Retinal vessel oxygen saturation and vessel diameter in healthy individuals during high-altitude exposure

Chronic venous disease of lower limbs in young men at high-altitude: A cross-sectional survey

OBJECTIVES

The aim of this study was to understand the prevalence of chronic venous disease (CVD) of lower limbs in young men at high-altitude in Xizang, and to provide prevention measures.

METHODS

The convenient sampling method was used to conduct a questionnaire survey among males aged 18 to 40 above an altitude of 3000 meters in Xizang in April 2023. The contents of the questionnaire included basic information, symptoms of CVD of lower limbs, protection status and training needs. Multivariate logistic regression model was calculated to evaluate the risk factors for CVD.

RESULTS

A total of 350 survey questionnaires were received, and 326 valid samples were collected. The prevalence of CVD of lower limbs (C1-C6) was 37.42% (95%CI: 32.17%-42.68%), the ratio of C0 to C5 were 62.58%, 27.30%, 3.07%, 4.60%, 2.15% and 0.31%, respectively, no one reached C6. The top three symptoms of CVD were lower limb fatigue (18.10%), heaviness (15.34%) and pain (13.19%). 46.01% of respondents were unaware of CVD, and 12.88% of respondents did not have any protective measures of CVD. Multivariate logistic regression showed that age (OR = 1.076, 95%CI: 1.018-1.137, p = .009), preference for spicy food (OR = 1.747, 95%CI: 1.083-2.818, p = .022), unbalanced diet (OR = 1.877, 95%CI: 1.049-3.358, p = .034) and physical exercise (OR 0.610, 95%CI: 0.377-0.986, p = .044) were the independent risk factors for CVD.

CONCLUSIONS

This study provided data on the prevalence of CVD in young men at high-altitude and the risk factors for CVD. The findings of this study may facilitate the development of individualized clinical assessments and targeted prevention programs.

Retinal vessel analysis to assess microvascular function in the healthy eye: A systematic review on the response to acute physiological and pathological stressors

The retina allows noninvasive in vivo assessment of the microcirculation. Autoregulation of the retinal microvasculature meets the changing requirements of local metabolic demand and maintains adequate blood flow. Analysis of the retinal vascular reactivity contributes to the understanding of regulatory physiology and its relationship to the systemic microcirculation. We conducted a literature review on the effect of different acute stimuli onto the retinal vasculature was conducted in accordance with the PRISMA guidelines. A literature search between 1-1-2005 and 17-10-2022 was performed in Medline, Embase, Web of Science and the Cochrane Library. We report the retinal vascular behavior of healthy individuals in response to both physiological and pathological stressors in 106 included articles. We provide ables of methodological characteristics for each stressor. Hypoxia, hypercapnia, high altitude, flicker light stimulation, rise of core temperature, blood pressure lowering, and the condition immediately after endurance exercise associate with larger retinal vessels. Hyperoxia, hypocapnia, blood pressure rise (Bayliss effect), and the condition during isometric exercise associate with smaller retinal vessels. The retinal vasculature is highly reactive to physiological and pathological stressors. This autoregulatory capacity is hypothesized to be a source of biomarkers for vascular health. Dynamic and static retinal vessel analysis are noninvasive methods to assess this (micro)vascular function. Exploring its diagnostic potential and application into clinical practice requires the development of standardized assessment methods, for which some recommendations are made.

