The relationship of intraocular pressure to intracranial pressure

Mechanical Thrombectomy for Cerebral Venous Sinus Occlusion Due to Ewing Sarcoma: A Case Report

Objective

To assess the efficacy of mechanical thrombectomy (MT) for cerebral venous sinus thrombosis associated with Ewing sarcoma invasion into the venous sinus.

Case Presentation

A 48-year-old woman presented to our hospital with left hemifacial paralysis. The patient had undergone surgical treatment for left subclavian Ewing sarcoma 24 years ago. Furthermore, the patient had undergone tumor resection for very late metastasis in the left occipital bone and mastoid air cells 3 years prior to her admission. As the Ewing sarcoma had extended to the left transverse sinus, the sinus was resected during craniotomy. The tumor remained in the mastoid air cells, and radiotherapy was administered. On admission to our hospital, FLAIR revealed hyper-intensities in the straight sinus and the superior sagittal sinus. Magnetic resonance venography revealed no signal in the posterior part of the superior sagittal sinus and the bilateral transverse sinuses. The patient was diagnosed with cerebral venous sinus thrombosis, and anticoagulation therapy was administered. However, the swelling and pain on the left side of the face worsened, and intraocular pressure (IOP) increased. Therefore, an MT was performed. After endovascular treatment, the patient's facial swelling and pain were reduced, and IOP returned to normal. Pathological examination of the captured thrombus revealed tumor cells, suggesting venous sinus invasion of Ewing sarcoma.

Conclusion

Although it was a palliative treatment, MT was effective in confirming the diagnosis of tumor invasion into the venous sinus and improving the patient's quality of life.

Influence of intraocular and blood pressure on brain volumes: Observational and Mendelian randomization analyses

Intraocular pressure (IOP) is closely correlated with blood pressure (BP), and while BP has been linked to brain volumes, the effect of IOP on brain volumes remains unclear. This study analyzed participants from the UK Biobank with MRI-measured brain volumes. Observational analyses included 8,634 participants for IOP and 36,069 for BP, followed by Mendelian randomization (MR) analyses of 37,410 participants. Observational analyses revealed that each 10-mmHg increase in diastolic BP was linked to a 0.13 mL larger white matter hyperintensity (WMH) after adjusting for covariates. Associations between IOP and brain volumes were more pronounced in younger individuals or those without hypertension. MR analyses confirmed significant relationships between diastolic BP and WMH, and each 5-mmHg increase in IOP reduced gray matter volumes by 3.24 mL. The study suggests that targeting IOP and BP could help prevent brain volume reduction.

Prediction model of contact forces and IOP during digital palpation of porcine eyes

Frequent intraocular pressure (IOP) measurements are desirable in the diagnosis and management of glaucoma. Most current tonometers utilize some form of corneal deformation to estimate the IOP, since trans-scleral tonometry suffers from loss of sensitivity. Tran-scleral and trans-palpebral tonometry, however, offer a pathway towards a non-invasive home tonometry. This article presents a mathematical model capturing the relationship between the IOP and the displacements imposed onto the sclera by externally applied forces. Similar to manual digital palpation tonometry, trans-scleral mechanical palpation makes use of two force probes that are advanced in a specific order and distance. Data from the applied forces and displacements, along with concurrent measurements of IOP is used to produce a phenomenological mathematical model. The experiments were carried out on enucleated porcine eyes. Two models are presented. Model 1 predicts IOP vs forces and displacements, while Model 2 predicts the baseline IOP (prior to applying the forces) as a function of the measured forces and displacements. The proposed models result in IOP errors of 1.65 mmHG and 0.82 mmHg, respectively. Model parameters were extracted using least-squares-based system identification methods. The results show that the proposed models can be used to estimate the baseline IOP with accuracy of ±1 mmHg over a pressure range of 10-35 mmHg, solely from measurement of tactile forces and displacements.

Lateralized Raise in Intraocular Pressure During Electroconvulsive Therapy: A Tonometry Pilot Study

Right unilateral ECT causes an increase in eye pressure that is partially lateralized, higher on the right side.

Objective

The aim of this study was to evaluate intraocular pressure (IOP) changes during and after electroconvulsive therapy.

Methods

In 20 patients, IOP was measured using a handheld iCare tonometer before, during, and up to 15 minutes after the seizure. Electrode placement was either right unilateral (RUL) or bilateral (BL). Statistical analyses were done at baseline, during, and 15 minutes after the seizure.

Results

In the RUL group (n = 14), the IOP in the left eye increased from 14.8 mm Hg before the seizure to 27.8 mm Hg during the seizure (P = 0.0001) and decreased to 14.0 mm Hg after the seizure (P = 0.0002). The IOP in the right eye increased from 15.4 mm Hg before the seizure to 34.4 mm Hg during the seizure (P = 0.0001) and decreased to 16.0 mm Hg after the seizure (P = 0.0002).

In the BL group (n = 6), the IOP in the left eye increased from 13.0 mm Hg before the seizure to 26.3 mm Hg during the seizure (P = 0.1250) and decreased to 14.5 mm Hg after the seizure (P = 0.250). In the right eye, the IOP increased from 13.3 mm Hg before the seizure to 28.4 mm Hg during the seizure (P = 0.1250) and decreased to 13.7 mm Hg after the seizure (P = 0.25).

When the results were compared between the 2 electrode placements, the difference in IOP between the right and left eye was higher in the RUL group during (RUL 6.7 mm Hg vs BL 2.0 mm Hg, P = 0.0231) and after (RUL 2.1 mm Hg vs BL −0.8 mm Hg, P = 0.0492) the seizure.

Conclusions

RUL stimulation with electroconvulsive therapy causes a rise in IOP that is partially lateralized, ipsilateral to the side of stimulation.

Prevalence, Characteristics, and Risk Factors of Retinal Hemorrhage among Full-Term Neonates in Southern China

Neonatal retinal hemorrhage (RH) is the most common ocular fundus disease among newborns. Early detection and timely intervention are vital for reducing the risk of visual impairment caused by RH. However, little is known about the prevalence, characteristics, and risk factors of RH in southern China. Full-term infants born in Qingyuan City during the first 10 days of each month in 2021 were included in this study. All infants underwent RetCam III retinal examinations. Detailed information on retinal hemorrhage, including involved eyes, bleeding severity, and affected area (extrafoveal macula, fovea, or optic disc), and clinical information on the neonates and their mothers was collected. The results showed that among the 1072 eligible neonates, 266 (24.8%) had neonatal retinal hemorrhage. Consistent bilateral retinal hemorrhage severity was observed in 83.2% of the cases. The prevalence of optic disc involved RH, extrafoveal macular involved RH and foveal involved RH were 23.7%, 81.2% and 2.63%, respectively. Multivariate logistic regression analysis showed that lower birth weight (OR, 0.63; 95% CI, 0.40-0.99; p < 0.05) and vaginal delivery (OR, 20.6; 95% CI, 9.10-46.5; p < 0.001) were risk factors of neonatal RH. The area under the ROC curve of vaginal delivery, combined with birth weight, as predictors of neonatal RH was 0.73, with 85.3% sensitivity and 23.9% specificity. The birth weight cutoff was 3460 g. Our results suggested that neonatal RH is common in full-term neonates in southern China. It usually has the same severity in both eyes and mostly involves the extrafoveal macular region. Vaginal delivery and low birth weight are risk factors for neonatal RH.

A Review of the Methods of Non-Invasive Assessment of Intracranial Pressure through Ocular Measurement

The monitoring of intracranial pressure (ICP) is essential for the detection and treatment of most craniocerebral diseases. Invasive methods are the most accurate approach to measure ICP; however, these methods are prone to complications and have a limited range of applications. Therefore, non-invasive ICP measurement is preferable in a range of scenarios. The current non-invasive ICP measurement methods comprise fluid dynamics, and ophthalmic, otic, electrophysiological, and other methods. This article reviews eight methods of non-invasive estimation of ICP from ocular measurements, namely optic nerve sheath diameter, flash visual evoked potentials, two-depth transorbital Doppler ultrasonography, central retinal venous pressure, optical coherence tomography, pupillometry, intraocular pressure measurement, and retinal arteriole and venule diameter ratio. We evaluated and presented the indications and main advantages and disadvantages of these methods. Although these methods cannot completely replace invasive measurement, for some specific situations and patients, non-invasive measurement of ICP still has great potential.

