The Mont Blanc Study: The effect of altitude on intra ocular pressure and central corneal thickness

Abstract

The aim of the Mont Blanc Study was to investigate the relationship between intraocular pressure (IOP), central corneal thickness (CCT), and altitude in healthy subjects. Thirtythree eyes of 33 healthy volunteers (mean age: 24.8 years, 17 females) had their IOP measured with Perkins and I-Care tonometers and their CCT using ultrasound pachymetry at three locations in Italy with different altitudes: Pavia, (PV), 77 meters above sea level (a.s.l); Courmayeur (CM), 1300 meters a.s.l; Pointe Helbronner (PH), 3466 meters a.s.l.). The measurements were performed at 9 am, 11 am, 1 pm and 3 pm (±30') in indoor settings (mean temperature of 19˚C) in PV and PH. At 9 am, CCT and IOP were measured outdoor (mean temperature of-1.4˚C) at PH. The mean values of the IOP curve decreased from PV to PH with the Perkins (p = 0.02) and I-Care tonometers (p = 0.001). Instead, CCT increased upon ascension from PV to PH (p = 0.01), and from CM to PH (p = 0.002). When exposed to sub-zero temperature, the IOP increased (p<0.001), while the CCT did not change (p = 0.30). The results suggest that IOP significantly decreased and CCT significantly increased upon ascension from the sea level to higher altitudes.

Physiology-Enhanced Data Analytics to Evaluate the Effect of Altitude on Intraocular Pressure and Ocular Hemodynamics

“…The MBS measured IOP, central corneal thickness (CCT), systolic BP (SBP), diastolic BP (DBP), heart rate (HR), and oxygen saturation in 33 healthy volunteers (17 females, 16 males; mean age: 24.8 ± 3.3) at 77 m (Pavia, Italy (PV)), at 1300 m (Courmayeur, Italy (CM)), and at 3466m (Pointe Helbronner, Mont Blanc Mountain, Italy (PH)) above sea level [32]. The ascent from CM was performed via a high-speed cableway, which took 15 min to reach PH (Skyway Mont Blanc cable car, Skyway Monte Bianco, Funivie Monte Bianco S.p.a, Aosta Valley, Italy).…”

“…Subjects were examined at 9 a.m., 11 a.m., 1 p.m., and 3 p.m. in an indoor setting at PV and PH. IOP and CCT were also measured outdoors at PH at 9 a.m. [32]. Subjects were not acclimatized, nor were they required to exert any physical effort.…”

“…In comparison, the literature regarding altitude-related alterations in IOP and ocular hemodynamics is much less clear. While several studies have indicated IOP may increase with altitude [6,[12][13][14][15][16][17][18][19][20][21][22], many have also found an opposing decrease in IOP with altitude [7,8,[23][24][25][26][27][28][29][30][31][32]. Additionally, studies have shown that short-term exposure to high altitudes can alter the retinal microcirculation in young, healthy subjects secondary to hypoxic endothelial dysfunction [33].…”

“…In this perspective, herein, we combined experimental measurements with mathematical modeling to better understand the relationships between altitude, IOP, and hemodynamic changes and the clinical significance of these alterations on ocular disease. Specifically, the data previously collected from the Mont Blanc Study (MBS) [32] were used as inputs for two mathematical models describing the physiology of ocular hemodynamics [39] and aqueous humor flow [40]. The outputs of these models provide estimates for variables that bear physiological interest but that cannot be measured directly.…”

Modeling the eye as a window on the body

“…From the clinical perspective, Carlo Bruttini (University of Pavia, Pavia, Italy) presented a review of the relationship between the eye and vascular systemic pathologies, with a special focus on diabetic retinopathy, 1,3 thrombosis and occlusions of ocular vessels, 3 and the effect of high altitude on the production and drainage of aqueous humor, 14 which regulates IOP.…”