Water drinking influences eye length and IOP in young healthy subjects

A first-in-human pilot study of a novel electrically-passive metamaterial-inspired resonator-based ocular sensor embedded contact lens monitoring intraocular pressure fluctuations

Glaucoma is a leading cause of blindness with no cure, but early treatment and effective monitoring can often slow the progression of the disease. Monitoring of glaucoma is based on the measurement of intra-ocular pressure (IOP) that is a physiological parameter related to the mechanical state and parameters of the eye. Conventionally, diagnosing and assessing the progression of glaucoma is based on the method of measuring IOP discretely at clinics. Recent studies have demonstrated the importance of continuously monitoring IOP for 24 h to elucidate the effect of circadian rhythm. In this work, a metamaterial-inspired electrically-passive sensor-embedded contact lens is presented to monitor the IOP fluctuations based on a first-in-human pilot study. The sensor inside the contact lens is an electrically passive, metamaterial-based resonator that can be measured using a wearable antenna patch. The system has been tested with six healthy volunteers during an experiment to induce deliberate IOP changes via water-loading and placing the individuals in supine position using a recliner seat. The initial data compared with tonometer measurements suggest that the system can be used to assess the variation of IOP continuously.

Near work, light levels and dioptric profile - Which factor dominates and influences the short-term changes in axial length?

PURPOSE

Given the agonistic nature of near work to promote axial elongation and the antagonistic nature of time outdoors to prevent myopia, we aimed to investigate the following: (a) how the short-term effect of near work performed outdoors (Experiment 1) influences axial length and (b) how near work performed in two different dioptric profiles (uncluttered and cluttered) alters the changes in central axial length (Experiment 2).

METHODS

Forty-six adults (age range: 19-32 years) participated in the study. In Experiment 1, 22 participants completed a 15-min distance task and a reading task in both the outdoor (~30,000 lux) and indoor (~70 lux) locations. In Experiment 2, 24 participants performed the same reading task at a study desk in uncluttered and cluttered reading environments. Pre- and post-task ocular biometry measurements were performed for each session using a non-contact biometer.

RESULTS

In Experiment 1, a significant increase in axial length from baseline was found after performing reading tasks in both outdoor (mean ± SEM: +12.3 ± 3.4 μm, p = 0.001) and indoor locations (+11.9 ± 3.1 μm, p = 0.001). In Experiment 2, axial length increased significantly from baseline to post reading task, in both uncluttered (+17.9 ± 3.5 μm, p < 0.001) and cluttered reading environments (+19.2 ± 2.9 μm, p < 0.001). No significant changes in axial length were observed either between outdoor and indoor locations (p = 0.92) or between the uncluttered and cluttered reading environment (p = 0.75).

CONCLUSION

Independent of light intensity (outdoor or indoor location) and dioptric profile of the near-work environment (uncluttered or cluttered), a 15-min reading task led to a significant increase in axial length. While the long-term effects of these findings need to be evaluated, practitioners should emphasise how near work can reduce the beneficial effects of time outdoors, while providing recommendations related to time outdoors for myopia control.

Effects of water drinking on corneal biomechanics: The association with intraocular pressure changes

Purpose:

We aimed to assess the impact of drinking water (500 and 1000 mL) on corneal biomechanics and determine the level of association between changes in intraocular pressure and variations in the different biomechanical properties of the cornea.

Methods:

A total of 39 healthy young adults ingested either 1000 mL (n = 21) or 500 mL (n = 18) of tap water in 5 min. The CorVis ST system was used to assess corneal biomechanics at baseline and at 15, 30, and 45 min after water ingestion.

Results:

Water drinking induced statistically significant changes in the deformation amplitude (P < 0.001, η² = 0.166), highest concavity time (P = 0.012, η² = 0.093), peak distance (P < 0.001, η² = 0.171), time and velocity of the first applanation (P < 0.001, η² = 0.288 and P = 0.016, η² = 0.087, respectively), and time and velocity of the second applanation (P = 0.030, η² = 0.074 and P = 0.001, η² = 0.132, respectively), being independent of the amount of water ingested (P > 0.05 in all cases). There were significant associations between changes in intraocular pressure and some parameters of corneal biomechanics

Conclusion:

Small variations in whole-body hydration status alter different biomechanical properties of the cornea, with these changes being associated with intraocular pressure levels. These findings indicate that whole-body hydration status can be considered for the diagnosis and management of different ocular conditions.