Non-Invasive Intracranial Pressure Monitoring and Its Applicability in Spaceflight

INTRODUCTION: Neuro-ophthalmic findings collectively defined as Spaceflight-Associated Neuro-ocular Syndrome (SANS) are one of the leading health priorities in astronauts engaging in long duration spaceflight or prolonged microgravity exposure. Though multifactorial in etiology, similarities to terrestrial idiopathic intracranial hypertension (IIH) suggest these changes may result from an increase or impairing in intracranial pressure (ICP). Finding a portable, accessible, and reliable method of monitoring ICP is, therefore, crucial in long duration spaceflight. A review of recent literature was conducted on the biomedical literature search engine PubMed using the search term “non-invasive intracranial pressure”. Studies investigating accuracy of noninvasive and portable methods were assessed. The search retrieved different methods that were subsequently grouped by approach and technique. The majority of publications included the use of ultrasound-based methods with variable accuracies. One of which, noninvasive ICP estimation by optical nerve sheath diameter measurement (nICP_ONSD), presented the highest statistical correlation and prediction values to invasive ICP, with area under the curve (AUC) ranging from 0.75 to 0.964. One study even considers a combination of ONSD with transcranial Doppler (TCD) for an even higher performance. Other methods, such as near-infrared spectroscopy (NIRS), show positive and promising results [good statistical correlation with invasive techniques when measuring cerebral perfusion pressure (CPP): r = 0.83]. However, for its accessibility, portability, and accuracy, ONSD seems to present itself as the up to date, most reliable, noninvasive ICP surrogate and a valuable spaceflight asset.Félix H, Santos Oliveira E. Non-invasive intracranial pressure monitoring and its applicability in spaceflight. Aerosp Med Hum Perform. 2022; 93(6):517–531.

The Utility of Universal Newborn Eye Screening: A Review

Universal newborn eye screening can identify ocular abnormalities early and help mitigate long-term visual impairment. Traditional neonatal and infant eye screening is administered by neonatologists and pediatricians using the red reflex test. If this test identifies an ocular abnormality, then the patient is examined by an ophthalmologist. Notably, the red reflex test may be unable to detect amblyogenic posterior segment pathology. Recent studies using fundus imaging and telemedicine show reduced cost of human resources and increased sensitivity compared with traditional approaches. In this review, the authors discuss universal newborn eye screening pilot programs with regard to disease prevalence, referral-warranted disease, and cost-effectiveness. [Ophthalmic Surg Lasers Imaging Retina. 2021;52:S6-S16.].

Effects of Acute Intracranial Pressure Changes on Optic Nerve Head Morphology in Humans and Pig Model

PURPOSE

The lamina cribrosa (LC) is a layer of fenestrated connective tissue tethered to the posterior sclera across the scleral canal in the optic nerve head (ONH). It is located at the interface of intracranial and intraocular compartments and is exposed to intraocular pressure (IOP) anteriorly and intracranial pressure (ICP) or Cerebrospinal fluid (CSF) pressure (CSFP) posteriorly. We hypothesize that the pressure difference across LC will determine LC position and meridional diameter of scleral canal (also called Bruch's membrane opening diameter; BMOD).

METHODS

We enrolled 19 human subjects undergoing a medically necessary lumbar puncture (LP) to lower CSFP and 6 anesthetized pigs, whose ICP was increased in 5 mm Hg increments using a lumbar catheter. We imaged ONH using optical coherence tomography and measured IOP and CSFP/ICP at baseline and after each intervention. Radial tomographic ONH scans were analyzed by two independent graders using ImageJ, an open-source software. The following ONH morphological parameters were obtained: BMOD, anterior LC depth and retinal thickness. We modeled effects of acute CSFP/ICP changes on ONH morphological parameters using ANOVA (human study) and generalized linear model (pig study).

RESULTS

For 19 human subjects, CSFP ranged from 5 to 42 mm Hg before LP and 2 to 19.4 mm Hg after LP. For the six pigs, baseline ICP ranged from 1.5 to 9 mm Hg and maximum stable ICP ranged from 18 to 40 mm Hg. Our models showed that acute CSFP/ICP changes had no significant effect on ONH morphological parameters in both humans and pigs.

CONCLUSION

We conclude that ONH does not show measurable morphological changes in response to acute changes of CSFP/ICP. Proposed mechanisms include compensatory and opposing changes in IOP and CSFP/ICP and nonlinear or nonmonotonic effects of IOP and CSFP/ICP across LC.

Noninvasive intracranial pressure real-time waveform analysis monitor during prostatectomy robotic surgery and Trendelenburg position: case report

Both robotic surgery and head-down tilt increase intracranial pressure by impairing venous blood outflow. Prostatectomy is commonly performed in elderly patients, who are more likely to develop postoperative cognitive disorders. Therefore, increased intracranial pressure could play an essential role in cognitive decline after surgery. We describe a case of a 69-year-old male who underwent a robotic prostatectomy. Noninvasive Brain4care^TM intraoperative monitoring showed normal intracranial compliance during anesthesia induction, but it rapidly decreased after head-down tilt despite normal vital signs, low lung pressure, and adequate anesthesia depth. We conclude that there is a need for intraoperative intracranial compliance monitoring since there are major changes in cerebral compliance during surgery, which could potentially allow early identification and treatment of impaired cerebral complacency.

Case report: Vitreous hemorrhage as the presenting sign of retinal cavernous hemangioma in a newborn

Purpose

To report a case of vitreous hemorrhage as the presenting sign of retinal cavernous hemangioma (RCH) in a newborn.

Observations

A five-week-old full-term male with a history of seizures and birth trauma underwent ophthalmology screening. Initial eye examination revealed vitreous hemorrhage. Subsequent examination under anesthesia with multi-modal imaging revealed vitreous hemorrhage and an intra-retinal mass with numerous sac-like aneurysmal dilatations, consistent with RCH.

Conclusions and importance

Vitreous hemorrhage in a neonate is an atypical presentation of RCH. Clinicians should be aware that birth trauma may lead to vitreous hemorrhage from RCH. This is the first description of RCH, a rare retinal vascular tumor, in a newborn.

Retinopathy of prematurity screening and retinal hemorrhages - Our experience among Indian babies

Purpose

To evaluate the clinical characteristics of intraocular hemorrhages among babies screened for retinopathy of prematurity (ROP) and thereby their additional risk to the progression of ROP.

Methods

A descriptive study was conducted at a tertiary referral hospital, which included 108 eyes of 60 neonates who were discovered to have retinal hemorrhages on retinal screening of 540 babies at risk for ROP. Maternal, obstetric, and neonatal risk factors were assessed in neonates with retinal hemorrhages. Retinal hemorrhages were assessed in terms of type, area, and relation to different retinal zones.

Results

Among 540 neonates who were screened, retinal hemorrhages were found in 11.2% (n = 60 babies). Elderly primigravida mothers and spontaneous vaginal deliveries with prolonged second stage of labor were a common maternal risk factors for retinal hemorrhages. Low birth weight and preterm were fetal risk factors with neonatal retinal hemorrhages. These hemorrhages were more often bilateral (no. of babies = 48, 80%). Flame-shaped hemorrhages were more common than dot and blot ones. The majority of cases (no. of eyes = 74, 65%) resolved within 4 weeks, whereas four babies (8 eyes, 7.4%) progressed to ROP were treated with laser.

