Influence of vasospasm on visual function

Role of ocular blood flow in normal tension glaucoma

Background

Normal tension glaucoma (NTG) is a multifactorial disease in the pathogenesis of which intraocular pressure (IOP)-independent factors play a key role.

Main text

There is considerable evidence that impairment of the ocular blood flow (OBF) is involved both in the onset and progression of this disease. With the development of the hypothesis of OBF in NTG, various imaging techniques have been developed to evaluate the OBF and blood vessels. Moreover, vascular dysregulation, which is a main factor in Flammer syndrome, was frequently observed in NTG patients. Disturbed OBF leads to increased oxidative stress, which plays an important role in the pathogenesis of glaucomatous optic neuropathy. These results suggested that IOP-independent management may provide alternative treatment options for NTG patients.

Conclusions

In this review, we mainly focus on the mechanisms of the abnormal OBF in NTG.

Ocular blood flow as a clinical observation: Value, limitations and data analysis

Alterations in ocular blood flow have been identified as important risk factors for the onset and progression of numerous diseases of the eye. In particular, several population-based and longitudinal-based studies have provided compelling evidence of hemodynamic biomarkers as independent risk factors for ocular disease throughout several different geographic regions. Despite this evidence, the relative contribution of blood flow to ocular physiology and pathology in synergy with other risk factors and comorbidities (e.g., age, gender, race, diabetes and hypertension) remains uncertain. There is currently no gold standard for assessing all relevant vascular beds in the eye, and the heterogeneous vascular biomarkers derived from multiple ocular imaging technologies are non-interchangeable and difficult to interpret as a whole. As a result of these disease complexities and imaging limitations, standard statistical methods often yield inconsistent results across studies and are unable to quantify or explain a patient's overall risk for ocular disease. Combining mathematical modeling with artificial intelligence holds great promise for advancing data analysis in ophthalmology and enabling individualized risk assessment from diverse, multi-input clinical and demographic biomarkers. Mechanism-driven mathematical modeling makes virtual laboratories available to investigate pathogenic mechanisms, advance diagnostic ability and improve disease management. Artificial intelligence provides a novel method for utilizing a vast amount of data from a wide range of patient types to diagnose and monitor ocular disease. This article reviews the state of the art and major unanswered questions related to ocular vascular anatomy and physiology, ocular imaging techniques, clinical findings in glaucoma and other eye diseases, and mechanistic modeling predictions, while laying a path for integrating clinical observations with mathematical models and artificial intelligence. Viable alternatives for integrated data analysis are proposed that aim to overcome the limitations of standard statistical approaches and enable individually tailored precision medicine in ophthalmology.

Transient visual field impairment after cold provocation in glaucoma patients with Flammer syndrome

Background:

It is still debatable whether visual field defects in glaucoma have a reversible component and to what extent a temporary loss can be provoked.

Objective:

To investigate the response of the visual function to a cold provocation in glaucoma patients, particularly to test whether subjects with Flammer syndrome (FS) behaved differently from subjects without FS.

Methods:

Ten (10) primary open-angle glaucoma (POAG) patients with FS, 7 POAG patients without FS, and 11 healthy controls were tested with program G2 on the Octopus 101 perimeter before and after putting one hand in cold water (4°C) for 2 min. The mean sensitivity (MS) of each visual field was included in the statistical analysis.

Results:

In glaucoma patients with FS, the mean MS significantly decreased after cold provocation (delta MS = –0.91 dB, CI = –1.43 to –0.39, p = 0.0014). In contrast, the mean MS in glaucoma patients without FS did not change significantly (delta MS = 0.17 dB, CI = –0.43 to 0.78, p = 0.56). Likewise, the mean MS did not change significantly in the healthy controls (delta MS = 0.23 dB, CI = –0.27 to 0.72, p = 0.36).

Conclusions:

Cold provocation induced a transient visual field deterioration in the glaucoma patients with FS but not in the glaucoma patients without FS or in the healthy controls. We assume this effect to be the result of a transient reduction of ocular blood flow.

Influence of Nifedipine on the Visual Fields of Patients with Optic-Nerve-Head Diseases

Calcium-channel blockers have long been employed in coronary disease, and recent investigations have indicated their efficacy in improving the visual field in low-tension glaucoma or presumed vasospasm, possibly by enhancing ocular circulation. We evaluated the short-term influence of a typical calcium-channel blocker, nifedipine, on 59 patients with visual-field defects, some with optic-nerve-head pathology (n = 38) and some with normal-appearing optic nerve heads (n = 21). On the average, a statistically significant improvement of 1.2 dB was observed. Different types of patients, however, behaved quite differently. The younger the patient, the greater the improvement. Patients with normal optic nerve heads improved by 1.54 dB, whereas patients with optic-nerve-head excavation improved by only 0.66 dB. No response was observed in patients with anterior ischemic neuropathy. Marked deterioration was noted in one glaucoma patient with low systemic blood pressure. The visual-field changes were observed in the scotomatous and non-scotomatous areas. Thus, the calcium-channel blocker nifedipine can be effective in some selected diseases whose pathogenesis probably involves vascular dysregulation though it may even be contraindicated in others

Taurine protects against retinal and optic nerve damage induced by endothelin-1 in rats via antioxidant effects

Endothelin-1 (ET-1), a potent vasoconstrictor, is involved in retinal vascular dysregulation and oxidative stress in glaucomatous eyes. Taurine (TAU), a naturally occurring free amino acid, is known for its neuroprotective and antioxidant properties. Hence, we evaluated its neuroprotective properties against ET-1 induced retinal and optic nerve damage. ET-1 was administered intravitreally to Sprague-Dawley rats and TAU was injected as pre-, co- or post-treatment. Animals were euthanized seven days post TAU injection. Retinae and optic nerve were examined for morphology, and were also processed for caspase-3 immunostaining. Retinal redox status was estimated by measuring retinal superoxide dismutase, catalase, glutathione, and malondialdehyde levels using enzyme-linked immuosorbent assay. Histopathological examination showed significantly improved retinal and optic nerve morphology in TAU-treated groups. Morphometric examination showed that TAU pre-treatment provided marked protection against ET-1 induced damage to retina and optic nerve. In accordance with the morphological observations, immunostaining for caspase showed a significantly lesser number of apoptotic retinal cells in the TAU pre-treatment group. The retinal oxidative stress was reduced in all TAU-treated groups, and particularly in the pre-treatment group. The findings suggest that treatment with TAU, particularly pre-treatment, prevents apoptosis of retinal cells induced by ET-1 and hence prevents the changes in the morphology of retina and optic nerve. The protective effect of TAU against ET-1 induced retinal and optic nerve damage is associated with reduced retinal oxidative stress.