How a dynamic optical system maintains image quality: Self-adjustment of the human eye

The eyeball is continually subjected to forces that cause alterations to its shape and dimensions, as well as to its optical components. Forces that induce accommodation result in an intentional change in focus; others, such as the effect of intraocular pressure fluctuations, are more subtle. Although the mechanical properties of the eyeball and its components permit mediation of such subtle forces, the concomitant optical changes are not detected by the visual system. Optical self-adjustment is postulated as the mechanism that maintains image quality. The purpose of this study was to investigate how self-adjustment occurs by using an optical model of the eyeball and to test the requisite optical and biometric conditions.

Effect of Topical Pilocarpine on Choroidal Thickness in Healthy Subjects

SIGNIFICANCE

This is a proof-of-concept study showing the possibility of pharmacological control for choroidal thickness using pilocarpine as an agent that causes 2 to 5% choroidal thinning in healthy eyes after the instillation.

PURPOSE

The purpose of this article was to study the effect of instillation of 1% pilocarpine on choroidal thickness in healthy subjects.

METHODS

Sixteen healthy individuals (seven males and nine females; mean ± standard deviation age, 25.8 ± 3.3 years) were included. All participants received optical coherence tomography to evaluate subfoveal choroidal thickness (SCT) and choroidal area on cross-sectional scan within 4-mm central area. Axial length was measured using optical biometry. Optical coherence tomography was performed before and after pilocarpine was instilled six times for a 75-minute period in one eye; the fellow eye was used as the control. Subfoveal choroidal thickness and choroidal area were measured by two masked graders in random fashion and averaged for analysis.

RESULTS

After instillation of 1% pilocarpine, percentage SCT change in study and control eye was -3.3 ± 3.8% and 0.4 ± 3.2%, respectively (P = .03). Percentage change choroidal area in study and control eye was -2.3 ± 2.5% and 0.8 ± 3.3%, respectively (P < .001). There was a correlation between percentage SCT change and axial length (r = -0.56, P < .001), as well as between percentage SCT change and baseline SCT (r = 0.72, P < .001).

CONCLUSIONS

Instillation of 1% pilocarpine causes a decrease of choroidal thickness, which is more substantial in eyes with short axial length and thick choroid.

Intraocular pressure response affected by changing of sitting and supine positions

PURPOSE

To assess the intraocular pressure (IOP) time response to change in body position from sitting to supine and from supine to sitting immediately and during rest in each position.

METHODS

Forty-four visually healthy volunteers were recruited for the study. The experiment consisted of the initial sitting position (baseline state), the subsequent lying period and the final sitting period. Both periods were 30 min long. The IOP was measured in the baseline state, immediately after each position change and then in minutes 5, 15, 25 and 30 during each period. The Icare Pro^® rebound tonometer was used.

RESULTS

The mean IOP increased after each position change (2.6 ± 2.4 mmHg after lying down and 2.1 ± 3.1 mmHg after sitting up) and then gradually decreased with time. The mean IOP was 1.41 ± 2.4 mmHg higher in the lying period than in the sitting period; the mean difference was smaller for the lower baseline (0.9 ± 2.2 mmHg) than the higher baseline (1.9 ± 2.5 mmHg). The mean IOP in the final sitting was significantly lower (2.5 ± 1.9 mmHg) than in the initial sitting position. The effect of sex was insignificant.

CONCLUSIONS

There was an immediate increase in IOP as a response to both changes in the body position and the subsequent gradual decrease with time. The IOP difference between lying and sitting position was depended on baseline.

Intraocular Pressure Is a Poor Predictor of Hydration Status following Intermittent Exercise in the Heat

Current hydration assessments involve biological fluids that are either compromised in dehydrated individuals or require laboratory equipment, making timely results unfeasible. The eye has been proposed as a potential site to provide a field-based hydration measure. The present study evaluated the efficacy and sensitivity of intraocular pressure (IOP) to assess hydration status. Twelve healthy males undertook two 150 min walking trials in 40°C 20% relative humidity. One trial matched fluid intake to body mass loss (control, CON) and the other had fluid restricted (dehydrated, DEH). IOP (rebound tonometry) and hydration status (nude body mass and serum osmolality) were determined every 30 min. Body mass and serum osmolality were significantly (p < 0.05) different between trials at all-time points following baseline. Body mass losses reached 2.5 ± 0.2% and serum osmolality 299 ± 5 mOsmol.kg⁻¹ in DEH. A significant trial by time interaction was observed for IOP (p = 0.042), indicating that over the duration of the trials IOP declined to a greater extent in the DEH compared with the CON trial. Compared with baseline measurements IOP was reduced during DEH (150 min: −2.7 ± 1.9 mm Hg; p < 0.05) but remained stable in CON (150 min: −0.3 ± 2.4 mm Hg). However, using an IOP value of 13.2 mm Hg to predict a 2% body mass loss resulted in only 57% of the data being correctly classified (sensitivity 55% and specificity 57%). The use of ΔIOP (−2.4 mm Hg) marginally improved the predictive ability with 77% of the data correctly classified (sensitivity: 55%; specificity: 81%). The present study provides evidence that the large inter-individual variability in baseline IOP and in the IOP response to progressive dehydration, prevents the use of IOP as an acute single assessment marker of hydration status.