Conclusion

Retinal hemorrhages in neonates are commonly associated with prolonged duration of second stage of labor, advanced maternal age, and anemia. Although not all progress to ROP, recognizing preterm and low birth weight babies with junctional hemorrhages is crucial not to delay the treatment. Regular follow-up until the clearance of hemorrhages and monitoring systemic conditions in these babies of amblyogenic age-group are required.

Gravitational effects on intracranial pressure and blood flow regulation in young men: a potential shunting role for the external carotid artery

We sought to determine whether gravity-induced changes in intracranial pressure influence cerebral blood flow regulation. Accordingly, nine young healthy men were studied while supine (0°) and during mild changes in hydrostatic pressure induced by head-up tilt at +20° and +10° (HUT+20 and HUT+10) and head-down tilt at -20° and -10° (HDT-20, HDT-10). Blood flows were measured in the internal and external carotid and vertebral arteries (ICA, ECA, and VA). Intraocular pressure (IOP) was measured as an indicator of hydrostatic changes in intracranial pressure. A posture change from HUT+20 to HDT-20 increased IOP by +5.1 ± 1.9 mmHg (P < 0.001) and ECA blood flow (from 61.7 ± 26.1 to 87.6 ± 46.4 mL/min, P = 0.004) but did not affect ICA (P = 0.528) or VA (P = 0.101) blood flow. The increase in ECA flow correlated with the tilt angle and resultant changes in intracranial pressures (by IOP), thus indicating a passive hydrostatic gravitational dependence (r = 0.371, P = 0.012). On the contrary, ICA flow remained constant and thus well protected against moderate orthostatic stress. When ICA flow was corrected for the gravitational changes in intracranial pressures (by IOP), it demonstrated the same magnitude of gravitational dependence as ECA. These findings suggest that passive hydrostatic increases in intracranial pressure outbalance the concurrent increase in arterial feeding pressure to the brain and thus prevent cerebral hyperperfusion during HDT. The mechanism for maintaining constant cerebral flow was by increased ECA flow, thus supporting the role of these vascular beds as a shunting pathway.NEW & NOTEWORTHY We investigated whether gravity-induced changes in intracranial pressure influence cerebral blood flow regulation in young men. We recorded extra- and intracerebral blood flow during changes in posture, and data indicate that the external carotid artery may serve as an overflow pathway to prevent cerebral hyperperfusion during increases in cerebral arterial blood pressure.

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

PURPOSE

Orbital veins such as the retinal veins and episcleral veins drain into the cavernous sinus, an intracranial venous structure. We studied the effects of acute intracranial pressure (ICP) elevation on episcleral venous pressure, intraocular pressure and retinal vein diameter in an established non-survival pig model.

METHODS

In six adult female domestic pigs, we increased ICP in 5 mm Hg increments using saline infusion through a lumbar drain. We measured ICP (using parenchymal pressure monitor), intraocular pressure (using pneumatonometer), episcleral venous pressure (using venomanometer), retinal vein diameter (using OCT images) and arterial blood pressure at each stable ICP increment. The average baseline ICP was 5.4 mm Hg (range 1.5-9 mm Hg) and the maximum stable ICP ranged from 18 to 40 mm Hg. Linear mixed models with random intercepts were used to evaluate the effect of acute ICP increase on outcome variables.

RESULTS

With acute ICP elevation, we found loss of retinal venous pulsation and increased episcleral venous pressure, intraocular pressure and retinal vein pressure in all animals. Specifically, acute ICP increase was significantly associated with episcleral venous pressure (β = 0.31; 95% CI 0.14-0.48, p < .001), intraocular pressure (β = 0.37, 95%CI 0.24-0.50; p < .001) and retinal vein diameter (β = 11.29, 95%CI 1.57-21.00; p = .03) after controlling for the effects of arterial blood pressure.

CONCLUSION

We believe that the ophthalmic effects of acute ICP elevation are mediated by increased intracranial venous pressure producing upstream pressure changes within the orbital and retinal veins. These results offer exciting possibilities for the development of non-invasive ophthalmic biomarkers to estimate acute ICP elevations following significant neuro-trauma.

A new novel method for assessing intracranial pressure using non-invasive fundus images: a pilot study

Arteriole and venule diameter ratio (A/V-ratio) can be measured using fundus photography. In this pilot study, we correlated changes in the intracranial pressure with the diameter of vessels of the retina. We investigated whether increased intracranial pressure (ICP) was reflected in a measurable and quantifiable distention of the venule diameter, leading to a decreased A/V-ratio. This was demonstrated by assessment of the A/V-ratio in patients already undergoing conventional ICP monitoring with a cerebral intraparenchymal pressure monitor. Our method shows a correlation between A/V ratio and ICP and suggests an easily obtainable and usable point-of-care (POC), non-invasive method to estimate the intracranial pressure without the necessity of mydriatic drugs. Furthermore, the sensitivity/specificity analysis with a cut-off of < 0.8015 A/V-ratio, showed a sensitivity of 94% [85-98%] and a specificity of 50% [34-66%] with a positive likelihood ratio of 9.0. This means that in a clinical setting there is a 94% chance of correctly identifying individuals with ICP ≥ 20 mmHg.

Hypercapnia augments resistive exercise-induced elevations in intraocular pressure in older individuals

NEW FINDINGS

What is the central question of this study? Astronauts on-board the International Space Station (ISS) perform daily exercises designed to prevent muscle atrophy and bone demineralization: what is the effect of resistive exercise performed by subjects while exposed to the same level of hypercapnia as on the ISS on intraocular pressure (IOP)? What is the main finding and its importance? The static exercise-induced elevation in IOP during 6° prone head-down tilt (simulating the headward shift of body fluids in microgravity) is augmented by hypercapnia and exceeds the ocular hypertension threshold.

ABSTRACT

The present study assessed the effect of 6° head-down (establishing the cephalad fluid displacement noted in astronauts in microgravity) prone (simulating the effect on the eye) tilt during rest and exercise (simulating exercise performed by astronauts to mitigate the sarcopenia induced by unloading of weight-bearing limbs), in normocapnic and hypercapnic conditions (the latter simulating conditions on the International Space Station) on intraocular pressure (IOP). Volunteers (mean age = 57.8 ± 6 years, n = 10) participated in two experimental sessions, each comprising: (i) 10 min rest, (ii) 3 min static handgrip exercise (30% max), and (iii) 2 min recovery, inspiring either room air (NCAP) or a hypercapnic mixture (1% CO₂ , HCAP). We measured IOP in the right eye, cardiac output (CO), stroke volume (SV), heart rate (HR) and mean arterial pressure (MAP) at regular intervals. Baseline IOP in the upright seated position while breathing room air was 14.1 ± 2.9 mmHg. Prone 6° head-down tilt significantly (P < 0.01) elevated IOP in all three phases of the NCAP (rest: 27.0 ± 3.7 mmHg; exercise: 32.2 ± 4.8 mmHg; recovery: 27.4 ± 4.0 mmHg) and HCAP (rest: 27.3 ± 4.3 mmHg; exercise: 34.2 ± 6.0 mmHg; recovery: 29.1 ± 5.8 mmHg) trials, with hypercapnia augmenting the exercise-induced elevation in IOP (P < 0.01). CO, SV, HR and MAP were significantly increased during handgrip dynamometry, but there was no effect of hypercapnia. The observed IOP measured during prone 6° HDT in all phases of the NCAP and HCAP trials exceeded the threshold pressure defining ocular hypertension. The exercise-induced increase in IOP is exacerbated by hypercapnia.

Intracranial pressure modulates aqueous humour dynamics of the eye

KEY POINTS

An elevation in intracranial pressure (ICP) lowers conventional outflow facility (increases aqueous outflow resistance) of rat eyes. The reduction in outflow facility correlates with an increase in intraocular pressure (IOP). The effect of ICP elevation on outflow facility and IOP is blocked by TTX. The results indicate that aqueous humour dynamics is modulated by ICP-driven neural feedback from the brain. This feedback mechanism may act to stabilize translaminar pressure across the optic nerve head and may provide a new avenue for glaucoma therapy.

