Twenty-four hourly variations in the inflow of the aqueous humour

Remote and low-cost intraocular pressure monitoring by deep learning of speckle patterns

Significance

Glaucoma, a leading cause of global blindness, disproportionately affects low-income regions due to expensive diagnostic methods. Affordable intraocular pressure (IOP) measurement is crucial for early detection, especially in low- and middle-income countries.

Aim

We developed a remote photonic IOP biomonitoring method by deep learning of the speckle patterns reflected from an eye sclera stimulated by a sound source. We aimed to achieve precise IOP measurements.

Approach

IOP was artificially raised in 24 pig eyeballs, considered similar to human eyes, to apply our biomonitoring method. By deep learning of the speckle pattern videos, we analyzed the data for accurate IOP determination.

Results

Our method demonstrated the possibility of high-precision IOP measurements. Deep learning effectively analyzed the speckle patterns, enabling accurate IOP determination, with the potential for global use.

Conclusions

The novel, affordable, and accurate remote photonic IOP biomonitoring method for glaucoma diagnosis, tested on pig eyes, shows promising results. Leveraging deep learning and speckle pattern analysis, together with the development of a prototype for human eyes testing, could enhance diagnosis and management, particularly in resource-constrained settings worldwide.

Intraocular pressure remote photonic biomonitoring based on temporally encoded external sound wave stimulation

Continuous noninvasive measurement of intraocular pressure (IOP) is an important tool in the evaluation process for glaucoma. We present a methodology enabling high-precision, noncontact, reproducible, and continuous monitoring of IOP based on the value of the damping factor of transitional oscillations obtained at the surface of the eye after terminating its stimulation by a sound wave. The proposed configuration includes projection of a laser beam and usage of a fast camera for analyzing the temporal-spatial variations of the speckle patterns backscattered from the iris or the sclera following the above-mentioned sound waves external stimulation. The methodology was tested on an artificial eye and a carp fish eye under varying pressure as well as on human eyes.

Agonistic Autoantibodies to the β2-Adrenergic Receptor Involved in the Pathogenesis of Open-Angle Glaucoma

Glaucoma is a frequent ocular disease that may lead to blindness. Primary open-angle glaucoma (POAG) and ocular hypertension (OHT) are common diseases with increased intraocular pressure (IOP), which are mainly responsible for these disorders. Their pathogenesis is widely unknown. We screened the sera of patients with POAG and OHT for the prevalence of autoantibodies (AAb) against G protein-coupled receptors (GPCRs) in comparison to controls. Employing frequency modulation of spontaneously contracting neonatal rat cardiomyocytes in vitro, agonistic GPCR AAb were to be detected in roughly 75% of the patients with POAG and OHT, however, not in controls. Using inhibitory peptides the AAb’ target was identified as β2 adrenergic receptor (β2AR). The AAb interact with the second extracellular loop of β2AR. The peptides 181–187 and 186–192 were identified as binding sites of the AAb within the extracellular loop II. The binding of the AAb to β2ARs was verified by surface-plasmon-resonance analysis. The isotype of the AAb was (immunoglobulin) IgG3. In an additional pilot principal-of-proof study, including four patients with POAG, the removal of the AAb against the β2AR and other immunoglobulins G by immunoadsorption resulted in a transient reduction of IOP. These findings might indicate a possible role of agonistic AAb directed against β2ARs in the dynamics of aqueous humor and might support a contribution of adaptive autoimmunity in the etiopathogenesis of POAG and OHT.

