Fluids in the anterior part of the optic nerve in health and disease

The Ocular Glymphatic System-Current Understanding and Future Perspectives

The ocular glymphatic system subserves the bidirectional polarized fluid transport in the optic nerve, whereby cerebrospinal fluid from the brain is directed along periarterial spaces towards the eye, and fluid from the retina is directed along perivenous spaces following upon its axonal transport across the glial lamina. Fluid homeostasis and waste removal are vital for retinal function, making the ocular glymphatic fluid pathway a potential route for targeted manipulation to combat blinding ocular diseases such as age-related macular degeneration, diabetic retinopathy, and glaucoma. Several lines of work investigating the bidirectional ocular glymphatic transport with varying methodologies have developed diverging mechanistic models, which has created some confusion about how ocular glymphatic transport should be defined. In this review, we provide a comprehensive summary of the current understanding of the ocular glymphatic system, aiming to address misconceptions and foster a cohesive understanding of the topic.

Risk of glaucoma after vitreoretinal surgery - Findings from a population-based cohort study

PURPOSE

To investigate the association between different types of vitrectomy and risk of different types of glaucoma and to determine the effect of systemic medication and diabetes status on this risk.

METHODS

A population-based nested case-control study included individuals of age ≥ 18 years who had undergone single vitrectomy, vitrectomy with retinal procedure, or combined phaco-vitrectomy between 2001 and 2010. End of follow-up was 2017. Odds ratio (OR) for the development of glaucoma after different types of vitrectomy and 95% confidence interval (CI) were based on conditional logistic regression models. For every glaucoma case, five controls were matched by age, sex, start of follow-up year, and hospital district.

RESULTS

The cohort (n = 37 687), of which 52.8% was female, consisted of 6552 individuals diagnosed with glaucoma and 31 135 controls matched by age, sex, and hospital district. Vitrectomy was performed on 103 eyes in the glaucoma group and 158 eyes in the control group. As regards the risk of any glaucoma, the risk was lowest in eyes that underwent combined phaco-vitrectomy (OR: 2.7, 95% CI: 1.8-4.1), followed by single vitrectomy (OR: 3.15, 95% CI: 2.1-4.8), and highest in eyes that underwent vitrectomy with retinal procedure (OR: 4.5, 95% CI: 2.7-7.4). Diabetes had no effect (OR: 0.96, 95% CI: 0.92-1.01), but 5-year systemic statin use slightly decreased glaucoma risk (OR: 0.86, 95% CI: 0.77-0.97).

CONCLUSIONS

Vitreoretinal surgery was associated with an increased glaucoma risk; the risk being related to the complexity of vitrectomy. Long-term systemic statin therapy may decrease glaucoma risk, while diabetes had no association.

Intereye Comparison of Focal Lamina Cribrosa Defect in Normal-Tension Glaucoma Patients with Asymmetric Visual Field Loss

INTRODUCTION

To evaluate the association of focal lamina cribrosa (LC) defect with asymmetric visual field (VF) loss in normal-tension glaucoma (NTG) through intereye comparisons.

METHODS

Paired eyes were divided into better and worse eyes according to the mean deviation (MD), and ocular parameters were compared between them. Furthermore, patients in the asymmetric group were classified as subgroup A (one eye with LC defect and the fellow one without), subgroup B (both eyes without LC defect), and subgroup C (both eyes with LC defect). Generalized estimation equation approach was used to evaluate the association between ocular parameters and asymmetric VF.

RESULTS

A total of 140 eyes of 70 NTG patients were included in the asymmetric group. LC defects were more common in better eyes than that in worse eyes (27/70 [38.57%] vs. 10/70 [14.29%], p = 0.001), and all eyes with LC defect had myopia. Multivariate analysis revealed that the presence of LC defect was significantly associated with better eyes in the asymmetric group (odds ratio, 0.27; p = 0.001). For subgroup A, eyes with LC defects exhibited lower peak IOP (p = 0.011) and lower mean IOP (p = 0.018) than the fellow eyes without. In addition, longer AL (p = 0.025) and larger tilt ratio (p = 0.032) were found in eyes with LC defects. For subgroup B without LC defects, larger tilt ratio was shown to be a risk factor for VF loss (odds ratio, 6.13; p = 0.001). There was no significant difference of binocular parameters except for MD (p < 0.001) in subgroup C.

CONCLUSIONS

LC defects in myopia were suggested to be associated with better eyes in NTG with asymmetric VF loss. However, in patients without LC defect, larger tilt ratio was a risk factor for VF defect. There might be different pathological mechanisms in asymmetric VF loss for different NTG subtypes.

Relief of Cystoid Macular Edema-Induced Focal Axonal Compression with Anti-Vascular Endothelial Growth Factor Treatment

Purpose

To evaluate the mechanical compression of retinal nerve fiber layer (RNFL) by intraretinal cysts in macular edema and its relief with anti-vascular endothelial growth factor (anti-VEGF) treatment.

Methods

Optical coherence tomography scans were used to measure RNFL thickness and reflectance at seven preselected points at and around the peak of the edema before and after anti-VEGF treatment in 10 patients (11 eyes) with branch retina vein occlusion (BRVO) and diabetic macular edema (DME). Scans through nonedematous retina and from the fellow eyes were taken as controls. Correlations were sought between the changes in retinal and RNFL thickness, RNFL reflectance, and the size of the intraretinal cysts.

Results

Postinjection RNFL thickness decreased significantly only at peak point of the edema (18.1 ± 2.7 vs. 13.8 ± 1.2 µm; P = 0.038), at its nasal edge (20.1 ± 2.7 vs. 15.5 ± 1.4 µm; P = 0.026), and 500 µm away from its nasal border (35.7 ± 6.0 vs. 20.1 ± 2.7 µm; P = 0.006) suggesting focal stagnation of the axoplasmic flow owing to compression at its peak point. Significant postinjection decreases in RNFL reflectivity were also noted at peak point of the cyst (164.9 ± 10.3 vs. 141.5 ± 12.6 arbitrary units [AU]; P = 0.037), at its nasal edge (166.8 ± 7.8 vs. 135.1 ± 10.2 AU; P = 0.02), and 1500 µm away from temporal edge (160.2 ± 6.2 vs. 141.1 ± 6.4 AU; P = 0.022). Cyst proximity to RNFL (D₅₀ = 50 µm) was the only determinant significantly affecting the magnitude of the RNFL thickness change after anti-VEGF treatment (P = 0.001).

Conclusions

Intraretinal cysts due to BRVO and DME locally compress overlying axons and induce anatomic changes suggestive of axoplasmic stagnation. This compression can be relieved with anti-VEGF treatment.

