Partial Contact Indentation Tonometry for Measurement of Corneal Properties-Independent Intraocular Pressure

Inter-individual differences in corneal properties are ignored in existing methods for measuring intraocular pressure IOP, a primary parameter used in screening and monitoring of glaucoma. The differences in the corneal stiffness between individuals can be more than double and this difference would lead to IOP measurement errors up to 10 mmHg. In this study, an instrumented partial-contact indentation measurement and analysis method that can account for inter-individual corneal difference in stiffness is developed. The method was tested on 12 porcine eyes ex vivo and 7 rabbit eyes in vivo, and the results were compared to the controlled IOPs to determine the method's validity. Analyses showed that without corneal stiffness correction, up to 10 mmHg of measurement error was found between the existing approach and the controlled IOP. With the instrumented indentation and analysis method, less than 2 mmHg of differences were founded between the measured IOP and the controlled IOP. These results showed that instrumented partial-contact indentation can effectively account for inter-individual corneal variations in IOP measurement.     

Chronophysiology of the cardiovascular system

The development of ambulatory blood pressure monitoring devices and the beat-by-beat measurement of heart rate have enabled it to be established that there are circadian rhythms in heart rate and blood pressure in subjects living normally. Investigations of these variables have led to quantification of their fall at night, and rapid rise on awakening and becoming active in the morning. These changes are of particular interest insofar as abnormalities in them are associated with cardiovascular problems and morbidity in patients and also act as risk factors in otherwise healthy individuals. It has also been shown that there are many other variables of the cardiovascular system. The causes of the circadian rhythms in heart rate and blood pressure are outlined, with particular stress upon the role of the autonomic nervous system, as assessed from low- and high-frequency components of the variation in heart rate measured beat-by-beat. Activity increases blood pressure, but there is evidence that this “reactivity” varies with time of day, and this also might be related to cardiovascular morbidity. Based upon data from several sources, including night work, resting subjects and bed-ridden patients, it is concluded that the contribution of the “body clock” to producing the circadian rhythm in heart rate and blood pressure is relatively small. A bias towards an exogenous cause applies also to most other circadian rhythms in the cardiovascular system. Knowledge of circadian rhythmicity in cardiovascular system, together with an understanding of its causes, provides a rationale for advice to reduce cardiovascular risk and to assess the efficacy of therapies.     

Circadian Intraocular Pressure Rhythms in Athletic Horses under Different Lighting Regime

The present study was undertaken to investigate the existence of intraocular pressure (IOP) rhythms in athletic thoroughbred horses maintained under a 24 h cycle of light and darkness (LD) or under constant light (LL) or constant dark (DD) conditions. We identified an IOP circadian rhythm that is entrained to the 24 h LD cycle. IOP was low during the dark phase and high during the light phase, with a peak at the end of the light phase (ZT10). The circadian rhythm of IOP persisted in DD (with a peak at CT9.5), demonstrating an endogenous component in IOP rhythm. As previously shown in other mammalian species, horse IOP circadian rhythmicity was abolished in LL. Because tonometry is performed in horses for the diagnosis of ophthalmologic diseases, such as glaucoma or anterior uveitis, the daily variation in IOP must be taken into account in clinical practice to properly time tests and to interpret clinical findings.     

Development of a Device in Detection of Glaucoma for Rural Eye Care Using Additive Manufacturing and TRIZ

Purpose: The main purpose of this study is to develop a device for the indicative measurement of intraocular pressure (IOP) of eyeball, a key cause for glaucoma. In early diagnosis and treatment of glaucoma accurate measurement of IOP is important. The methods and devices which are available for the measurement of IOP have their own limitations which cause discomfort to the patients during measurement and needs anesthesia. There is a dare need of a device for the measurement of intraocular pressure by making the contact of plunger with closed eyelid eliminating the need of anesthesia and expert ophthalmologist. Method: Additive manufacturing (AM) is an era of technical development and innovation. Developing a device for detecting glaucoma by using AM and TRIZ ‘The theory of inventive problem solving’ (A Collaborative approach) can overcome the disadvantages that classic tonometer have. The field of Ophthalmology will be experiencing a paradigm shift towards the use of collaborative approach of TRIZ with AM. The developed new device was tested on 40 patient’s eye at Government Hospital Bhandara, (M. S.), India. The results of new device were cross verified by expert clinicians using calibrated Schiotz’s tonometer and digital palpation technique. Result: The developed new device was tested on patient’s eye through eyelid and results were compared with calibrated Schiotz’s tonometer. The results from the new device were found in good agreement with results from Schiotz’s tonometer with the average error of 0.033 ± 0.18 (mean ± SD) mm of Hg and mean relative error was -0.0018 ±0.0096 (mean ± SD). Conclusion: There is a substantial need for early detection and diagnosis of glaucoma in rural and remote areas (worldwide). A new device for detection of glaucoma using AM and TRIZ was introduced in this paper and measurements by the new device were by currently well accepted Schiotz’s tonometer. The new device will help the medical practitioners in rural and remote areas for early detection of glaucoma.     

