVEPs were abnormal (asymmetry indices > 0.40) when the viewing eye was in an adducted or abducted position of gaze. No correlation was found between the MVEP asymmetry index and the velocity of latent nystagmus. CONCLUSIONS: MVEP asymmetries in infantile strabismus remain robust under conditions that eliminate or greatly reduce the oscillations of latent nystagmus. MVEP asymmetries and ocular motor abnormalities both characterize infantile strabismus, but the ocular motor defects do not cause the MVEP asymmetries. The nasotemporal asymmetry of MVEPs and the nasotemporal asymmetry of pursuit and latent nystagmus are likely caused by deficits in related but separate binocular visual cortical circuits.

Adult↗
PubMed1997

Nasotemporal asymmetries in V1: ocular dominance columns of infant, adult, and strabismic macaque monkeys.

To quantify asymmetries of input from the two eyes into each cerebral hemisphere, we measured ocular dominance column (ODC) widths and areas in the striate visual cortex (area V1) of macaque monkeys. Ocular dominance stripes in layer 4C were labeled by using transneuronal transport of intraocularly injected wheat germ agglutinin-horseradish peroxidase (WGA-HRP) or cytochrome oxidase (CO) histochemistry, after deafferentation of one eye or even by leaving afferent input intact. In infant monkey aged 4 and 8 weeks, ocular dominance stripes labeled by WGA-HRP appeared adultlike with smooth, sharply defined borders. In normal infant and normal adult macaque, ocular dominance stripes driven by the nasal retina (i.e., contralateral eye) were consistently wider than stripes driven by the temporal retina (i.e., ipsilateral eye). Asymmetries in the percentage of area V1 driven by nasal vs. temporal ODCs showed a similar "nasal bias": in infant macaque, approximately 58% of ODCs in V1 were driven by nasal retina, and in adult macaque approximately 57%. The asymmetries tended to be slightly smaller in opercular V1 and greater in calcarine V1. "Spontaneous" ocular dominance stripes were revealed by CO staining of V1 in a naturally strabismic monkey and in a monkey made strabismic by early postnatal alternating monocular occlusion. In these animals, ocular dominance stripes and CO blobs corresponding to the nasal retina stained more intensely for CO in both the right and left V1. ODC spacing and the nasotemporal asymmetry in ODC width and area were similar in strabismic and normal monkeys. Our results in normal monkeys extend the observations of previous investigators and verify that nasotemporal inputs to opercular and calcarine V1 are unequal, with a consistent bias favoring inputs from the nasal retina. The CO results in strabismic macaque suggest that the nasal ODC bias promotes interocular suppression when activity in neighboring ODCs is decorrelated by abnormal binocular experience in infancy.

Aging↗
PubMed1997

Variants of congenital ocular motor apraxia: associations with hydrocephalus, pontocerebellar tumor, and a deficit of vertical saccades.

BACKGROUND: Congenital ocular motor apraxia (COMA) is characterized by the inability to generate volitional horizontal saccadic eye movements in the absence of other focal neurologic abnormalities. SUBJECTS: We report on two children (ages 5 months and 3 years) whose COMA did not adhere to these classic criteria. The children were followed up clinically with serial ocular motor examinations and neuroimaging over a period of 3 years. RESULTS: In the first child horizontal COMA was associated initially with neonatal communicating hydrocephalus. Two and one half years after the first signs of COMA, a fourth ventricle medulloblastoma appeared. The second child, who recovered from a periventricular hemorrhage caused by perinatal asphyxia, manifested vertical COMA and compensatory vertical head thrusts. CONCLUSIONS: COMA may be associated with hydrocephalus, pontocerebellar tumor, and periventricular hemorrhage. These rare variants of COMA emphasize that the eye movement deficits may arise from several locations, cerebral as well as pontocerebellar, in the neuronal pathways generating saccades.

Apraxias↗
PubMed1996

Prevalence of retinal hemorrhages in infants after extracorporeal membrane oxygenation.

PURPOSE: To determine the prevalence of vision-threatening retinal hemorrhages in infants after venoarterial extracorporeal membrane oxygenation, and possible correlation between retinal hemorrhages and brain hemorrhages, thrombocytopenia, carotid reanastomosis, or death after extracorporeal membrane oxygenation. METHODS: We reviewed the findings of dilated ophthalmoscopic examinations performed on 37 children an average of 16 days after extracorporeal membrane oxygenation (35 neonates and two 1-year-old children). RESULTS: Five (13%) of the 37 children examined had small (< or = 1 disk diameter) intraretinal hemorrhages. Presence or absence of retinal hemorrhages did not correlate with presence of cerebral hemorrhage, mean platelet count during extracorporeal membrane oxygenation, a history of reanastomosis of the carotid artery, or subsequent death. CONCLUSION: Retinal hemorrhages observed after extracorporeal membrane oxygenation are not necessarily caused by extracorporeal membrane oxygenation; some hemorrhages may be benign and related to parturition. Children who undergo venoarterial extracorporeal membrane oxygenation are at low risk for vision-threatening retinal hemorrhage.

