Intraorbital implantation of a stimulating electrode for an optic nerve visual prosthesis. Case report

Research into visual prosthetics is expected to revolutionize the treatment of blind patients with incurable outer retinal degenerative disease. Substantial evidence shows that useful visual sensations can be produced by controlled electrical stimulation of the optic nerve. To make the optic nerve visual prosthesis more acceptable, implantation techniques safer and less invasive than those previously used have been developed. A medial transconjunctival approach is now used to implant a stimulating electrode around the intraorbital section of the optic nerve. This new technique allows sufficient exposure of the nerve after detaching only one rectus muscle and performing a lateral canthotomy. Previously, an electrode was implanted in the intracranial part of the optic nerve, which required more invasive surgery. The new technique was first developed in cadavers and in patients undergoing eye enucleations. Finally, a 68-year-old blind man suffering from retinitis pigmentosa underwent long-term implantation. In this case report the authors describe the technique and outline some of the challenges involved.     

Estimation of Phosphene Spatial Variability for Visual Prosthesis Applications

Visual prostheses are the focus of intensive research efforts to restore some measure of useful vision to blind or near‐blind patients. The development of such technology is being guided to an extent by tools that simulate prosthesis behavior for healthy sighted subjects in order to assess system requirements and configurations. These simulators, however, typically assume purely deterministic phosphene properties and thus do not apply any variability to phosphene size, intensity, or location. We address this issue by presenting data on phosphene variability measured in a blind human subject fitted with an optic nerve prosthesis. In order to correct for normal limitations in human‐pointing accuracy, the experimental conditions were repeated with sighted subjects. We conclude that identical optic nerve stimulations can result in phosphenes whose perceived locations vary by up to 5° of deviation angle and 10° of position angle. The consistency of phosphenes presented in the peripheral field of view can vary by an additional 3°.     

Optic nerve arteriovenous malformation causing optic apoplexy: case report

OBJECTIVE AND IMPORTANCE: Vascular malformations in the optic pathway are rare. Only one case of pathologically confirmed arteriovenous malformation (AVM) of the optic nerve has been reported previously. We document the case of a patient with an optic nerve AVM who presented with optic apoplexy that was diagnosed with the use of magnetic resonance imaging. CLINICAL PRESENTATION: A 15-year-old girl developed left visual disturbance of sudden onset while playing badminton. A magnetic resonance imaging scan disclosed left optic nerve swelling and intraoptical hemorrhage, although an angiogram did not reveal abnormal vessels. INTERVENTION: The patient underwent total removal of the hematoma and tangles of the abnormal vessels in the left optic nerve, which was diagnosed pathologically as an AVM. The patient recovered visual acuity, but the left visual field defect remained unchanged. CONCLUSION: Along with cavernous malformations and optic gliomas, AVMs can be a rare cause of optic nerve apoplexy. T2-weighted magnetic resonance imaging is useful in rendering the diagnosis of an optic nerve AVM, observed as a mass lesion consisting of serpiginous, tangled, low-intensity bands. Early surgical treatment is recommended to obtain a rapid recovery.     

Retinal and optic nerve diseases

A variety of disease processes can affect the retina and/or the optic nerve, including vascular or ischemic disease, inflammatory or infectious disease, and degenerative disease. These disease processes may selectively damage certain parts of the retina or optic nerve, and the specific areas that are damaged may have implications for the design of potential therapeutic visual prosthetic devices. Outer retinal diseases include age-related macular degeneration, pathologic myopia, and retinitis pigmentosa. Although the retinal photoreceptors may be lost, the inner retina is relatively well-preserved in these diseases and may be a target for retinal prosthetic devices. Inner retinal diseases include retinal vascular diseases such as diabetic retinopathy, retinal venous occlusive disease, and retinopathy of prematurity. Other retinal diseases such as ocular infections (retinitis, endophthalmitis) may affect all retinal layers. Because the inner retinal cells, including the retinal ganglion cells, may be destroyed in these diseases (inner retinal or whole retinal), prosthetic devices that stimulate the inner retina may not be effective. Common optic nerve diseases include glaucoma, optic neuritis, and ischemic optic neuropathy. Because the ganglion cell nerve fibers themselves are damaged, visual prosthetics for these diseases will need to target more distal portions of the visual pathway, such as the visual cortex. Clearly, a sound understanding of retinal and optic nerve disease pathophysiology is critical for designing and choosing the optimal visual prosthetic device.     