Measurement of Outflow Facility Using iPerfusion

Elevated intraocular pressure (IOP) is the predominant risk factor for glaucoma, and reducing IOP is the only successful strategy to prevent further glaucomatous vision loss. IOP is determined by the balance between the rates of aqueous humour secretion and outflow, and a pathological reduction in the hydraulic conductance of outflow, known as outflow facility, is responsible for IOP elevation in glaucoma. Mouse models are often used to investigate the mechanisms controlling outflow facility, but the diminutive size of the mouse eye makes measurement of outflow technically challenging. In this study, we present a new approach to measure and analyse outflow facility using iPerfusion^™, which incorporates an actuated pressure reservoir, thermal flow sensor, differential pressure measurement and an automated computerised interface. In enucleated eyes from C57BL/6J mice, the flow-pressure relationship is highly non-linear and is well represented by an empirical power law model that describes the pressure dependence of outflow facility. At zero pressure, the measured flow is indistinguishable from zero, confirming the absence of any significant pressure independent flow in enucleated eyes. Comparison with the commonly used 2-parameter linear outflow model reveals that inappropriate application of a linear fit to a non-linear flow-pressure relationship introduces considerable errors in the estimation of outflow facility and leads to the false impression of pressure-independent outflow. Data from a population of enucleated eyes from C57BL/6J mice show that outflow facility is best described by a lognormal distribution, with 6-fold variability between individuals, but with relatively tight correlation of facility between fellow eyes. iPerfusion represents a platform technology to accurately and robustly characterise the flow-pressure relationship in enucleated mouse eyes for the purpose of glaucoma research and with minor modifications, may be applied in vivo to mice, as well as to eyes from other species or different biofluidic systems.     

Implantable self‐aligning fiber‐optic optomechanical devices for in vivo intraocular pressure‐sensing in artificial cornea

Artificial cornea is an effective treatment of corneal blindness. Yet, intraocular pressure (IOP) measurements for glaucoma monitoring remain an urgent unmet need. Here, we present the integration of a fiber‐optic Fabry‐Perot pressure sensor with an FDA‐approved keratoprosthesis for real‐time IOP measurements using a novel strategy based on optical‐path self‐alignment with micromagnets. Additionally, an alternative noncontact sensor‐interrogation approach is demonstrated using a bench‐top optical coherence tomography system. We show stable pressure readings with low baseline drift (<2.8 mm Hg) for >4.5 years in vitro and efficacy in IOP interrogation in vivo using fiber‐optic self‐alignment, with good initial agreement with the actual IOP. Subsequently, IOP drift in vivo was due to retroprosthetic membrane (RPM) formation on the sensor secondary to surgical inflammation (more severe in the current pro‐fibrotic rabbit model). This study paves the way for clinical adaptation of optical pressure sensors with ocular implants, highlighting the importance of controlling RPM in clinical adaptation.     