Microvascular Density Analysis of Patients with Inactive Systemic Lupus Erythematosus-A Two-Year Follow-Up Optical Coherence Tomography Angiography Study

Background/Objectives: This study aims to investigate the long-term effect of inactive systemic lupus erythematosus (SLE) on the retinal microcirculation measured via optical coherence tomography angiography (OCT-A). Methods: Twenty-four eyes of 24 patients with inactive SLE under hydroxychloroquine (HCQ) therapy were included. The OCT-A data (mainly vessel density (VD) and foveal avascular zone (FAZ) data of the superficial and of the deep capillary plexus (SCP, DCP) and the choriocapillaris (CC)) were analyzed and compared between the baseline examination (t0) and 2 years later (t1). Results: At t1, VD in the whole en face SCP and in the CC was notably reduced compared to t0 (SCP: p = 0.001, CC: p = 0.013). VD in the DCP, CRT and FAZ area showed no difference at t1 compared to t0 (DCP: p = 0.128, FAZ: p = 0.332, CRT fovea: p = 0.296). Correlation analysis between the increase in cumulative doses of HCQ between t0 and t1 and the VD of the whole en face SCP did not show any correlation (Spearman r = 0.062 (95% CI -0.367; 0.477). Conclusions: SLE patients demonstrated a decrease in the retinal VD of the SCP and CC over a 2-year period. There was no correlation with the change in cumulative doses of HCQ. These results suggest an ongoing effect of the disease on the retinal and choriocapillary microcirculation.

Influence of high altitude on choroid thickness, retinal thickness, and myopia: A cross-sectional study comparing adolescents in Shanghai and Tibet

PURPOSE

This study aimed to explore the influence of high altitude on myopia, macular choroidal thickness (mCT), and macular retinal thickness (mRT) in adolescents.

METHODS

Two schools, one in Shanghai (at sea level) and one in Shigatse, Tibet (more than 4000 m above sea level), were selected. Refractive error was measured by an autorefractor instrument and subjective refraction, and mCT and mRT were measured at three concentric circles by optical coherence tomography. Student's t -test, Chi-square test, and multiple linear regression analyses were used to analyze the data.

RESULTS

A total of 1114 participants (657 and 457 in Shanghai and Tibet, respectively) were enrolled in this cross-sectional study. The average age of the participants was 18.81 ± 1.10 years, and 44.34% were males. The spherical equivalent (SE) of adolescents in Shanghai was significantly lower than that of adolescents in Tibet (-4.14 ± 2.37 D and -2.12 ± 1.87 D, P < 0.01). The prevalence of myopia and high myopia among adolescents in Shanghai (94.52%, 19.48%) was significantly higher than those among adolescents in Tibet (44.74%, 2.41%) ( P < 0.01). The mCT of Tibetan adolescents was significantly thicker than that of Shanghai adolescents (295.80 ± 62.46 μm and 218.71 ± 61.42 μm, P < 0.01), especially the central mCT. The mRT of Tibetan adolescents was also thicker than that of Shanghai adolescents (301.42 ± 23.26 μm and 281.04 ± 12.24 μm, P < 0.01).

CONCLUSIONS

Compared with Shanghai adolescents, the choroid of Tibet adolescents is thicker, and the myopia prevalence is lower. It is speculated that increased altitude is associated with the thickening of mCT and a low myopia prevalence.

Dynamic Changes in Retinal Vessel Diameters and Arteriovenous Ratio within 10 Days of Birth

PURPOSE

This study monitored the dynamic changes in retinal vascular width and the AVR in full-term neonates within 1-10 days of birth.

METHODS

It was conducted at hospitals in the Anhui province from October 2020 to March 2022. A total of 700 full-term, healthy infants were chosen randomly within 10 days of birth, and the Star Pupil Medical Cloud Data System (XBDS) was used to collect fundus images. Infants within 6 days of birth were grouped into groups one to six, while those within the 7th to 10th days were grouped into group seven. The fundus photographs were imported into Image-Pro-Plus (IPP) software. The optic disc diameter was measured. The retinal artery and vein's diameter was measured at a distance between 0.5- and 1.0-disc diameter from the optic disc's margin. The AVR was also calculated. Finally, each group's retinal vessel diameters and AVR were compared separately to show their dynamic changes.

RESULTS

There were differences in the retinal artery diameter between groups one and two, three and four, four and five, and five and six. For retinal vein diameter, there were differences between groups one and two and groups six and seven. There were also differences in the AVR between all groups. In addition, there was a significant positive correlation between the small retinal artery and vein diameters.