Relationship between normal tension glaucoma and Flammer syndrome

BACKGROUND

Besides intraocular pressure, vascular factors play a role in the pathogenesis of glaucomatous optic neuropathy. One of these potential vascular factors is Flammer syndrome. The purpose of the present study was to determine in a Korean population whether signs and symptoms of Flammer syndrome occur more often in normal tension glaucoma patients than in control subjects.

METHODS

Two hundred forty-six normal tension glaucoma patients and 1116 control subjects responded to a multiple-choice questionnaire asking about 15 signs and symptoms of Flammer syndrome.

RESULTS

Seven of the 15 signs and symptoms of Flammer syndrome (increased drug sensitivity, good smell perception, reversible skin blotches, tinnitus, long sleep onset time, tendency to perfectionism, and cold hands/feet) were significantly more often positive in normal tension glaucoma patients than in controls. Six additional signs and symptoms (migraines, low blood pressure, headaches, dizziness, increased pain sensation, and feeling cold) also occurred more often, but did not reach statistical significance. Only two items (low body weight and reduced feeling of thirst) were more frequently (not significant) positive in the controls.

CONCLUSION

There is an association between normal tension glaucoma and Flammer syndrome. If future studies confirm this relationship, treatment of Flammer syndrome may help to prevent normal tension glaucoma or to slow down its progression.

The discovery of the Flammer syndrome: a historical and personal perspective

This review describes the clinical and basic research that led to the description of Flammer syndrome. It is narrated from a personal perspective. This research was initiated by the observation of an increased long-term fluctuation of visual fields in a subgroup of glaucoma patients. As these patients had strikingly cold hands, peripheral blood flow was tested with a capillary microscopy, and vasospastic syndrome (VS) was diagnosed. Further studies on these patients revealed frequently weakened autoregulation of ocular blood flow and increased flow resistivity in retroocular vessels. Their retinal vessels were more rigid and irregular and responded less to flickering light. Holistic investigation demonstrated low blood pressure, silent myocardial ischaemia, altered beat-to-beat variation, altered gene expression in the lymphocytes, slightly increased plasma endothelin level and increased systemic oxidative stress. This combination of signs and symptoms was better described by the term primary vascular dysregulation (PVD) than by VS. Subsequent studies showed additional symptoms frequently related to PVD, such as low body mass index, cold extremities combined with slightly increased core temperature, prolonged sleep onset time, reduced feelings of thirst, increased sensitivity to smell and also for certain drugs and increased retinal venous pressure. To better characterise this entire syndrome, the term Flammer syndrome (FS) was introduced. Most subjects with FS were healthy. Nevertheless, FS seemed to increase the risk for certain eye diseases, particularly in younger patients. This included normal-tension glaucoma, anterior ischaemic optic neuropathy, retinal vein occlusions, Susac syndrome and central serous chorioretinopathy. Hereditary diseases, such as Leber’s optic neuropathy or retinitis pigmentosa, were also associated with FS, and FS symptoms and sings occurred more frequent in patients with multiple sclerosis or with acute hearing loss. Further research should lead to a more concise definition of FS, a precise diagnosis and tools for recognizing people at risk for associated diseases. This may ultimately lead to more efficient and more personalised treatment.

New directions in the treatment of normal tension glaucoma

Glaucoma is a progressive optic neuropathy that causes characteristic changes of the optic nerve and visual field in relation to intraocular pressure (IOP). It is now known that glaucoma can occur at statistically normal IOPs and prevalence studies have shown that normal tension glaucoma (NTG) is more common than previously thought. While IOP is believed to be the predominant risk factor in primary open angle glaucoma (POAG), IOP-independent risk factors, such as vascular dysregulation, are believed to play an important part in the pathogenesis of NTG. Though certain distinguishing phenotypic features of NTG have been reported, such as an increased frequency of disc hemorrhages, acquired pits of the optic nerve and characteristic patterns of disc cupping and visual field loss, there is much overlap of the clinical findings in NTG with POAG, suggesting that NTG is likely part of a continuum of open angle glaucomas. However, IOP modification is still the mainstay of treatment in NTG. As in traditional POAG, reduction of IOP can be achieved with the use of medications, laser trabeculoplasty or surgery. Studies now show that the choice of medication may also be important in determining the outcomes of these patients. Though it is likely that future treatment of NTG will involve modification of both IOP and IOP-independent risk factors, current efforts to develop IOP-independent neuroprotective treatments have not yet proven to be effective in humans.

Decreased endothelin-1 plasma levels in multiple sclerosis patients: a possible factor of vascular dysregulation?

BACKGROUND

Multiple sclerosis (MS) is a demyelinating autoimmune disease of the central nervous system with possible involvement of vascular dysregulation secondary to endothelial dysfunction caused by destruction of the vessel wall. Vascular dysregulation leads to excessive vasoconstriction or insufficient vasodilatation, resulting in vasospasm mediated by endothelin-1 (ET-1), the most potent and long-lasting mediator. Vascular dysregulation can play an important role in the pathogenesis of some eye disorders and it has been hypothesized that it is a vascular risk factor for glaucomatous optic neuropathy. The aim of this study was to estimate endothelin-1 (ET-1) plasma levels in patients with MS.