Translational Relevance

Focal compression of RFNL by retinal cysts may indicate a need for early treatment of macular edema to prevent axonal loss, especially in patients with low axonal reserve

Choroidal Thickness in Acute Non-arteritic Anterior Ischemic Optic Neuropathy

Purpose

To compare the choroidal thickness in eyes with acute non-arteritic anterior ischemic optic neuropathy (NAION) with healthy contralateral eye and normal controls.

Methods

Thirty-eight eyes with NAION, thirty-eight unaffected fellow eyes, and seventy-four eyes from 37 healthy, age- and sex-matched subjects were included in this prospective comparative case-control study. Choroidal thickness was measured by enhanced depth imaging (EDI) of spectral domain optical coherence tomography (SD-OCT). Peripapillary choroidal thickness (PCT) was measured at 1000 and 1500 μm from Bruch's membrane opening (BMO). Subfoveal choroidal thickness (SFCT) was measured in central subfoveal area, and 500 microns apart in temporal and nasal sides. Choroidal thickness among NAION eyes, uninvolved fellow eyes, and control eyes were compared.

Results

The mean of PCT at 1000 μm was significantly thicker in NAION and fellow eyes compared to control eyes (169.7 ± 47, 154.4 ± 42.1, and 127.7 ± 49.9 μm, respectively, P< 0.001 and P = 0.42). The mean PCT at 1500 μm was also significantly thicker in NAION and fellow eyes compared to control eyes (178.6 ± 52.8, 162.6 ± 46.1, and 135.1 ± 59 μm, respectively, P = 0.007 and P = 0.048). The mean PCT at 1000 and 1500 μm was significantly greater in NAION compared to fellow eyes (P = 0.027 and P = 0.035, respectively). The mean of SFCT was significantly thicker in NAION compared to control eyes (P = 0.032); however, there was no significant difference between uninvolved fellow and control eyes (P = 0.248).

Conclusion

Thicker choroidal thickness in acute NAION and uninvolved fellow eyes compared to normal eyes suggests a primary choroidal role in NAION pathophysiology.

Elevated Intraocular Pressure Causes Abnormal Reactivity of Mouse Retinal Arterioles

Objective

Glaucoma is a leading cause of severe visual impairment and blindness. Although high intraocular pressure (IOP) is an established risk factor for the disease, the role of abnormal ocular vessel function in the pathophysiology of glaucoma gains more and more attention. We tested the hypothesis that elevated intraocular pressure (IOP) causes vascular dysfunction in the retina.

Methods

High IOP was induced in one group of mice by unilateral cauterization of three episcleral veins. The other group received sham surgery only. Two weeks later, retinal vascular preparations were studied by video microscopy in vitro. Reactive oxygen species (ROS) levels and expression of hypoxia markers and of prooxidant and antioxidant redox genes as well as of inflammatory cytokines were determined.

Results

Strikingly, responses of retinal arterioles to stepwise elevation of perfusion pressure were impaired in the high-IOP group. Moreover, vasodilation responses to the endothelium-dependent vasodilator, acetylcholine, were markedly reduced in mice with elevated IOP, while no differences were seen in response to the endothelium-independent nitric oxide donor, sodium nitroprusside. Remarkably, ROS levels were increased in the retinal ganglion cell layer including blood vessels. Expression of the NADPH oxidase isoform, NOX2, and of the inflammatory cytokine, TNF-α, was increased at the mRNA level in retinal explants. Expression of NOX2, but not of the hypoxic markers, HIF-1α and VEGF-A, was increased in the retinal ganglion cell layer and in retinal blood vessels at the protein level.

Conclusion

Our data provide first-time evidence that IOP elevation impairs autoregulation and induces endothelial dysfunction in mouse retinal arterioles. Oxidative stress and inflammation, but not hypoxia, appear to be involved in this process.

Estimating three-dimensional outflow and pressure gradients within the human eye

In this paper we set the previously reported pressure-dependent, ordinary differential equation outflow model by Smith and Gardiner for the human eye, into a new three-dimensional (3D) porous media outflow model of the eye, and calibrate model parameters using data reported in the literature. Assuming normal outflow through anterior pathways, we test the ability of 3D flow model to predict the pressure elevation with a silicone oil tamponade. Then assuming outflow across the retinal pigment epithelium is normal, we test the ability of the 3D model to predict the pressure elevation in Schwartz-Matsuo syndrome. For the first time we find the flow model can successfully model both conditions, which helps to build confidence in the validity and accuracy of the 3D pressure-dependent outflow model proposed here. We employ this flow model to estimate the translaminar pressure gradient within the optic nerve head of a normal eye in both the upright and supine postures, and during the day and at night. Based on a ratio of estimated and measured pressure gradients, we define a factor of safety against acute interruption of axonal transport at the laminar cribrosa. Using a completely independent method, based on the behaviour of dynein molecular motors, we compute the factor of safety against stalling the dynein molecule motors, and so compromising retrograde axonal transport. We show these two independent methods for estimating factors of safety agree reasonably well and appear to be consistent. Taken together, the new 3D pressure-dependent outflow model proves itself to capable of providing a useful modeling platform for analyzing eye behaviour in a variety of physiological and clinically useful contexts, including IOP elevation in Schwartz-Matsuo syndrome and with silicone oil tamponade, and potentially for risk assessment for optic glaucomatous neuropathy.