Role of cyclic AMP in the eye with glaucoma

Glaucoma is characterized by a slow and progressive degeneration of the optic nerve, including retinal ganglion cell (RGC) axons in the optic nerve head (ONH), leading to visual impairment. Despite its high prevalence, the biological basis of glaucoma pathogenesis still is not yet fully understood, and the factors contributing to its progression are currently not well characterized. Intraocular pressure (IOP) is the only modifiable risk factor, and reduction of IOP is the standard treatment for glaucoma. However, lowering IOP itself is not always effective for preserving visual function in patients with primary open-angle glaucoma. The second messenger cyclic adenosine 3′,5′-monophosphate (cAMP) regulates numerous biological processes in the central nervous system including the retina and the optic nerve. Although recent studies revealed that cAMP generated by adenylyl cyclases (ACs) is important in regulating aqueous humor dynamics in ocular tissues, such as the ciliary body and trabecular meshwork, as well as cell death and growth in the retina and optic nerve, the functional role and significance of cAMP in glaucoma remain to be elucidated. In this review, we will discuss the functional role of cAMP in aqueous humor dynamics and IOP regulation, and review the current medications, which are related to the cAMP signaling pathway, for glaucoma treatment. Also, we will further focus on cAMP signaling in RGC growth and regeneration by soluble AC as well as ONH astrocytes by transmembrane ACs to understand its potential role in the pathogenesis of glaucoma neurodegeneration

[Quantitative evaluation of uveoscleral outflow for optimization of glaucoma treatment]

The leading role in glaucoma treatment is now played by prostaglandin analogues (PGAs), whose point of application is the uveoscleral outflow of aqueous humor. Quantitative evaluation of the latter is, however, a problem yet unsolved.

AIM

To assess the clinical applicability of a new method for quantitative evaluation of the uveoscleral outflow in human eyes, which is meant to help with optimization of glaucoma therapy.

MATERIAL AND METHODS

Patients with early (n=33) and advanced (n=30) primary open-angle glaucoma (POAG) were enrolled. Besides the routine ophthalmic examination, all patients had their uveoscleral outflow quantified with our method. Basing on these findings, we have analyzed the effect of different hypotensive eye drops, namely, betaxolol 0.5% (selective beta-1-blocker), brinzolamid 1% (carbonic anhydrase inhibitor), travoprost 0.004% (prostaglandin analogue) and travoprost 0.004%/timolol 0.5% fixed combination (TTFC; prostaglandin analogue plus non-selective beta-blocker).

RESULTS

In early POAG, the uveoscleral outflow facility (Cfu) without treatment was 0.06±0.06, after betaxolol 0.5% as well as brinzolamid 1% use - 0.05±0.03, while after travoprost 0.004% and FCTT use - 0.10±0.06 and 0.08±0.05 correspondingly. In advanced POAG, Cfu was 0.04±0.03 without treatment, 0.06±0.04 - after betaxolol 0.5% or brinzolamid 1% use, 0.1±0.05 - after travoprost 0.004% use, and 0.1±0.04 - after FCTT use.

CONCLUSION

Quantitative evaluation of the uveoscleral outflow with the new method that has not only been justified, but also clinically tested, provides an opportunity to optimize POAG treatment.

Variability of Heidelberg Retina Tomograph parameters during exercise

PURPOSE

The purpose of this study was to determine whether exercise affects the stereometric parameters representing optic nerve head (ONH) topography.

METHODS

ONH topography, intraocular pressure (IOP) and blood pressure of 30 healthy volunteers were monitored before, during and after dynamic exercise raising systolic blood pressure by a minimum of 30 mmHg. Change in the stereometric ONH parameters was calculated.

RESULTS

IOP decreased and blood pressure increased during exercise, resulting in an increase in mean ocular perfusion pressure. Exercise was associated with an increase in variance in 17 of the 18 stereometric ONH parameters. The increase in variance was statistically significant in eight parameters, including rim area, cup/disc area ratio and cup shape measure. There was no statistically significant change in image quality. The absolute change from baseline in rim area, cup area, cup/disc area ratio, rim/disc area ratio and rim volume showed a statistically significant (p < 0.05) correlation with change in mean ocular perfusion pressure.

CONCLUSIONS

Exercise increases variability in stereometric ONH parameters. To avoid increased variance in the stereometric parameters, ONH imaging should be performed after allowing sufficient time to rest.