A passive pressure sensor for continuously measuring the intraocular pressure in glaucomatous patients

ObjectiveThe main risk factor for the development of glaucoma, a retinal disease leading to blindness, is an increase in the intraocular pressure (IOP). Reducing this IOP can be obtained by eye drops but unfortunately the disease can still progress because IOP increases are painless, can fluctuate and, thus remain undetected during a visit to an ophthalmologist. The “MATEO” ANR project aims to develop sensors embedded in a contact lens for continuously IOP monitoring.Materials and methodsPressure sensors were produced by MEMS technology and tested with pig eyes obtained at a local slaughterhouse. Solution was injected by 50 μL steps in the eye with a Hamilton syringe while IOP was monitored in parallel with a TonoVET system and an industrial pressure transducer inserted in the injection tubing system.ResultsOur first pressure sensor prototypes were generated and inserted in a lens compatible with eye application. A wireless system was developed to excite the sensor. At same time, it was recorded the data in components inserted into spectacles and a pocket recorder. In parallel, we showed that injecting a solution in the eye anterior chamber triggered an IOP increase smaller and more stable than injections in the posterior chamber. Finally, a direct correlation was observed between IOP measured on the corneal surface with the TonoVET and the pressure transducer placed close to eye injection point.DiscussionOur results indicate that our in vitro model on pig eyes is adequate to test our new lens sensor. Finally, the pressure sensor was successfully inserted in contact lens opening the way for their in vitro and in vivo preclinical validation.     

Glaucoma: An Extension of Various Chronic Neurodegenerative Disorders

The eyes are the window of the brain; various pathologies of the eyes can be explained on the basis of neurological disorders and vice versa. Today, our only approach for the management of glaucoma is intraocular pressure (IOP) reduction, whether by pharmacological or surgical methods. Available methods may effectively control IOP but fall short of stopping the progression of glaucoma. IOP is just one of the risk factors our therapy addresses, so we need to work towards shifting our approach towards addressing other factors involved in the etiopathogenesis of the disease. Pathogenesis of glaucoma at molecular level can be compared with that of common neurodegenerative diseases like Alzheimer’s and Parkinsonism. Targets for therapeutic intervention in chronic neurodegenerative diseases and glaucoma include apoptosis, axonal transport, free radical damage, role of polyunsaturated fatty acids, chaperones, gene regulation, etc. p38MAPK is a common pathway involved in all the neurodegenerative disease and glaucoma as well, and more research in this direction can be really beneficial for the development of novel diagnostic and therapeutic measures.     

System for Rapid,Precise Modulation of Intraocular Pressure,toward Minimally-Invasive In Vivo Measurement of Intracranial Pressure

Pathologic changes in intracranial pressure (ICP) are commonly observed in a variety of medical conditions, including traumatic brain injury, stroke, brain tumors, and glaucoma. However, current ICP measurement techniques are invasive, requiring a lumbar puncture or surgical insertion of a cannula into the cerebrospinal fluid (CSF)-filled ventricles of the brain. A potential alternative approach to ICP measurement leverages the unique anatomy of the central retinal vein, which is exposed to both intraocular pressure (IOP) and ICP as it travels inside the eye and through the optic nerve; manipulating IOP while observing changes in the natural pulsations of the central retinal vein could potentially provide an accurate, indirect measure of ICP. As a step toward implementing this technique, we describe the design, fabrication, and characterization of a system that is capable of manipulating IOP in vivo with <0.1 mmHg resolution and settling times less than 2 seconds. In vitro tests were carried out to characterize system performance. Then, as a proof of concept, we used the system to manipulate IOP in tree shrews (Tupaia belangeri) while video of the retinal vessels was recorded and the caliber of a selected vein was quantified. Modulating IOP using our system elicited a rapid change in the appearance of the retinal vein of interest: IOP was lowered from 10 to 3 mmHg, and retinal vein caliber sharply increased as IOP decreased from 7 to 5 mmHg. Another important feature of this technology is its capability to measure ocular compliance and outflow facility in vivo, as demonstrated in tree shrews. Collectively, these proof-of-concept demonstrations support the utility of this system to manipulate IOP for a variety of useful applications in ocular biomechanics, and provide a framework for further study of the mechanisms of retinal venous pulsation.     