MATERIAL AND METHODS

The MS group consisted of 39 patients (9 males, 30 females), mean age: 38.8 ± 10.02 years, range: 22-62. The control group consisted of 27 healthy volunteers (3 males and 24 females), mean age: 37.4 ± 10.88 years, range: 20-62; clinically, in a non-active stage of the disease. ET-1 plasma levels were measured using the Endothelin-1 ELISA Kit (Immuno-Biological Laboratories Co., Japan). Statistical analysis was performed with the nonparametric Mann-Whitney U test for independent groups.

RESULTS

Endothelin-1 (ET-1) plasma levels were significantly lower in MS patients compared to healthy controls: mean value 0.55 ± 0.44 pg/ml (146.05 ± 118.27 fmol/ml) vs. 0.95 ± 0.48 pg/ml (252.83 ± 127.16 fmol/ml); P=0.012.

CONCLUSIONS

Significantly decreased ET-1 plasma levels in the MS patients could reflect the non-active disease at the time of ET-1 measurements or the effects of immunomodulatory treatment, but it cannot be excluded that decreased ET-1 plasma levels in these patients might result from vascular dysregulation.

A hierarchical cluster analysis of normal-tension glaucoma using spectral-domain optical coherence tomography parameters

PURPOSE

Normal-tension glaucoma (NTG) is a heterogenous disease, and there is still controversy about subclassifications of this disorder. On the basis of spectral-domain optical coherence tomography (SD-OCT), we subdivided NTG with hierarchical cluster analysis using optic nerve head (ONH) parameters and retinal nerve fiber layer (RNFL) thicknesses.

PATIENTS AND METHODS

A total of 200 eyes of 200 NTG patients between March 2011 and June 2012 underwent SD-OCT scans to measure ONH parameters and RNFL thicknesses. We classified NTG into homogenous subgroups based on these variables using a hierarchical cluster analysis, and compared clusters to evaluate diverse NTG characteristics.

RESULTS

Three clusters were found after hierarchical cluster analysis. Cluster 1 (62 eyes) had the thickest RNFL and widest rim area, and showed early glaucoma features. Cluster 2 (60 eyes) was characterized by the largest cup/disc ratio and cup volume, and showed advanced glaucomatous damage. Cluster 3 (78 eyes) had small disc areas in SD-OCT and were comprised of patients with significantly younger age, longer axial length, and greater myopia than the other 2 groups.

CONCLUSIONS

A hierarchical cluster analysis of SD-OCT scans divided NTG patients into 3 groups based upon ONH parameters and RNFL thicknesses. It is anticipated that the small disc area group comprised of younger and more myopic patients may show unique features unlike the other 2 groups.

Calcium channels and their blockers in intraocular pressure and glaucoma

Several factors besides high intraocular pressure assumed to be associated with the development and progression of glaucoma, and calcium channel blockers (CCBs) have been an anticipated option for glaucoma treatment by improving ocular perfusion and/or exerting neuroprotective effects on retinal ganglion cells with safety established in wide and long-term usage. Decrease in IOP has been reported after topical application of CCBs, however, the effect is much smaller and almost negligible after systemic application. Various CCBs have been reported to increase posterior ocular blood flow in vivo and to exert direct neuroprotection in neurons in vitro. Distribution of the drug at a pharmacologically active concentration in the posterior ocular tissues across the blood-brain barrier or blood-retina barrier, especially in the optic nerve head and retina where the ganglion cells mainly suffer from glaucomatous damage, is essential for clinical treatment of glaucoma. Improved visual functions such as sensitivity in the visual field test have been reported after administration of CCBs, but evidences from the randomized studies have been limited and effects of CCBs on blood flow and direct neuroprotection are hardly distinguished from each other.

The primary vascular dysregulation syndrome: implications for eye diseases

Vascular dysregulation refers to the regulation of blood flow that is not adapted to the needs of the respective tissue. We distinguish primary vascular dysregulation (PVD, formerly called vasospastic syndrome) and secondary vascular dysregulation (SVD). Subjects with PVD tend to have cold extremities, low blood pressure, reduced feeling of thirst, altered drug sensitivity, increased pain sensitivity, prolonged sleep onset time, altered gene expression in the lymphocytes, signs of oxidative stress, slightly increased endothelin-1 plasma level, low body mass index and often diffuse and fluctuating visual field defects. Coldness, emotional or mechanical stress and starving can provoke symptoms. Virtually all organs, particularly the eye, can be involved. In subjects with PVD, retinal vessels are stiffer and more irregular, and both neurovascular coupling and autoregulation capacity are reduced while retinal venous pressure is often increased. Subjects with PVD have increased risk for normal-tension glaucoma, optic nerve compartment syndrome, central serous choroidopathy, Susac syndrome, retinal artery and vein occlusions and anterior ischaemic neuropathy without atherosclerosis. Further characteristics are their weaker blood–brain and blood-retinal barriers and the higher prevalence of optic disc haemorrhages and activated astrocytes. Subjects with PVD tend to suffer more often from tinnitus, muscle cramps, migraine with aura and silent myocardial ischaemic and are at greater risk for altitude sickness. While the main cause of vascular dysregulation is vascular endotheliopathy, dysfunction of the autonomic nervous system is also involved. In contrast, SVD occurs in the context of other diseases such as multiple sclerosis, retrobulbar neuritis, rheumatoid arthritis, fibromyalgia and giant cell arteritis. Taking into consideration the high prevalence of PVD in the population and potentially linked pathologies, in the current article, the authors provide recommendations on how to effectively promote the field in order to create innovative diagnostic tools to predict the pathology and develop more efficient treatment approaches tailored to the person.

Corneal hysteresis and Beta-zone parapapillary atrophy

PURPOSE

To evaluate the relationship between β-zone parapapillary atrophy (βPPA) and corneal hysteresis (CH) in patients with glaucoma.

DESIGN

Prospective, cross-sectional study.

METHODS

Glaucoma patients aged 18 to 90 years with disc photographs within 12 months of the study visit were consecutively enrolled. Exclusion criteria included ocular surgery other than clear corneal phacoemulsification, myopia >6 diopters, contact lens use, and corneal abnormality. CH was measured using the Ocular Response Analyzer (ORA). Disc photographs were evaluated in a masked fashion for βPPA.

