Clinicopathologic correlations in eyes enucleated after uveal melanoma resection with positive surgical margins

We identified three eyes that had undergone enucleation after transscleral resection of uveal melanoma. Two enucleated eyes with microscopically positive margins of resection exhibited no evidence of residual melanoma and these patients were alive without metastasis with at least four years′ follow-up. One eye with a transected melanoma contained residual melanoma and that patient died with metastatic melanoma to the liver three years after enucleation. There appear to be at least two general types of positive surgical margins of resection of uveal melanoma: microscopically positive margins and macroscopically positive (transected) margins of resection.

Posterior uveal melanoma treated with I-125 brachytherapy or primary enucleation

PURPOSE

To study the incidence, clinical findings, and tumour characteristics of posterior uveal melanoma in Western Norway, and to report the results of a consistent treatment strategy (I-125 brachytherapy or primary enucleation) over a 13-year period.

METHODS

The clinical records of all patients with posterior uveal melanoma referred between January 1993 and December 2005 were reviewed. Clinical data, radiation parameters, visual outcome, and mortality were analysed in a dedicated database.

RESULTS

The study included 111 consecutive patients. The annual age-adjusted incidence (per million population) of posterior uveal melanoma was 8.5 for women and 8.9 for men. Fifty-six patients underwent I-125 brachytherapy, 52 were enucleated, and three received no treatment. The median follow-up time was 36 months (mean, 52 months; range, 2 months to 13 years). In the brachytherapy group, two eyes were enucleated owing to tumour recurrence and two because of neovascular glaucoma. A visual acuity of 0.1 or better, present in 87% of the patients before brachytherapy, was retained in 40% after a median follow-up of 61 months. After brachytherapy, the 5- and 10-year melanoma-specific mortality rates were 13.4 and 23.8%, respectively. The corresponding mortality rates for patients treated with primary enucleation were 49.5 and 49.5%.

CONCLUSION

After brachytherapy, many patients lost useful vision due to radiation-induced complications. The probability of retaining the eye was high and only two patients experienced recurrent tumour growth. The mortality rates compare well with published series, and the differences in tumour size explain the difference in mortality between the two treatment groups.

A modified in vitro method for aqueous humor outflow studies in enucleated porcine eyes

The aim of this study was to develop and test a short-term in vitro method for aqueous humour outflow studies using enucleated porcine eyes. The method used was a modification of two methods that have previously been used: whole eyes and anterior segment cultures. The advantage of the model used in this study was that the anterior part of the eye, including the anterior and posterior chambers, remained intact as in whole enucleated eyes, but neither iridotomia nor trephination through the cornea was needed. The deepening of the anterior chamber during perfusion was avoided by regulating the "vitreal" pressure. Test compounds were administered topically or intracamerally to an anatomically normal anterior chamber. Fresh porcine eyes (n = 48) were sectioned at the equator, and the vitreous mass was carefully removed. This anterior bisection was bound around a specific plastic chamber, thus creating a closed eye. The anterior chamber was perfused at a pressure of 15 mmHg. The mean outflow rate in the nonmedicated eye group was 3.7 +/- 0.20 microL/min (mean +/- standard error of the mean), and it increased by 18% during 9 h owing to a wash-out effect. Compounds known to enhance the aqueous outflow were used for testing the validity of the preparation.

Contactin1a expression is associated with oligodendrocyte differentiation and axonal regeneration in the central nervous system of zebrafish

Contactin1a (Cntn1a) is a zebrafish homolog of contactin1 (F3/F11/contactin) in mammals, an immunoglobulin superfamily recognition molecule of neurons and oligodendrocytes. We describe conspicuous Cntn1a mRNA expression in oligodendrocytes in the developing optic pathway of zebrafish. In adults, this expression is only retained in glial cells in the intraretinal optic fiber layer, which contains 'loose' myelin. After optic nerve lesion, oligodendrocytes re-express Cntn1a mRNA independently of the presence of regenerating axons and retinal ganglion cells upregulate Cntn1a expression to levels that are significantly higher than those during development. After spinal cord lesion, expression of Cntn1a mRNA is similarly increased in axotomized brainstem neurons and white matter glial cells in the spinal cord. In addition, reduced mRNA expression in the trigeminal/anterior lateral line ganglion in erbb3-deficient mutant larvae implies Cntn1a in Schwann cell differentiation. These complex regulation patterns suggest roles for Cntn1a in myelinating cells and neurons particularly in successful CNS regeneration.