Diurnal Alterations of Refraction, Anterior Segment Biometrics, and Intraocular Pressure in Long-Time Dehydration due to Religious Fasting

PURPOSE

To investigate the effects of dehydration due to fasting on diurnal changes of intraocular pressure, anterior segment biometrics, and refraction.

SUBJECTS AND METHODS

The intraocular pressures, anterior segment biometrics (axial length: AL; Central corneal thickness: CCT; Lens thickness: LT; Anterior chamber depth: ACD), and refractive measurements of 30 eyes of 15 fasting healthy male volunteers were recorded at 8:00 in the morning and 17:00 in the evening in the Ramadan of 2013 and two months later. The results were compared and the statistical analyses were performed using the Rstudio software version 0.98.501. The variables were investigated using visual (histograms, probability plots) and analytical methods (Kolmogorov-Smirnov/Shapiro-Wilk test) to determine whether or not they were normally distributed.

RESULTS

The refractive values remained stable in the fasting as well as in the control period (p = 0.384). The axial length measured slightly shorter in the fasting period (p = 0.001). The corneal thickness presented a diurnal variation, in which the cornea measured thinner in the evening. The difference between the fasting and control period was not statistically significant (p = 0.359). The major differences were observed in the anterior chamber depth and IOP. The ACD was shallower in the evening during the fasting period, where it was deeper in the control period. The diurnal IOP difference was greater in the fasting period than the control period. Both were statistically significant (p = 0.001). The LT remained unchanged in both periods.

CONCLUSIONS

The major difference was shown in the anterior chamber shallowing in the evening hours and IOP. Our study contributes the hypothesis that the posterior segment of the eye is more responsible for the axial length alterations and normovolemia has a more dominant influence on diurnal IOP changes.

The short-term effects of exercise on intraocular pressure, choroidal thickness and axial length

Purpose

To explore ocular changes in healthy people after exercise.

Methods

Twenty five volunteers underwent exercise for 15 minutes on a treadmill. Measurements of choroidal thickness, intraocular pressure (IOP), ocular biometry, and blood pressure were taken before and after exercise. Enhanced Depth Imaging optical coherence tomography (EDI-OCT) was used to measure choroidal thickness at the fovea. Intraocular pressure (IOP) was measured by Goldmann applanation tonometry. Ocular biometric measures were collected using A scan ultrasound. Blood pressure was measured concurrently with the acquisition of the scans.

Results

Twenty five volunteers (25 eyes) with a mean age of 25.44±3.25 years were measured. There was a significant increase in systolic and diastolic pressure after exercise (P<0.05). The IOP showed a significant decrease after exercise (P<0.05). However there was no significant difference in the mean choroidal thickness, ocular axial length, anterior chamber depth, lens thickness, or vitreous length before and after exercise measurements (P>0.05).

Conclusion

There was a significant decrease in IOP from exercise without a change in choroidal thickness and ocular biometric measures. IOP and choroidal thickness were not correlated, suggesting that the IOP decrease from exercise is not due to changes in choridal thickness.

Does fundus fluorescein angiography procedure affect ocular pulse amplitude?

Purpose. This study examines the effects of fundus fluorescein angiography (FFA) procedure on ocular pulse amplitude (OPA) and intraocular pressure (IOP). Materials and Methods. Sixty eyes of 30 nonproliferative diabetic retinopathy patients (15 males, 15 females) were included in this cross-sectional case series. IOP and OPA were measured with the Pascal dynamic contour tonometer before and after 5 minutes of intravenous fluorescein dye injection. Results. Pre-FFA mean OPA value was 3.05 ± 1.36 mmHg and post-FFA mean OPA value was 2.93 ± 1.28 mmHg (P = 0.071). Pre-FFA mean IOP value was 17.97 ± 1.99 mmHg and post-FFA mean IOP value was 17.81 ± 2.22 mmHg (P = 0.407). Conclusion. Although both mean OPA and IOP values were decreased after FFA procedure, the difference was not statistically significant. This clinical trial is registered with Australian New Zealand Clinical Trials Registry number ACTRN12613000433707.

