Quantitative fiber tracking of the optic radiation is correlated with visual-evoked potential amplitude in preterm infants

BACKGROUND AND PURPOSE

Children born preterm are at risk for adverse outcome, including visual impairment. We examined the relationship between neonatal DTI and sVEP in children born preterm to determine whether visual outcomes are related to early measurements of brain microstructure.

MATERIALS AND METHODS

Subjects were born at <34 weeks gestation and imaged before term-equivalent age. DTI fiber tracking was used to delineate the optic radiations and measure tract-specific average FA, D(av), and parallel and transverse diffusivity. Visual-evoked response amplitudes were measured as a function of spatial frequency, contrast, and vernier offset size with sVEP at 6-20 months after birth. The association between DTI and sVEP was assessed by using the Spearman correlation coefficient and linear regression for repeated measures.

RESULTS

Nine children with 15 scans were included. The peak response amplitudes for spatial frequency sweeps were associated with increasing FA and decreasing D(av) and transverse diffusivity (P ≤ .006) but not with parallel diffusivity (P = 1). There was only modest association with the swept contrast condition and no detectable association with the vernier offset sweeps.

CONCLUSIONS

Microstructure of the optic radiations measured shortly after birth is associated with quantitatively measured responses elicited by moderate-to-high contrast spatiotemporal gratings in infancy. These findings are in keeping with studies showing a relationship between brain microstructure and function. While the clinical impact is not known, quantitative neuroimaging of white matter may ultimately be important for predicting outcome in preterm neonates.

Ketamine anaesthesia for paediatric ophthalmology surgery

AIMS

Children with treatable, vision impairing conditions may not have access to surgical care when they live in regions where anaesthesia is unavailable. The use of ketamine anaesthesia in a developing region was studied to determine its safety and effectiveness.

METHODS

This is a consecutive series of 679 children who had a variety of paediatric eye disorders necessitating a short general anaesthesia. Ketamine was administered intravenously by a paediatrician with training in paediatric resuscitation procedures. Both intraocular and extraocular procedures were performed. The location of treatment was the Tilganga Eye Hospital in Kathmandu, Nepal, a developing region of the world. The study took place over a 5 year period.

RESULTS

All procedures were performed without any anaesthetic complications. No child required unanticipated resuscitation or laryngeal intubation. Postoperative dysphoria occurred occasionally and was difficult to measure quantitatively. This side effect of ketamine resolved by the first postoperative day.

CONCLUSION

Ketamine is an effective agent for both intraocular and extraocular surgery in the paediatric age group. None of the children in this series needed resuscitation or intubations, and the ophthalmic surgery was carried out safely. Ketamine can be used safely in any ophthalmic procedure of short duration by a person having some training in anaesthetic resuscitation procedures. Because of its simplicity and safety, ketamine may be useful in a simple ophthalmic setup in the developing word.

Tubedown-1 in remodeling of the developing vitreal vasculature in vivo and regulation of capillary outgrowth in vitro