Lymphatic vessels of the eye - old questions - new insights

Due to its accessible position and tissue heterogeneity, the eye is ideally suited for studying the lymphatic system. As early as the 19th century, questions about the origin and function of this system were discussed. For example, whether Schlemm's canal, which is of particular importance in the pathogenesis of glaucoma, is a lymphatic vessel, or does this vascular system begin with finger-shaped protuberances? Despite the discovery of lymphatic endothelial molecules and the use of molecular imaging technologies, these questions are still discussed controversially today. Leber demonstrated in 1873 with a solution consisting of two dyes of different particle size that only the smaller particles from the anterior chamber of the eye filled the episcleral and conjunctival veins around the corneal margin. He believed to have proven - to be read in the historical review of our article - that the Canalis Schlemmii in humans is a venous circular vessel and not a lymphatic vessel. In our own investigations, we reduced the rather contradictory and complex question of whether there are lymphatic vessels in the eye to the question of whether there are drainage connections between the different sections of the eye and the lymphatic system or not. With different radioactive tracers and combined with unilateral ligation of cervical lymph vessels, we observed outflow from the subconjunctival and retrobulbar space, from the anterior chamber and the vitreous body. The rate of discharge of the radioactive tracer was determined by the radiopharmaceutical and injection site. In analogy to the lymphatic drainage of the head we found a segmental drainage of lymphatic substances on the eye. Vitreous humour and retrobulbar space were drained by lymphatic vessels, predominantly to the deep cervical lymph nodes, while anterior chamber and subconjunctival space drains predominated over the superficial cervical lymph nodes. Eyeball tattoos - as loved by some fan communities - should therefore cause a coloured staining of the superficial cervical lymph nodes. The boundary of the drained segments would be in the area of the eyeball's equator. According to the textbooks, the lymph is actively removed from finger-shaped initial segments via pre-collectors and collectors with properly functioning intraluminal valves and smooth muscle cells in the vessels' media. In patients with spontaneous conjunctival bleeding, however, we observed phenomena in the conjunctival lymph vessels, which ca not be explained with old familiar ideas. At nozzle-shaped vessel constrictions separation of blood components occurred. The erythrocytes formed partially a so-called fluidic "resting bulk layer". Parallel vessel parts caused a retrograde filling of already emptied segments. These observations led our experimental investigations. In the literature, there are different scanning electron microscopy (SEM) images of lymphatic endothelial surfaces; nevertheless they are unassigned to a particular vessel segment. In the conjunctiva, we studied the question whether there is a dependence between vessel diameter and the surface characteristics of endothelial cells (after unfolding by lymphography). A constantly applied photo-mathematical procedure for all specimens allowed determining the size of the cross sections. The specimens were randomized into seven groups with diameters of 0.1-1.0mm and above and examined by SEM. In the smallest vessels (diameter=0.11mm), the impressions of the occasionally occurring nuclei in the lumen were clearly impressive. With increasing diameter, these impressions were lost and the individual endothelial nuclei could no longer be identified. Rather, one recognized only wall-like structures. In vessels of intermediate diameter (0.3-0.4mm), structures could be seen on the surface similar to reticular fibres. With increasing diameters, their prominent character weakened. In the group with diameters above 0.5mm, wavy surface structures were shown. Finally, in vessels of diameters over 1.0mm, a uniform, flat surface was observed. Regardless of the collection site of the specimens, we found certain surface characteristics related to the vessels' calibre. In further investigations by means of interstitial dye lymphography, we were able to demonstrate in the conjunctiva that under increasing injection pressure, additional vessels stained from finger-shaped processes. At least in the conjunctiva, the existence of so-called "blind-ending initial segments" seems doubtful (despite the fact that initial segments or "initial lymphatics" would begin in periphery, not end). Rather, these are likely to be temporary filling states. SEM investigations were carried out on the internal structure of these dome-shaped vessel parts by means of a specially developed preparation technique. Despite numerous variants in the lymphographic design of the blind bags - in the form of finger, balloon, dome, piston, pyramidal, double-humped and spearhead-like endings - slot-shaped, lip-shaped and saw blade-like structures were repeatedly found, similar to a zipper. These findings suggest preformed connections to the next segment and may control lymphatic flow. To clarify the retrograde fluid movements, we examined the lymph vessels' valves or those structures that were previously interpreted as valves. The different structures found could be subdivided into three groups. The lack of common bicuspid structures provides an explanation for retrograde fluid movement. That nevertheless a directional flow is possible, is explained by the flow model developed by Gerhart Liebau. Conjunctival lymphatics show intraluminal structures by double contrast injection, which we divided into four groups due to anatomical differences: An accurate statement about the occurrence of certain intraluminal vascular structures in certain vascular calibres was possible only conditionally. However, complex and extended structures (group d) were found almost exclusively in larger vessel calibres (diameter>0.9mm). The structures are reminiscent of published findings in the "collector channel orifices of Schlemm's canal". They should play an important role in the regulation of the intraocular pressure, or the balance between production and outflow of the aqueous humour. The influence of such structures on the function of the lymphatic vessels is not yet known. As an approach models could be used, which for instance are applied in the water industry for the drainage, the degradation of introduced substances, or the detention pond. The latter serves for the retention and purification of drainage water (storage, treatment and reuse of drainage water). Dead zones, barriers, short-circuit currents and swirling are further hydraulic terms. Can intraluminal vascular structures, for example, affect the lymphatic flow and thus the mechano-sensitivity of lymphatic endothelial cells? Whatever interpretation model we use, the warning of the Swiss anatomist His from 1862 is still true today that all theories about the formation and movement of lymph should be based on precise anatomical basics. This review article therefore tries to make a contribution therefore. Despite knowing of lymphatic endothelial molecules, despite the discovery of the role of lymphangiogenic growth factors in diseases and the use of molecular imaging technologies, we still know too little about the anatomy and function of the lymphatic system.

The Central Bright Spot Sign: A Potential New MR Imaging Sign for the Early Diagnosis of Anterior Ischemic Optic Neuropathy due to Giant Cell Arteritis

BACKGROUND AND PURPOSE

A rapid identification of the etiology of anterior ischemic optic neuropathy is crucial because it determines therapeutic management. Our aim was to assess MR imaging to study the optic nerve head in patients referred with anterior ischemic optic neuropathy, due to either giant cell arteritis or the nonarteritic form of the disease, compared with healthy subjects.

MATERIALS AND METHODS

Fifteen patients with giant cell arteritis-related anterior ischemic optic neuropathy and 15 patients with nonarteritic anterior ischemic optic neuropathy from 2 medical centers were prospectively included in our study between August 2015 and May 2016. Fifteen healthy subjects and patients had undergone contrast-enhanced, flow-compensated, 3D T1-weighted MR imaging. The bright spot sign was defined as optic nerve head enhancement with a 3-grade ranking system. Two radiologists and 1 ophthalmologist independently performed blinded evaluations of MR imaging sequences with this scale. Statistical analysis included interobserver agreement.

RESULTS

MR imaging scores were significantly higher in patients with giant cell arteritis-related anterior ischemic optic neuropathy than in patients with nonarteritic anterior ischemic optic neuropathy (P ≤ .05). All patients with giant cell arteritis-related anterior ischemic optic neuropathy (15/15) and 7/15 patients with nonarteritic anterior ischemic optic neuropathy presented with the bright spot sign. No healthy subjects exhibited enhancement of the anterior part of the optic nerve. There was a significant relationship between the side of the bright spot and the side of the anterior ischemic optic neuropathy (P ≤ .001). Interreader agreement was good for observers (κ = 0.815).

CONCLUSIONS

Here, we provide evidence of a new MR imaging sign that identifies the acute stage of giant cell arteritis-related anterior ischemic optic neuropathy; patients without this central bright spot sign always had a nonarteritic pathophysiology and therefore did not require emergency corticosteroid therapy.

