The Effects of Acute Intracranial Pressure Changes on the Episcleral Venous Pressure, Retinal Vein Diameter and Intraocular Pressure in a Pig Model

Intracranial pressure affects retinal venular complexity in idiopathic intracranial hypertension: a retrospective observational study

BACKGROUND

Increased intracranial pressure (ICP) in patients with idiopathic intracranial hypertension (IIH) affects the retinal microvasculature, which can be imaged and quantified by optical coherence tomography angiography (OCTA). We aimed to identify the mediating factor between ICP and OCTA parameters association in IIH patients.

METHODS

IIH patients with active intracranial hypertension were enrolled. OCTA imaging was performed after ICP measurement. We quantified the branching complexity of the retinal arterioles and venules from the superficial vascular complex of the OCTA image. Eyes of IIH patients were stratified into eyes with papilledema (IIH-P) and eyes without papilledema (IIH-WP). All participants underwent visual acuity (VA) examination.

RESULTS

One hundred and thirty-eight eyes from 70 IIH patients and 146 eyes from 73 controls were included. Compared to the control group, IIH patients and IIH-P had reduced arteriole complexity and increased venule complexity (p < 0.05). For IIH patients and IIH-P, increased retinal venule complexity correlated with increased ICP and reduced VA (p < 0.05); while decreased arteriole complexity only correlated with Frisen scores (p = 0.026). Papilledema mediated the effect (p < 0.001) between ICP and arteriole complexity while ICP had a direct effect (p < 0.001) on venule complexity.

CONCLUSION

Retinal venules imaged via OCTA may reflect ICP levels and may underpin the direct effect of increased ICP in IIH patients.

Decompression of Axillary Vein: An Essential Adjunct for Advanced Lymphedema

BACKGROUND

In advanced lymphedema, lymphovenous anastomosis (LVA) can be a solution based on using the pressure gradient between the high-pressure lymphatics and the low-pressure veins. If the vein pressure is high, the effect of surgery will be less optimal. This study evaluated the effect of axillary vein perivascular scar release on LVA.

METHODS

This is a retrospective study of 40 upper limb stage 2 and 3 lymphedema patients divided into 2 groups with an average follow-up of 33 months (minimum of at least 12 months): the scar release group ( n = 25) and the control group ( n = 15). All patients underwent LVA with or without lymph node transfer. Demographic data, outcome (volumetric change and bioimpedence analysis [BIA]), and major vein (axillary, basilic, and cephalic) diameter changes were evaluated.

RESULTS

Both groups showed significant reduction in volume and BIA parameters after LVA. The scar release group (24 of 25 with lymph node transfer and 1 without) showed statistically higher reduction of BIA analysis compared with the control group at 1, 6, and 12 months after LVA. The changes in the major veins after axilla scar release showed significant changes in all 3 veins. There was a significant correlation between cephalic vein diameter reduction and BIA measurement.

CONCLUSIONS

The release of perivascular scar in the axillary vein may result in better outcome after LVA. This is based on the finding that scar release shows correlation between cephalic vein diameter reduction and BIA measurement suggesting reduction of venous pressure in the peripheral vein increasing the pressure gradient between the lymphatic and venous system allowing better outflow after LVA.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, III.

High myopia at high altitudes

Background: Optic nerve sheath diameter (ONSD) increases significantly at high altitudes, and is associated with the presence and severity of acute mountain sickness (AMS). Exposure to hypobaria, hypoxia, and coldness when hiking also impacts intraocular pressure (IOP). To date, little is known about ocular physiological responses in trekkers with myopia at high altitudes. This study aimed to determine changes in the ONSD and IOP between participants with and without high myopia (HM) during hiking and to test whether these changes could predict symptoms of AMS. Methods: Nine participants with HM and 18 without HM participated in a 3-day trek of Xue Mountain. The ONSD, IOP, and questionnaires were examined before and during the trek of Xue Mountain. Results: The ONSD values increased significantly in both HM (p = 0.005) and non-HM trekkers (p = 0.018) at an altitude of 1,700 m. In the HM group, IOP levels were greater than those in the non-HM group (p = 0.034) on the first day of trekking (altitude: 3,150 m). No statistically significant difference was observed between the two groups for the values of ONSD. Fractional changes in ONSD at an altitude of 1,700 m were related to the development of AMS (r pb = 0.448, p = 0.019) and the presence of headache symptoms (r pb = 0.542, p = 0.004). The area under the ROC curve for the diagnostic performance of ONSD fractional changes at an altitude of 1,700 m was 0.859 for predicting the development of AMS and 0.803 for predicting the presence of headache symptoms. Conclusion: Analysis of changes in ONSD at moderate altitude could predict AMS symptoms before an ascent to high altitude. Myopia may impact physiological accommodation at high altitudes, and HM trekkers potentially demonstrate suboptimal regulation of aqueous humor in such environments.