Genome-wide analysis identified 17 new loci influencing intraocular pressure in Chinese population

Intraocular pressure(IOP) is a major risk factor for glaucoma. Genetic determinants of intraocular pressure can provide critical insights into the genetic architecture of glaucoma and, as a result, open new avenues for therapeutic intervention. We performed a genome-wide association study and replication analysis of 8,552 Chinese participants. In the genome-wide association study, we identified 51 loci that surpassed the significance of P9×10~(-7), and we formally replicated these loci. A combined discovery and replication meta-analysis identified 21 genome-wide loci that surpassed the genome-wide significance of P5×10~(-8), including 4 previously reported loci: rs145063132(7 p21.2, ETV1/DGKB), rs548030386(7 q31.2, ST7 near CAV1/CAV2), rs7047871(9 p24.2, GLIS3), and rs2472494(9 q31.1, ABCA1/SLC44 A1). Of the 17 newly identified loci, five were reported to have ocular related phenotypes: PTCH2(rs7525308 in 1 p34.1), LRIF1/DRAM2(rs1282146 in 1 p13.3), COLEC11(rs201143466 in 2 p25.3),SPTBN1(rs4514918 in 2 p16.2), and CRK(rs11078446 in 17 p13.3). The genetic loci identified in this study not only increase our understanding of the genes involved in intraocular pressure but also provide important genetic markers to improve future genetic screening and drug discovery for intraocular pressure disorders.     

Common genetic determinants of intraocular pressure and primary open-angle glaucoma

Intraocular pressure (IOP) is a highly heritable risk factor for primary open-angle glaucoma and is the only target for current glaucoma therapy. The genetic factors which determine IOP are largely unknown. We performed a genome-wide association study for IOP in 11,972 participants from 4 independent population-based studies in The Netherlands. We replicated our findings in 7,482 participants from 4 additional cohorts from the UK, Australia, Canada, and the Wellcome Trust Case-Control Consortium 2/Blue Mountains Eye Study. IOP was significantly associated with rs11656696, located in GAS7 at 17p13.1 (p = 1.4×10⁻⁸), and with rs7555523, located in TMCO1 at 1q24.1 (p = 1.6×10⁻⁸). In a meta-analysis of 4 case-control studies (total N = 1,432 glaucoma cases), both variants also showed evidence for association with glaucoma (p = 2.4×10⁻² for rs11656696 and p = 9.1×10⁻⁴ for rs7555523). GAS7 and TMCO1 are highly expressed in the ciliary body and trabecular meshwork as well as in the lamina cribrosa, optic nerve, and retina. Both genes functionally interact with known glaucoma disease genes. These data suggest that we have identified two clinically relevant genes involved in IOP regulation.     

24-Hour Assessment of Performance on a Palmtop Computer: Validating a Self-Constructed Test Battery

Serious adverse cardiovascular events, including myocardial infarction, sudden cardiac death, and stroke, frequently result from rupture of atherosclerotic plaques with superimposed thrombosis and exhibit a pronounced circadian rhythmicity, peaking in the morning hours. Two potentially synergistic mechanisms play a pathogenic role in the circadian variation of arterial thrombotic events. A morning surge in sympathetic activity alters hemodynamic forces and predisposes vulnerable coronary atherosclerotic plaques to rupture. Day–night variations of hemostatic and fibrinolytic factors result in morning hypercoagulability and hypofibrinolysis, promoting intraluminal thrombus formation at the same time when the risk for plaque rupture is highest. Diabetic patients have a very high cardiac event rate but fail to show normal circadian fluctuations in the occurrence of myocardial infarction. Alterations in the circadian variation autonomic tone, blood pressure, and the thrombotic–thrombolytic equilibrium have been documented in diabetic patients. These include reduced or absent 24-h periodicity in autonomic tone, fibrinolytic activity, and thrombotic tendency, and a blunted decline in nocturnal blood pressure. Disruption of these circadian rhythms explains the lack of significant circadian distribution of cardiac events in diabetic patients. Moreover, the loss of these normal biorhythms results in a continuous susceptibility to thrombotic events throughout the day and may contribute to the excess cardiovascular mortality and morbidity in these patients. (Chronobiology International, 18(1), 109–121, 2001)     