Standing enucleation in the horse: a report of 5 cases

Enucleation was performed in 5 horses under local anesthesia and sedation with the horse standing. Minimal hemorrhage occurred during the surgical procedure, and there were no other reported complications. Standing enucleation is a surgery that is safe to perform in horses.

UK national survey of enucleation, evisceration and orbital implant trends

AIM

To evaluate current clinical practice in the UK in the management of the anophthalmic socket; choice of enucleation, evisceration, type of orbital implant, wrap, motility pegging and complications.

METHODS

All consultant ophthalmologists in the UK were surveyed by postal questionnaire. Questions included their practice subspecialty and number of enucleations and eviscerations performed in 2003. Specific questions addressed choice of implant, wrap, motility pegging and complications.

RESULTS

456/896 (51%) consultants responded, of which 162 (35%) had a specific interest in oculoplastics, lacrimal, orbits or oncology. Only 243/456 (53%) did enucleations or eviscerations. 92% inserted an orbital implant after primary enucleation, 69% after non-endophthalmitis evisceration, whereas only 43% did so after evisceration for endophthalmitis (50% as a delayed procedure). 55% used porous orbital implants (porous polyethylene, hydroxyapatite or alumina) as their first choice and 42% used acrylic. Most implants inserted were spherical, sized 18-20 mm in diameter. 57% wrapped the implant after enucleation, using salvaged autogenous sclera (20%), donor sclera (28%) and synthetic Vicryl or Mersilene mesh (42%). A minority (7%) placed motility pegs in selected cases, usually as a secondary procedure. 14% of respondents reported implant exposure for each type of procedure and extrusion was reported by 4% after enucleation and 3% after evisceration.

CONCLUSIONS

This survey highlights contemporary anophthalmic socket practice in the UK. Most surgeons use porous orbital implants with a synthetic wrap after enucleation and only few perform motility pegging.

Enhancement of vision by monocular deprivation in adult mice

Plasticity of vision mediated through binocular interactions has been reported in mammals only during a "critical" period in juvenile life, wherein monocular deprivation (MD) causes an enduring loss of visual acuity (amblyopia) selectively through the deprived eye. Here, we report a different form of interocular plasticity of vision in adult mice in which MD leads to an enhancement of the optokinetic response (OKR) selectively through the nondeprived eye. Over 5 d of MD, the spatial frequency sensitivity of the OKR increased gradually, reaching a plateau of approximately 36% above pre-deprivation baseline. Eye opening initiated a gradual decline, but sensitivity was maintained above pre-deprivation baseline for 5-6 d. Enhanced function was restricted to the monocular visual field, notwithstanding the dependence of the plasticity on binocular interactions. Activity in visual cortex ipsilateral to the deprived eye was necessary for the characteristic induction of the enhancement, and activity in visual cortex contralateral to the deprived eye was necessary for its maintenance after MD. The plasticity also displayed distinct learning-like properties: Active testing experience was required to attain maximal enhancement and for enhancement to persist after MD, and the duration of enhanced sensitivity after MD was extended by increasing the length of MD, and by repeating MD. These data show that the adult mouse visual system maintains a form of experience-dependent plasticity in which the visual cortex can modulate the normal function of subcortical visual pathways.

Clinical analysis of hydroxyapatite orbital implantation after ocular trauma in 211 cases

OBJECTIVE

To evaluate the therapeutic effects and complications of hydroxyapatite (HA) orbital implantation on patients after trauma-related surgeries.