RESULTS

We enrolled 99 patients (mean age 67.6 years; 45 men, 54 women). Univariate analysis showed no significant difference in CH between eyes with and without βPPA (8.72 ± 0.23 vs 8.15 ± 0.27 mm Hg, P = .11). There were no differences in corneal resistance factor (CRF) (P = .47), central corneal thickness (CCT) (P = .11), ORA wave score (P = .23), age (P = .23), sex (P = .40), IOP (P = .86), or visual field mean deviation (VFMD) (P = .45). Eyes with βPPA were more myopic (-1.49 ± 0.27 vs -0.22 ± 0.31 diopters, P = .003). Multivariate analysis showed no significant difference in CH between eyes with and without βPPA (P = .38). Eyes with asymmetric βPPA also showed no significant difference in CH (8.97 ± 0.22 vs 9.10 ± 0.22 mm Hg, P = .69).

CONCLUSIONS

We found no significant differences in CH between eyes with and without βPPA or between fellow eyes with asymmetric βPPA.

The effect of vasopressin on choroidal blood flow, intraocular pressure, and orbital venous pressure in rabbits

PURPOSE

To investigate the effects of arginine-vasopressin (AVP) on intraocular pressure (IOP), orbital venous pressure (OVP), and choroidal blood flow (ChorBF) regulation in anesthetized rabbits.

METHODS

Mean arterial pressure (MAP), IOP, and OVP were measured by direct cannulation of the central ear artery, the vitreous, and the orbital venous sinus, respectively. Laser Doppler flowmetry was used to record ChorBF. To change the perfusion pressure (PP), MAP was manipulated mechanically with occluders around the aorta and vena cava. In the first group of animals (n = 11) the dose-response relationship was measured. In the second group of animals (n = 8) pressure-flow relationships were determined at baseline and in response to intravenous application of a low (0.08 ng/kg/min) and a high (1.33 ng/kg/min) infusion rate of AVP.

RESULTS

AVP caused a dose-dependent increase of MAP and choroidal vascular resistance (ChorR), whereas IOP, OVP, ChorBF, and heart rate (HR) were decreased. In contrast to the high infusion rate, the low infusion rate of AVP had no effect on baseline ChorBF. However, the pressure-flow relationship was shifted downward significantly by both infusion rates at PP below baseline.

CONCLUSIONS

AVP reduces IOP and OVP significantly and is a potent vasoconstrictor in the choroidal vascular bed. In the choroid, the effect of AVP is not only dose-dependent, but also PP-dependent, which is indicated by the reduced perfusion relative to control with low-dosed AVP at low PP.

Dynamic focal retinal arteriolar vasospasm in migraine

A 48-year-old man presented following an episode of sudden onset simultaneous inferior altitudinal visual loss in his left eye and visual obscuration with shimmering in the inferonasal quadrant of the right eye. Clinical examination demonstrated left superior hemiretinal artery occlusion and an area of focal dynamic spasm along the right superior temporal branch retinal artery, the arteriolar spastic cycle was about 2 sec in duration. Hematological (including complete blood count, thrombophilia screen, vasculitic screen and serum magnesium), carotid, and cardiac investigations were normal. He was given acetazolamide 500 mg orally, timolol maleate 0.5% eye drops once daily and sublingual amyl-nitrate 0.8 mg, and maintained on felodipine 10 mg/day and aspirin 100 mg/day. The area of focal arteriolar spasm in the right eye resolved over two months. To our knowledge there are no prior reports of photographically documented dynamic focal retinal vascular spasm on a MEDLINE and PUBMED search.

Topical carbonic anhydrase inhibitors and visual function in glaucoma and ocular hypertension

BACKGROUND

Dorzolamide and brinzolamide are topical carbonic anhydrase inhibitors (CAI) indicated for patients with glaucoma and ocular hypertension.

SCOPE

An evidence-based review of clinical trials of dorzolamide and brinzolamide was undertaken to determine an effect of these medications on visual function (primarily visual field) in open-angle glaucoma and ocular hypertension. Using the keywords 'dorzolamide' and 'brinzolamide', all articles describing trials of these medications reporting on visual acuity, contrast sensitivity and visual field from September 1966 to July 2009 were found in MEDLINE and EMBASE databases. No information from other sources was included in this review.

FINDINGS

A relatively modest number of trials was identified, where impact of therapy on one or more of the visual function modes was reported. In the studies of less than 1 year duration (3 days to 1 year, 23 studies) in all but three studies treatment with topical CAIs did not influence visual function, in two studies with dorzolamide some improvement in the contrast sensitivity was observed and in one open-label retrospective no-control-group study with dorzolamide visual field indices improved significantly. A different picture was seen in long-term studies, which were designed and powered to detect changes in visual field. One large study (European Glaucoma Prevention Study) with dorzolamide versus placebo failed to detect significant protective effect of the drug on glaucoma occurrence in ocular hypertensives. Several interesting aspects of this study are discussed in detail. The other two long-term studies reported on the superiority of adding dorzolamide over timolol therapy alone, and the superiority of the combination of dorzolamide and timolol over brinzolamide and timolol in terms of improving ocular blood flow (retrobulbar Color Doppler Imaging--CDI parameters) as well as in terms of visual field preservation in glaucoma patients over 4 to 5 years.

CONCLUSION

For the first time one study could demonstrate that an improvement in ocular blood flow in the long run results in preservation of visual field in glaucoma patients. Dorzolamide, combined with the beta-blocker timolol, seems to be superior in this regard to brinzolamide plus timolol.

Intrinsic vasomotricity and adrenergic effects in a model of isolated rabbit eye

PURPOSE

We aimed to investigate the responsiveness of the ocular arteries to adrenergic drugs in a model of perfused isolated rabbit eye.

METHODS

Rabbit external ophthalmic arteries (n = 15) in a head-mounted preparation were cannulated and the retinal and uveal vasculature perfused at a constant flow with warmed tyrode. The three-way polypropylene catheter was further connected to a pressure transducer and intraluminal pressure was taken as a measure of vascular resistance. Effects of intra-arterial injections of phenylephrine (group A, n = 5), prazosin (group B, n = 5) and phentolamine (group C, n = 5) on the recorded pressure were obtained. Student's paired-t test and one-way analysis of variance were used for statistical analysis (p < 0.05).