Systemic hypertension, headache, and ocular hemodynamics: a new hypothesis

The association between systemic hypertension and headache remains controversial and its pathophysiologic basis is uncertain. A rather characteristic early-morning pulsating headache is commonly seen in hypertensive patients, and a recent meta-analysis supports the link between these 2 entities. Epidemiologic evidence has paradoxically suggested a negative association between hypertension and headache. Unpredictable clinical association between severe hypertension and headache indicates that another cranial perfusion-related variable exerts a critical role. Neuroanatomically, head and neck pain primarily involves the ophthalmic division of the trigeminal nerve (V1). A link between systemic hypertension, pulsatile choroidal blood flow (CBF), and intraocular pressure (IOP) has been established. I propose that a trait ocular sympathetic hypofunction permits rapid episodic ocular choroidal overperfusion that stretches the ocular globe in the cohort of hypertensive patients with headache. Rapid distension of the pain-sensitive corneoscleral envelope can stimulate corneoscleral and iridial pain-sensitive V1 nerve endings and generate headache. Ocular tamponade function physiologically limits choroidal overperfusion. A higher basal IOP in some patients with moderate-to-severe hypertension may dampen pulsatile CBF and account for the negative epidemiologic link between sustained systemic hypertension and headache. Besides activation of the baroreceptor reflex, the association of hypalgesia with hypertension probably involves activation of the vasopressin-endorphin adaptive system consequent to mechanical stimulation of V1. The analogy between hypertensive headache and angle-closure glaucoma is rather limited because typical ocular and visual signs and symptoms of angle-closure glaucoma are not seen in hypertension-related headache. Hypertensive crises, including those associated with pheochromocytoma, are not accompanied by attacks of angle-closure glaucoma. Glaucoma is not associated with ocular choroidal congestion, but with reduced pulsatile CBF. The predisposition to develop angle-closure glaucoma is theoretically not associated with ocular autonomic hypofunction and should be conceptually dissociated from this hypothesis. The hypothesis can be evaluated by establishing significant circadian elevations of blood pressure, including nondipping nighttime pattern as well as circadian and periheadache measurements of IOP in patients with attacks of hypertension-related headache.     

Effects of Topical Bimatoprost 0.01% and Timolol 0.5% on Circadian IOP,Blood Pressure and Perfusion Pressure in Patients with Glaucoma or Ocular Hypertension: A Randomized,Double Masked,Placebo-Controlled Clinical Trial

PurposeTo compare the 24-hour (24h) effects on intraocular pressure (IOP) and cardiovascular parameters of timolol 0.5% and bimatoprost 0.01% in open angle glaucoma and ocular hypertensive subjects.MethodsIn this prospective, randomized, double masked, crossover, clinical trial, after washout from previous medications enrolled subjects underwent 24h IOP, blood pressure (BP) and heart rate (HR) measurements and were randomized to either topical bimatoprost 0.01% at night plus placebo in the morning or to timolol 0.5% bid. After 8 weeks of treatment a second 24h assessment of IOP, BP and HR was performed and then subjects switched to the opposite treatment for additional 8 weeks when a third 24h assessment was performed. The primary endpoint was the comparison of the mean 24h IOP after each treatment. Secondary endpoints included the comparisons of IOP at each timepoint of the 24h curve and the comparison of BP, HR, ocular perfusion pressure and tolerability.ResultsMean untreated 24h IOP was 20.3 mmHg (95%CI 19.0 to 21.6). Mean 24h IOP was significantly lower after 8 weeks of treatment with bimatoprost 0.01% than after 8 weeks of treatment with timolol 0.5% bid (15.7 vs 16.8 mmHg, p = 0.0003). Mean IOP during the day hours was significantly reduced from baseline by both drugs while mean IOP during the night hours was reduced by -2.3 mmHg (p = 0.0002) by bimatoprost 0.01% plus placebo and by -1.1 mmHg by timolol 0.5% bid (p = 0.06). Timolol 0.5% significantly reduced the mean 24h systolic BP from baseline, the diastolic BP during the day hours, the HR during the night hours, and the mean 24h systolic ocular perfusion pressure.ConclusionBoth Bimatoprost 0.01% and Timolol 0.5% are effective in reducing the mean 24h IOP from an untreated baseline but Bimatoprost 0.01% is more effective than timolol 0.5% throughout the 24h. Timolol 0.5% effect on IOP is reduced during the night hours and is associated with reduced BP, HR and ocular perfusion pressure.