Pathogenesis of optic disc edema in raised intracranial pressure

Optic disc edema in raised intracranial pressure was first described in 1853. Ever since, there has been a plethora of controversial hypotheses to explain its pathogenesis. I have explored the subject comprehensively by doing basic, experimental and clinical studies. My objective was to investigate the fundamentals of the subject, to test the validity of the previous theories, and finally, based on all these studies, to find a logical explanation for the pathogenesis. My studies included the following issues pertinent to the pathogenesis of optic disc edema in raised intracranial pressure: the anatomy and blood supply of the optic nerve, the roles of the sheath of the optic nerve, of the centripetal flow of fluids along the optic nerve, of compression of the central retinal vein, and of acute intracranial hypertension and its associated effects. I found that, contrary to some previous claims, an acute rise of intracranial pressure was not quickly followed by production of optic disc edema. Then, in rhesus monkeys, I produced experimentally chronic intracranial hypertension by slowly increasing in size space-occupying lesions, in different parts of the brain. Those produced raised cerebrospinal fluid pressure (CSFP) and optic disc edema, identical to those seen in patients with elevated CSFP. Having achieved that, I investigated various aspects of optic disc edema by ophthalmoscopy, stereoscopic color fundus photography and fluorescein fundus angiography, and light microscopic, electron microscopic, horseradish peroxidase and axoplasmic transport studies, and evaluated the effect of opening the sheath of the optic nerve on the optic disc edema. This latter study showed that opening the sheath resulted in resolution of optic disc edema on the side of the sheath fenestration, in spite of high intracranial CSFP, proving that a rise of CSFP in the sheath was the essential pre-requisite for the development of optic disc edema. I also investigated optic disc edema with raised CSFP in patients, by evaluating optic disc and fundus changes by stereoscopic fundus photography and fluorescein fundus angiography. Based on the combined information from all the studies discussed above, it is clear that the pathogenesis of optic disc edema in raised intracranial pressure is a mechanical phenomenon. It is primarily due to a rise of CSFP in the optic nerve sheath, which produces axoplasmic flow stasis in the optic nerve fibers in the surface nerve fiber layer and prelaminar region of the optic nerve head. Axoplasmic flow stasis then results in swelling of the nerve fibers, and consequently of the optic disc. Swelling of the nerve fibers and of the optic disc secondarily compresses the fine, low-pressure venules in that region, resulting in venous stasis and fluid leakage; that leads to the accumulation of extracellular fluid. Contrary to the previous theories, the various vascular changes seen in optic disc edema are secondary and not primary. Thus, optic disc edema in raised CSFP is due to a combination of swollen nerve fibers and the accumulation of extracellular fluid. My studies also provided information about the pathogeneses of visual disturbances in raised intracranial pressure.

Fast circulation of cerebrospinal fluid: an alternative perspective on the protective role of high intracranial pressure in ocular hypertension

As ocular hypertension refers to a condition in which the intraocular pressure is consistently elevated but without development of glaucoma, study of it may provide important clues to factors that may play a protective role in glaucoma. β-amyloid, one of the key histopathological findings in Alzheimer's disease, has been reported to increase by chronic elevation of intraocular pressure in animals with experimentally induced ocular hypertension and to cause retinal ganglion cell death, pointing to similarities in molecular cell death mechanisms between glaucoma and Alzheimer's disease. On the other hand, recent studies have reported that intracranial pressure is higher in patients with ocular hypertension compared with controls, giving rise to the idea that elevated intracranial pressure may provide a protective effect for the optic nerve by decreasing the trans-lamina cribrosa pressure difference. The speculation that the higher intracranial pressure reported in ocular hypertension patients may protect against glaucoma mainly through a lower trans-lamina cribrosa pressure difference remains at least questionable. Here, we present an alternative viewpoint, according to which the protective effect of higher intracranial pressure could be due, at least in part, to a pressure-independent mechanism, namely faster cerebrospinal fluid production leading to increased cerebrospinal fluid turnover with enhanced removal of potentially neurotoxic waste products that accumulate in the optic nerve. This suggests a new hypothesis for glaucoma, which, just like Alzheimer's disease, may be considered then as an imbalance between production and clearance of neurotoxins, including β-amyloid. If confirmed, then strategies to improve cerebrospinal fluid flow are reasonable and could provide a new therapeutic approach for stopping the neurotoxic β-amyloid pathway in glaucoma.

Cerebrospinal fluid pressure in the pathogenesis of glaucoma

The optic nerve head forms the interface between the intraocular compartment and the retrobulbar compartment. The former is characterized by what we term intraocular pressure (IOP) and the latter by orbital cerebrospinal fluid pressure (CSFP). The trans-lamina cribrosa pressure difference (TLCPD) is defined as the difference between the pressures in the two compartments. Any change in one of them can be associated with a disturbance of homeostasis of the optic nerve head, such as papilledema or glaucomatous optic neuropathy. In particular, glaucomatous optic neuropathy may be due to either an elevated IOP and/or an abnormally low orbital CSFP, or due to a change in the time-dependent relationship between the pulse-synchronous changes in IOP and orbital CSFP. Based on the triangular relationships between IOP, CSFP, and blood pressure, glaucoma may be described as an imbalance between these three pressure parameters, eventually leading to an increased TLCPD. Because the retinal and choroidal venous blood drains through the CSFP space, elevated CSFP may be associated with dilated retinal veins, increased incidence of retinal vein occlusions, higher prevalence and severity of diabetic retinopathy, and thicker choroid.

A new glaucoma hypothesis: a role of glymphatic system dysfunction

In a recent review article titled “A new look at cerebrospinal fluid circulation”, Brinker et al. comprehensively described novel insights from molecular and cellular biology as well as neuroimaging research, which indicate that cerebrospinal fluid (CSF) physiology is much more complex than previously believed. The glymphatic system is a recently defined brain-wide paravascular pathway for CSF and interstitial fluid exchange that facilitates efficient clearance of interstitial solutes, including amyloid-β, from the brain. Although further studies are needed to substantiate the functional significance of the glymphatic concept, one implication is that glymphatic pathway dysfunction may contribute to the deficient amyloid-β clearance in Alzheimer’s disease. In this paper, we review several lines of evidence suggesting that the glymphatic system may also have potential clinical relevance for the understanding of glaucoma. As a clinically acceptable MRI-based approach to evaluate glymphatic pathway function in humans has recently been developed, a unique opportunity now exists to investigate whether suppression of the glymphatic system contributes to the development of glaucoma. The observation of a dysfunctional glymphatic system in patients with glaucoma would provide support for the hypothesis recently proposed by our group that CSF circulatory dysfunction may play a contributory role in the pathogenesis of glaucomatous damage. This would suggest a new hypothesis for glaucoma, which, just like Alzheimer’s disease, might be considered then as an imbalance between production and clearance of neurotoxins, including amyloid-β.