Choristoma of the optic nerve: case report

OBJECTIVE AND IMPORTANCE: Optic nerve choristoma is a rare lesion composed of adipose tissue and smooth muscle involving the optic nerve. Few cases have been reported. CLINICAL PRESENTATION: A 20-year-old woman presented with a history of slowly progressive visual loss in the left eye. On T1-weighted magnetic resonance imaging studies, after frequency-selective fat saturation, an optic nerve mass was detected at the level of the optic canal with signal characteristics suggesting the diagnosis of optic nerve lipoma. INTERVENTION: At left frontotemporal craniotomy, the intracranial optic nerve appeared thin and atrophic proximally and was covered by abundant adipose tissue distally. Because no cleavage plane could be identified between the fatty lesion and the optic nerve, which appeared splayed within the adipose tissue, the nerve was resected after an intraoperative biopsy. The presence of two heterotopic mesodermal elements, a rim of adipose tissue admixed with bundles of mature smooth muscle, extending into the nerve septa, warranted a diagnosis of optic nerve choristoma. CONCLUSION: Optic nerve choristoma is an uncommon optic nerve lesion. Even if imaging studies are highly suggestive of the diagnosis, pathological confirmation is required because of the high adipose tissue content in the majority of cases. The lesion, most likely malformative and nonneoplastic in nature, can be the cause of progressive visual loss.     

Surgically verified case of optic sheath nerve meningocele: Case report with review of the literature

Optic sheath meningocele is rare; only approximately 31 cases have been reported. The term optic sheath meningocele has recently been proposed by Garrity and Forbes to describe primary CSF cysts of the optic nerve sheath, without apical mass or malformation of the cranio-orbital junction. Presenting symptoms are often related to involvement of the optic nerve, with a slow or rapid decrease of visual acuity.CT and MRI studies reveal a tubular-cystic enlargement of the optic nerve/optic sheath complex (on/onsc), with thickening of the optic nerve. Radiological differential diagnosis should include optic nerve tumors such as gliomas, meningiomas, and arachnoid cysts involving the optic nerve sheath. Up to now, it seems that early surgical management by means of optic nerve/optic nerve sheath decompression affords an improvent of visual function with minimal morbidity in patients who present a rapid decrease of visual acuity within 3–6 months.We present an additional case and discuss the clinical, radiological, and operative features of this pathological condition of the optic nerve sheath.     

Optic nerve evoked potentials elicited by electrical stimulation

This study investigated whether the optic nerve evoked potential (ONEP) elicited by electrical stimulation of the optic nerve can serve as a reliable intraoperative indicator of visual function. In the experimental study, two silver-ball stimulating electrodes were placed on the dog optic nerve adjacent to the apex of the orbit and one recording electrode was placed on the optic nerve near the chiasm. The nerve was stimulated with 0.1 to 10 mA rectangular pulses. Stable and reproducible ONEPs were obtained. The ONEPs were not influenced by electromyographic potentials and were recorded more clearly on the optic nerve than on the surrounding tissue. Stepwise incremental transection of the thickness of the nerve resulted in incremental amplitude reduction proportional to the transected area. No response was recorded after complete sectioning of the nerve. In the clinical study, recordings were obtained from 15 patients after craniotomy to treat parasellar tumors or cerebral aneurysms. Reproducible ONEPs were recorded intraoperatively from the electrode placed on the optic nerve near the chiasm in 14 of 15 patients. In the remaining patient, the ONEP, recorded only after tumor removal because the optic nerve was stretched and extremely thin, was remarkably small and the patient developed unilateral blindness postoperatively. These experimental and clinical results suggest the possibility of intraoperative monitoring of visual function in patients undergoing craniotomy for the treatment of lesions near the optic nerve.     