CONCLUSION

The retinal artery and vein diameters and AVR in neonates change dynamically during the first 10 days of life. The AVR undergoes the most dramatic change daily and is considerably smaller than the AVR in adults. Hence, this study found that the external environment undergoes significant changes following birth that affect the microcirculation. Then, the retinal central vascular system undergoes similar emergency and adaptive alterations.

Quantify retinal structure in high-altitude residents with and without high altitude polycythemia

BACKGROUND

To assess retinal structural parameters in high-altitude (HA) residents with and without high altitude polycythemia (HAPC) and to elucidate the relationship between retinal structural parameters and hemoglobin (HGB).

METHODS

This cross-sectional study included 55 HAPC patients and 52 healthy HA residents. Retinal structural parameters included retinal nerve fiber layer (RNFL) thickness, optic nerve head (ONH) parameters and retinal vessel diameter. RNFL thickness were acquired from spectral domain optical coherence tomography (SD-OCT) built-in software. ONH parameters including neuroretina rim height, cup area, disc area and vertical cup/disc ratio were obtained by OCT built-in software and ImageJ software. Retinal vessel measurements including central retinal artery equivalent (CRAE), central retinal vein equivalent (CRVE) and AVR (artery/vein ratio) were calculated by revised formulas for summarizing retinal vessel diameters. All parameters were compared between HAPC group versus healthy HA group. The associations between retinal parameters and HGB were assessed by Pearson correlation analyses.

RESULTS

In comparison of HAPC group versus healthy HA group, RNFL thickness was thicker in the nasal quadrant of the optic disc in HAPC group (74.82 ± 14.4 VS. 66.06 ± 13.71 μm, P = 0.002). Bigger disc area and bigger cup area were also observed in HAPC group (all P < 0.05). Meanwhile, the value of CRVE was higher in HAPC group which suggested that retinal veins dilated significantly in HAPC patients (P < 0.001), however, CRAE and AVR were comparable between groups. Pearson analyses revealed that HGB was positive correlated with CRVE in HAPC group (r = 0.469, P = 0.003).

CONCLUSIONS

long-term HA exposure secondary HAPC could result in thickened RNFL, enlarged ONH and dilated retinal veins. Moreover, increased blood viscosity caused by HGB should be responsible for dilated veins, but not for thickened RNFL and enlarged ONH. This study deepens the understanding of the impact of HA environment on retina.

Effects of long-term high-altitude exposure on retinal and choroidal microcirculation

PURPOSE

To quantify the effect of long-term high-altitude (HA) exposure on retinal and choroidal microcirculation and to relate these changes to high-altitude polycythemia (HAPC), as a proxy for etiopathogenesis of high-altitude related retinopathy (HAR).

METHODS

Fifty-one HAPC patients, 50 healthy HA residents, and 43 low altitude (LA) residents were recruited in this study. Optical coherence tomography angiography (OCTA) and enhanced depth imaging (EDI)-OCT images were analyzed. Retinal microvascular metrics included vessel density (VD), skeleton density (SD), fractal dimension (FD), and foveal avascular zone (FAZ). Choroidal microvascular metrics included subfoveal choroidal thickness (SFCT) and choroidal vascularity index (CVI). All metrics were calculated by ImageJ software and compared among HAPC group, healthy HA group, and LA group.

RESULTS

In HAPC group, VD (30.62 ± 3.67%), SD (13.25 ± 1.64%), FD (1.79 ± 0.04), and the CVI (63.01 ± 1.42%) were significant lower and SFCT (403.25 ± 94.3 μm) was significant thicker than healthy HA group (all P < 0.001). FAZ area was comparable between two groups (0.42 ± 0.1 vs. 0.4 ± 0.11 mm², P = 0.411). However, these metrics were not different between healthy HA group and LA group (all P > 0.05) except for FD was lower in HA group (P < 0.001). Pearson's correlation analyses revealed HGB was negatively related with VD (r =  - 0.562, P < 0.001) and positively related with SFCT (r = 0.505, P < 0.001) in healthy HA group; however, no associations between HGB and vascular metrics in HAPC group were detected (all P > 0.05).