Region-related and layer-specific permeability of the iris vasculature with morphological mechanism: A novel understanding of blood-aqueous barrier

The permeability of iris blood vessels has an important role in maintaining aqueous humor (AH) homeostasis, contributing to variation in iris volume and probably the pathogenesis of angle closure glaucoma. This study investigates the permeability of the iris microvasculature to plasma-derived protein and correspond it with the morphologic characteristics of vascular mural cells (MCs). Twenty-two enucleated porcine eyes were used in this study. 12 eyes were micro-perfused with vehicle alone as control or with FITC-albumin as a marker of protein leakage and histological sections subsequently made to examine for FITC-albumin presence. The other 10 eyes were immunolabeled via micro-perfusion for αSMA and VE-cadherin to investigate their topographic distribution in the porcine iris vasculature, and to cross correspond with the locations of FITC-albumin deposits. Distribution of FITC-signals exhibited a site-dependent pattern and time-dependent change in the iris. Fluorescence was initially detected around capillaries in the superficial and deep layer of the iris microvascular network. The pupillary region and the iris root retained more fluorescent signal than the iridal ciliary region. At low magnification, αSMA labelling displayed a regional variation which was inversely correlated with vascular permeability. At the cellular level, αSMA labeling corresponded with vascular MCs distribution in the iris vascular network. The correspondence between iris microvascular permeability to FITC-albumin and the pattern of αSMA distribution and MCs coverage adds to the understanding of the elements comprising the blood-aqueous barrier with implications for the bio-mechanics of iris volume change.

Retinal vessel dynamics analysis as a surrogate marker for raised intracranial pressure in patients with suspected idiopathic intracranial hypertension

INTRODUCTION

Retinal vessel dynamics analysis has proven to be a viable, non-invasive surrogate marker for increased intracranial pressure. We aimed to test this method in patients with suspected idiopathic intracranial hypertension.

METHODS

Patients with suspected idiopathic intracranial hypertension were prospectively enrolled for hand-held fundus-videography during diagnostic lumbar puncture. After extracting optic disc images, peripapillary arteriole-to-venule-ratios were measured using machine-learning algorithms with manual identification control. A general linear model was applied to arteriole-to-venule-ratios and corresponding lumbar opening pressures to estimate cerebrospinal fluid pressure.

RESULTS

Twenty-five patients were included with a significant difference in arteriole-to-venule-ratio between patients with (n = 17) and without (n = 8) idiopathic intracranial hypertension (0.78 ± 0.10 vs 0.90 ± 0.08, p = 0.006). Arteriole-to-venule-ratio correlated inversely with lumbar opening pressure (slope regression estimate -0.0043 (95% CI -0.0073 to -0.0023), p = 0.002) and the association was stronger when lumbar opening pressure exceeded 15 mm Hg (20 cm H₂O) (slope regression estimate -0.0080 (95% CI -0.0123 to -0.0039), p < 0.001). Estimated cerebrospinal fluid pressure predicted increased lumbar opening pressure >20 mm Hg (27 cm H₂O) with 78% sensitivity and 92% specificity (AUC 0.81, p = 0.02). A stand-alone arteriole-to-venule-ratio measurement predicting lumbar opening pressure >20 mm Hg (27 cm H₂O) was inferior with a 48% sensitivity and 92% specificity (AUC 0.73, p = 0.002).

CONCLUSION

Retinal vessel dynamics analysis with the described model for estimating cerebrospinal fluid pressure is a promising non-invasive method with a high sensitivity and specificity for detecting elevated intracranial pressure at follow-up assessments of patients with confirmed idiopathic intracranial hypertension if initial lumbar opening pressure and arteriole-to-venule-ratio data are available.

Noninvasive methods to monitor intracranial pressure

PURPOSE OF REVIEW

Intracranial pressure (ICP) is determined by the production of and outflow facility of cerebrospinal fluid. Since alterations in ICP are implicated in several vision-threatening and life-threatening diseases, measurement of ICP is necessary and common. All current clinical methods to measure ICP are invasive and carry the risk for significant side effects. Therefore, the development of accurate, reliable, objective, and portal noninvasive devices to measure ICP has the potential to change the practice of medicine. This review discusses recent advances and barriers to the clinical implementation of noninvasive devices to determine ICP.

RECENT FINDINGS

Many noninvasive methods to determine ICP have been developed. Although most have significant limitations limiting their clinical utility, several noninvasive methods have shown strong correlations with invasively obtained ICP and have excellent potential to be developed further to accurately quantify ICP and ICP changes.

SUMMARY

Although invasive methods remain the mainstay for ICP determination and monitoring, several noninvasive biomarkers have shown promise to quantitatively assess and monitor ICP. With further refinement and advancement of these techniques, it is highly possible that noninvasive methods will become more commonplace and may complement or even supplant invasively obtained methods to determine ICP in certain situations.

Retinal Vein Changes as a Biomarker to Guide Diagnosis and Management of Elevated Intracranial Pressure

Retinal vein changes, which can be observed on clinical exam or ophthalmic imaging, are promising non-invasive biomarkers for elevated intracranial pressure (ICP) as a complement to other markers of high ICP including optic nerve head swelling. Animal and human studies have demonstrated increase in retinal vein pressure associated with elevated ICP mediated by increase in cerebral venous pressure, compression of venous outflow by elevated cerebral spinal fluid pressure in the optic nerve sheath, and compression of venous outflow by optic nerve head swelling. Retinal vein pressure can be estimated using ophthalmodynamometry. Correlates of retinal vein pressure include spontaneous retinal venous pulsations, retinal vein diameter, and retinal vein tortuosity. All of these have potential for clinical use to diagnose and monitor elevated ICP. Challenges include diagnostic prediction based on single clinical measurements and accurate assessment of retinal vein parameters in cases where optic nerve head swelling limits visualization of the retinal veins.