Optic Nerve Decompression for Orbitofrontal Fibrous Dysplasia

Orbitofrontal fibrous dysplasia often involves the bony orbit and the optic canal. Although fibrous dysplasia reportedly produces compression of the optic nerve leading to visual distrubances, optic nerve decompression in patients without clinical signs of optic neuropathy is still controversial. We describe two patients with orbitofrontal fibrous dysplasia without signs of visual disturbance and one patient with McCune-Albright syndrome and progressive visual impairment. Optic nerve decompression was performed prophylactically for two patients and therapeutically for one patient through the transcranial extradural route. Dystopias and craniofacial deformities induced by fibrous dysplasia also were corrected. The micropressure suction-irrigation system was especially effective for decreasing heat transfer and thereby preventing thermal injury of the optic nerve. The orbitofrontal area was reconstructed from cranial bone, iliac bone, and ribs. Postoperative follow-up revealed no disturbances in visual function and no evidence of cerebrospinal fluid leakage. These findings suggest that optic nerve decompression may be effective in preventing visual disturbances with minimal risk of other neurological sequelae. Subsequent orbital reconstruction yielded satisfactory cosmetic results.     

Surgical treatment of progressive visual loss in traumatic optic neuropathy. Report of two cases

In two patients with traumatic optic neuropathy progressive visual loss was reversed by surgical decompression of the optic nerve sheath. The first patient with hemorrhage beneath the optic nerve sheath had progressive loss of vision from counting fingers to no light perception within 24 hours after the injury. Surgical evacuation of the hematoma improved visual acuity to 8/30. The second patient had progressive visual loss from 20/20 to 20/400 within the 1st week after injury. Drainage of an arachnoid cyst of the optic nerve sheath improved visual acuity to 20/25. Computerized axial tomography disclosed the hemorrhage in the first case and enlargement of the optic nerve sheath in the second. While the management of traumatic optic neuropathy is controversial, surgical intervention for an arachnoid cyst and hematoma involving the optic nerve is clearly beneficial.     

Electrophysiological reactions to intraoperative irritation of the optic nerve. Case report and review of possible mechanisms

BackgroundIntraoperative control of optic nerve function conservation during neurosurgical operations currently relies mainly on visual evoked potential monitoring. Unfortunately, this detects peril only when the visual pathways are already compromised, sometimes irreversibly. In contrast, electrophysiological stimulation mapping of the nerves can be a fully preventive measure. However, direct sensory nerve mapping requires the patient to be awake during surgery, which is unfeasible for surgeries targeting the optic nerve area. Another possible approach to sensory nerve mapping involves unconditioned electrophysiological responses evoked by sensory nerve stimulation. The key point for this approach is the possibility of obtaining such responses for a particular sensory nerve under surgical anesthesia.Case reportA 52-year-old woman presented with meningioma in the area of right optic nerve and chiasm. She underwent microsurgical removal of the tumor through the transciliary supraorbital approach. During surgery, electrodes at the inferior margin of the right orbit repeatedly recorded electrophysiological reactions following contacts and displacements of the right optic nerve by the surgical instruments.ConclusionsThe observed reactions suggest that either the unconditioned blink reflex or antidromic electroretinographic response to optic nerve irritation was conserved under total intravenous anesthesia. This observation might be of value for development of intraoperative optic nerve mapping. This in turn could increase patient safety by identifying the exact optic nerve location before any negative impact on it.     

Optic nerve elongation: does it exist?

The length of the optic nerves is a reflection of normal postnatal cranio-orbital development. Unilateral elongation of an optic nerve has been observed in two patients with orbital and skull base neoplasms. In the first case as compared to the patient's opposite, normal optic nerve, an elongated length of the involved optic nerve of 45 mm was present. The involved optic nerve in the second patient was 10 mm longer than the normal opposite optic nerve. The visual and extraocular function was preserved in the second patient. The first patient had only light perception in the affected eye. In this paper, the embryology, anatomy, and physiology of the optic nerve and its mechanisms of stretch and repair are discussed.     