ABSTRACT

While intraocular pressure (IOP) is a well-known risk factor for glaucoma, intracranial pressure (ICP) is attracting heightened interest because of its influence on optic nerve head biomechanics. Studies have shown that ICP can have marked impacts on posterior eye health by modifying the translaminar pressure gradient across the optic nerve. There is also growing evidence that IOP and ICP may be interconnected, although the mechanism of their putative interaction is unknown. We sought to test the hypothesis that ICP modulates IOP by altering aqueous humour dynamics. The anterior chamber and lateral ventricle of anaesthetized Brown-Norway rats were cannulated with fine-gauge needles connected to a programmable pump and saline reservoir, respectively. ICP was manipulated by varying reservoir height, and eye outflow facility (C) was determined from the pump flow rate required to hold IOP at different levels. C was 22 ± 4 nl/min/mmHg at resting ICP and 13 ± 3 nl/min/mmHg when ICP was raised 15 mmHg, a reduction of 41 ± 13% (n = 18). The decrease in outflow facility was independent of blood pressure, reversible, scaled with ICP elevation and correlated with increases in resting IOP. It was physiological in origin because C returned to baseline values after the rats were killed and corneal application of TTX though ICP remained elevated. These results indicate that a neural feedback mechanism driven by ICP regulates conventional outflow facility in rats. The mechanism may protect the eye from translaminar pressure swings and may offer a new target for glaucoma treatment.

Review of non-invasive intracranial pressure measurement techniques for ophthalmology applications

Assessment and monitoring of intracranial pressure (ICP) are important in the management of traumatic brain injury and other cerebral pathologies. In the eye, ICP elevation and depression both correlate with optic neuropathies, the former because of papilledema and the latter related to glaucoma. While the relationship between ICP elevation and papilledema is well established, the relationship between low ICP and glaucoma is still poorly understood. So far, ICP monitoring is performed invasively, but this entails risks including infection, spurring the study of non-invasive alternatives. We review 11 methods of non-invasive estimation of ICP including correlation to optic nerve sheath diameter, intraocular pressure, ophthalmodynamometry and two-depth transcranial Doppler of the ophthalmic artery. While none of these methods can fully replace invasive techniques, certain measures show great potential for specific applications. Although only used in small studies to date, a MRI based method known as MR-ICP, appears to be the best non-invasive technique for estimating ICP, with two-depth transcranial ultrasound and ophthalmodynamometry showing potential as well.

Traumatic shaking: The role of the triad in medical investigations of suspected traumatic shaking

The Swedish Agency for Health Technology Assessment and Assesment of Social Services (SBU) is an independent national authority, tasked by the government with assessing methods used in health, medical and dental services and social service interventions from a broad perspective, covering medical, economic, ethical and social aspects. The language in SBU's reports are adjusted to a wide audience. SBU's Board of Directors has approved the conclusions in this report. The systematic review showed the following graded results: There is limited scientific evidence that the triad (Three components of a whole. The triad associated with SBS usually comprises subdural haematoma, retinal haemorrhages and encephalopathy.) and therefore, its components can be associated with traumatic shaking (low-quality evidence). There is insufficient scientific evidence on which to assess the diagnostic accuracy of the triad in identifying traumatic shaking (very low-quality evidence). Limited scientific evidence (low-quality evidence) represents a combined assessment of studies of high or moderate quality which disclose factors that markedly weaken the evidence. It is important to note that limited scientific evidence for the reliability of a method or an effect does not imply complete lack of scientific support. Insufficient scientific evidence (very low-quality evidence) represents either a lack of studies or situations when available studies are of low quality or show contradictory results. Evaluation of the evidence was not based on formal grading of the evidence according to GRADE but on an evaluation of the total scientific basis.

Intraocular pressure in children after congenital heart surgery: A single-center study

Background:

The impact of varied cardiac physiologies on intraocular pressure (IOP) among children undergoing heart operations is unknown.

Aim:

The aim of this study was to determine the IOP among children with varying cardiovascular physiologies and varying hemodynamics after their heart operation.

Setting and Design:

This was a prospective, observational study.

Materials and Methods:

Patients ≤18 years undergoing congenital heart surgery were included in this study. IOP measurement was performed by Icare® tonometer between 3 and 14 days after heart operation.

Statistical Analysis:

Summary statistics were estimated for all demographic, anthropometric, and clinical data.

Results:

A total of 116 eyes from 58 children were included. The mean and standard deviation age was 28.4 (45.8) months. Single-ventricle anatomy was present in 26 patients (45%). Despite similar heart rate and blood pressure, the mean IOP among the patients with single-ventricle anatomy was significantly elevated as compared to patients with two-ventricle anatomy (18 mm Hg vs. 12 mm Hg, P < 0.001). There was no difference in IOP measurements based on the complexity of operation performed. We noted that patients undergoing surgical palliation with central shunt (21 mm Hg), Fontan operation (19 mm Hg), bidirectional Glenn operation (19 mm Hg), Norwood operation (19 mm Hg), or definitive repairs such as tetralogy of Fallot repair (17 mm Hg), and atrioventricular canal repair (19 mm Hg) were associated with the highest IOPs in the study cohort.

Conclusions:

This study demonstrates that IOPs vary with varying cardiovascular physiology after pediatric cardiac surgery.

Reduced Free Communication of the Subarachnoid Space Within the Optic Canal in the Human

PURPOSE

Recent studies in patients demonstrated that cerebrospinal fluid does not flow continuously between the intracranial subarachnoid space (SAS) and the space around the optic nerve in the orbit. Its anatomic basis remains elusive. The objective of this study was to use a novel anatomic technology, the epoxy sheet plastination, to reveal the configuration of the fibrous structures within the optic canal and their relationship with the optic nerve, SAS, and ophthalmic artery.

DESIGN

A human cadaveric study.

METHODS

Nine cadaveric heads (subject age 54-87 years) without optic neuropathy were prepared as sets of transverse, coronal, and sagittal plastinated sections. Three of them were pretreated with hematoxylin staining via the SAS irrigation before sectioning and plastination. The prepared sections were examined under a stereoscope and a confocal microscope.

RESULTS

The results showed that (1) the pia and arachnoid maters merged within the optic canal, (2) a dense trabecular mesh network was distributed in the orbital part of the canal, and (3) some optic nerve sheath (ONS) fibers intermingled with the tendinous fibers of the extraocular muscles and attached to the periosteum of the sphenoid bone, rather than entirely continuing with the inner layer of the dura mater.

CONCLUSIONS

This study identified and traced the fibrous components within the optic canal and revealed their nature, architecture, and relationship with surroundings and concluded that in the human, free communication of the SAS between the intracranial cavity and ONS was significantly reduced.

Noninvasive monitoring intracranial pressure - A review of available modalities

Background:

Intracranial pressure (ICP) monitoring is important in many neurosurgical and neurological patients. The gold standard for monitoring ICP, however, is via an invasive procedure resulting in the placement of an intraventricular catheter, which is associated with many risks. Several noninvasive ICP monitoring techniques have been examined with the hope to replace the invasive techniques. The goal of this paper is to provide an overview of all modalities that have been used for noninvasive ICP monitoring to date.

Methods:

A thorough literature search was conducted on PubMed, selected articles were reviewed in completion, and pertinent data was included in the review.

Results:

A total of 94 publications were reviewed, and we found that over the past few decades clinicians have attempted to use a number of modalities to monitor ICP noninvasively.

Conclusion:

Although the intraventricular catheter remains the gold standard for monitoring ICP, several noninvasive modalities that can be used in settings when invasive monitoring is not possible are also available. In our opinion, measurement of optic nerve sheath diameter and pupillometry are the two modalities which may prove to be valid options for centers not performing invasive ICP monitoring.