METHODS

Retrospective analysis was made from 211 cases (211 eyes) who underwent HA orbital implant placement after trauma-related enucleation or evisceration, including 68 cases of evisceration and primary HA implant placement, 77 cases of enucleation and HA implant placement wrapped with multi-windowed sclera, 66 cases of enucleation and HA implant placement free of wrapping. All the cases were followed up for 1-5 years to observe the therapeutic effects and major complications.

RESULTS

Five of 211 cases had wound dehiscence. Ten cases had HA implants exposure, including 1 case suffering severe orbital infection and requiring HA implant removal. The implants exposure incidences by the three surgical methods were from 1.30% to 10.06% and averaged 4.74%. Significant difference was found in late exposure incidence and total incidence from the three methods (chi(2)=13.372, P < 0.01 and chi(2)=7.540, P < 0.05). Two cases had shrinkage of the lower fornix. Enophthalmos occurred in 1 case treated by method 1 and was corrected by implanting porous polyethylene (Medpor) plate into the bottom of orbit. In 210 cases, the artificial eye moved well and the cosmetic results were satisfactory.

CONCLUSIONS

Different surgical methods have their own merit and disadvantage. Enucleation and placement of HA implant wrapped with multi-windowed sclera has corroborated fewer complications than others.

Early blindness results in abnormal corticocortical and thalamocortical connections

Studies in congenitally blind and bilaterally enucleated individuals show that an early loss of sensory driven activity can lead to massive functional reorganization. However, the anatomical substrate for this functional reorganization is unknown. In the present study, we examined patterns of corticocortical and thalamocortical connections in adult opossums that had been bilaterally enucleated neonatally, prior to the formation of retinogeniculate and geniculocortical connections. We show that in addition to normal thalamocortical projection patterns from visual nuclei, enucleated animals also receive input from nuclei associated with the somatosensory (ventral posterior nucleus, VP), auditory (medial geniculate nucleus, MGN), motor (ventrolateral nucleus, VL), and limbic/hippocampal systems (anterior dorsal nucleus, AD; and anterior ventral nucleus, AV). Likewise, in addition to normal corticocortical projections to area 17, bilaterally enucleated opossums also receive input from auditory, somatosensory, and multimodal cortex. These aberrant patterns of thalamocortical and corticocortical connections can account for alterations in functional organization observed in the visual cortex of bilateral enucleated animals, and indicate that factors extrinsic to the cortex play a large role in cortical field development and evolution. On the other hand, the maintenance of normal patterns of connections in the absence of visual input suggests that there are formidable constraints imposed on the developing cortex that highly restrict the types of evolutionary change possible.

Differential regulation of the neuronal isoform of nitric oxide synthase in the superior colliculus and dorsal lateral geniculate nucleus of the adult rat brain following eye enucleation

Nitric oxide has been shown to play various physiological and pathological roles in the visual system. We studied here the expression of the neuronal isoform of nitric oxide synthase in the rat superior colliculus and in the dorsal lateral geniculate nucleus after unilateral enucleation, by means of immunohistochemistry, immunoblotting, and real-time PCR. Immunohistochemistry revealed an increase of nitric oxide synthase-positive neurons in specific layers of the superior colliculus and in the dorsal lateral geniculate nucleus between 1 and 30 days post-lesion. Immunoblotting analyses confirmed that the neuronal isoform of nitric oxide synthase is upregulated in the superior colliculus and in the dorsal lateral geniculate nucleus after retinal removal. Diaminofluorescein histochemistry suggested that nitric oxide production was increased in both deafferented retinorecipient areas. Our real-time PCR results indicated that nitric oxide synthase transcript levels in the superior colliculus were not significantly altered after monocular enucleation, although an upregulation of the enzyme transcription was detected into the deafferented dorsal lateral geniculate nucleus. These findings indicated that neuronal nitric oxide synthase may undergo different forms of regulation in the adult deafferented visual system.