Tubedown-1 (tbdn-1) is a mammalian homologue of the N-terminal acetyltransferase subunit NAT1 of Saccharomyces cerevisiae and copurifies with an acetyltransferase activity. Tbdn-1 expression in endothelial cells becomes downregulated during the formation of capillary-like structures in vitro and is regulated in vivo in a manner which suggests a functional role in dampening blood vessel development. Here we show that tbdn-1 is expressed highly in the vitreal vascular network (tunica vasculosa lentis and vasa hyaloidea propria) during the pruning and remodeling phases of this transient structure. The vitreal blood vessels of mice harboring a targeted inactivation of TGF-beta2 fail to remodel and abnormally accumulate, a phenomenon reminiscent of the ocular pathology resembling persistent fetal vasculature (PFV) in humans. Since suppression of normal tbdn-1 expression has been previously observed in retinal vessel proliferation, we analyzed vitreal vascular changes and tbdn-1 expression in TGF-beta2(-/-) eyes. The nuclei of vitreal vessel endothelial cells in TGF-beta2(-/-) eyes express proliferating cell nuclear antigen (PCNA) and exhibit increased levels of active (P42/44)mitogen-activated protein kinase (phospho-(P42/44)MAPK), characteristics consistent with proliferative endothelial cells. In contrast to normal vitreal vessels, collagen IV expression exhibited a disorganized pattern in the TGF-beta2(-/-) vitreal vessels, suggesting vessel disorganization and possibly a breakdown of vessel basal laminae. Moreover, vitreal vessels of TGF-beta2(-/-) mice lack expression of pericyte markers (CD13, alpha smooth muscle actin) and show ultrastructural changes consistent with pericyte degeneration. The accumulating vitreal blood vessels of TGF-beta2(-/-) mice, while maintaining expression of the endothelial marker von Willebrand Factor, show a significant decrease in the expression of tbdn-1. We addressed the functional role of tbdn-1 in the regulation of vitreal blood vessels using an in vitro model of choroid-retina capillary outgrowth. Clones of the RF/6A fetal choroid-retina endothelial cell line showing suppression of tbdn-1 levels after overexpression of an antisense TBDN-1 cDNA display a significant increase in the formation of capillary-like structures in vitro compared with controls. These findings suggest that tbdn-1 inhibits capillary-like formation in vitro and may serve to dampen vitreal blood vessel formation preceding the regression of the vitreal vasculature during development. Our results also suggest that tbdn-1 may participate with TGF-beta2 in regulating normal development of the vitreal vasculature.

Suppressed expression of tubedown-1 in retinal neovascularization of proliferative diabetic retinopathy

PURPOSE

Retinal neovascularization occurring as a complication of diabetes mellitus can cause vision loss and blindness. The identification and study of novel genes involved in retinal angiogenesis may define new targets to suppress retinal neovascularization in diabetes and other ocular diseases. A novel acetyltransferase subunit, tubedown-1 (tbdn-1), has been isolated, the expression of which is regulated during blood vessel development. Tbdn-1 is not detected in most adult vascular beds but persists at high levels in the adult ocular vasculature. The purpose of this study was to gain insight into the possible role of tbdn-1 in retinal blood vessels by characterizing its expression patterns in adult homeostasis and in retinal neovascularization associated with diabetes.

METHODS

Western blot analysis and immunohistochemistry were performed to study the expression patterns of tbdn-1 during adult homeostasis in normal human retinas, in a model of choroid-retina endothelial capillary outgrowth in vitro, and in retinas showing neovascularization in patients with proliferative diabetic retinopathy (PDR).

RESULTS

In adults during homeostasis, tbdn-1 was expressed highly in normal endothelium of retinal and limbic blood vessels. Tbdn-1 was also expressed in RF/6A, a rhesus macaque choroid-retina-derived endothelial cell line. In an in vitro model system using the RF/6A cell line, tbdn-1 expression was downregulated during the outgrowth of these cells into capillary-like structures on a reconstituted basement membrane matrix. Similar to this in vitro model, tbdn-1 expression is specifically suppressed in the endothelial cells of blood vessels and capillary fronds in vivo in both the neural retinal tissue and in preretinal membranes in eyes of patients with PDR.

CONCLUSIONS

High levels of expression of tbdn-1 are associated with ocular endothelial homeostasis in adults. Conversely, low levels of tbdn-1 expression are associated with endothelial capillary outgrowth in vitro and retinal neovascularization in vivo. Because the tbdn-1 acetyltransferase subunit is a member of a family of regulatory enzymes that are known to control a range of processes, including cell growth and differentiation, through posttranslational modification, the current results support a hypothesis that tbdn-1 may be involved in maintaining homeostasis and preventing retinal neovascularization.

Retinopathy of prematurity

The majority of cases of ROP regress spontaneously, but better treatment methods are needed to prevent retinal detachment and other effects of ROP such as myopia. In the future, molecular mechanisms may be exploited to treat ROP.