Intravitreal triamcinolone injections in non-arteritic anterior ischemic optic neuropathy

BACKGROUND

In non-arteritic anterior ischemic optic neuropathy (NA-AION), no treatments have demonstrated to be effective in recovering visual loss in randomized clinical trials. Oral steroids have been evaluated, and small series of intravitreal triamcinolone acetonide (IVTA) injection in NA-AION have been reported. The purpose of our study was to report the visual outcome and morphological changes in response to a single IVTA injection as a treatment for patients with NA-AION.

PATIENTS AND METHODS

The charts of 36 patients with visual symptoms and optic disc swelling caused by NA-AION were evaluated. Twenty-one patients had received 4 mg IVTA and were compared with 15 non-treated patients. Visual acuity (VA), retinal nerve fiber layer thickness and static visual field were evaluated after 6 months.

RESULTS

VA improvement at 6 months is statistically better in the treated group than in the non-treated group (p = 0.0035). In the treated group, there was a significant inverse correlation between the delay of the injection and the visual acuity achieved at 6 months (p < 0.0083**, r = -0.56). A significant improvement of the visual field was noted in the injected group when compared with the non-treated group at 6 months (p < 0.0028).

DISCUSSION

In this retrospective study, patients receiving IVTA in the acute phase of NA-AION have better improvement of VA and visual field during the follow-up period of 6 months. However, only a large randomized controlled trial may enable to evaluate the benefits of IVTA Injections on visual outcome in NA-AION.

Macular Involvement and Response to Steroid Therapy Demonstrated by Optical Coherence Tomography in Non-arteritic Anterior Ischaemic Optic Neuropathy

Two consecutive patients with anterior non-arteritic ischaemic optic neuropathy were evaluated with spectral-domain optical coherence tomography. The optical coherence tomographic scans revealed subfoveal fluid and intraretinal fluid extending from the optic disc margin toward the fovea that made us think that the submacular fluid appeared to arise from the peripapillary region. Fluorescein angiography showed no accumulation in the macular area, whereas leakage and staining of the optic nerve was present. After systemic corticosteroid therapy, the submacular fluid decreased promptly and the visual acuity improved. Subretinal-fluid-associated disc oedema may develop in some patients with NAION and contribute to the visual loss associated with this condition. Optical coherence tomography should be performed to follow macular involvement in patients with neuro-ophthalmic disease as well as to monitor patients' response to treatment.

Ischemic optic neuropathy

Anterior ischemic optic neuropathy (AION) is a common cause of visual loss in patients over 50 years of age. Optical coherence tomography has provided new information which may have implications regarding future approaches to management.

Mapping the surface astrocytes of the optic disc: a fluid-conducting role of the astrocytic covering of the central vessels

BACKGROUND

The vitreous interface of the optic nerve has been studied to delimit the covering of Elschnig's astrocytes and interstitial pathways of flow through the prelaminar region.

METHODS

Perfusion of the prelaminar tissue under controlled pressure with a fluorescent marker injected into the vitreous cavity in pig eyes. The prelaminar region of the optic nerve and adjacent retina was fixed and flatmounted or frozen and cryosectioned and examined with the confocal laser microscope. Samples were also prepared for conventional transmission electron microscopy.

RESULTS

The surface of the vitreous surface of the optic nerve is covered by a cobblestone-like pavement made of astrocytic projections. Intensely stained passages of different thickness indicate the presence of wide interconnected intercellular spaces in the covering of Elschnig's astrocytes. Those passages are absent in the intervascular areas occupied by axons and axon-linked astrocytes.

CONCLUSIONS

Delineation of the astrocytic pavement and the preferred flow routes formed by wide extracellular spaces are conspicuous features of the prelaminar region when examined with the confocal laser microscope and the help of sticky fluorescent tracer. This suggests that excess extracellular fluid can be interchanged with the vitreous by a network of interconnected extracellular spaces or preferred flow routes. Some pathogenic mechanisms can be related to fluid interchange in the optic nerve head.

Nonarteritic anterior ischemic optic neuropathy: refractive error and its relationship to cup/disc ratio

OBJECTIVE

To investigate refractive error in eyes with nonarteritic anterior ischemic optic neuropathy (NA-AION) and its relationship to cup/disc (C/D) ratio.

DESIGN

Cohort study.

PARTICIPANTS

A total of 608 consecutive patients with NA-AION.

METHODS

At first visit, all patients had a comprehensive ophthalmic evaluation, including recording best-corrected visual acuity, visual fields, anterior segment examination, ophthalmoscopy, and fluorescein fundus angiography. Morphometric measurement of C/D ratio was performed in 65 fellow normal eyes in patients with unilateral NA-AION. Refraction was converted into spherical equivalent for data analysis. The data were analyzed using Pearson correlation, Mantel-Haenszel chi-square test, Cochran-Mantel-Haenszel test, chi-square goodness-of-fit test, and segmented linear regression.

MAIN OUTCOME MEASURES

Refractive error in NA-AION eyes and any association between refractive error and C/D ratio.

RESULTS

Mean age of patients with NA-AION was 60.9 (standard deviation [SD] = 12.6; range 20.5-95.2) years. Median time from onset to refraction was 2 weeks (interquartile range 1-5 weeks). There was a significant association between spherical equivalent and age (P<0.0001). Comparison of refraction in patients with NA-AION who were aged >or=50 years with that of an age-matched general population in the Framingham study cohort showed no significant difference between the 2 groups (P = 0.289). Comparison with the age-matched US population from the 1999-2000 National Health and Nutrition Examination Survey showed a higher proportion of NA-AION eyes with spherical equivalent from -0.5 to 0.5 diopters and a smaller proportion with -3 to <-0.5 and >0.5 to +3 diopters (P<0.001). For horizontal C/D ratio, a higher degree of myopia and higher degree of hyperopia were significantly associated with a larger C/D ratio (P<0.021). A similar pattern was seen for vertical C/D ratio in hyperopia (P = 0.057) but not in myopia (P = 0.428).

CONCLUSIONS

There was a significant association between spherical equivalent refraction and age (P<0.0001). C/D ratio in persons with NA-AION is significantly smaller than that seen in the general population. Morphometric study in patients with NA-AION showed that a higher degree of myopia and higher degree of hyperopia are significantly associated with a larger C/D ratio.

FINANCIAL DISCLOSURE(S)

The authors have no proprietary or commercial interest in any materials discussed in this article.