Labeled lines in the retinotectal system: markers for retinorecipient sublaminae and the retinal ganglion cell subsets that innervate them

Axons of retinal ganglion cells (RGCs) carry visual information to the brain. In most vertebrates, the major synaptic target of RGCs is the optic tectum. In the chick, RGC axons form synapses in just 4 of 16 histologically recognizable laminae (the retinorecipient laminae [RRLs]), and arbors of individual RGCs are confined to a single RRL. To analyze the development and function of these parallel pathways, markers are required that selectively label them. Here, we have identified molecular markers for individual RRLs and for RGCs that project to them. Some of the markers may mediate or modulate signaling through the separate pathways: neuropeptides (substance P, neuromedin B, somatostatin-I and -II) and their receptors (substance P receptor), neurotransmitter synthetic enzymes (choline acetyltransferase) and the corresponding receptors (acetylcholine receptor beta2) and calcium-binding proteins (parvalbumin and calbindin). Other markers are adhesive proteins that could mediate selective connectivity of RGC subsets within specific RRLs (cadherin-7, cadherin-11, reelin and neuropilin-1). We further show that RGC subsets whose axons project to specific RRLs are heterogeneous with respect to the retinal sublaminae within which their dendrites arborize. Our results define laminar-specified circuits from retina to brain and support a model in which RGCs transmit information from multiple sources to single central laminae, where it can be integrated.

Scleral ossification in phthisical eyes

Heterotopic secondary ossification of the eye usually affects intraocular tissues. Although calcium deposition in the scleral lamellae is not uncommonly observed, bone formation is only rarely associated with chromosomal abnormalities or colobomatous eyes. Herein two cases of both scleral and intraocular ossification in patients with long-standing ocular phthisis are reported. The cases of idiopathic scleral ossification, albeit exceedingly rare, suggest that osteogenic precursor cells may reside in the sclera, as well and though very rarely, these cells can also be stimulated to form heterotopic bone by a traumatic or inflammatory local event.

Predictability and limitations of non-invasive murine tonometry: Comparison of two devices

Our purpose was to evaluate the accuracy, reproducibility and predictive ability of two non-invasive tonometers developed for intraocular pressure (IOP) measurements in the mouse. The prototype impact-rebound tonometer (I-R) and a prototype optical interferometry tonometer (OIT) utilizing a fiberoptic pressure sensor, were compared. Enucleated eyes from C57/BL6 mice were used for the calibration. The anterior chamber was cannulated and the IOP was adjusted in increments of 5 cm of H2O (open stopcock method). A calibration curve was generated for each individual eye along with a master calibration curve for all eyes. Two operators measured the IOP. The instruments were then used in alternating order to measure the IOP in C57/BL6 and in DBA2/J animals. The same eyes were subsequently cannulated and the error of the non-invasive tonometers was determined. Both tonometers yielded almost equivalent ex vivo calibration curves with individual R2 of 0.9878 and 0.9902 respectively. Both instruments were highly reproducible. In vivo the I-R tonometer underestimated while the OIT overestimated the IOP. This error was systematic and therefore predictable. The confidence intervals of this error were determined by comparing the IOP estimates provided by each tonometer with the measurements obtained invasively by cannulation in vivo. The 95% CI of the error were 2.36 mmHg for the I-R and 2.62 mmHg for the OIT respectively. Non-invasive tonometry in the mouse is feasible. Both non-invasive instruments provide accurate and reproducible measurements with the OIT requiring calibration curves for each individual investigator.