Variations nycthémérales de la pression intraoculaire et leurs implications cliniques

Intraocular pressure follows a circadian rhythm like many of the body's parameters. These fluctuations in intraocular pressure were recently identified as a risk factor for visual field loss, in addition to intraocular pressure itself. Furthermore, the pressure curve seems to have a different profile in glaucomatous patients: the peak occurs later compared with normal subjects. Better knowledge of pressure fluctuations and their physiological mechanisms is essential for optimal management of glaucomatous patients not only to interpret the single ocular tension recordings, but also to use the available treatments rationally, both drugs and surgery. The authors review different studies that have contributed to the current knowledge on the circadian rhythm of intraocular pressure, aquous humor flow regulation, and the effects of topical hypotensive drugs on the pressure curve.

Intraocular pressure over 24 hours after repeated administration of latanoprost 0.005% or timolol gel-forming solution 0.5% in patients with ocular hypertension

PURPOSE

To compare the effect on intraocular pressure (IOP) over 24 hours after 4 weeks of treatment with latanoprost 0.005% and timolol gel 0.5%.

DESIGN

Randomized, open, crossover single-center study.

PARTICIPANTS

Twenty-seven patients with ocular hypertension.

METHODS

The patients were randomly assigned to 4 weeks of latanoprost 0.005% once daily or timolol gel 0.5% once daily, with a 4-week washout period before switching therapy.

MAIN OUTCOME MEASURES

Measurement of IOP during 24 hours of hospitalization. Blood pressure and heart rate were also measured repeatedly over the 24 hours. Daytime mean IOP, nighttime mean IOP, and 24-hour mean IOP were calculated as IOP area under the curve (AUC) divided by time in hours.

RESULTS

The mean IOP during daytime (7 AM to 10 PM) was 13.5 +/- 0.4 mmHg (daytime IOP, AUC/15 hours, least square mean +/- standard error of the mean [SEM]) in the latanoprost group, and 14.8 +/- 0.4 mmHg in the timolol gel group. This difference of 1.3 +/- 0.3 mmHg was statistically significant in favor of latanoprost (P < 0.001; 95% confidence interval [CI], 0.7, 2.0). The mean IOP at night (10 PM to 7 AM) was 13.7 +/- 0.4 mmHg for latanoprost (nighttime IOP, AUC/9 hours, least square mean +/- SEM) and 15.9 +/- 0.5 mmHg for timolol gel, with a difference of 2.2 +/- 0.3 mmHg (P < 0.001; 95% CI, 1.5, 2.8). At every measured time point during the 24 hours, latanoprost reduced IOP more than timolol. There was no difference between the two treatment groups regarding blood pressure and heart rate.

CONCLUSIONS

Latanoprost reduced mean 24-hour IOP, mean daytime IOP, and mean nighttime IOP statistically significantly more than timolol. Also, latanoprost reduced IOP more effectively at every measured time point over the 24 hours compared with timolol gel.

The effect of dorzolamide on aqueous humor dynamics in normal human subjects during sleep

OBJECTIVE

The purpose of the study was to measure the effect of the topical carbonic anhydrase inhibitor, 2% dorzolamide hydrochloride, on the rate of aqueous humor flow in sleeping humans.

DESIGN

A randomized, double-masked, placebo-controlled study.

PARTICIPANTS

Twenty-five normal human subjects.

INTERVENTION

Topical instillation of 2% dorzolamide hydrochloride versus topical placebo.

MAIN OUTCOME MEASURES

Rate of aqueous humor flow in sleeping humans and intraocular pressure immediately after awakening from sleep.

RESULTS

The rate of flow in sleeping subjects at night (12 AM to 6 AM) was 1.28 +/- 0.30 microliters/min (mean +/- standard deviation; n = 25) in placebo-treated eyes, whereas the nighttime flow in dorzolamide-treated eyes was 1.17 +/- 0.38 microliters/min (P = < 0.001), resulting in a nighttime reduction of 9% (P = 0.032). In contrast, the daytime (8 AM to 4 PM) rate of flow in ambulatory subjects was 2.97 +/- 0.64 microliters/min in placebo-treated eyes and 2.60 +/- 0.63 microliters/min (P = 0.032) in dorzolamide-treated eyes, resulting in a daytime reduction of 13% (P = < 0.001).