CONCLUSIONS

Long-term exposure to HA environment induces retinal and choroidal microcirculation disturbance in HAPC patients. However, these changes were not evident in healthy HA residents because of adaptation.

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

Altitude affects intraocular pressure (IOP); however, the underlying mechanisms involved and its relationship with ocular hemodynamics remain unknown. Herein, a validated mathematical modeling approach was used for a physiology-enhanced (pe-) analysis of the Mont Blanc study (MBS), estimating the effects of altitude on IOP, blood pressure (BP), and retinal hemodynamics. In the MBS, IOP and BP were measured in 33 healthy volunteers at 77 and 3466 m above sea level. Pe-retinal hemodynamics analysis predicted a statistically significant increase (p < 0.001) in the model predicted blood flow and pressure within the retinal vasculature following increases in systemic BP with altitude measured in the MBS. Decreased IOP with altitude led to a non-monotonic behavior of the model predicted retinal vascular resistances, with significant decreases in the resistance of the central retinal artery (p < 0.001) and retinal venules (p = 0.003) and a non-significant increase in the resistance in the central retinal vein (p = 0.253). Pe-aqueous humor analysis showed that a decrease in osmotic pressure difference (OPD) may underlie the difference in IOP measured at different altitudes in the MBS. Our analysis suggests that venules bear the significant portion of the IOP pressure load within the ocular vasculature, and that OPD plays an important role in regulating IOP with changes in altitude.

CILIORETINAL ARTERIES INFLUENCE OPTIC NERVE HEAD, PERIPAPILLARY, AND MACULAR VESSEL DENSITIES IN HEALTHY EYES: An Optical Coherence Tomography Angiography Study

BACKGROUND/PURPOSE

To analyze the influence of a cilioretinal artery (CRA) on macular and peripapillary vessel density in healthy eyes as measured using optical coherence tomography angiography.

METHODS

A total of 83 eyes of 83 patients were included in this study. Optical coherence tomography angiography was performed using the RTVue XR Avanti with AngioVue (Optovue Inc). The macula was imaged with a 3 × 3-mm scan, whereas for the optic nerve head a 4.5 × 4.5-mm scan was taken. Optical coherence tomography angiography images of the optic nerve head were screened for the presence of a CRA.

RESULTS

In 31 eyes, a CRA was detected (37.3%). The vessel density in eyes with a CRA was significantly lower within the optic nerve head (P = 0.005) but higher in the peripapillary capillary network (P < 0.001) and (whole en face) macular superficial capillary plexus (P = 0.025), when compared with eyes with no CRA.

CONCLUSION

Our findings reveal that in eyes with a CRA, the vessel density in the peripapillary and macular superficial capillary plexus is increased, whereas the optic nerve head perfusion (as indicated by vessel density in the inside disk region) is decreased. This has to be considered when analyzing quantitative optical coherence tomography angiography parameters in scientific and clinical applications.

Retinal oxygen saturation and vessel diameter in patients with chronic kidney disease

PURPOSE

To investigate changes in retinal oximetry and the diameter of retinal vasculature in patients with chronic kidney disease (CKD) and relationships between retinal vasculature and the estimated glomerular filtration rate (eGFR), provide a scientific basis for the early detection and diagnosis of CKD.

METHODS

Eighty-three patients with CKD and 103 healthy individuals were included after providing informed consent. All participants were examined using a noninvasive technology (Oxymap Inc., Reykjavik, Iceland) for measuring the arterial (SaO₂ ) and venous (SvO₂ ) oxygen saturation and the arteriovenous difference in oxygen saturation (Sa-vO₂ ). The corresponding retinal vessel diameters of these arterioles (D-A) and venules (D-V) were measured. The eGFR of patients with CKD was calculated from the serum creatinine concentration.