Effects of bilateral and unilateral ophthalmectomy on plasma melatonin in Rana tadpoles and froglets under various experimental conditions

The effect of ophthalmectomy (enucleation) on plasma melatonin in Rana tadpoles and froglets was studied under various experimental conditions to determine if ocular melatonin is released into the circulation from the eyes and to study the factors which might affect this process. Where operations occurred in early or mid-photophase on a 12 light:12 dark (12L:12D) cycle (light onset at 08:00 h), sampling in mid-light and mid-dark revealed that scotophase plasma melatonin was reduced at all developmental stages, with the more significant effects occurring before metamorphic climax. Experiments sampling prometamorphic tadpoles six times in a 24h period on 18L:6D, 12L:12D, or 6L:18D five days after enucleation also showed a significant lowering of plasma melatonin in the dark, so that the scotophase peak was virtually eliminated on all the LD cycles. These findings indicated that the reduction in plasma melatonin after bilateral eye removal was independent of the LD cycle and the metamorphic stage, and that it abolished the diel melatonin rhythm at the expense of the scotophase peak. Experiments carried out for 5 weeks suggested that compensatory secretion of melatonin by other organs after eye removal might partially restore the plasma melatonin level over time. Unilateral ophthalmectomy tended to reduce, but not eliminate, the night peak of plasma melatonin, and did not result in a compensatory increase in ocular melatonin in the remaining eye. Ophthalmectomized tadpoles exhibited darkening of the skin after the operation, which was not associated with a significant change in pituitary alpha-melanotropin. The findings overall indicate that the eyes in Rana tadpoles and froglets contribute up to somewhat over one-half of the circulating melatonin, particularly during the scotophase, and provide experimental evidence for ocular secretion into the blood for the first time in the Amphibia.

Management of a blind painful eye

Debilitating ocular pain poses a significant challenge to the ophthalmologist. When the pain is intractable and the eye has very poor vision and is disfigured, surgical removal of the eye has traditionally been the definitive treatment of choice. Because many people are uncomfortable psychologically with removal of their eye, however painful, and other patients are not good surgical candidates, an alternative to enucleation is sometimes warranted, and injection of a neurolytic substance can often induce long-lasting anesthesia for a blind painful eye. This article reviews a range of options for management of blind painful eye from anesthesia to enucleation.

Retinoblastoma: a proposal for a multimodal treatment concept for intraocular retinoblastoma in Austria

Retinoblastoma is the most common intraocular malignancy in childhood. If confined to the globe and managed with current treatment strategies, more than 90% of children survive with preservation of vision in at least one eye, even in bilateral retinoblastoma. Enucleation of the involved eye in unilateral retinoblastoma and of the more involved eye in bilateral disease, together with external beam radiotherapy in advanced bilateral retinoblastoma, formed the two cornerstones of treatment for many years and led to an increase in survival to over 90%. In the early 1990s the extent of the risk of second cancers in the field of radiation became known, the risk increasing by 10% per decade of life. As a consequence, chemotherapy-based regimens were developed as alternative treatments. During the past ten years retinoblastoma treatment has fundamentally changed, with a trend away from enucleation and external beam radiotherapy towards conservative treatments aiming at preservation of the affected globe(s) in selected patients. Systemic neoadjuvant chemotherapy induces tumor regression (chemoreduction), and residual regressed tumor is then treated focally with, for example, transpupillary thermotherapy, cryotherapy and plaque radiotherapy (consolidation). Between 1984 and 2004, 27 patients were treated at the department of ophthalmology in collaboration with the department of pediatrics at the Medical University of Graz. Before 2001, the affected eyes of all patients with unilateral retinoblastoma were enucleated (10 of 10), as were 6 of 7 of the more involved eyes of patients with bilateral disease. A globe-sparing strategy was introduced in 2001 and since then eligible patients have been treated with chemoreduction and focal therapy; 2 of 5 eyes with unilateral disease were salvaged, and both eyes of a patient with bilateral disease. We discuss current treatment options and present a proposal for the management of intraocular retinoblastoma in children in Austria, the Austrian retinoblastoma study, RB A-2003.

Mersilene mesh versus sclera in wrapping hydroxyapatite orbital implants

PURPOSE

To compare Mersilene mesh versus sclera in wrapping hydroxyapatite orbital implants used in primary enucleation.