CONCLUSIONS

Topically administered dorzolamide hydrochloride is effective for reducing the rate of aqueous humor flow in normal human eyes during the day and at night during sleep. The efficacy of dorzolamide at these two times is approximately half that of systematically administered acetazolamide.

Combined corticosteroid and catecholamine stimulation of aqueous humor flow

PURPOSE

Epinephrine is known to stimulate aqueous humor flow in humans. Corticosteroids are known to augment the effect of beta-adrenergic agonists on the ciliary body. This experiment was carried out to determine whether a corticosteroid can increase the stimulatory effect of epinephrine on aqueous humor flow.

METHODS

Twenty human volunteers were studied for 24 hours. Hydrocortisone was given orally and epinephrine was given intravenously during sleep while aqueous flow was monitored. Flow was compared with a second 24-hour study when oral and intravenous placebos were given. The sequence of administration was randomized. Subjects and investigators were masked. The flows also were compared with a previously published study in which the same dose of epinephrine was administered without steroid.

RESULTS

Epinephrine plus hydrocortisone compared with placebos increased aqueous flow 42% in subjects during sleep. The combination of epinephrine and hydrocortisone was a more potent stimulus to aqueous flow than epinephrine alone, which increased aqueous flow by only 27% (P = 0.045).

CONCLUSION

The two major hormones of the adrenal gland work in concert to increase the rate of aqueous humor flow in humans.

The effect of melatonin on aqueous humor flow in humans during the day

BACKGROUND

Aqueous humor flow through the anterior chamber of the eye undergoes a circadian cycle. The rate of flow during the day is twice as high as the rate of flow at night. The pineal hormone, melatonin, also undergoes a circadian cycle. Melatonin levels are high at night, whereas aqueous humor flow is low. The authors studied the effect of oral melatonin on aqueous humor flow in humans.

METHODS

The effect of melatonin on aqueous humor flow was evaluated in 19 healthy human volunteers in a randomized, masked crossover study with a placebo control. The hormone or placebo was administered orally during the day when endogenous levels of melatonin are low. Aqueous flow was measured by fluorophotometry for 8 hours.

RESULTS

The mean rate of flow during melatonin treatment was 2.71 +/- 0.64 microliters/minute (+/- standard deviation). The rate of flow during placebo treatment was 2.80 +/- 0.66 microliters/minute. There is no statistically significant difference between these two rates (P = 0.4). With a sample size of 19, the study has a power of 92% to detect at least a 15% difference in the rate of flow under the two conditions. Measurement of plasma concentration of melatonin in five subjects confirmed that concentrations after oral dosage reached peaks comparable with the normal endogenous nocturnal peaks.

CONCLUSIONS

The authors conclude that melatonin concentrations during the day, comparable with plasma concentrations that occur spontaneously during sleep, do not suppress aqueous humor formation. The authors find no support for the idea that plasma melatonin, per se, can suppress aqueous formation or that the circadian rhythm of plasma melatonin is primarily responsible for the circadian rhythm of aqueous humor flow.

Investigation of parameters influencing intraocular pressure increases during sleep

In previous studies, we have observed that young normal subjects show an increase in intraocular pressure (IOP) after sleep. Here we describe three experiments which investigated: (i) the effects of sleep in five groups of subjects: glaucoma, suspect glaucoma, young high-normal IOP, old high-normal IOP groups and an elderly control group, (ii) the effect of exposure to bright light (2500 lux) during sleep on associated IOP changes, and (iii) the relationship between changes in IOP and plasma melatonin during sleep. For all experiments IOP was measured before and after sleep. We found that IOP increased significantly after sleep. There was also a significant difference between the five groups with the old high-normal group showing the greatest increase, and the young high-normal group showing the lowest increase in IOP. The increase in IOP after sleep was reduced when the same subjects slept in bright light compared to that recorded when subjects slept in the dark. Plasma melatonin levels, as well as IOP, increased after sleep in the dark although there was no correlation between these changes for individual subjects.