Cerebral Hemorrhage↗
PubMed1996

[Functional and structural abnormalities in the visual cortex in early childhood strabismus].

BACKGROUND: To investigate the structural basis for functional deficits in infantile strabismus we used a neuroanatomic tracer and a histochemical label to examine the primary visual cortex (area V1) of adult esotropic macaque monkeys. ANIMALS AND METHODS: The animals had developed natural esotropia in the first months of life, alternated fixation, and exhibited the ocular motor signs that typify strabismus with onset in infancy. After behavioral and VEP testing, ocular dominance columns (ODCs) in V1 were injected with a neuronal traser and labeled for cytochrome oxidase activity. RESULTS: The strabismic monkeys showed striking deficits in binocular luminance visually-evoked potentials (VEPs) and characteristic directional asymmetries in motion VEPs. Binocular horizontal connections between ODCs were reduced an average of 50-60% in strabismic as compared to normal monkeys. ODCs also showed unequal metabolic activity with contralaterally (i.e. nasal retina) driven ODCs showing greater activity in each V1. DISCUSSION AND CONCLUSION: The maldevelopment of connections in upper V1 layers correlates with the abnormalities in binocular and motion VEPs. The unequal metabolic activity suggests interocular suppression. These results provide the first neuroanatomic evidence for cerebral cortex maldevelopments in natural infantile esotropia.

Animals↗
PubMed1996

Biases of motion perception revealed by reversing gratings in humans who had infantile-onset strabismus.

Motion perception was tested by requiring adult subjects to view gratings that remained stationary but reversed in contrast several times per second. Subjects viewed monocularly and judged whether the gratings were stationary, or moving in one direction, in successive 3s trials. Subjects who had early-onset strabismus most frequently perceived vertically oriented gratings to be moving nasalward, and horizontally oriented gratings to be moving up or down. Normal subjects and subjects who had late-onset strabismus most frequently perceived the gratings to be stationary. The asymmetries of motion perception in early-onset strabismus imply that the visual motion neurons of cerebral cortex develop properly only if they receive normal binocular input during infancy.

Adolescent↗
PubMed1996

Surgery for esotropia with a high accommodative convergence/accommodation ratio: effects on accommodative vergence and binocularity.

BACKGROUND AND OBJECTIVE: To determine the effectiveness of strabismus surgery as an alternative treatment for high accommodative convergence/accommodation (AC/A) ratio (nonrefractive accommodative) esotropia. PATIENTS AND METHODS: Twenty-three consecutive children with an AC/A ratio of 5:1 or greater and a distance-near disparity of 10 prism diopters (PD) or more were studied in a prospective design. Each patient was treated by recession of both medial rectus muscles for the full amount of esotropia measured at near fixation through the full distance hyperopic correction. The magnitude of eso deviation, the AC/A ratio, and the grade of binocularity were measured before and a minimum of 4 months after strabismus surgery. RESULTS: Surgery reduced the mean preoperative eso deviation at near fixation by a factor of 4 (from a mean of 37 PD to a mean of 9 PD). Surgery eliminated the need for bifocals in 96 percent of the patients. The grade of binocular fusion or stereopsis improved in 70 percent of the patients, remained unchanged in 26 percent, and was degraded in 4 percent. Three (13 percent) of the children became exophoric; none of the children were exotropic. CONCLUSION: These results demonstrate that strabismus surgery is an effective alternative to the long-term use of bifocals in the treatment of high AC/A ratio esotropia. Surgery may be more effective than bifocals in restoring normal stereopsis and binocular fusion.

Accommodation, Ocular↗
PubMed1995

Unrecognized retention of intraorbital graphite pencil fragments: the role of computerized tomography.

Children with unrecognized intraorbital pencil fragments may come to attention because of surrounding abscess and granuloma formation, after a long delay, and may be suspected to have an intraorbital neoplasm. Two such patients are reported, with emphasis on CT findings. Recognition of the CT manifestations of intraorbital pencil fragments may allow a more conservative surgical intervention than that for presumed intraorbital neoplasm.

Child↗