Effect of High Altitude Exposure on Intraocular Pressure Using Goldmann Applanation Tonometry

Willmann, Gabriel, Kai Schommer, Maximilian Schultheiss, M. Dominik Fischer, Karl-Ulrich Bartz-Schmidt, Florian Gekeler, and Andreas Schatz. Effect of high altitude exposure on intraocular pressure using Goldmann applanation tonometry. High Alt Med Biol. 18:114-120, 2017.

AIMS

The aim of the study was to quantify changes of intraocular pressure (IOP) during exposure to 4559 m using the state-of-the-art method of Goldmann applanation tonometry for IOP measurement and to detect correlations between IOP and acute mountain sickness (AMS) in a prospective manner.

METHODS

IOP was measured using a Goldmann applanation tonometer AT 900^® (Haag-Streit, Switzerland) and central corneal thickness (CCT) with the anterior segment module of a Spectralis™ HRA+OCT^® device (Heidelberg Engineering, Germany) at baseline and high altitude. Assessment of AMS was performed using the Lake Louise and AMS-C questionnaires, and Pearson's correlation coefficient was calculated for association between IOP and AMS.

RESULTS

Raw IOP values at high altitude were not significantly changed compared to baseline. IOP adjusted to the increase in CCT at high altitude, which is known to alter IOP levels, showed a significant reduction for corrected IOP values on day 3 of exposure (morning -2.1 ± 1.2 mmHg; evening -2.3 ± 1.1 mmHg; p < 0.05). No correlation of IOP with AMS or clinical parameters (heart rate and SpO₂) at high altitude was noted.

CONCLUSIONS

IOP showed a significant reduction of IOP levels when corrected for increased CCT values at high altitude. Furthermore, the prospective measurement of IOP is not useful in diagnosing AMS or for the prediction of more severe high altitude related illnesses as the decrease in IOP and symptoms of AMS do not correlate during altitude exposure.

Dynamic changes of the intraocular pressure and the pressure of cerebrospinal fluid in nonglaucomatous neurological patients

PURPOSE

To describe the dynamic changes of the intraocular pressure (IOP) and intracranial pressure (ICP) with normal or pathological values (intracranial hypertension) in nonglaucomatous neurological patients during lumbar punction (LP).

METHODS

Case-control study, prospective measurement of tonometry in both groups referred for LP. Intraocular pressure, ICP and translaminar pressure difference (TPD) were compared pre- and post-LP.

RESULTS

Thirty-six patients (72 eyes) with mean age of 38.5 (16-64) years and BMI of 26.81 kg/m² were analysed. The initial mean ICP was 12.81 (± 6.6) mmHg. The mean TPD before and after the LP was 1.48 mmHg and 0.65 mmHg, respectively. The mean IOP of both eyes decreased to 0.8 mmHg post-LP in patients with pathological ICP (p = 0.0193) and normal ICP (p = 0.006).

CONCLUSIONS

We found a statistically significant decrease of the IOP post-LP compared to the pre-LP in both groups, being higher in patients with pathological ICP. There were no significant differences of the IOP in patients with normal versus pathological ICP pre-LP/post-LP; neither was found a correlation between ICP and IOP.

Non-invasive intracranial pressure assessment

Assessing intracranial pressure (ICP) remains a cornerstone in neurosurgical care. Invasive techniques for monitoring ICP remain the gold standard. The need for a reliable, safe and reproducible technique to non-invasively assess ICP in the context of early screening and in the neurocritical care environment is obvious. Numerous techniques have been described with several novel advances. While none of the currently available techniques appear independently accurate enough to quantify raised ICP, there is some promising work being undertaken.

Intracranial pressure and glaucoma

Our understanding of the potential role intracranial pressure (ICP) may play in the pathophysiology of glaucoma is evolving. ICP can have a profound effect on the optic nerve; edema of the optic disc is an accepted consequence of elevation in ICP, and optic disc blood flow is known to be affected by ICP. Deformation of the orbit also is a known consequence of aberrations in ICP. Therefore, it is plausible that local alterations in optic nerve structure, blood supply, or axonal transport could result from changes in ICP. This article will summarize the relationship between ICP and the eye, specifically focusing on hypothesized relationships between ICP and glaucoma and the current evidence supporting or refuting ICP as a risk factor for glaucoma.

Retinal and Optic Nerve Hemorrhages in the Newborn Infant: One-Year Results of the Newborn Eye Screen Test Study

PURPOSE

To report the birth prevalence, risk factors, characteristics, and location of fundus hemorrhages (FHs) of the retina and optic nerve present in newborns at birth.

DESIGN

Prospective cohort study at Stanford University School of Medicine.

PARTICIPANTS

All infants who were 37 weeks postmenstrual age or older and stable were eligible for screening. Infants with known or suspected infectious conjunctivitis were excluded.

METHODS

Infants born at Lucile Packard Children's Hospital (LPCH) from July 25, 2013, through July 25, 2014, were offered universal newborn screening via wide-angle digital retinal photography in the Newborn Eye Screen Test study. Maternal, obstetric, and neonatal factors were obtained from hospital records. The location, retinal layer, and laterality of FH were recorded by 1 pediatric vitreoretinal specialist.

MAIN OUTCOME MEASURES

Birth prevalence of FH. Secondary outcomes included rate of adverse events, risk factors for FH, hemorrhage characteristics, and adverse events.

RESULTS

The birth prevalence of FH in this study was 20.3% (41/202 infants). Ninety-five percent of FHs involved the periphery, 83% involved the macula, and 71% involved multiple layers of the retina. The fovea was involved in 15% of FH cases (birth prevalence, 3.0%). No cases of bilateral foveal hemorrhage were found. Fundus hemorrhages were more common in the left eye than the right. Fundus hemorrhages were most commonly optic nerve flame hemorrhages (48%) and white-centered retinal hemorrhages (30%). Retinal hemorrhages were found most frequently in all 4 quadrants (35%) and more often were multiple than solitary. Macular hemorrhages most often were intraretinal (40%). Among the risk factors examined in this study, vaginal delivery compared with cesarean section (odds ratio [OR], 9.34; 95% confidence interval [CI], 2.57-33.97) showed the greatest level of association with FH. Self-identified ethnicity as Hispanic or Latino showed a protective effect (OR, 0.43; 95% CI, 0.20-0.94). Other study factors were not significant.

CONCLUSIONS

Fundus hemorrhages are common among newborns. They often involve multiple areas and layers of the retina. Vaginal delivery was associated with a significantly increased risk of FH, whereas self-identified Hispanic or Latino ethnicity was protective against FH in this study. The long-term consequences of FH on visual development remain unknown.

Exploring the controversy in child abuse pediatrics and false accusations of abuse

There is a controversy in child abuse pediatrics between an established corps of child abuse pediatricians aligned with hospital colleagues and law enforcement, and a multi-specialty challenger group of doctors and other medical professionals working with public interest lawyers. The latter group questions the scientific validity of the core beliefs of child abuse pediatricians and believes that there are a substantial number of false accusations of abuse occurring. An unproven primary hypothesis, crafted around 1975 by a small group of pediatricians with an interest in child abuse, lies at the foundation of child abuse pediatrics. With no scientific study, it was hypothesized that subdural hemorrhage (SDH) and retinal hemorrhage (RH) were diagnostic of shaking abuse. That hypothesis became the so-called "shaken baby syndrome." Through the period 1975-1985, in a coordinated manner, these child abuse specialists coalesced under the American Academy of Pediatrics and began working with district attorneys and social workers, informing them of the ways in which their hypothesis could be applied to prosecutions of child abuse and life-altering social service interventions. In a legal context, using then-prevailing evidentiary rules which treated scientific expert testimony as valid if it was "generally accepted" in the field, they represented falsely that there was general acceptance of their hypothesis and therefore it was valid science. As the ability to convict based on this unproven prime hypothesis (SDH and RH equals abuse) increased, some defense attorneys were professionally compelled by their own doubts to reach out to experts from other fields with experience with SDH and RH, trauma, and biomechanics, for second opinions. Medical and legal challenges to the established thinking soon emerged, based on both old and new evidenced-based literature. As the intensity of the controversy increased, the probability of false accusation became more apparent and the need to address the issue more pressing. Since false accusations of child abuse are themselves abusive, efforts to eliminate such false accusations must continue.