RESULTS

In general, patients with CKD had higher mean SaO₂ values than healthy individuals (100.15 ± 4.68% versus 97.14 ± 4.22%; p < 0.001, mean ± SD). The mean SaO₂ in the superior temporal, superior nasal and inferior nasal quadrants significantly increased. There was no significant difference measured in the SvO₂ when patients with CKD (63.66 ± 5.29%) and healthy individuals (62.70 ± 5.27%) were compared. The mean Sa-vO₂ of the CKD group (36.49 ± 4.98%) was increased compared with normal subjects (34.44 ± 4.76%) (p = 0.005). The retinal arteriole diameter was narrower in patients with CKD than in normal individuals (117.53 ± 14.88 μm versus 126.87 ± 14.98 μm; p < 0.001, mean ± SD), and the arteriovenous ratio was smaller than in normal individuals (0.71 ± 0.09 versus 0.77 ± 0.09; p < 0.001, mean ± SD). Pearson's two-tailed correlation showed a significant correlation between the SaO₂ and eGFR (R = -0.363, p = 0.001), and narrower retinal arterial calibre was significantly associated with a lower eGFR (R = 0.415, p < 0.001).

CONCLUSION

Based on our results, there were alterations in retinal oxygen saturation and vascular diameter in patients with CKD. Further studies are needed to determine whether such changes play a role in the development of CKD.

Intraocular Pressure Changes of Healthy Lowlanders at Different Altitude Levels: A Systematic Review and Meta-Analysis

Background: High altitude, characterized by hypobaric hypoxia, low temperature, and intensive ultraviolet radiation, is identifiably one of the examples of scientific enquiry into aviation and space analogs. However, little is known about the ocular physiological response, especially intraocular pressure (IOP) changes at high altitude. Objectives: This study aimed to systematically review of high altitude exposure on IOP for healthy lowlanders with unoperated eyes. Methods: A comprehensive systematic literature search was conducted in the electronic databases until September 1st, 2019. A meta-analysis was performed following the preferred reporting items for systematic review and meta-analysis statement (PRISMA). We systematically searched the studies conducted over 2,000 m above sea level (a.s.l) in healthy lowlanders with measurements of IOP. Meta-analyses (random effect model and heterogeneity tests), subgroup analyses (altitude, duration, type, and pattern of exposure), sensitivity analysis, funnel plot, Begger's and Egger's test for publication bias were performed. Quality assessment was conducted using the Newcastle-Ottawa scale. The meta-analysis was registered in the PROSPERO database (CRD42019136865). Results: Of 9595 publications searched, 20 publications (n = 745) qualified for inclusion, with non-significant decrease in overall IOP [standardized mean difference (SMD): 0.14, 95% CI: -0.12-0.40; p = 0.30] with high heterogeneity (p < 0.001, I 2 = 82%). However, subgroup analyses revealed significant decrease of IOP at high altitude of 3,000-5,500 m a.s.l (SMD: 0.57, 95% CI: 0.07-1.06; p = 0.03) whereas increase of IOP at extreme altitude of over 5,500 m a.s.l (SMD: -0.34, 95% CI: -0.61-0.06; p = 0.02). And the duration of exposure more than 72 hours (h) was likely to induce a decrease of IOP bordering on statistical significance at the 5% level (SMD: 1.29, 95% CI: 0.02-2.56; p = 0.05). Simultaneously, we also observed significant decrease of IOP for active exposure (e.g., physical activity and hiking, SMD: 0.81, 95% CI: 0.05-1.57; p = 0.04). Conclusion: Our analysis shows exposure to the altitude over 3,500 m a.s.l, duration of exposure more than 72 h and active exposure pattern may have modest, but significant effects on IOP. The higher altitude, the duration of exposure as well as physical activity seem to play crucial roles in the effects of high-altitude exposure on IOP.