RESULTS

Intrinsic vasomotricity was observed in all preparations prior to any drug administration. Phenylephrine produced an increase in total vascular resistance. Intrinsic vasomotricity became more evident, showing a lower frequency but higher amplitude of oscillations. Evoked vasomotor responses with phenylephrine (250 microg/ml) were inhibited by intra-arterial administration of the selective alpha(1)-adrenergic antagonist, prazosin (0.5 mg/ml), as well as the non-selective alpha-adrenergic antagonist phentolamine (6 mg/ml).

CONCLUSIONS

Rabbit external ophthalmic arteries showed spontaneous contractions under constant perfusion. Phenylephrine elicited a vasoconstrictor response that was inhibited by adrenergic antagonists. In addition, the intrinsic vasomotricity was enhanced by phenylephrine and blocked by adrenergic antagonists. These results show that under in vitro perfusion the territory presents similar responses to adrenergic drugs to those observed in in vivo models and also provides evidence of myogenic autoregulatory properties in the rabbit ophthalmic artery and/or choroid.

What can we learn from the disc appearance about the risk factors in glaucoma?

The author has been involved in 3 studies, the multicentre collaborative normal-tension glaucoma study, a study of 4 phenotypes of glaucomatous disc appearances and their associations, and a study reporting on biostatistical evidence for 2 distinct chronic open-angle glaucoma populations. These studies have some common threads whose clinical implications are discussed.

Vasospasm in Glaucoma: Clinical and Laboratory Aspects

During the last decade, the presumed etiology of glaucoma has moved from a pure pressure concept to a combined mechanical and vascular theory. Evidence of a localized vascular insufficiency leading to perfusion deficits of ocular structures, including the optic nerve head, the retina, the choroid, and the retrobulbar vessels, is now clear. This article evaluates the role of vasospasm as the primary cause of such a vascular failure. The role of both ocular and systemic vasospasms and their clinical correlations are discussed. At a cellular level, the function of the modulating role of the vascular endothelium is reviewed. Evidence of abnormalities of the vascular endothelium and its vasoactive peptides as a conduit for vasospasm is mounting. Herein lies exciting prospects for potential pharmacologic targets in future glaucoma management.

Correlation Between Finger Blood Flow and Changes in Optic Nerve Head Blood Flow Following Therapeutic Intraocular Pressure Reduction

PURPOSE

To correlate finger blood flow and changes in optic nerve head (ONH) blood flow following therapeutic intraocular pressure (IOP) reduction in open-angle glaucoma (OAG) and ocular hypertension (OHT).

METHODS

Seventeen open-angle glaucoma patients and nineteen ocular hypertension patients underwent therapeutic IOP reduction followed by a minimum of 4 weeks of follow-up. Optic nerve head blood flow measurements were obtained by scanning laser Doppler flowmetry using full-field perfusion image analysis. Finger blood flow was measured using the Transonic laser Doppler Flowmeter. Finger blood flow was measured at baseline, after immersion in warm water (40 degrees C) for 2 minutes (Flow Max), and after immersion in cold water (4 degrees C) for 10 seconds (Flow Min). Patients were identified as vasospastic if their Flow Max/Flow Min >7. Statistical comparisons were performed using two-tailed distribution paired T-test and Pearson's correlation factor.

RESULTS

For similar mean percentage intraocular pressure reduction, vasospastic patients had greater improvements in rim blood flow than did non-vasospastic patients [+35% versus +13%] (P = 0.01). While there was no difference in rim blood flow changes in the vasospastic versus the non-vasospastic OAG group, the vasospastic ocular hypertension group showed 18% increase in rim blood flow whereas the non-vasospastic ocular hypertension group showed an 8% decrease. A significant negative correlation was also found in the open-angle glaucoma group between rim blood flow change and Flow Max (-0.681, P = 0.003). In contrast, no such correlation was found in the ocular hypertension group (+0.144, P = 0.556).

CONCLUSION

OAG patients had a significant negative correlation between changes in rim blood flow and maximum finger Doppler flow. Among ocular hypertension patients, increased rim blood flow was only found in the vasospastic group, though this increase was not statistically significant. These results suggest that open-angle glaucoma and ocular hypertension patients with the most severe vasospastic disease may show the greatest improvements in rim blood flow after sustained intraocular pressure reduction.

New thoughts on normal tension glaucoma

Normal tension glaucoma (NTG) is considered a primary optic neuropathy within the glaucoma family. Whereas NTG shares many of the same pathologic characteristics as primary open angle glaucoma (POAG), there are several differences such as pattern of visual field defect and incidence of disc hemorrhaging. The most notable difference is that NTG does not manifest a recordable intraocular pressure (IOP) greater than 21 mmHg. Debate has existed as to whether NTG is a pressure-sensitive neuropathy and if pressure reduction affects the course of the disease. Likely, there are aspects in the pathophysiology of NTG that are both pressure sensitive and insensitive, and the etiology of NTG has never been adequately explained.

The Low-pressure Glaucoma Treatment Study (LoGTS)

OBJECTIVE

The Low-Pressure Glaucoma Treatment Study (LoGTS) seeks to evaluate visual field stability in low-pressure glaucoma patients randomized to intraocular pressure reduction in both eyes with topical twice daily brimonidine tartrate 0.2% versus twice daily timolol maleate 0.5%. This article describes the LoGTS design and presents baseline characteristics of the subjects.

DESIGN

Randomized, multicenter, double-masked clinical trial.

PARTICIPANTS

Low-pressure glaucoma patients 30 years of age or older were identified. Exclusion criteria included an untreated pressure of more than 21 mmHg, advanced visual field loss, and contraindications to study medications.

INTERVENTIONS

Randomization of both eyes to double-masked monotherapy with brimonidine or timolol. Follow-up visits included Humphrey 24-2 full-threshold perimetry, tonometry every 4 months, and annual optic disc photography.

MAIN OUTCOME MEASURE

Progression of visual field loss.