METHODS

In a prospective, randomized, interventional comparative case series, 60 eyes from 60 consecutive patients were included and randomly allocated for primary enucleation and either Mersilene mesh-wrapped hydroxyapatite (MHA) orbital implant (30 cases, 50%) or sclera-wrapped hydroxyapatite (SHA) orbital implant (30 cases, 50%) under general anesthesia. Complete socket examination was performed at 1 week, 1 month, and then every 3 months after surgery.

RESULTS

Mean age was not significantly different (P = 0.08) between patients with MHA (36.43 years) and SHA (28.50 years) orbital implants. The most common cause of enucleation was trauma in both groups (P = 0.09). Patients with MHA had significantly (P = 0.005) longer follow-up time (mean, 11.40 months) than those with SHA (mean, 9.40 months). No exposure was found at last follow-up in the MHA group, but one patient in the SHA group had a small exposure (1 x 1 mm) 1 month after surgery that was conservatively treated. There were no significant postoperative soft tissue complications in either group.

CONCLUSIONS

Sclera and Mersilene mesh could be used as a wrapping material for hydroxyapatite orbital implants without significant complications. Absence of disease transmission, low cost, and availability are the main advantages of Mersilene mesh.

Prolonged bradycardia after secondary orbital implant

A patient who suffered a 36 hour symptomatic bradycardia following secondary orbital implant is described. The possible causes and implications are discussed.

The multiple dorsoventral origins and migratory pathway of tectal oligodendrocytes in the developing chick

Oligodendrocytes have been considered to originate in a restricted ventricular zone of the ventral neural tube and to migrate and mature in their final targets. However, recent studies indicate that oligodendrocytes arise from multiple distinct dorsoventral origins. In this study, we investigate oligodendrocyte lineage cells in the embryonic optic tectum of chick, which develops from the dorsal region of the neural tube and invasion of optic tract. Oligodendrocyte precursor cells (OPCs) first appeared bilaterally on either side of the floor plate at E5. With further development, OPCs increased and spread laterally and dorsally to populate the optic tectum. At E7, OPCs appeared in another site along the ventral midline of the third ventricle, just dorsal to the optic chiasm. To examine the migration routes of these ventrally derived OPCs, we used DiI tracing in the organic culture and retinal denervation. Our results reveal that OPCs dispersed bilaterally along the optic tract and then migrated to the optic tectum in the stratum opticum (SO). In addition to these extrinsic OPCs, OPCs intrinsic to the tectal ventricle zone were identified at E14 using a combination of immunohistochemistry and retroviral mediated lineage tracing studies. These data support stage-specific dorsoventral origins and distribution of oligodendrocytes populating the optic tectum.

Bovine pericardium (Tutopatch) wrap for hydroxyapatite implants

PURPOSE

To evaluate bovine pericardium (Tutopatch) as a wrapping material for hydroxyapatite implants in patients undergoing enucleation for uveal melanoma.

METHOD

Prospective cohort study of patients who had enucleation for uveal melanoma between January 2003 and August 2003 were included in the study. Any patient with less than 3 months follow-up was excluded. Enucleation was performed under general anaesthesia followed by insertion of hydroxyapatite implants wrapped in bovine pericardium (Tutopatch). The recti muscles were sutured directly to the wrap. The tenon's capsule and conjunctiva were closed in two layers. A conformer was inserted at 1 week and artificial eye at 2-3 months. The patients were followed up regularly and were assessed for cosmetic result, exposure of implant, and the need for any further surgical procedures.

RESULTS

A total of 19 patients (seven male and 12 female) were included in the study. Median age at diagnosis was 63 years (range 38-80 years). Median follow-up was 26 months (range 22-30 months). No patient developed postoperative complications of wound dehiscence. The overall cosmetic result was excellent in all the patients. The rate of postoperative complications compared favourably with published data using other wrapping materials/implants.