Intracranial pressure and cerebral perfusion pressure monitoring in non-TBI patients: special considerations

The effect of intracranial pressure (ICP) and the role of ICP monitoring are best studied in traumatic brain injury (TBI). However, a variety of acute neurologic illnesses e.g., subarachnoid hemorrhage, intracerebral hemorrhage, ischemic stroke, meningitis/encephalitis, and select metabolic disorders, e.g., liver failure and malignant, brain tumors can affect ICP. The purpose of this paper is to review the literature about ICP monitoring in conditions other than TBI and to provide recommendations how the technique may be used in patient management. A PubMed search between 1980 and September 2013 identified 989 articles; 225 of which were reviewed in detail. The technique used to monitor ICP in non-TBI conditions is similar to that used in TBI; however, indications for ICP monitoring often are intertwined with the presence of obstructive hydrocephalus and hence the use of ventricular catheters is more frequent. Increased ICP can adversely affect outcome, particularly when it fails to respond to treatment. However, patients with elevated ICP can still have favorable outcomes. Although the influence of ICP-based care on outcome in non-TBI conditions appears less robust than in TBI, monitoring ICP and cerebral perfusion pressure can play a role in guiding therapy in select patients.

Advances in cerebral monitoring for the patient with traumatic brain injury

A brief overview of the most common invasive and noninvasive monitoring tools collectively referred to using the term "multimodal monitoring" is provided. Caring for the critically ill patient with traumatic brain injury requires careful monitoring to prevent or reduce secondary brain injury. Concurrent to the growth of the subspecialty of neurocritical care, there has been a concerted effort to discover novel mechanisms to monitor the physiology of brain injury. The past 2 decades have witnessed an exponential growth in neurologic monitoring in terms of intracranial pressure, blood flow, metabolism, oxygenation, advanced neuroimaging, and electrophysiology.

Update in intracranial pressure evaluation methods and translaminar pressure gradient role in glaucoma

Glaucoma is one of the leading causes of blindness worldwide. Historically, it has been considered an ocular disease primary caused by pathological intraocular pressure (IOP). Recently, researchers have emphasized intracranial pressure (ICP), as translaminar counter pressure against IOP may play a role in glaucoma development and progression. It remains controversial what is the best way to measure ICP in glaucoma. Currently, the 'gold standard' for ICP measurement is invasive measurement of the pressure in the cerebrospinal fluid via lumbar puncture or via implantation of the pressure sensor into the brains ventricle. However, the direct measurements of ICP are not without risk due to its invasiveness and potential risk of intracranial haemorrhage and infection. Therefore, invasive ICP measurements are prohibitive due to safety needs, especially in glaucoma patients. Several approaches have been proposed to estimate ICP non-invasively, including transcranial Doppler ultrasonography, tympanic membrane displacement, ophthalmodynamometry, measurement of optic nerve sheath diameter and two-depth transcranial Doppler technology. Special emphasis is put on the two-depth transcranial Doppler technology, which uses an ophthalmic artery as a natural ICP sensor. It is the only method which accurately and precisely measures absolute ICP values and may provide valuable information in glaucoma.

The increase of intra-abdominal pressure can affect intraocular pressure

Objective. This study aims to explore the usage of intraocular pressure measurements as the early indicator of the increase in intra-abdominal pressure. Methods. In this prospective study, 40 patients undergoing elective surgery were included. Patients were divided into four groups of 10 patients. The control group (Group C) was not subjected to laparoscopic intervention. Laparoscopic surgery was, respectively, performed with an intra-abdominal pressure of 9, 12, and 15 mmHg in Groups L (low), M (medium), and H (high pressure). Intraocular pressure was measured binocularly in each patient at three different times (before, during, and end of surgery) using a contact tonometer. Results. Patients' gender, age, body mass index (BMI), American Society of Anesthesiology (ASA) class, and operative times were not different among the groups. No complications occurred with either the surgery or measurement of intraocular pressure. Intubation was associated with a severe rise in IOP (P < 0.05). An increase in intraocular pressure was seen in groups M and H (P < 0.05). Conclusion. Intraocular pressure was increased in the groups with an intra-abdominal pressure of 12 mmHg or more. Measuring the intraocular pressure might be a useful method to estimate the intra-abdominal pressure. This trial is registered with NCT02319213.

Accuracy of noninvasive intraocular pressure or optic nerve sheath diameter measurements for predicting elevated intracranial pressure in cryptococcal meningitis

Intraocular pressure measurement by tonometry and optic nerve sheath diameter measurement by ultrasound have imprecise but statistical correlation with intracranial pressure. Neither technique is an effective surrogate measure of intracranial pressure in cryptococcal meningitis; manometry should be used.

Background

 Cryptococcal meningitis is associated with increased intracranial pressure (ICP). Therapeutic lumbar puncture (LP) is recommended when the initial ICP is >250 mm H₂O, yet the availability of manometers in Africa is limited and not always used where available. We assessed whether intraocular pressure could be a noninvasive surrogate predictor to determine when additional therapeutic LPs are necessary.

Methods

 Ninety-eight human immunodeficiency virus-infected Ugandans with suspected meningitis (81% Cryptococcus) had intraocular pressure measured using a handheld tonometer (n = 78) or optic nerve sheath diameter (ONSD) measured by ultrasound (n = 81). We determined the diagnostic performance of these methods for predicting ICP vs a standard manometer.

Results

 The median ICP was 225 mm H₂O (interquartile range [IQR], 135–405 mm H₂O). The median intraocular pressure was 28 mm Hg (IQR, 22–37 mm Hg), and median ultrasound ONSD was 5.4 mm (IQR, 4.95–6.1 mm). ICP moderately correlated with intraocular pressure (ρ = 0.45, P < .001) and with ultrasound ONSD (ρ = 0.44, P < .001). There were not discrete threshold cutoff values for either tonometry or ultrasound ONSD that provided a suitable cutoff diagnostic value to predict elevated ICP (>200 mm H₂O). However, risk of elevated ICP >200 mm H₂O was increased with an average intraocular pressure >28 mm Hg (relative risk [RR] = 3.03; 95% confidence interval [CI], 1.55–5.92; P < .001) or an average of ONSD >5 mm (RR = 2.39; 95% CI, 1.42–4.03; P = .003). As either intraocular pressure or ONSD increased, probability of elevated ICP increased (ie, positive predictive value increased).

Conclusions

 Noninvasive intraocular pressure measurements by tonometry or ultrasound correlate with cerebrospinal fluid opening pressure, but both are a suboptimal replacement for actual ICP measurement with a manometer.

Intraocular pressure is not associated with acute mountain sickness

OBJECTIVE

Acute mountain sickness (AMS) is common at high altitude and may lead to high altitude cerebral edema (HACE) if not properly recognized. Previous studies have suggested that AMS is associated with increases in intracranial pressure (ICP). Increased ICP has been associated with increased intra-ocular pressure (IOP). This study was designed to determine the association between IOP and AMS.

METHODS

Subjects were recruited from a convenience sample of travelers in the Khumbu region of Nepal, elevation 14,410 ft (4392 m). Study participation involved completion of a questionnaire to assess for AMS by the Lake Louise Score (LLS), followed by three IOP measurements in each eye. Investigators were blinded to the LLS. Subjects with a history of ocular surgery were excluded. Three IOP measurements per eye were made using an applanation tonometer (Tono-Pen XL(®), Reichart Technologies) and averaged across both eyes. Multivariable logistic regression analysis was used to estimate the association between IOP and AMS while adjusting for age, ascent or descent, and use of acetazolamide. IOP and blood O2 saturation were compared using a Spearman correlation coefficient.