Trial Registration

EU Clinical Trial Register and EudraCT# 2010-024272-26     

Mesor-hypertension: hints by chronobiologists

Circadian systems are intermodulated by networks of specialized neural, hormonal and cellular functions, with time structures that are interdependent. In cardiovascular pathophysiology, circadian and ultradian rhythms of clinical interest have been demonstrated. Cardiac output, heart rate, arterial pressure and blood volume are the best known. Systolic and diastolic blood pressure and heart rate have circadian patterns in health and therefore arterial pressure cannot be evaluated by a single measurement during a 24-h span. With correct monitoring for at least 48-h it is possible to detect the mesor-hypertension and the possible amplitude-hypertension that precedes the mesor-hypertension. Prolonged elevation of blood pressure can cause irreparable harm to sensitive tissues. To quantify the damage, the concept of hyperbaric impact has been introduced. This is a measure of the excess load exerted upon the arterial walls. Studies of the beta-blocker penbutolol with correct automatic monitoring have shown the persistence of the physiological circadian variation in the cardiovascular parameters during penbutolol administration. The so-called elimination of the circadian rhythm in blood pressure, which would not really be desirable, was not seen in any of our patients, whose cardiovascular parameters were monitored continuously, day and night, while taking penbutolol. The amplitudes of the rhythms were always prominent. A phase shift, a delay of about 100 degrees, was demonstrated in the heart rate of one 63-year-old mesor-normotensive woman.     

Blood pressure modifies retinal susceptibility to intraocular pressure elevation

Primary open angle glaucoma affects more than 67 million people. Elevated intraocular pressure (IOP) is a risk factor for glaucoma and may reduce nutrient availability by decreasing ocular perfusion pressure (OPP). An interaction between arterial blood pressure and IOP determines OPP; but the exact contribution that these factors have for retinal function is not fully understood. Here we sought to determine how acute modifications of arterial pressure will affect the susceptibility of neuronal function and blood flow to IOP challenge. Anaesthetized (ketamine:xylazine) Long-Evan rats with low (∼60 mmHg, sodium nitroprusside infusion), moderate (∼100 mmHg, saline), or high levels (∼160 mmHg, angiotensin II) of mean arterial pressure (MAP, n = 5–10 per group) were subjected to IOP challenge (10–120 mmHg, 5 mmHg steps every 3 minutes). Electroretinograms were measured at each IOP step to assess bipolar cell (b-wave) and inner retinal function (scotopic threshold response or STR). Ocular blood flow was measured using laser-Doppler flowmetry in groups with similar MAP level and the same IOP challenge protocol. Both b-wave and STR amplitudes decreased with IOP elevation. Retinal function was less susceptible to IOP challenge when MAP was high, whereas the converse was true for low MAP. Consistent with the effects on retinal function, higher IOP was needed to attenuated ocular blood flow in animals with higher MAP. The susceptibility of retinal function to IOP challenge can be ameliorated by acute high BP, and exacerbated by low BP. This is partially mediated by modifications in ocular blood flow.     

Chronobiologically interpreted ambulatory blood pressure monitoring: past,present, and future

Research at the Halberg Chronobiology Center focused to a large extent on the monitoring of blood pressure (BP) and heart rate (HR). Self-measurements and later ambulatory BP monitoring yielded new knowledge of interest to basic science and clinical practice. After a brief review of BP measurement, we outline developments in methods of data analysis that paralleled technological advances in the measurement of BP. We review work done in cooperation with colleagues worldwide to illustrate how a chronobiological approach led to the mapping of spontaneous circadian and other rhythms for the derivation of refined reference values and to the assessment of response rhythms underlying chronotherapy. BIOCOS members work in different fields, spanning from cardiology and nutrition to obesity, diabetes, exercise physiology and rehabilitation, but all strive for “pre-habilitation”. The early recognition of increased risk can prompt the timely institution of prophylactic intervention. As technology continues to improve, studies on groups are complemented by longitudinal self-surveillance for health maintenance. Longitudinal records serve for the investigation of environmental influences on human physiology, the topic of chronomics. As current advances in technology and wireless communication will likely impact the future of healthcare, chronobiological methods and concepts should be an integral part of this seachange.     