RESULTS

One hundred ninety patients were randomized between 1998 and 2000. Mean age (+/-standard deviation) was 64.9+/-10.7 years. Women comprised 59.5% of the patients. Fifty-three patients (27.9%) had unilateral field loss. The 137 patients with bilateral field loss were older than those with unilateral field loss: 65.7 versus 62.3 years of age (P<0.05). Mean untreated diurnal intraocular pressures were similar between the eyes of the bilateral patients (mean, 15.5 mmHg in both eyes) and unilateral patients (mean, 16.0 mmHg in field loss vs. 15.6 mmHg in fellow eyes). Visual field mean deviation for all eyes was -5.4+/-4.7 decibels. Central corneal thickness in 168 phakic patients was 543 +/- 35 microm (range, 435-655 microm); thickness was less than 500 microm in 15 eyes and was more than 600 microm in 11 eyes. Mean vertical cup-to-disc ratio for all eyes was 0.67+/-0.15. Unilateral field loss patients had a larger cup-to-disc ratio in the field loss eye (0.75+/-0.12) than the fellow eye with a normal field (0.60+/-0.17, P<0.0001). Disc hemorrhage was present at baseline in 29 patients (32 eyes).

CONCLUSIONS

The LoGTS was successfully able to recruit and enroll patients with open-angle glaucoma and statistically normal intraocular pressure into a longitudinal, prospective clinical trial comparing 2 different glaucoma medications. Baseline characteristics of note were a preponderance of females, unilateral field loss in 27.9% of participants, and frequent optic disc hemorrhage. Central corneal thickness had a normal distribution and did not account for false low-pressure measurements in LoGTS patients.

Clinical potential of lomerizine, a Ca2+ channel blocker as an anti-glaucoma drug: effects on ocular circulation and retinal neuronal damage

Glaucoma is defined as an optic neuropathy with characteristic changes in the optic nerve head and ultimate loss of visual field. Previous studies have suggested that (a) mechanical damage due to raised intraocular pressure and (b) a compromised tissue circulation in the optic nerve head play significant roles in the development of glaucomatous damage in the optic nerve head. Recently, we found that lomerizine, a new Ca(2+) channel blocker, increased ocular circulation and protected neuronal cells against retinal neurotoxicity both in vitro and in vivo with minimal cardiovascular side effects. We examined the effect of lomerizine on the ocular circulation and compared it with those of other Ca(2+) channel blockers in normal rabbits and in rabbits with an endothelin-1-disturbed circulation in the optic nerve head. In anesthetized rabbits, lomerizine and the other Ca(2+) channel blockers increased the ocular circulation and also inhibited the hypoperfusion induced in optic nerve head tissue by an intravitreous injection of endothelin-1. Whereas the other Ca(2+) channel blockers produced changes in blood pressure and heart rate, the effects of lomerizine on these parameters were slight. In healthy humans, lomerizine increased blood velocity in the optic nerve head, without significantly altering blood pressure or heart rate. Moreover, lomerizine reduced retinal damage in rats both in vitro and in vivo, presumably through a Ca(2+) channel blocking effect via an action that may involve a direct protection of retinal neurons as well as an improvement in the ocular circulation. These results indicate that lomerizine may be useful as a therapeutic drug against ischemic retinal diseases (such as glaucoma and retinal vascular occlusive diseases) that involve a disturbance of the ocular circulation.

[Mechanisms of neuroprotection against glaucoma]

The goal of neuroprotection in glaucoma treatment is to employ agents that prevent or delay apoptosis of retinal ganglion cells (RGC) and facilitate regeneration of already damaged calls. The following contribution discusses the mechanisms of RGC death and current status of neuroprotective in vivo studies and investigations on cell cultures and animal models. Discussions on the etiopathogenesis of PCOAG center on elevated IOP and ocular disorders of vascular function. The mechanisms of axonal damage induced by ischemia are explained and the resultant possible neuroprotective effect mechanisms are discussed (Na(+) or Ca(2+) channel blockers, role of reactive astrocytes). Substitution of axonal survival factors and especially the role of BDNF are described. Glutamate excitotoxicity also plays a role in glaucomatous antegrade RGC death. Relevant questions and possible therapeutic approaches are discussed. The three phases of apoptosis cascade and the key role of mitochondria in the insult-induced apoptosis are considered as well as the still relatively unexplored possibilities of RGC regeneration. Finally, perspectives of neuroprotective treatment of PCOAG are presented.

Hormone therapy and ophthalmic artery blood flow changes in women with primary open-angle glaucoma

OBJECTIVE

To compare the effects of hormone therapy (HT) on plasma viscosity and Doppler flow parameters in normal, healthy, postmenopausal women and in women with normal-tension and chronic, open-angle glaucoma.

DESIGN

Eight postmenopausal women with glaucoma (group I) and 15 controls (group II) were given HT. The duration of the study was 6 months, and the women were examined in basal condition and at the end of the treatment. All women underwent ultrasonographic evaluation of pelvic organs and color Doppler analysis of uterine, internal carotid, and ophthalmic arteries. Also, plasma viscosity was assayed.

RESULTS

The ultrasonographic analysis showed that none of the women presented with irregular endometrial echoes, polyps, or intracavitary fluid. In addition, endometrial thickness never exceeded the normal range (5 mm). Plasma viscosity and Doppler parameters significantly improved during therapy. However, the ophthalmic artery mean improvements of pulsatility index (-43% v -28%; P = 0.001), peak systolic blood flow velocity (+35% v +24%; P = 0.026), and time-averaged maximum velocity (+44% v +32%; P = 0.031) were significantly more evident in the control group than in the glaucoma group.

CONCLUSIONS

Although, in people with glaucoma, vasospasm can increase the risk of visual loss by inducing a retrobulbar blood flow reduction, HT seems to beneficially affect the ocular vascularization.

Pathogenetic aspects of the glaucomatous optic neuropathy: fluorescein angiographic findings in patients with primary open angle glaucoma

PURPOSE

To identify and quantify the role of retinal circulation, capillary leakage and/or nonperfusion of the optic nerve head in digital fluorescein angiography in normal subjects and patients with open angle glaucoma.