RESULTS

161 subjects were enrolled with a median age of 36 (IQR: 29-45) years; 60% were male, 75% were ascending, and 64% were taking acetazolamide; additionally, 38%, (95% CI: 31%-47%) were diagnosed with AMS (LLS ≥3). The median IOP was 21 (IQR 18-24) mmHg. The logistic regression model demonstrated no association between IOP and AMS as measured by LLS (odds ratio [OR] 1.0, 95% CI: 0.9-1.1),age (OR 1.0, 95% CI: 0.9-1.0) or with use of acetazolamide (OR 1.4, 95% CI: 0.6-2.6). Ascent (OR 0.4, 95% CI: 0.2-0.9) was negatively associated with IOP but not significantly so. IOP and O2 saturation were not correlated (p=0.93).

CONCLUSIONS

IOP measured at high altitude is not associated with the diagnosis of AMS. Other approaches to diagnose AMS easily and accurately are needed.

Diagnostic accuracy of intraocular pressure measurement for the detection of raised intracranial pressure: meta-analysis: a systematic review

OBJECT

Because clinical examination and imaging may be unreliable indicators of intracranial hypertension, intraocular pressure (IOP) measurement has been proposed as a noninvasive method of diagnosis. The authors conducted a systematic review and meta-analysis to determine the correlation between IOP and intracranial pressure (ICP) and the diagnostic accuracy of IOP measurement for detection of intracranial hypertension.

METHODS

The authors searched bibliographic databases (Ovid MEDLINE, Ovid EMBASE, and the Cochrane Central Register of Controlled Trials) from 1950 to March 2013, references of included studies, and conference abstracts for studies comparing IOP and invasive ICP measurement. Two independent reviewers screened abstracts, reviewed full-text articles, and extracted data. Correlation coefficients, sensitivity, specificity, and positive and negative likelihood ratios were calculated using DerSimonian and Laird methods and bivariate random effects models. The I(2) statistic was used as a measure of heterogeneity.

RESULTS

Among 355 identified citations, 12 studies that enrolled 546 patients were included in the meta-analysis. The pooled correlation coefficient between IOP and ICP was 0.44 (95% CI 0.26-0.63, I(2) = 97.7%, p < 0.001). The summary sensitivity and specificity for IOP for diagnosing intracranial hypertension were 81% (95% CI 26%-98%, I(2) = 95.2%, p < 0.01) and 95% (95% CI 43%-100%, I(2) = 97.7%, p < 0.01), respectively. The summary positive and negative likelihood ratios were 14.8 (95% CI 0.5-417.7) and 0.2 (95% CI 0.02-1.7), respectively. When ICP and IOP measurements were taken within 1 hour of another, correlation between the measures improved.

CONCLUSIONS

Although a modest aggregate correlation was found between IOP and ICP, the pooled diagnostic accuracy suggests that IOP measurement may be of clinical utility in the detection of intracranial hypertension. Given the significant heterogeneity between included studies, further investigation is required prior to the adoption of IOP in the evaluation of intracranial hypertension into routine practice.

Traumatic brain injury, axonal injury and shaking in New Zealand sea lion pups

Trauma is a common cause of death in neonatal New Zealand sea lion pups, and subadult male sea lions have been observed picking up and violently shaking some pups. In humans, axonal injury is a common result of traumatic brain injury, and can be due to direct trauma to axons or to ischaemic damage secondary to trauma. 'Shaken baby syndrome', which has been described in human infants, is characterised by retinal and intracranial subdural haemorrhages, and has been associated with axonal injury to the brain, spinal cord and optic nerve. This study identifies mechanisms of traumatic brain injury in New Zealand sea lion pups, including impact injuries and shaking-type injuries, and identifies gross lesions of head trauma in 22/36 sea lion pups found dead at a breeding site in the Auckland Islands. Despite the high frequency of such gross lesions, only three of the pups had died of traumatic brain injury. Observational studies confirmed that shaking of pups occurred, but none were shown to die as a direct result of these shaking events. Axonal injury was evaluated in all 36 pup brains using β-amyloid precursor protein immunohistochemistry. Immunoreactive axons were present in the brains of all pups examined including seven with vascular axonal injury and two with diffuse axonal injury, but the severity and pattern of injury was not reliably associated with death due to traumatic brain injury. No dead pups had the typical combination of gross lesions and immunohistochemical findings that would conform to descriptions of 'shaken baby syndrome'. Axonal injury was present in the optic nerves of most pups, irrespective of cause of death, but was associated with ischaemia rather than trauma.

Poor correlation between intracranial pressure and intraocular pressure by hand-held tonometry

PURPOSE

The aim of this study is to provide data on the controversial issue of whether handheld measurements of intraocular pressure (IOP) are capable of accurately predicting elevated intracranial pressure (ICP) in patients undergoing lumbar puncture (LP).

METHODS

All patients over the age of 18 years who underwent an LP in the emergency or neurological departments at the Tel Aviv Medical Center for any reason between October 2007 and July 2010 were eligible to participate in this prospective observational pilot study. IOP was measured with the Tono-Pen XL while patients were in the supine position before undergoing LP. ICP was measured in the lateral recumbent position. ICP and bilateral IOP were measured, and the mean and maximum values of IOP were calculated. The association between ICP and each one of the four IOP measures was evaluated by the Pearson correlation coefficient.

RESULTS

Twenty-four patients (mean age 37.8 ± 15.8 years, ten males and 14 females) were enrolled. The reasons for their requiring an LP were headache (19/24 patients), evaluation for hemiparesis (2/24), cognitive deterioration (1/24), and seizures (2/24). Nine had elevated mean opening pressure (>20 cm H2O), six had an elevated mean IOP (>20 mmHg), and four of these six also had an elevated opening pressure. There was no significant correlation between the ICP measurements and any of the IOP measurements.

CONCLUSION

Handheld ocular tonometry has poor sensitivity and specificity for the prediction of increased ICP and is not an effective tool for screening for ICP in the ED or in the neurology department.

Intraocular pressure vs intracranial pressure in disease conditions: a prospective cohort study (Beijing iCOP study)

Background

The correlation between intracranial pressure (ICP) and intraocular pressure (IOP) is still controversial in literature and hence whether IOP can be used as a non-invasive surrogate of ICP remains unknown. The aim of the current study was to further clarify the potential correlation between ICP and IOP.

Methods

The IOP measured with Goldmann applanation tonometer was carried out on 130 patients whose ICP was determined via lumber puncture. The Pearson correlation coefficient between ICP and IOP was calculated, the fisher line discriminated analysis to evaluate the effectivity of using IOP to predict the ICP level.

Results

A significant correlation between ICP and IOP was found. ICP was correlated significantly with IOP of the right eyes (p < 0.001) and IOP of the left eyes (p = 0.001) and mean IOP of both eyes (p < 0.001), respectively. However, using IOP as a measurement to predict ICP, the accuracy rate was found to be 65.4%.

Conclusion

Our data suggested that although a significant correlation exists between ICP and IOP, caution needs to be taken when using IOP readings by Goldmann applanation tonometer as a surrogate for direct cerebrospinal fluid pressure measurement of ICP.