Changes in choroidal thickness, axial length, and ocular perfusion pressure accompanying successful glaucoma filtration surgery

PURPOSE

To investigate the changes in choroidal thickness (CT), axial length (AL), and ocular perfusion pressure (OPP) accompanying intraocular pressure (IOP) reduction after trabeculectomy. methods: Thirty-nine eyes of 39 patients with primary open-angle glaucoma uncontrolled by medical therapy were included in this prospective and interventional study. All patients underwent a fornix-based trabeculectomy. The CT was measured by enhanced depth imaging-optical coherence tomography. IOP, AL, and systolic/diastolic blood pressure were also measured, and OPP was calculated. All measurements were performed at baseline and 1 month after surgery.

RESULTS

The mean IOP was 25.0 ± 5.8 mm Hg at baseline and 11.7 ± 2.6 mm Hg after trabeculectomy (P<0.001), and the mean subfoveal CT was 295 ± 84 mm Hg at baseline and 331 ± 82 mm Hg after trabeculectomy (P<0.001). The mean AL was 23.64 ± 0.98 mm at baseline and 23.54 ± 0.96 mm after trabeculectomy (P<0.001), whereas the mean OPP was 38.8 ± 6.2 mm Hg preoperatively, and 51.1 ± 7.3 mm Hg postoperatively (P<0.001). The change in CT negatively correlated with the change in IOP (r=-0.785, P<0.001) and AL (r=-0.693, P<0.001), whereas it positively correlated with the change in OPP (r=0.418, P=0.008).

CONCLUSION

These results suggest that the large IOP decrease following trabeculectomy causes choroidal thickening. In addition, CT changes are associated with IOP and AL reduction as well as OPP increase.

Changes in choroidal thickness and optical axial length accompanying intraocular pressure increase

PURPOSE

To measure changes in choroidal thickness (CT), retinal thickness (RT), and axial length (AL) accompanying intraocular pressure (IOP) increase and to investigate the changes in axial eye dimensions induced by IOP increase.

METHODS

Thirty-four eyes of 34 patients undergoing a diagnostic provocative test for primary angle closure (PAC). Patients with other macular diseases were excluded. Patients underwent the darkroom prone provocative test (DR-PPT) for 1 h. We measured CT and RT at the fovea by optical coherence tomography with the enhanced depth imaging method and AL with noncontact, partial coherence laser interferometry before and after the DR-PPT.

RESULTS

There was a statistically significant increase in the mean (SD) IOP of 7.3 (9.2) mmHg and the mean (SD) AL of 0.06 (0.12) mm after the DR-PPT (P < 0.001 and P = 0.014, respectively). There was a statistically significant decrease in the mean (SD) subfoveal CT of 30.0 (36.8) μm (P < 0.001), while there was no significant change in the mean foveal RT. The change in subfoveal CT was negatively correlated with the changes in IOP (r = -0.71, P < 0.001) and AL (r = -0.54, P = 0.004).

CONCLUSIONS

In eyes suspected of having PAC, acutely increased IOP accompanies choroid thinning and corresponding elongation of the optical axis.

The short-term influence of exercise on axial length and intraocular pressure

PURPOSE

The aim of this study is to investigate the short-term influence of a period of dynamic exercise on axial length (AXL) and intraocular pressure (IOP) in young adult subjects.

PATIENTS AND METHODS

In all, 20 young adult subjects (10 myopes and 10 emmetropes) participated. Baseline measures of ocular biometrics, IOP and ocular pulse amplitude (OPA) were taken following a 20-min rest period. Subjects then performed 10 min of moderate intensity, low impact dynamic exercise (bicycle ergometry). Measures of ocular biometrics, IOP and OPA were repeated immediately after, and then 5 and 10 min after this exercise task. Systemic blood pressure and pulse rate were also monitored. A repeated measures analysis of variance was used to investigate the changes in the measured parameters.

RESULTS

Exercise resulted in significant changes in a range of ocular parameters. A small but significant decrease in AXL was observed following exercise (P<0.0001). The largest change in AXL was noted immediately following exercise (mean decrease -17±10 μm). IOP and OPA also decreased significantly following exercise (P<0.0001). A moderate but significant positive association was found between the changes in AXL and the changes in IOP (r(2)=0.36, P<0.0001). There were no significant differences found between the myopic and emmetropic subjects in the magnitude of changes observed in ocular parameters following exercise.

CONCLUSION

The physiological effects of dynamic exercise lead to changes in a range of ocular parameters, including significant reductions in IOP, OPA and decreases in AXL.