Development of a quantitative method to measure vision in children with chronic cortical visual impairment

PURPOSE

Cortical visual impairment (CVI) is the most common cause of bilateral vision impairment in children in Western countries. Better quantitative tools for measuring vision are needed to assess these children, to allow measurement of their visual deficit, and to monitor their response to treatment and rehabilitation. The author performed a series of experiments to assess the use of the sweep visual evoked potential (VEP) as a quantitative tool for measuring vision in CVI.

METHODS

The first experiment was a reliability measure (test/retest) of VEP grating acuity thresholds of 23 children with CVI. To validate the VEP procedure, VEP grating acuity was compared to a clinical measure of vision, the Huo scale, and to a psychophysical measure of vision, the Teller Acuity Card procedure. Finally, the sweep VEP was tested as a tool for defining optimal luminance conditions for grating acuity in 13 children with CVI, by measuring grating thresholds under 2 different luminance conditions: 50 and 100 candela per square meter (cd/m2).

RESULTS

Retest thresholds were similar to original thresholds (r2 = 0.662; P = .003, 1-tailed t test). Grating VEP measures correlate significantly with the clinical index (r2 = 0.63; P = .00004). Teller acuity measurements are also similar to VEP measures in children (r2 = 0.64; P = .0005) but show lower acuities compared to the VEP for children with particularly low vision. Finally, 3 of 13 children tested under 2 background luminance conditions showed paradoxical improvement in grating threshold with dimmer luminance.

CONCLUSIONS

The sweep VEP tool is a reliable and valid means for measuring grating acuity in children with CVI. The tool also shows promise as a means of determining the optimal visual environment for children with CVI.

Chronic cortical visual impairment in children: aetiology, prognosis, and associated neurological deficits

BACKGROUND/AIMS

To evaluate prevalence, aetiology, prognosis, and associated neurological and ophthalmological problems in children with cortical visual impairment (CVI).

METHODS

The records of 7200 outpatients seen in the paediatric ophthalmology practice over the past 15 years were reviewed in order to compile data concerning CVI. In addition, the authors devised and applied a system for grading visual recovery in order to assess prognosis.

RESULTS

CVI occurred in 2.4% of all patients examined. The four most common causes of CVI were perinatal hypoxia (22%), cerebral vascular accident (14%), meningitis (12%), and acquired hypoxia (10%). Most children with CVI had associated neurological abnormalities. The most common were seizures (53%), cerebral palsy (26%) hemiparesis (12%), and hypotonia (5%). Associated ophthalmological problems were esotropia (19%), exotropia (18%), optic nerve atrophy (16%), ocular motor apraxia (15%), nystagmus (11%), and retinal disease (3%). On average, CVI patients improved by two levels as measured by the authors' scale.

CONCLUSION

The majority of children with CVI showed at least some recovery. In this group of children, CVI is often accompanied by additional ophthalmological problems and is nearly always associated with other, serious neurological abnormalities.

Macular folds and poor vision associated with zone III retinopathy of prematurity

PURPOSE

To describe two cases of zone III retinopathy of prematurity associated with macular folds and poor vision.

METHOD

Case reports.

RESULTS

Two premature infants with zone III retinopathy of prematurity developed clinically notable elevation of the neovascular ridge with macular folds and poor vision.

CONCLUSIONS

Retinopathy of prematurity in zone III may lead to compromised anatomic and functional outcomes. Notable elevation of the neovascular ridge may be an important risk factor for an adverse outcome.

Healing of corneal epithelial defects in plasminogen- and fibrinogen-deficient mice

PURPOSE

The local deposition of fibrinogen and other plasma products from tears within corneal wounds and the expression of plasminogen activator by corneal epithelial cells suggest that the coagulation and fibrinolytic systems play an important role in corneal wound healing. The authors used mouse lines deficient in plasminogen (Plg), fibrinogen (Fib), or both to elucidate the roles of these key fibrinolytic and coagulation factors in the healing of corneal epithelial defects.

METHODS

Mice were anesthetized, and corneal epithelial defects (3 mm) were created with a blade. The authors conducted histologic examination and immunohistochemical analysis on the healing of injured corneas.

