Intraocular pressure

Intraocular pressure is not associated with acute mountain sickness

Authors: Cushing T, Paterson R, Haukoos J, Harris NS.

Intraocular pressure is not associated with acute mountain sickness. High Alt Med Biol 14:342-345, 2013.-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 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.

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

Authors: Li Z, Yang Y, Lu Y, Liu D, Xu E, Jia J, Yang D, Zhang X, Yang H, Wang N, Ma D.

BACKGROUND: Whether intraocular pressure (IOP) can be used as a non-invasive surrogate of intracranial pressure (ICP) remains unknown. The aim of the current study was to determine whether there was a 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.

Space obstructive syndrome: intracranial hypertension, intraocular pressure, and papilledema in space

Authors: Wiener TC.

Humans undergo several consistent and measurable changes of fluid distribution and regulation in the course of adapting to microgravity. Recently, a syndrome of objective findings has been described by Mader et al. associated with long-duration missions, including hyperopic shifts, mildly elevated intracranial pressure, papilledema, globe flattening, choroidal folds, and other anatomic findings. Experience with venous obstructive lesions leads the author to propose a primary obstructive process, unique to or exacerbated by microgravity, acting at the level of the proximal internal jugular veins, termed Space Obstructive Syndrome (SOS). Literature, anatomy, and ultrasound observations revealed four major potential compression zones of the internal jugular vein, with Zone I between the sternocleidomastoid muscle and the carotid artery as the primary area of compression, both in 1 G in an upright position and in microgravity. Internal jugular vein compression, along with loss of gravitationally induced cranial outflow of blood in the vertebral veins and collaterals, may lead to intracranial venous hypertension with resultant facial/head and upper airway swelling, increased intraocular pressure, intracranial hypertension, and papilledema. Further study and proof of concept will necessitate ultrasound, Doppler flow study, and internal jugular vein pressure measurements on orbit in the International Space Station. If proven, SOS will give researchers opportunity for study and development of mitigation strategies such as artificial gravity systems.

The relation between intracranial and intraocular pressures: study of 50 patients

Authors: Sajjadi SA, Harirchian MH, Sheikhbahaei N, Mohebbi MR, Malekmadani MH, Saberi H.

OBJECTIVE: We evaluated the correlation between intracranial (ICP) and intraocular pressure (IOP).

METHODS: Of the 77 patients who underwent a lumbar puncture, 27 were excluded secondary to a history of glaucoma, using drugs effective on IOP, and abnormal funduscopic examination. ICP was measured by lumbar puncture. IOP was measured by two scales of Schiotz tonometer in both eyes, and the mean was calculated.

RESULTS: We found a significant correlation between ICP and mean IOP (p < 0.001; r = 0.955). Body mass index, age, and disease type had no significant effect on this correlation.

INTERPRETATION: IOP is correlated with ICP.

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