Non-arteritic anterior ischemic optic neuropathy: role of systemic corticosteroid therapy

OBJECTIVE

To investigate systematically the role of systemic corticosteroid therapy in non-arteritic anterior ischemic optic neuropathy (NA-AION).

METHODS

The study consists of a cohort of 613 consecutive patients (696 eyes), first seen in our clinic from 1973 to 2000. Of this cohort, 312 patients (364 eyes) voluntarily opted for systemic steroid therapy, and 301 (332 eyes) for no treatment. At first visit, all patients in both groups had a detailed ophthalmic and medical history, and comprehensive ophthalmic evaluation. Visual evaluation was done by recording Snellen visual acuity, and visual fields with a Goldmann perimeter. The same ophthalmic evaluation was performed at each follow-up visit. Patients in the steroid-treated group were initially given 80 mg Prednisone daily for 2 weeks, and then tapered down to 70 mg for 5 days, 60 mg for 5 days, and then cutting down by 5 mg every 5 days. Visual outcome in the two groups was compared

RESULTS

Median follow-up was 3.8 years. At 6 months from onset of NA-AION, of the eyes with initial visual acuity 20/70 or worse and seen within 2 weeks of onset, there was visual acuity improvement in 69.8% (95% confidence interval (CI): 57.3%, 79.9%) in the treated group, compared to 40.5% (95% CI: 29.2%, 52.9%) in the untreated group (odds ratio of improvement: 3.39; 95% CI:1.62, 7.11; p = 0.001). Comparison of visual field defect at 6 months from onset of NA-AION, among those seen within 2 weeks of NA-AION onset with moderate to severe initial visual field defect, there was improvement in 40.1% (95% CI: 33.1%, 47.5%) of the treated group, and 24.5% (95% CI: 17.7%, 32.9%) of the untreated group (odds ratio: 2.06, 95% CI: 1.24, 3.40; p = 0.005). In both treated and untreated groups, the visual acuity and visual fields kept improving up to about 6 months from onset of NA-AION, and very little thereafter.

CONCLUSION

This study suggested that NA-AION eyes treated during the acute phase with systemic corticosteroids resulted in a significantly higher probability of improvement in visual acuity (p = 0.001) and visual field (p = 0.005) than in the untreated group. Both visual acuity and visual fields improved up to 6 months after onset of NA-AION.

Does the blood-brain barrier play a role in Glaucoma?

The optic nerve head, although part of the central nervous system, lacks classical blood-brain barrier properties. The tissue of Elschnig does not totally separate the optic nerve head from fenestrated peripapillary choriocapillaries. The microvessels in the prelaminar region of the optic nerve head have less effective barriers than those in the laminar or retrolaminar regions. In glaucoma, the blood-brain barrier in the optic nerve head may even be weaker. Incomplete blood-brain barrier renders circulating molecules, such as endothelin-1 (ET-1), direct access to smooth vascular muscle cells and pericytes both in the prelaminar part of the optic nerve head and to adjacent retinal tissue. This potentially leads to some vasoconstriction as observed in the peri-papillary retinal vessel in glaucoma patients. In extreme situations, this may provoke retinal vein occlusion. The direct access of these molecules also influences the barrier function. If, simultaneously, ET-1 reduces endothelial tight-junctions and matrix-metalloproteinase (MMP)-9 degrades the basement membrane, not only macromolecules but even red blood cells may cross the blood-brain barrier and lead to what is clinically observed as optic disk hemorrhages.

What is the link between vascular dysregulation and glaucoma?

The need of blood flow to different organs varies rapidly over time which is why there is sophisticated local regulation of blood flow. The term dysregulation simply means that blood flow is not properly adapted to this need. Dysregulative mechanisms can lead to an over- or underperfusion. A steady overperfusion may be less critical for long-term damage. A constant underperfusion, however, can lead to some tissue atrophy or in extreme situations to infarction. Unstable perfusion (underperfusion followed by reperfusion) leads to oxidative stress. There are a number of causes that lead to local or systemic vascular dysregulation. Systemic dysregulation can be primary or secondary of nature. A secondary dysregulation is due to other autoimmune diseases such as rheumatoid arthritis, giant cell arteritis, systemic lupus erythematodes, multiple sclerosis, colitis ulcerosa, or Crohns disease. Patients with a secondary vascular dysregulation normally have a high level of circulating endothelin-1 (ET-1). This increased level of ET-1 leads to a reduction of blood flow both in the choroid and the optic nerve head but has little influence on autoregulation. In contrast, primary vascular dysregulation has little influence on baseline ocular blood flow but interferes with autoregulation. This, in turn, leads to unstable oxygen supply, which seems to be a relevant component in the pathogenesis of glaucomatous optic neuropathy.

Optic disc edema in non-arteritic anterior ischemic optic neuropathy

We investigated the clinical characteristics, time to resolution and the factors that influence it, and evolutionary pattern of optic disc edema (ODE) in non-arteritic anterior ischemic optic neuropathy (NA-AION). Our study was conducted in 591 consecutive patients (749 eyes) with NA-AION who fulfilled our inclusion criteria. On their first visit to our clinic, all patients had a detailed ophthalmic and medical history, a comprehensive ophthalmic evaluation, and stereoscopic color fundus photography and fluorescein fundus angiography. On each follow-up visit, the same ophthalmic evaluation was performed, except for fluorescein fundus angiography. The effect of steroid therapy on ODE was evaluated in a "patient choice study" in 723 eyes, i.e., patients who voluntarily opted to have (343 eyes) or not have (380 eyes) this therapy. To identify the factors that influence time to ODE resolution, parametric regression models for interval-censored data were fitted by maximum likelihood estimation using an SAS procedure. Our results indicate that the overall median time (25-75th percentile) to spontaneous resolution of ODE from the onset of visual loss was 7.9 (5.8-11.4) weeks. The ODE resolution time was longer in diabetics than in non-diabetics (p = 0.003) in the single factor model. Multi-factor analysis showed that worse initial visual field defects (p < 0.0001) and worse visual acuity (p = 0.04) were associated with a faster resolution of ODE. Those treated with steroid therapy within 2 weeks after onset of NA-AION had significantly (p = 0.0006) faster ODE resolution than untreated cases. Severity of initial visual loss and systemic diseases were identical in steroid treated and untreated patients. A characteristic evolutionary pattern of ODE in NA-AION was observed. In conclusion, our study showed that in NA-AION the time course for resolution of ODE is shorter with greater severity of initial visual field and visual acuity loss, which may relate to the number of axons permanently damaged during the acute stage. Steroid therapy was associated with shorter time to resolution of ODE. Resolution of ODE goes through a characteristic evolutionary process.