RESULTS

The corneal epithelial defects of wild-type mice with transparent corneas healed quickly in 7 days, whereas the healing of plasminogen-deficient mice was impaired and complicated by severe and persistent inflammatory responses, the formation of retrocorneal fibrin deposits, corneal cloudiness caused by scar-tissue formation, and often stromal neovascularization. To determine whether these defects in corneal wound repair were specifically related to an impediment in fibrinolysis, corneal wound healing was compared in mice with a combined deficiency in plasminogen and fibrinogen. The loss of fibrinogen in mice lacking plasminogen resulted in the restoration of normal healing with transparent corneas in 7 days, similar to that of wild-type mice.

CONCLUSIONS

These results provide direct evidence that hemostatic factors play a crucial role in corneal wound repair despite the lack of local hemorrhage. Furthermore, they demonstrate that the essential role of plasmin in corneal would healing is fibrinolysis. It prevents the adverse inflammatory responses caused by prolonged fibrin and fibrinogen deposition in injured corneas.

Norrie disease in a family with a manifesting female carrier

OBJECTIVES

To show that Norrie disease can occur in a girl and to describe her ophthalmologic and genetic features.

METHODS

Amplification of DNA polymerase chain reaction and sequencing of asymmetric polymerase chain reaction for exon 3 were performed on the blood specimen obtained from a girl born with bilateral retinal detachments.

PATIENT

A female child with bilateral retinal detachment who had 2 uncles in whom Norrie disease had already been diagnosed.

RESULTS

The child had a mutation in the third exon (T776-->A; Ile 123-->Asn) identical to the mutation found in her uncles.

CONCLUSIONS

Norrie disease can occur in girls. The most likely explanation is nonrandom or unfavorable X inactivation, although timing of development of the peripheral retina and its blood supply could render it vulnerable to effects of the mutant allele at a critical developmental phase.

Cortical visual impairment caused by twin pregnancy

PURPOSE

To report a possible relationship between twin pregnancy and cortical visual impairment.

METHODS

Three children who had been the products of twin pregnancies were identified as having cortical visual impairment. One child (Patient 2), a dizygotic twin, developed cortical visual impairment after a preterm birth. Two children (Patients 1 and 3), the products of monochorionic pregnancies, developed cortical visual impairment. All children were examined ophthalmologically and neurologically.

RESULTS

An evaluation of the gestations of these children indicates that twin pregnancy per se was probably etiologic in the development of cortical visual impairment. In Patient 2, twin pregnancy probably caused preterm birth and resulting cortical visual impairment. In Patients 1 and 3, twin-to-twin transfusion syndrome was the cause of cortical visual impairment. In Patient 1, fetal demise precipitated an acute twin-to-twin transfusion syndrome.

CONCLUSIONS

Children who show cortical visual impairment at or shortly after birth should be evaluated for the possibility of twin pregnancy. Twin pregnancy increases the risk of neurologic damage, including damage to the visual cortex, to optic radiations, or both.

An elevated level of copper zinc superoxide dismutase fails to prevent oxygen induced retinopathy in mice

BACKGROUND

To determine whether a higher level of copper zinc superoxide dismutase (CuZnSOD) can reduce the severity of oxygen induced retinopathy (OIR) in a mouse model.

METHODS

CuZnSOD transgenic mice with a threefold increase in CuZnSOD activity and control non-transgenic mice were exposed to 90% oxygen for 12 hours a day during the first 5 days of life. After oxygen treatment, all mice were reared in room air for 10 days. Another group of transgenic and non-transgenic mice were kept in room air for 15 days and served as control groups for the oxygen effect. At day 15, all mice were killed and perfused with India ink. The retinas were flat mounted on slides and examined with a light microscope.

RESULTS

There was a statistically significant increase in the incidence of OIR in mice exposed to high levels of oxygen, whether or not they were transgenic. However, there was no statistically significant difference in the severity of OIR between oxygen treated transgenic and non-transgenic mice.