Structural and functional neuroprotection in glaucoma: role of galantamine-mediated activation of muscarinic acetylcholine receptors

Glaucoma is the leading cause of irreversible blindness worldwide. Loss of vision due to glaucoma is caused by the selective death of retinal ganglion cells (RGCs). Treatments for glaucoma, limited to drugs or surgery to lower intraocular pressure (IOP), are insufficient. Therefore, a pressing medical need exists for more effective therapies to prevent vision loss in glaucoma patients. In this in vivo study, we demonstrate that systemic administration of galantamine, an acetylcholinesterase inhibitor, promotes protection of RGC soma and axons in a rat glaucoma model. Functional deficits caused by high IOP, assessed by recording visual evoked potentials from the superior colliculus, were improved by galantamine. These effects were not related to a reduction in IOP because galantamine did not change the pressure in glaucomatous eyes and it promoted neuronal survival after optic nerve axotomy, a pressure-independent model of RGC death. Importantly, we demonstrate that galantamine-induced ganglion cell survival occurred by activation of types M1 and M4 muscarinic acetylcholine receptors, while nicotinic receptors were not involved. These data provide the first evidence of the clinical potential of galantamine as neuroprotectant for glaucoma and other optic neuropathies, and identify muscarinic receptors as potential therapeutic targets for preventing vision loss in these blinding diseases.     

Ocular Hypotensive Effects of the ATP-Sensitive Potassium Channel Opener Cromakalim in Human and Murine Experimental Model Systems

Elevated intraocular pressure (IOP) is the most prevalent and only treatable risk factor for glaucoma, a leading cause of irreversible blindness worldwide. Unfortunately, all current therapeutics used to treat elevated IOP and glaucoma have significant and sometimes irreversible side effects necessitating the development of novel compounds. We evaluated the IOP lowering ability of the broad spectrum K_ATP channel opener cromakalim. Cultured human anterior segments when treated with 2 μM cromakalim showed a decrease in pressure (19.33 ± 2.78 mmHg at 0 hours to 13.22 ± 2.64 mmHg at 24 hours; p<0.001) when compared to vehicle treated controls (15.89 ± 5.33 mmHg at 0 h to 15.56 ± 4.88 mmHg at 24 hours; p = 0.89). In wild-type C57BL/6 mice, cromakalim reduced IOP by 18.75 ± 2.22% compared to vehicle treated contralateral eyes (17.01 ± 0.32 mmHg at 0 hours to 13.82 ± 0.37 mmHg at 24 hours; n = 10, p = 0.002). Cromakalim demonstrated an additive effect when used in conjunction with latanoprost free acid, a common ocular hypotensive drug prescribed to patients with elevated IOP. To examine K_ATP channel subunit specificity, K_ir6.2^(-/-) mice were treated with cromakalim, but unlike wild-type animals, no change in IOP was noted. Histologic analysis of treated and control eyes in cultured human anterior segments and in mice showed similar cell numbers and extracellular matrix integrity within the trabecular meshwork, with no disruptions in the inner and outer walls of Schlemm’s canal. Together, these studies suggest that cromakalim is a potent ocular hypotensive agent that lowers IOP via activation of K_ir6.2 containing K_ATP channels, its effect is additive when used in combination with the commonly used glaucoma drug latanoprost, and is not toxic to cells and tissues of the aqueous humor outflow pathway, making it a candidate for future therapeutic development.     

Mutant myocilin nonsecretion in vivo is not sufficient to cause glaucoma

Glaucoma is a leading cause of blindness, affecting over 70 million people worldwide. Vision loss is the result of death of the retinal ganglion cells. The best-known risk factor for glaucoma is an elevated intraocular pressure (IOP); however, factors leading to IOP elevation are poorly understood. Mutations in the MYOC gene are an important cause of open-angle glaucoma. Over 70 MYOC mutations have been identified, and they lead to approximately 5% of all primary open-angle glaucoma cases. Nevertheless, the pathogenic mechanisms by which these mutations elevate IOP are presently unclear. Data suggest that a dominant interfering effect of misfolded mutant MYOC molecules may be pathogenic. To test this hypothesis, we have generated mice carrying a mutant allele of Myoc that is analogous to a human mutation that leads to aggressive glaucoma in patients. We show that mutant MYOC is not secreted into the aqueous humor. Instead of being secreted, mutant MYOC accumulates within the iridocorneal angle of the eye, consistent with the behavior of abnormally folded protein. Surprisingly, the accumulated mutant protein does not activate the unfolded protein response and lead to elevated intraocular pressure or glaucoma in aged mice of different strains. These data suggest that production, apparent misfolding, and nonsecretion of mutant MYOC are not, by themselves, sufficient to cause glaucoma in vivo.