METHODS

Eighteen patients with primary open angle glaucoma (POAG) and 18 healthy age matched subjects were included. Fluorescein angiograms were performed using the scanning laser ophthalmoscope. The arteriovenous passage time (AVP) was assessed by dye dilution technique and describes the shortest passage through a retinal vascular segment. Optic nerve head nonperfusion was marked manually in early angiographic images and is given as percentage of the optic disk area. The fluorescence of the optic nerve head (as measure of the disruption of the blood-brain barrier) and the surrounding retina (ratio of leakage) was measured using digital imaging analysis in the late phases of the angiogram (9-10min).

RESULTS

The AVP time was significantly prolonged ( P=0.001) in patients with open angle glaucoma (AVP 2.29+/-0.32 s) compared to healthy subjects (AVP 1.37+/-0.42 s). The mean percentage of the optic nerve head nonperfusion was 16%. The ratio of optic nerve head fluorescence compared to retinal reference loci was significantly increased (P = 0.02) in patients with glaucoma (1.32+/-0.25) compared with normal subjects (1.32+/-0.19).

CONCLUSIONS

Fluorescein angiography revealed altered retinal perfusion along with optic nerve head nonperfusion and increased vascular leakage in open angle glaucoma patients. These factors appear to influence each other, with ultrastructural changes of the lamina cribrosa accompanying changes in the vasculature and nerve fibers. Longitudinal and interventive studies should help better elucidate the relationship between circulatory and neural loss, adding vasoprotective therapeutic approaches to interfere with the glaucomatous neurodegenerative chain of events.

Effects of betaxolol and flunarizine on visual fields and intraocular pressure in patients with migraine

Fifty-one patients with migraine were divided into four groups to investigate the effects of topical betaxolol and systemic calcium channel blocker flunarizine on visual fields (VF) and intraocular pressure (IOP). The first group (Group 0) was followed with no medications, topical betaxolol (bid) was precribed to the second group (Group B), oral flunarizine (10 mg daily) was prescribed to the third group (Group F), and the last group (Group BF) was assigned for combined betaxolol and flunarizine treatment. After a mean follow-up time of 4.2 +/- 1.2 months (3-6 months), IOP measurements and VF tests were repeated. Group B and Group BF were found to be statistically different from the other groups in terms of IOP reduction and VF improvement according to mean deviation and corrected pattern standard deviation indices in the second examinations. On the other hand, Group F and Group BF differed from the other two groups considering the improvement in migrainous complaints. VF findings which are probably influenced by perfusion problems due to vasospastic mechanisms in migraineurs, improved following topical betaxolol treatment. However, systemic use of flunarizine--a calcium channel blocker--did not seem to be effective on visual fields although it had beneficial effects on migraine.

Effect of Ginkgo biloba extract on preexisting visual field damage in normal tension glaucoma

OBJECTIVE

To evaluate the effect of Ginkgo biloba extract (GBE) on preexisting visual field damage in patients with normal tension glaucoma (NTG).

DESIGN

Prospective, randomized, placebo-controlled, double-masked cross-over trial.

PARTICIPANTS

Twenty-seven patients with bilateral visual field damage resulting from NTG.

INTERVENTION

Patients received 40 mg GBE, administered orally, three times daily for 4 weeks, followed by a wash-out period of 8 weeks, then 4 weeks of placebo treatment (identical capsules filled with 40 mg fructose). Other patients underwent the same regimen, but took the placebo first and the GBE last. Visual field tests, performed at baseline and at the end of each phase of the study, were evaluated for changes.

MAIN OUTCOME MEASURES

Change in visual field and any ocular or systemic complications.

RESULTS

After GBE treatment, a significant improvement in visual fields indices was recorded: mean deviation (MD) at baseline versus MD after GBE treatment, 11.40 +/- 3.27 dB versus 8.78 +/- 2.56 dB (t = 8.86, P = 0.0001, chi-square test); corrected pattern standard deviation (CPSD) at baseline versus CPSD after GBE treatment, 10.93 +/- 2.12 dB versus 8.13 +/- 2.12 dB (t = 9.89, P = 0.0001, chi-square test). No significant changes were found in intraocular pressure, blood pressure, or heart rate after placebo or GBE treatment. Any ocular and systemic side effects were recorded for the duration of the trial.

CONCLUSIONS

Ginkgo biloba extract administration appears to improve preexisting visual field damage in some patients with NTG.

Analysis of risk factors that may be associated with progression from ocular hypertension to primary open angle glaucoma

BACKGROUND

As a multifactorial disease, glaucoma may be associated with pressure-dependent and pressure-independent factors. Ocular hypertension (OHT) may develop into primary open angle glaucoma (POAG) for many patients. Groups with OHT and POAG were compared for pressure-dependent and independent risk factors. A high prevalence of any factor(s) could indicate a contribution to progression from OHT to POAG.

METHODS

A sample of patients with POAG (n = 438) and with OHT (n = 301) were selected from those attending a tertiary referral private glaucoma practice, and data were collected regarding age and intraocular pressure at the time of diagnosis, sex, family history of glaucoma, systemic hypertension, diabetes, Raynaud's phenomenon, migraine and myopia.

RESULTS

After multivariate analysis, older age at time of diagnosis (chi(2)(5) = 73.89, P < 0.001), myopia (odds ratio [OR] = 1.5, 95% confidence interval [CI] 1.0-2.2; P < 0.05), a family history of glaucoma (OR = 1.6, 95% CI 1.1-2.3; P < 0.01) and a high intraocular pressure (chi(2)(4) = 16.96; P = 0.002) were found to be more prevalent among those with POAG. No other significant differences could be found between the two groups.

CONCLUSION

Patients who have OHT may be at higher risk of developing POAG if they also have myopia, a family history of glaucoma or are of older age.