CONCLUSION

A threefold higher CuZnSOD activity does not protect against OIR in mice. This is an unexpected finding, since oxygen radicals are considered a major factor causing OIR, and increased CuZnSOD activity has reduced oxygen radical induced damage in several neuronal and non-neuronal systems. The possibility of a damaging role for other radicals not affected by CuZnSOD cannot be excluded.

Cytomegalovirus retinitis and optic neuritis in a child with severe combined immunodeficiency syndrome

BACKGROUND

Although cytomegalovirus (CMV) infection of the retina and brain is common in patients with acquired immunodeficiency syndrome (AIDS), it is exceedingly rare in patients with immunodeficiencies due to other causes. This is the first report on ocular and cerebral histopathology of disseminated CMV in a child with severe combined immunodeficiency syndrome (SCID).

METHODS

The authors examined by routine histopathologic methods the eyes of a 2-year-old white boy with SCID and bilateral CMV retinitis who died after failure of a third attempt at allogeneic bone marrow transplantation (BMT).

RESULTS

Cytomegalovirus inclusions were found in the necrotic retinal remnants, in the hyperplastic and scarred retinal pigment epithelium, and bilaterally in the optic nerves. There were infiltrates of macrophages in response to the infection or the infused silicon, but no lymphoid infiltrates. Cytomegalovirus inclusions also were found in brain tissue.

CONCLUSION

The histologic features resembled those of CMV retinitis and optic neuritis in AIDS.

Hypertropia and the posterior blowout fracture: Mechanism and management

OBJECTIVE

To better understand the pathophysiology and proper management of a subgroup of patients with orbital blowout fracture which manifests by a vertical diplopia and hypertropia on the affected side.

PATIENTS AND METHODS

This report is based on a series of ten consecutive patients with orbital floor blowout fractures who had diplopia and hypertropia on the affected side. All patients were followed through at least 13 days of conservative care. Computed tomography demonstrated a characteristic depressed fracture of the posterior orbital floor extending to the posterior wall of the maxillary sinus in all patients. In many patients, the inferior rectus looped inferiorly and then rose to contact the globe at a steep angle. Diplopia did not spontaneously resolve in any patient. At surgery, the orbital contents were elevated to the posterior extent of the fracture, and the floor defects were bridge. Patients were followed for resolution of diplopia.

RESULTS

Eight patients had resolution of the hypertropia and diplopia within 2 months of surgery, and two patients had residual diplopia in extreme downgaze but were significantly improved.

CONCLUSIONS

When hypertropia and vertical diplopia are noted after orbital trauma, a posterior blowout fracture should be suspected. In these patients, infraduction may be diminished due to changes in the effective origin and insertion of the inferior rectus muscle. The diagnosis of a posterior blowout fracture should be supported by characteristic findings on computed tomography. If the motility abnormality persists for 10 to 14 days, posterior orbital exploration and fracture repair should be undertaken.

Neurologic and ophthalmologic findings in children exposed to cocaine in utero

We studied a cohort of 73 children exposed to cocaine in utero to characterize the spectrum of neurologic and ophthalmologic abnormalities; 36 children with no documented in utero drug exposure were selected as a control group. Most referrals of cocaine-exposed children to the child neurologist were made in the 1st year of life (81%). Reasons for referral were hypertonia (29%), seizures (22%), developmental delay (11%), tremulousness (11%), and hypotonia (4%). The most common abnormal finding in the cocaine-exposed children was hypertonia/hyperreflexia (63%), which was rarely seen in the control group. In addition, hypertonia/hyperreflexia was underdiagnosed by referring physicians. Similarly, hypotonia was seen on neurologic examination of cocaine-exposed children more frequently than documented by referral (16% versus 4%). Hypotonia was rarely seen in the control group. Twelve (43%) of 28 cocaine-exposed children seen by a pediatric ophthalmologist had structural ophthalmologic abnormalities. Neurologic and ophthalmologic findings suggesting structural lesions of the nervous system must be considered in cocaine-exposed children.