Configuration‐Based Processing of Phosphene Pattern Recognition for Simulated Prosthetic Vision

Visual prosthesis can elicit phosphenes by stimulating the retina, optic nerve, or visual cortex along the visual pathway. Psychophysical studies have demonstrated that visual function can be partly recovered with phosphene‐based prosthetic vision. This study investigated the cognitive process of prosthetic vision through a face recognition task. Both behavioral response and the face‐specific N170 component of event‐related potential were analyzed in the presence of face and non‐face stimuli with natural and simulated prosthetic vision. Our results showed that: (i) the accuracy of phosphene face recognition was comparable with that of the normal one when phosphene grid increased to 25 × 21 or more; (ii) shorter response time was needed for phosphene face recognition; and (iii) the N170 component was delayed and enhanced under phosphene stimuli. It was suggested that recognition of phosphene patterns employ a configuration‐based holistic processing mechanism with a distinct substage unspecific to faces.     

Unilateral visual field defect due to optic nerve compression by sclerotic internal carotid artery: a case report

A case of unilateral visual field defect due to optic nerve compression by a sclerotic internal carotid artery was reported. A 71-year-old woman was admitted to our department because of constricted visual field of the right eye. MRI showed elevation of the right optic nerve compressed by an internal carotid artery. The right carotid angiography revealed elevation and distortion of the C1-2 portion. Frontal craniotomy was carried out and the optic nerve was visualized on this side. The right optic nerve was found to have been compressed by the sclerotic internal carotid artery. The optic canal was then unroofed. The post-operative course was uneventful. The visual field was improved. When last seen 6 months after surgery, her visual field remained in the improved condition. Nasal field abnormalities are most frequently encountered in retinal and anterior optic nerve pathology. Our success in improving the visual field disturbance may be accounted for by the fact that the preoperative period was short and the operation was performed before atrophy of ocular fundi occurred. Nasal field loss caused by intracranial lesions of the optic pathway is rare. It is probably impossible to determine degree of the symptomatology caused by direct-pressure compression as opposed to that caused by ischemia secondary to occlusion of small arterial supply branches. Vascular compressive neuropathy of optic nerve should not be diagnosed simply by the radiological finding of the optic nerve dislocation. However, optic nerve compression by surrounding arteries should be remembered as one of the possible causes of visual field defect which needs to be treated surgically.     

Optic Nerve Elongation: Does It Exist?

The length of the optic nerves is a reflection of normal postnatal cranio-orbital development. Unilateral elongation of an optic nerve has been observed in two patients with orbital and skull base neoplasms. In the first case as compared to the patient's opposite, normal optic nerve, an elongated length of the involved optic nerve of 45 mm was present. The involved optic nerve in the second patient was 10 mm longer than the normal opposite optic nerve. The visual and extraocular function was preserved in the second patient. The first patient had only light perception in the affected eye. In this paper, the embryology, anatomy, and physiology of the optic nerve and its mechanisms of stretch and repair are discussed.     

显微手术治疗外伤性视神经损伤

目的总结经额入路行显微视神经减压术辅助药物治疗对外伤性视神经损伤的疗效,探讨其治疗原则。方法16例患者经额或额颞入路开颅,显微镜下清除骨折或出血,磨开视神经管,剪开视神经鞘行视神经减压;辅以大剂量皮质类固醇激素、能量合剂和神经营养药物。结果15例患者随访6个月至1年,10例有效,视力不同程度恢复,1例失访。结论经额或额颞入路开颅行显微视神经减压是治疗外伤性视神经损伤有效方法,辅以药物的显微外科治疗是治疗外伤性视神经损伤的一种较理想的治疗方案。     

Penetration of the optic nerve by an internal carotid artery-ophthalmic artery aneurysm: case report and literature review

OBJECTIVE AND IMPORTANCE: Although it is well known that large or giant internal carotid artery-ophthalmic artery aneurysms can cause visual deficits, penetration and schism of the optic nerve by an aneurysm are very rare. CLINICAL PRESENTATION: A 48-year-old man presented with an acute onset of right visual deterioration after an episode of severe headache. Magnetic resonance imaging demonstrated penetration of the right optic nerve by an intracranial aneurysm. Cerebral angiography revealed an internal carotid artery-ophthalmic artery aneurysm of 12 x 7 mm. The aneurysm was directed superomedially and appeared to have a "waist" within the penetration. INTERVENTION: Intraoperatively, we observed that part of the aneurysm wall was visible through the optic nerve fibers at the junction with the optic chiasm. CONCLUSION: Although there was no direct evidence of subarachnoid hemorrhage on imaging scans or with operative exploration, we think that the patient must have experienced sentinel hemorrhaging, leading to visual deterioration. We describe the case in detail and review the world literature.     