Incipient nonarteritic anterior ischemic optic neuropathy

OBJECTIVE

To describe the clinical entity of incipient nonarteritic anterior ischemic optic neuropathy (NAION).

DESIGN

Cohort study.

PARTICIPANTS

Fifty-four patients (60 eyes) seen in our clinic from 1973 through 2000.

METHODS

At their first visit to our clinic, all patients gave a detailed ophthalmic and medical history and underwent a comprehensive ophthalmic evaluation, color fundus photography, and fluorescein fundus angiography. At each follow-up visit (of 49 patients [55 eyes]), the same ophthalmic evaluation was performed, except for fluorescein fundus angiography.

MAIN OUTCOME MEASURES

Clinical features of incipient NAION.

RESULTS

Mean age (+/- standard deviation) of the patients was 58.7+/-15.9 years. Median follow-up time was 6.3 years (interquartile range [IQR], 2.1-8.5). At initial visit, all had optic disc edema (ODE) without any visual loss attributable to NAION. In 55%, the fellow eye had classic NAION; in 25%, incipient progressed to classic NAION (after a median time of 5.8 weeks [IQR, 3.2-10.1]); and in 20%, classic NAION developed after resolution of the first episode of incipient NAION. Patients with incipient, compared with classic, NAION had a greater prevalence of diabetes mellitus (P<0.0001) and lower prevalence of ischemic heart disease (P = 0.046). Patients who progressed to classic NAION versus those who did not were significantly younger (P = 0.025), and their visual acuity worsened in 31% and 0%, respectively, and remained stable in 62% and 98%, respectively; in the eyes with progression, central (in 31%) and peripheral (in 77%) visual fields worsened compared with only 1 eye and 2 eyes, respectively, that did not (P = 0.01 and P<0.0001, respectively); and median time to resolution of ODE in the progressed group was 5.8 weeks (IQR, 4.6-8.7) versus 9.6 weeks (IQR, 6.0-17.7) in those who did not progress.

CONCLUSIONS

The results show that incipient NAION is a distinct clinical entity, with asymptomatic ODE and no visual loss attributable to NAION. When a patient seeks treatment with asymptomatic ODE, incipient NAION must be borne in mind as a strong possibility in those who have had classic NAION in the fellow eye, in diabetics of all ages, and in those with high risk factors for NAION; this can avoid unnecessary and expensive investigations.

The optic nerve: radiologic, clinical, and pathologic evaluation

The radiologic investigation of the optic nerve plays an integral part in the diagnostic evaluation of diverse lesions of the optic pathways including inflammatory diseases, vascular disorders and benign and malignant tumors and these radiologic modalities consist principally of CT and MR imaging and, in vascular lesions, MR angiography and conventional angiography. The selection of radiologic studies and their focus is based on the ophthalmologic examination where the ophthalmologist can often determine the suspected location of lesions in the anterior or posterior visual pathways. Furthermore, inspection of the eye, including adnexal structures and funduscopy, provides additional information in the clinical assessment of these patients. With technical advances in the last few years, CT and MR imaging can detect lesions and determine their location and extent with high sensitivity and specificity. This article discusses the radiologic, clinical, and pathologic evaluation of the optic nerve.

NONAXOPLASMIC TRANSFER OF INDOCYANINE GREEN INTO THE OPTIC NERVE AFTER INTRAVITREAL APPLICATION

PURPOSE

To investigate whether indocyanine green (ICG) migrates into the optic nerve after intravitreal application in the rabbit eye.

METHODS

Gas vitrectomy was performed in one eye of adult Dutch belted rabbits by pars plana injection of 0.4 ml of 100% C3F8 (n = 10). One week later, vitrectomy was performed and 0.2 ml of 0.25% ICG was instilled into the vitreous cavity of these vitrectomized eyes. After 30 seconds of ICG application, the vitreous cavity was rinsed with balanced salt solution plus. Unoperated rabbits served as controls (n = 2). Globes, optic nerves, and the entire brain were removed, and ICG fluorescence of the specimens was examined with a digital fundus camera starting from the first day to the fourth postoperative week. Other rabbit eyes (n = 2) were injected with ICG directly into the vitreous without vitrectomy, and assessed for ICG signal after 1 day of ICG application. In the second part of the experiment, four rabbit eyes were gas vitrectomized and ICG was instilled onto retina after blockage of axonal flow by vinblastine. They were evaluated on the first (n = 2) and seventh postoperative days (n = 2).

RESULTS

No fluorescein was detected in the visual pathways and the brains of the control group of rabbits. The optic nerves of the ICG-instilled eyes were stained diffusely with ICG starting from the first day after surgery. ICG injected nonvitrectomized eyes showed similar ICG staining patterns when compared with vitrectomized eyes. ICG staining pattern of the optic nerve did not differ in vinblastine-pretreated eyes. Fluorescence extended along the intraorbital portion of the optic nerve but did not transport more posteriorly in all animals. At the fourth week after vitrectomy, ICG signal was still detectable, but staining was less intense.

CONCLUSION

Intravitreal ICG injection results in nonaxoplasmic extension into the optic nerve in the rabbit.

Fundus manifestations of orbital disease and treatment of orbital disease

Disorders of the orbit can secondarily involve the eye. Although nonspecific, changes which can be noted on funduscopic examination including abnormalities of the retina, choroid, and optic nerve, can be secondary to an underlying orbital process. Awareness of these findings and their association with orbital disease is of great importance to the practicing ophthalmologist, since many orbital disorders are treatable and indeed, some are life-threatening. In addition, treatment of these disorders can potentially result in a variety of ocular complications. An understanding of the potential risks is of the utmost importance in planning treatment of an orbital disease.

Optic nerve sheath meningiomas

Meningiomas are benign neoplastic lesions arising from meningothelial cells of the meninges. Primary orbital meningiomas, originating in the optic nerve sheath, represent 1-2% of all meningiomas, and are the second most common optic nerve tumor after gliomas. They primarily affect middle-aged adults. Patients typically present with visual loss, frequently associated with optic atrophy and often with optociliary shunt vessels. The lesion is usually unilateral, but is bilateral in about 5% of cases. Meningiomas show characteristic indolent growth over years, progressing inexorably to blindness in the affected eye. Management should be conservative in most cases. In very rare situations, surgery has improved visual prognosis. In most patients, however, surgery offers no benefit, and should be reserved for those with blindness or severe proptosis, or when extension toward the optic canal is documented. Although preliminary results of radiotherapy are encouraging, very few patients have been treated using this modality, and the long-term advantage for vision remains unproven. Even when untreated, the prognosis for life is excellent, with an overall tumor-related mortality of 0%.