Visually impaired children with sensory defect nystagmus, normal appearing fundi and normal ERGS

The differentiation of congenital motor nystagmus (CMN) from sensory defect nystagmus (SDN) in early life is a common diagnostic problem, since their wave forms are indistinguishable. A diagnosis of SDN is made when fundal or ERG abnormalities are present. CMN is generally diagnosed by exclusion. This approach can lead to late or incorrect diagnosis, and to the overlooking of important genetic implications. In addition, the classification of congenital nystagmus into pure motor and sensory types is inadequate. The authors present case reports illustrating this problem and suggest strict criteria for a diagnosis of CMN. They also point out that a miscellaneous group of rare disorders of the macula tend to be overlooked and misdiagnosed.

Vogt-Koyanagi-Harada syndrome in a 4-year old child

PURPOSE

We studied a case of severe bilateral Vogt-Koyanagi-Harada syndrome in a 4-year-old boy.

METHODS

We evaluated the patient's clinical course.

RESULTS

The patient had severe bilateral, nongranulomatous uveitis and mild uveitic glaucoma. Initial examination and laboratory evaluation failed to provide a diagnosis. The patient subsequently developed areas of vitiligo, alopecia, and poliosis, suggesting the diagnosis of Vogt-Koyanagi-Harada syndrome. This diagnosis was confirmed by the eventual development of bilateral neurosensory retinal detachments. Vision was lost despite aggressive therapy with corticosteroids and chlorambucil.

CONCLUSION

Although uncommon, Vogt-Koyanagi-Harada may affect young children, and may be severe.

Familial paroxysmal kinesigenic choreo-athetosis in a child with visual hallucinations and obsessive-compulsive behaviour

A teenage male is described, in whom Tourette Syndrome was suspected, which was later replaced by attacks of paroxysmal kinesigenic choreo-athetosis. He also exhibited bizarre, episodic perceptual distortions of his visual environment and manifestations of an obsessive-compulsive disorder. Carbamazepine treatment not only completely eliminated the recurring attacks of his choreo-athetosis but also, contrary to expectations, the visual disturbances and even the symptoms of his obsessive-compulsive disorder. Obsessive compulsive disorder should be searched for by direct questioning in all patients with basal ganglia disorders.

Eye-poking

Eye-poking, -rubbing and -pressing are often incorrectly grouped together because of the assumption that they represent variations of the same self-stimulating behaviour. This prospective study of 21 children shows that eye-poking is a distinct, chronic, stereotyped, self-injurious act seen mainly among severely mentally disabled individuals, who may or may not be visually impaired. Eye-poking, which leads to intense, self-induced pain, is a harmful behaviour because it can result in permanent visual loss and even in total blindness. The cause is unclear, although it is probably multifactorial. The treatment is exceedingly difficult. Further studies are needed to develop specific management techniques to prevent eye-poking, which adds to the physical and emotional burden on the caregivers.

Inferior branch oculomotor nerve palsy. A case report

We describe a 34-year-old man with acute, nontraumatic inferior branch oculomotor nerve palsy. Complete ophthalmologic, neurologic, and systemic examinations were otherwise normal. The oculomotor nerve palsy resolved, but the patient subsequently developed bilateral upper extremity numbness and painful dysesthesias in the distribution of the median nerves. These observations suggest that inferior branch oculomotor nerve palsy, although uncommon, may occur as part of a more generalized neurologic disorder, presumed in our patient to be either vasculitic or demyelinating in nature.

Cortical visual impairment in children

Cortical visual impairment (CVI) in children is most commonly caused by peri- or post-natal hypoxia-ischemia, but may also occur following other insults, e.g., trauma, epilepsy, infections, drugs or poisons, and certain neurologic diseases. The disorder differs considerably in etiology, physical findings, and, perhaps, prognosis, from the cortical blindness seen in adults. The same event that causes CVI by damaging the geniculate and/or extrageniculate visual pathways may also damage other areas of the brain, or the retina, optic nerves, or chiasm. Thus, children with CVI often have other neurological problems. Diagnosis may require the participation of a multidisciplinary team and the use of special visual testing techniques. Due to the uncertainty concerning the prognosis in CVI, clinicians should remain optimistic about the child's potential for some vision recovery.