Role of cerebrospinal fluid pressure in the pathogenesis of glaucoma

The pathogenesis of normal (intraocular) pressure glaucoma has remained unclear so far. As hospital-based studies showed an association of normal-pressure glaucoma with low systemic blood pressure, particularly at night, and with vasospastic symptoms, it has been hypothesized that a vascular factor may play a primary role in the pathogenesis of normal-pressure glaucoma. That assumption may, however, be contradicted by the morphology of the optic nerve head. Eyes with normal-pressure glaucoma and glaucomatous eyes with high-intraocular pressure can show a strikingly similar appearance of the optic nerve head, including a loss of neuroretinal rim, a deepening of the optic cup, and an enlargement of parapapillary atrophy. These features, however, are not found in any (other) vascular optic neuropathy, with the exception of an enlargement and deepening of the optic cup in arteritic anterior ischaemic optic neuropathy. One may additionally take into account (i) that it is the trans-lamina cribrosa pressure difference (and not the trans-corneal pressure difference, i.e. the so-called intraocular pressure) which is of importance for the physiology and pathophysiology of the optic nerve head; (ii) that studies have shown that the anatomy of the optic nerve head including the intraocular pressure, the anatomy and biomechanics of the lamina cribrosa and peripapillary sclera, retrobulbar orbital cerebrospinal fluid pressure and the retrobulbar optic nerve tissue pressure may be of importance for the pathogenesis of the highly myopic type of chronic open-angle glaucoma; (iii) that studies have suggested a physiological association between the pressure in all three fluid filled compartments, i.e. the systemic arterial blood pressure, the cerebrospinal fluid pressure and the intraocular pressure; (iv) that an experimental investigation suggested that a low cerebrospinal fluid pressure may play a role in the pathogenesis of normal (intraocular) pressure glaucoma; and (v) that recent clinical studies reported that patients with normal (intraocular) pressure glaucoma had significantly lower cerebrospinal fluid pressure and a higher trans-lamina cribrosa pressure difference when compared to normal subjects. One may, therefore, postulate that a low cerebrospinal fluid pressure may be associated with normal (intraocular) pressure glaucoma. A low systemic blood pressure, particularly at night, could physiologically be associated with a low cerebrospinal fluid pressure, which leads to an abnormally high trans-lamina cribrosa pressure difference and as such to a similar situation as if the cerebrospinal fluid pressure is normal and the intraocular pressure is elevated. This model could explain why patients with normal (intraocular) pressure glaucoma tend to have a low systemic blood pressure, and why eyes with normal (intraocular) pressure glaucoma and eyes with high-pressure glaucoma, in contrast to eyes with a direct vascular optic neuropathy, show profound similarities in the appearance of the optic nerve head.

Evaluation of an acute focal epidural mass model to characterize the intracranial pressure-volume relationship in healthy Beagles

OBJECTIVE

To characterize the intracranial pressure-volume relationship (ICPVR) in dogs by use of an acute frontal-parietal mass lesion model.

ANIMALS

7 healthy adult female Beagles.

PROCEDURES

Dogs were anesthetized with isoflurane to achieve a surgical plane of anesthesia. A fiberoptic intracranial pressure (ICP) monitor was inserted to a depth of 1 cm in the parenchyma of the right frontal-parietal region of the brain. A Foley balloon-tipped catheter was placed in the epidural space of the left frontal-parietal area through a separate 1-cm burr hole. Baseline measurements were obtained with the balloon deflated. The balloon was then inflated incrementally with 0.5 mL of 0.9% NaCl solution every 10 minutes until ICP exceeded mean arterial blood pressure. Nonlinear regression analysis with 2-factor and 3-factor exponential equations was used to characterize the ICPVR.

RESULTS

The mean baseline ICP was 11 mm Hg, with a 95% confidence interval of 2 to 20 mm Hg. The ICPVR was well characterized by 2-factor or 3-factor exponential equations for all dogs (R² > 0.93). Balloon volumes of > 1. 2 mL were associated with ICP > 20 mm Hg.

CONCLUSIONS AND CLINICAL RELEVANCE

Characterization of the ICPVR may provide clinically useful information regarding the safety of obtaining CSF from the atlanto-occipital space or implantation of brachytherapy catheters and for determining the need for decompressive craniectomy in dogs with acute intracranial disease. High ICP should be suspected in dogs that have an acute frontal-parietal mass lesion estimated to exceed 2% of the brain volume.

Cerebrospinal fluid pressure in ocular hypertension

BACKGROUND

To assess the lumbar cerebrospinal fluid pressure (CSF-P) in ocular hypertensive subjects with elevated intraocular pressure (IOP) but without development of glaucomatous optic nerve damage.

METHODS

The prospective interventional study included 17 patients with ocular hypertension and 71 subjects of a nonglaucomatous control group. All patients underwent a standardized ophthalmologic and neurological examination including measurement of lumbar CSF-P. In the ocular hypertensive group, the IOP was corrected for its dependence on central corneal thickness (IOP(corrected) ). The trans-lamina cribrosa pressure difference (Trans-LCPD) was calculated as IOP(corrected) - CSF-P.

RESULTS

CSF-P was significantly (p < 0.001) higher in the ocular hypertensive group (16.0 ± 2.5 mmHg) than in the control group (12.9 ± 1.9 mmHg). CSF-P was significantly associated with IOP(corrected) (p < 0.001; r = 0.82). In multivariate analysis, CSF-P was significantly correlated with IOP(corrected) (p < 0.001) and marginally significantly with mean blood pressure (p = 0.05). Trans-LCPD was not associated significantly with blood pressure (p = 0.69).

CONCLUSION

Some ocular hypertensive subjects with increased intraocular pressure measurements (after correction for their dependence on central corneal thickness) had an abnormally high lumbar cerebrospinal fluid pressure. Assuming that lumbar cerebrospinal fluid pressure correlated with orbital cerebrospinal fluid pressure, one may postulate that the elevated retro-lamina cribrosa pressure compensated for an increased intraocular pressure. The elevated retro-lamina cribrosa pressure may have led to a normal trans-laminar pressure difference in the eyes with elevated intraocular pressure, so that glaucomatous optic nerve damage did not develop. Intraocular pressure, cerebrospinal fluid pressure and arterial blood pressure were correlated with each other.

Correlation of intraocular pressure with intracranial pressure in children with severe head injuries

OBJECTIVE

To determine whether there was a correlation between tonometric measurements of the intraocular pressure and transducer measurements of the intracranial pressure in the acute setting, and whether intraocular pressure can be used as a surrogate measure of intracranial pressure. Children with traumatic brain injuries commonly develop increased intracranial pressure requiring surgical placement of a pressure transducer to measure the intracranial pressure during the acute recovery period. The increased intracranial pressure may cause engorgement of the orbital compartments via dilation of the episcleral veins and manifest as increased intraocular pressure.

DESIGN

Prospective study.

SETTING

Tertiary academic pediatric intensive care unit.

PATIENTS

Children admitted with severe traumatic brain injury.

INTERVENTIONS

Tonometric intraocular pressure measurements.

MEASUREMENTS AND MAIN RESULTS

We performed an Institutional Review Board-approved, prospective study on 36 children (age range, 2.9-15.1 yrs) with traumatic brain injuries, requiring intracranial pressure monitoring. A total of 274 intraocular pressure measurements were made after placement of the pressure transducer, and concordance between the sites of injury and measurement was documented. The average age of the patients was 8.3 yrs. The mean intraocular pressure, intracranial pressure difference was -0.5 +/- 0.68 cm H2O, and the variance was 29.88 (sd, 5.47). The 95% confidence interval was between -11.22 and 10.22. With concordance between the sites of measurement and injury, the mean IOP, intracranial pressure difference was -0.02 +/- 0.61 cm H2O (variance, 23.28; sd, 4.82; 95% confidence interval, - 9.47 to 9.42). Concordance reduced the variance of the intraocular pressure, intracranial pressure discrepancy by 20.3%. The Pearson intraocular pressure-intracranial pressure regression coefficient and the Krippendorff's alpha reliability estimate analyses indicated good agreement. The patient's age or Paco2 did not influence the intraocular pressure, intracranial pressure difference. Using 20 cm H2O as a normal intracranial pressure cutoff, the intraocular pressure had a specificity of 0.7 and sensitivity of 0.97; with concordance, the values improved to 0.78 and 0.96, respectively.

CONCLUSIONS

Tonometry is a useful screening surrogate measure of intracranial pressure in children with traumatic brain injuries, but seems to lack the accuracy necessary for close management of intracranial pressure in the acute posttraumatic period.