Enlargement of the blind spot caused by papilledema

Blind spot enlargement in papilledema has been attributed to either mechanical disruption of the integrity of the peripapillary percipient elements by the swollen optic disk or to the Stiles-Crawford effect. We investigated the possibility that blind spot enlargement in papilledema is caused, at least in part, by a refractive scotoma due to peripapillary hyperopia. We reduced the enlarged blind spot in a patient with focal peripapillary hyperopia, without papilledema, to near normal size by using progressively stronger plus lenses. Similarly, with the addition of plus sphere, we reduced the size of the blind spot in five of six patients with papilledema, but in none of our normal subjects.

Anterior ischemic optic neuropathy. VIII. Clinical features and pathogenesis of post-hemorrhagic amaurosis

Visual disturbance after marked and/or recurrent blood loss has been known for at least 25 centuries, since Hippocrates; however, so far its clinical features have been controversial and its pathogenesis enigmatic. The author studied seven patients, four of whom were seen soon after the visual loss and followed prospectively. A detailed review of the extensive literature and analysis of the cases provide relevant information on the subject. The blood loss is usually from the gastrointestinal (GI) tract, less often from other sites. There is typically a time lag between the bleeding and the onset of visual loss--usually up to 10 days, less often even 2 to 3 weeks. The ocular findings are typically those of anterior ischemic optic neuropathy (AION) and are usually bilateral. Considerable evidence has accumulated that blood loss, with or without arterial hypotension, causes increase in release of renin and endogenous vasoconstrictor agents (e.g., angiotensin, epinephrine, and vasopressin) because of activation of the sympathoadrenergic system and vasomotor center. Our experimental studies on renovascular malignant hypertension indicate that endogenous vasoconstrictor agents produce choroidal ischemia and AION. In view of all the evidence, it is postulated that in the production of AION after blood loss, release of endogenous vasoconstrictor agents is probably a very important factor, with arterial hypotension an additional factor; increased platelet aggregation may also play a role.

Fundus lesions in malignant hypertension. V. Hypertensive optic neuropathy

We produced experimental renovascular arterial hypertension in 57 rhesus monkeys by modified Goldblatt's procedures. Hypertensive fundus changes were studied in detail by serial ophthalmoscopy and fluorescein fundus angiography in all animals on a long-term follow-up, and pathologically in 23 eyes. Initial evidence of hypertensive optic neuropathy was optic disc edema which developed at the median blood pressure (BP) of 190 mmHg (normal BP, 120 mmHg). On follow-up, mild to marked pallor of the optic disc developed. The optic disc changes were correlated with BP and other fundus changes. Pathogenesis of hypertensive optic neuropathy, which has been highly controversial so far, is discussed at length in the light of the findings of the present study and other recent evidence. All the available clinical and pathologic findings in the present study indicate that hypertensive optic neuropathy represents a form of anterior ischemic optic neuropathy, and that hypertensive optic neuropathy is a distinct entity. A caution is given against a precipitous reduction of BP in patients with hypertensive optic neuropathy because that may cause complete, permanent blindness.

How might demyelinating disorders and glaucoma modify synaptic function?

Latencies of visually evoked potentials (VEPs) tend to be abnormally long in multiple sclerosis (MS). Similar VEP delays are seen in glaucoma. Such delays could result in part from reduced intensities of synaptic inputs at post-retinal synaptic relays, and defects of axoplasmic transport might be one cause for this. The effective rate of synaptic activation of a given postsynaptic neuron can be decreased either by reducing the arrival-rate of presynaptic action potentials (e.g., by complete or partial blockage of conduction in some presynaptic axons), or by reducing the quantity of neurotransmitter released per action potential (e.g., as a consequence of presynaptic neurotransmitter depletion). It is proposed that in both glaucoma and MS, delayed VEPs may result from either or both of these mechanisms. Firstly, loss and functional impairment of optic nerve axons occurs in each disorder. Secondly, in glaucoma the increased intraocular pressure tends to block the rapid anterograde axoplasmic transport (RAAT) which brings neurotransmitter supplies to the axon terminals. This could result in neurotransmitter depletion in the lateral geniculate relay, decreased synaptic effectiveness of remaining normally-conducting optic nerve axons, and thereby increased VEP latencies. RAAT is also blocked by demyelinated lesions that have been produced experimentally by injection of diphtheria toxin. If it is impaired by the demyelinated plaques of multiple sclerosis, then VEP slowing by a similar presynaptic depletion mechanism could ensue.

Transient visual obscurations with elevated optic discs

The pathogenesis of the transient obscurations of vision that occur with papilledema is a subject of speculation and debate. We present four examples of transient obscurations of vision that were clinically indistinguishable from those of papilledema; they occurred in patients with elevated optic discs from causes not related to increased intracranial pressure. The underlying mechanism for visual obscurations in all of these patients appear to be transient ischemia of the optic nerve head consequent to increased tissue pressure. Axonal swelling, intraneural masses, and increased influx of interstitial fluid may all contribute to increases in tissue pressure in the optic nerve head. The consequent reduction in perfusion pressure renders the small, low-pressure vessels that supply the optic nerve head vulnerable to compromise. Brief fluctuations in intracranial or systemic blood pressure may then result in transient loss of function in the eyes. We postulate that such mechanisms may apply in all cases of optic disc elevation, including papilledema.

Swelling of the optic nerve head: a staging scheme

A staging scheme based on ophthalmoscopic signs of disturbed axoplasmic transport is described. A study employing fundus photographs showed good reproducibility among different observers. Specificity ranged between 88% and 96%, and sensitivity between 93% and 100%.

Meningiomas of the anterior visual system

Meningiomas, whether primary in the orbit, optic canal or intracranial area, typically cause slowly progressive loss of vision covering months to years. They usually occur in white women of middle age. Tumors in the orbit or optic canal almost always affect vision unilaterally; intracranial tumors, while usually causing unilateral visual loss initially, eventually cause bilateral loss of vision, often with blindness in one eye. Depending upon the size and location of the tumor, the ocular signs and symptoms of meningiomas may include visual field abnormalities, optic atrophy, edema of the ipsilateral optic disc, papilledema, diplopia, and proptosis. The diagnosis of meningiomas in all locations has been greatly facilitated by recent advances in computer assisted tomography. However, tumors confined to the optic canal or its foramina are small when vision is first lost and therefore are still difficult to detect. Hypocycloidal polytomography may be useful; other neuroradiologic studies rarely are. Treatment is surgical. Based on a review of more than 3000 meningiomas reported in the literature, the frequency and characteristics of the signs and symptoms of meningiomas in each location are discussed, as are the anatomy, pathology, natural history, and probable mechanisms.