Individual variability in the diurnal intraocular pressure curve

BACKGROUND

Reduction of intraocular pressure (IOP) is a primary goal of most glaucoma treatments. However, because the IOP varies during the day, single measurements performed in an ophthalmologist's office do not necessarily provide information on the peak level and fluctuation of the IOP.

METHODS

Home tonometry was performed to gain more information on the nature of the diurnal IOP curves and on their variability. One hundred seventy-six patients with open-angle glaucoma (OAG), 55 subjects with ocular hypertension (OHT), and 18 control individuals measured their IOP five times daily at home for 4 to 8 consecutive days using a self-tonometer.

RESULTS

Well-defined diurnal IOP variations were observed in all three groups with a predominance of curves with morning or mid-day maxima. Erratic IOP curves without a diurnal rhythm were present in OHT (22%) and OAG (16%) patients but not in control subjects. Differences between the curves of the two eyes of an individual were frequent in OHT (33%) and OAG (36%) patients but not in control subjects (6%). Finally, the majority of OHT (72%) and OAG (66%) patients showed a difference in their diurnal curve patterns on repeat home tonometry performed months apart.

CONCLUSION

The authors indicate that it is difficult to rely on one eye as a control for the other. They also indicate that changes in IOP observed in the office at different visits often may be due to a shift in the type of diurnal curve rather than to a true change in the mean IOP. Monitoring of the diurnal IOP may be necessary in some cases if the clinician relies, even partially, on the level of IOP when making a decision on patient management.

Melatonin does not increase IOP significantly in rabbits

New Zealand white rabbits have a circadian rhythm of intraocular pressure; pressure is higher during the dark than during the light. We explored the possibility that the dark phase increase of serum and/or ocular melatonin plays a role in regulating the rhythm of intraocular pressure. Exogenous melatonin was delivered by four routes: topical application (0.1 and 10 micrograms), intravenous injection (1 microgram), intravitreal injection (9 micrograms) and intra-arterial infusion (50 ng and 1 microgram). Melatonin delivered by these routes did not increase intraocular pressure. We also measured the concentration of melatonin in the aqueous after unilateral intra-arterial infusion to confirm that melatonin delivered by this route reached the eye. The concentration was 419 +/- 99 and 109 +/- 17 pg/ml (n = 8, p < 0.025) in the ipsilateral and contralateral eyes, respectively. The concentration of melatonin in the aqueous after intra-arterial infusion of saline was less than the sensitivity of the assay (< 16 pg/ml, n = 6). The results of these experiments indicate that melatonin does not increase IOP significantly under the experimental conditions employed in this study.

Cervical ganglionectomy alters the circadian rhythm of intraocular pressure in New Zealand White rabbits

A circadian rhythm of intraocular pressure in rabbits could provide a useful model for understanding the daily rhythm of intraocular pressure in humans and for studying mechanisms which regulate intraocular pressure. Our results confirm earlier work showing that New Zealand White rabbits housed in an environment with a lighting cycle of 12 hours light and 12 hours dark have a rhythm of intraocular pressure, and that this rhythm persists in constant dark. We show further that the cycle of light and dark is the zeitgeber for entrainment of the rhythm of intraocular pressure, and therefore persistence of this rhythm in constant dark establishes it as a circadian rhythm. Cervical ganglionectomy demonstrated that intact sympathetic innervation to the eye is required for maintenance of the normal circadian rhythm of intraocular pressure in rabbits. Intraocular pressure in sympathectomized eyes is no different from control eyes during the light, but is significantly reduced during the dark.

Decreased intraocular pressure and aqueous humor turnover rate during longitudinal ocular studies in the rabbit

One group of 5 pigmented rabbits, during a period of 10 weeks, and two groups of 8 albino rabbits, during 16 weeks, showed a fall in aqueous turnover rate and outflow facility of about 30%. A fall in intraocular pressure also occurred of about 10 mm Hg. The biochemical correlative mechanism, systemic and/or local, is conjectural (reduction of "stress"; homeostasis). Empirically a parallel completely untreated control group should accompany any longitudinal study group in order to differentiate these temporal trends from experimental effects.