The impact of ocular blood flow in glaucoma

Two principal theories for the pathogenesis of glaucomatous optic neuropathy (GON) have been described--a mechanical and a vascular theory. Both have been defended by various research groups over the past 150 years. According to the mechanical theory, increased intraocular pressure (IOP) causes stretching of the laminar beams and damage to retinal ganglion cell axons. The vascular theory of glaucoma considers GON as a consequence of insufficient blood supply due to either increased IOP or other risk factors reducing ocular blood flow (OBF). A number of conditions such as congenital glaucoma, angle-closure glaucoma or secondary glaucomas clearly show that increased IOP is sufficient to lead to GON. However, a number of observations such as the existence of normal-tension glaucoma cannot be satisfactorily explained by a pressure theory alone. Indeed, the vast majority of published studies dealing with blood flow report a reduced ocular perfusion in glaucoma patients compared with normal subjects. The fact that the reduction of OBF often precedes the damage and blood flow can also be reduced in other parts of the body of glaucoma patients, indicate that the hemodynamic alterations may at least partially be primary. The major cause of this reduction is not atherosclerosis, but rather a vascular dysregulation, leading to both low perfusion pressure and insufficient autoregulation. This in turn may lead to unstable ocular perfusion and thereby to ischemia and reperfusion damage. This review discusses the potential role of OBF in glaucoma and how a disturbance of OBF could increase the optic nerve's sensitivity to IOP.

Blood flow in the optic nerve head and factors that may influence it

In the recent past there has been great interest in the blood supply of the optic nerve head (ONH), how to evaluate ONH blood flow, and what factors influence it, in health and disease. This is because evidence has progressively accumulated that there is vascular insufficiency in the ONH in both anterior ischemic optic neuropathy (AION) and glaucomatous optic neuropathy (GON)-two major causes of blindness or of seriously impaired vision in man. For the management and prevention of visual loss in these two disorders, a proper understanding of the factors that influence the blood flow in the ONH is essential. The objective of this paper is, therefore, to review and discuss all these factors. The various factors that influence the vascular resistance, mean blood pressure and intraocular pressure are discussed, to create a better basic understanding of the ONH blood flow, which may help us toward a logical strategy for prevention and management of ischemic disorders of the ONH.

Vasospasm, its role in the pathogenesis of diseases with particular reference to the eye

Vasospasm can have many different causes and can occur in a variety of diseases, including infectious, autoimmune, and ophthalmic diseases, as well as in otherwise healthy subjects. We distinguish between the primary vasospastic syndrome and secondary vasospasm. The term "vasospastic syndrome" summarizes the symptoms of patients having such a diathesis as responding with spasm to stimuli like cold or emotional stress. Secondary vasospasm can occur in a number of autoimmune diseases, such as multiple sclerosis, lupus erythematosus, antiphospholipid syndrome, rheumatoid polyarthritis, giant cell arteritis, Behcet's disease, Buerger's disease and preeclampsia, and also in infectious diseases such as AIDS. Other potential causes for vasospasm are hemorrhages, homocysteinemia, head injury, acute intermittent porphyria, sickle cell disease, anorexia nervosa, Susac syndrome, mitochondriopathies, tumors, colitis ulcerosa, Crohn's disease, arteriosclerosis and drugs. Patients with primary vasospastic syndrome tend to suffer from cold hands, low blood pressure, and even migraine and silent myocardial ischemia. Valuable diagnostic tools for vasospastic diathesis are nailfold capillary microscopy and angiography, but probably the best indicator is an increased plasma level of endothelin-1. The eye is frequently involved in the vasospastic syndrome, and ocular manifestations of vasospasm include alteration of conjunctival vessels, corneal edema, retinal arterial and venous occlusions, choroidal ischemia, amaurosis fugax, AION, and glaucoma. Since the clinical impact of vascular dysregulation has only really been appreciated in the last few years, there has been little research in the according therapeutic field. The role of calcium channel blockers, magnesium, endothelin and glutamate antagonists, and gene therapy are discussed.

The impact of glaucoma medication on parameters of ocular perfusion

Whereas intraocular pressure is considered a major risk factor in glaucoma, growing evidence now indicates that ocular ischemia plays a major role too. By virtue of this and because many existing medications are able to interact with vasculature, altering ocular blood flow, it is essential that current and future medications for glaucoma be evaluated for their effect on ocular circulation. The authors review published papers examining the effect of topical and some systemic medications on ocular blood flow, focusing mostly on data from the human eye. The authors provide a comprehensive review on the effect of subclasses of medications (eg, carbonic anhydrase inhibitors, beta-blockers, alpha-adrenergic agonists, and prostaglandin analogues on optic nerve head, and on retinal, choroidal, and retrobulbar circulation. The various claims for enhancements or reduction of ocular circulation within each class of medication are reviewed and evaluated.

Effect of oral felodipine on ocular circulation

PURPOSE

To evaluate the effects of felodipine, a calcium channel blocker, on ocular circulation.

METHODS

In a double blind, randomized, crossover design, 10 volunteers received placebo or felodipine on 2 separate days. Bidirectional laser Doppler velocimetry (BLDV), laser Doppler flowmetry (LDF), and monochromatic fundus photography (MFP) were employed to assess retinal, choroidal, and optic nerve rim circulatory parameters. Measurements were obtained at baseline, 1.5, and 3 hours after dosing. Blood pressure, intraocular pressure (IOP), and heart rate were monitored, and perfusion pressure (PP) was calculated.

RESULTS

In comparison to placebo, significant average percentage decreases in diastolic blood pressure (BPd; p = 0.001), mean blood pressure (BPm; p = 0.003), and perfusion pressure (PP; p = 0.003) were observed 1.5 hours following felodipine. No significant differences were observed following placebo. Retinal, choroidal and optic nerve rim circulatory parameters showed no significant changes after placebo or felodipine. A significant positive correlation between BPd and optic nerve velocity (ONve1) was observed 3 hours following felodipine (R = +0.654; p = 0.040). In contrast, no significant correlation between BPd and ONve1 was noted (R = +0.198; p = 0.583) following placebo.

CONCLUSIONS

No significant change in retinal, optic nerve rim, or foveolar choroidal blood flow were observed, a factor that may be important in the treatment of systemic hypertension in patients with glaucoma.