CONCLUSION

Tutopatch is a safe wrapping material for hydroxyapatite orbital implants in patients undergoing enucleation for uveal melanoma.

Development and plasticity of the retina in the opossum Monodelphis domestica

We investigated the rate of cell proliferation and death in the retina of the Monodelphis opossum during its postnatal development and the influence of early monocular enucleation on these processes. Our results show that in the opossum, as in other marsupials, the peak of the retinal cells divisions occurs postnatally and that generation of retinal cells continues till the time of eye opening (P34), except of the marginal rim, where it continued till P60. Ganglion and amacrine cells are generated between postnatal days (P) P4 and P9, while bipolar cells and photoreceptors are generated simultaneously between P14 and P25. The peak of ganglion cell death as detected by the TUNEL method occurs around P14-19 in the center of retina. The second peak of apoptosis appears in the inner nuclear layer (INL) at P19-25. Gliogenesis takes place between P25 and P34. We also found that monocular enucleation performed during the early period of retinal development (P0-P7) did not influence proliferation, developmental apoptosis or other developmental processes in the retina of the remaining eye.

[Evaluation of results of enucleations with orbital implant in children and adolescents]

PURPOSE

The aim of the research is the assessment of results of enucleation with orbital implant in children.

MATERIAL AND METHODS

Examinations included the group of 99 children between 6 months and 19 years of age. The examined group consisted of 39 boys (39.4%) and 60 girls (60.6%). 96 eyes were removed because of non-regressive retinoblastoma (despite applied treatment), two eyes with buphtalmus (with no light perception), as a result of glaucoma, and one case of medulloepithelioma. The applied implants were: Castroviejo--in 28 patients, Medpor--in 24 patients, Hydroxyapatite--46 patients. In one patient was applied Baush and Lomb orbital implant.

RESULTS

In 91 patients (91.9%) no significant complications occurred. In 2 patients (2%), the hemorrhage occurred during the surgery. Postoperative complications included: in 6 patients (6.1%) exposition of orbital implant was observed; in one patient the exposition was enlarging which led to removal of the implant; in 2 patients with implant exposition (2%) inflammatory granuloma occurred on the edge of the exposition. In one patient (1%) cyst of conjunctiva in the postoperative scar area occurred 3 months after operation.

CONCLUSIONS

Enucleation with orbital implant enables normal development of the orbit and improves cosmetic effect. The frequency of complications depends on type of applied orbital implant.

Abducens internuclear neurons depend on their target motoneurons for survival during early postnatal development

The highly specific projection of abducens internuclear neurons onto medial rectus motoneurons in the oculomotor nucleus is a good model to evaluate the dependence on target cells for survival during development and in the adult. Thus, the procedure we chose to selectively deprive abducens internuclear neurons of their natural target was the enucleation of postnatal day 1 rats to induce the death of medial rectus motoneurons. Two months later, we evaluated both the extent of reduction in target size, by immunocytochemistry against choline acetyltransferase (ChAT) and Nissl counting, and the percentage of abducens internuclear neurons surviving target loss, by calretinin immunostaining and horseradish peroxidase (HRP) retrograde tracing. Firstly, axotomized oculomotor motoneurons died in a high percentage ( approximately 80%) as visualized 2 months after lesion. In addition, we showed a transient (1 month) and reversible down-regulation of ChAT expression in extraocular motoneurons induced by injury. Secondly, 2 months after enucleation, 61.6% and 60.5% of the population of abducens internuclear neurons appeared stained by retrograde tracing and calretinin immunoreaction, respectively, indicating a significant extent of cell death after target loss (38.4% or 39.5%). By contrast, in the adult rat, neither extraocular motoneurons died in response to axotomy nor abducens internuclear neurons died due to the loss of their target motoneurons induced by the retrograde transport of toxic ricin injected in the medial rectus muscle. These results indicate that, during development, abducens internuclear neurons depend on their target motoneurons for survival, and that they lose this dependence with maturation.