Optic nerve decompression in osteopetrosis

Osteopetrosis is a rare disorder characterized by generalized increased skeletal density with abnormalities of bone modeling. The skull base is usually involved. Loss of vision with optic nerve atrophy is the most common neurological finding and is traditionally believed to be the result of optic nerve compression within the compromised optic canal. However, retinal degeneration has recently been described and is hypothesized to be the etiology of the visual loss (thus challenging the value of surgical decompression). The authors report their experience with six children suffering from osteopetrosis and severe visual loss. All six patients underwent bilateral microsurgical optic nerve decompression through a supraorbital craniotomy. Improvement in visual acuity occurred postoperatively in five patients, and none had complications. Two technical points are emphasized: 1) optic nerve decompression should be wide and include not only unroofing of the canal but also drilling along both sides of the optic nerve, and 2) the thick, irregular, and highly domed orbital roof should be smoothed down by high-speed drilling to facilitate surgical exposure with minimal retraction of the frontal lobe.     

Optic nerve trauma: Clinical,electrophysiological and histological remarks

Summary 18 patients with post-traumatic visual disease of the optic nerve are presented. In the post-traumatic stage, visual evoked potentials were monitored. In amaurosis there was a high incidence of midface or frontobasal fractures. The severity of the trauma is not correlated with the severity of visual deficits. Flash evoked potential (FEP) findings were different: In most cases there was a correlation of clinical and FEP findings. In some we found false positive potentials in the acute stage. In smaller visual field deficits the alterations of FEP could not be correlated with the clinical disorders. FEP alterations depended on time.The pathophysiological mechanisms are discussed in regard to the pathological findings in 51 unselected autopsies with an investigation of the visual pathway from the intraorbital optic nerve to the visual cortex.Because of the different morphological alterations the clinical, neurological and ophthalmological examination should be followed by standard CT scanning to evaluate intracranial haematomas and by CT scanning with thin slices of the optic nerves and the soft tissue of the orbit. Visual evoked potentials (VEP) and in the unconscious patient, flash evoked potentials (FEP) do not give much more security for therapeutic decisions in comparison with former times. The histological findings do not support the hypothesis that operative decompression is successful.     

Carcinoma of the breast metastatic to the optic nerve mimicking an optic nerve sheath meningioma: case report and review of the literature.

Isolated metastatic tumors to the optic nerve are extremely rare. We describe a rare and unusual case of metastatic breast carcinoma to the optic nerve that mimicked an optic nerve sheath meningioma in its presentation due to its indolent symptom progression, initial radiological appearance, and minimal growth on serial imaging. The patient, a 46-year-old woman with a history of stable metastatic breast carcinoma, presented with progressive visual loss in her right eye over a 6-month interval. Magnetic resonance imaging revealed an enhancing lesion in the optic canal with an extension to the right anterior clinoid process and planum sphenoidale and into the right orbital apex, consistent with the presumptive diagnosis of optic nerve sheath meningioma. The tumor was resected and pathologically confirmed to be metastatic carcinoma of the breast. The clinical course, radiological features, surgical approach, and treatment strategies are reviewed.     

Optic nerve decompression for osteopetrosis in early childhood

Visual failure in osteopetrosis may result from retinal degeneration or compression of the optic nerve in the narrowed optic canals. We report the evaluation and treatment of five children with osteopetrosis whose optic nerve dysfunction seems to have been related to the latter etiology. Evaluation of visual function was carried out by means of behavioral observation and flash visual evoked responses. Of six nerves evaluated both pre- and postoperatively, the visual evoked responses seemed to improve in four. Three nerves were serially evaluated without an operation, and one showed changes consistent with maturation. One nerve was evaluated with serial postoperative evoked potentials and showed no change. We conclude that surgical decompression of the optic nerve in patients with documented optic nerve dysfunction and osteopetrosis allows improvement in visual function and is, therefore, an important consideration in the evaluation and management of patients with this disease.